Transcript for:
Key Chemistry Concepts and States of Matter

[Music] [Applause] [Music] now as always don't forget that i sell my perfect answer revision guides on my website if you click on this card you'll be able to go and purchase yourself a copy it is available now in all three sciences so if you enjoy my videos and you enjoy the way in which i describe and explain things that is where you will find a distillation of my videos you'll also find information about revision courses if you're keen on attending school licenses and private tuition however enough about that let's get started so we're going to start by looking at solids liquids and gases so when we look at solids liquids and gases be prepared to draw their particle diagrams notice that solids have particles which are in very fixed arrangements and that's because the particles vibrate around in fixed positions they have little kinetic energy and there are strong forces between them moving to liquids you see that the particles are slightly more widely spaced apart they're not touching quite as much so they have intermediate forces between them and they vibrate more and they don't have fixed positions gases now so you need your particles to be further apart this is because they have large amounts of kinetic energy obviously they're not held in fixed position and there are weak forces between the particles and here's your summary now let's start naming the correct conversions between all these various states of matter so remember if you're going from a solid to a liquid that is melting like a solid ice block turns into water melting if you go the other way and the water turns into ice clearly that will be freezing if you have a liquid and it turns into a gas that will be boiling or evaporating and then when you have a gas and it turns back into a liquid that is condensation so that's what happens when you have a shower and you see it getting all misted up on the windows condensation is occurring here touching slightly more on evaporation so how does the evaporation of a puddle or any liquid happen really so what you find is that particles have differing kinetic energy now those particles with the most amount of energy will evaporate first and they will leave the surface of the liquid and what will happen is it will mean that the remaining particles have lower average kinetic energy do notice that in a closed container condensation and evaporation will be occurring simultaneously which means at the same time the specification now touches on diffusion which you should be aware from biology so diffusion is the net movement of particles from an area of high concentration to an area of low concentration and because that's down the concentration gradient you find that no energy is required it is a passive process so that means in any scenario where you have large amounts of particles in one place they will drift and move across to somewhere some region which has a lower density or concentration of these particles and the example we like to look at in chemistry is you might have seen your teacher go through in class you've got this huge glass tube on one end you have ammonia the other end you have hydrochloric acid and effectively their concentrations are high either end of the tube and obviously the particles start to diffuse so the ammonia starts to move towards the hydrochloric acid and where they meet a chemical reaction takes place and ammonium chloride is produced which we see as a white ring now the location at which this white ring occurs will tell you something about how quickly diffusion is happening because clearly if the white ring occurs in the middle of the tube it means that the ammonia and hydrochloric acid diffuse equally quickly across however this isn't true what actually happens is that the ring forms much closer to the hydrochloric end and that means that the ammonia has diffused further and faster and what is the reason for this is simply because it has a lower relative atomic mass looking at some fundamentals which underpin chemistry we need to look at an atom element mixturing compound so an atom is the smallest particle of a substance that can exist there are probably more accurate definitions for this and that will involve high level physics but for all intents and purposes for your chemistry gcse this is what you need to know an element contains only one type of atom and it cannot be split by any any chemical means so basically if you're given a list of substances and you're asked which is the element cross-reference the list to the periodic table and you'll soon be able to see if what you have is an element or not if it's not in a periodic table it is not an element compounds now well that's when you have two or more elements which are chemically combined and what that means is you cannot separate them back into their constituent elements and a good analogy for this is when you make a cake so you add flour eggs sugar and effectively when you bake it it turns into a cake and that's the equivalent of a compound because there's no way you can separate those cake particles back up into eggs flour sugar that's not going to happen and that's due to the chemical reaction that's taken place a mixture is different to this a mixture contains as you would imagine two or more elements this time not chemically combined so theoretically you should be able to separate your mixture into its constituent components and now i'm just going to bring up an example table showing elements compounds and mixtures and you should have a go at potentially separating them out yourself and make sure you can tell the difference back to basic chemistry then so we're looking at periodicity i've already told you then atom is the smallest part of a chemical element which can exist so what is a molecule well that is two or more atoms bonded together and the atoms could be the same element such as h2 so hydrogen or it could be different elements such as carbon dioxide but the point to notice is that with a molecule it's just two atoms stuck together so looking at the structure of an atom remember that we have the nucleus in the middle that contains the protons and the neutrons surrounding that we have circles which we call shells and these are shells of electrons do you remember when you're drawing electronic configuration diagrams that the first shell can contain a maximum of two electrons and after that you can contain a maximum of eight so let's compare the masses and charges of protons neutrons and electrons so protons and neutrons both have a mass of one so they're much heavier than electrons and that's why we say most of the mass is found in the nucleus of an atom an electron has a much smaller mass and different examples will say different things but i tend to say that it has a mass of one divided by two thousand so a very small number indeed looking at the charges now neutron neutron so neutral has no charge because it is neutral a proton pro positive has a positive one charge and electron has a minus one charge so when we look at an atom we know that it is uncharged which therefore means it must have equal numbers of electrons and protons when we look at the periodic table you must be really familiar with how to use the periodic table and what it's telling you so make sure you use the key because that will tell you which is the mass number and which is the atomic number but generally speaking the top number tends to be the mass number and the bottom number tends to be the atomic number so the atomic number is actually the number of protons found in an atom so for carbon that would be six and i told you already that atoms are neutral which means their proton number equals their electron number which means the electron number of carbon will also be six and if we draw the electronic configuration diagram we know that two electrons go into the first shell and the remaining four go into the second shell now looking at the mass number now the mass number is the total number of protons and neutrons so if carbon has an atomic number of six that means the proton number is six it has a mass number of twelve that means you can work out the neutral number by taking the atomic number away from the mass number so the neutral number of carbon is six small thing to notice is the nuclear number and that's just the total number of particles found within the nucleus of an atom so it's the total of the protons and neutrons i.e it's also the mass number so they're very closely linked going back to the periodic table then looking at group numbers and period numbers so the group numbers are the numbers that run along the top of the periodic table the group number corresponds to the number of electrons in the outer shell so group one elements will all have one electron in that outer shell now the period numbers run down the side and they refer to the rows and the period number will correspond to the number of shells of electrons why do elements in the same group tend to have the same chemical properties that's due to the number of electrons in the outer shell so the answer here is because they have the same number of electrons in the outer shell so why do fluorine and chlorine behave similarly because they're both in group seven and therefore they both have seven electrons in that outer shell let's look at group zero now what is their name otherwise known as it is the noble gases and why are they so unreactive and that's because they have full outer shells which means they don't really want to get involved in bonding as a quick overview of the periodic table do notice there's a step line on the right hand side and therefore the metals occur on the left hand side of that step line and the non-metals appear on the right hand side with hydrogen appearing by itself at the top because it behaves very differently from all other elements isotopes now so if you look in the periodic table you will see that some mass numbers aren't whole numbers such as chlorine which is 35.5 and that's because chlorine exists as an isotope which means that there some chlorine atoms have a high mass number of 37 and other ones have a mass number of 35 and when you work out an average you actually find that it's 35.5 and that's because they're far more chlorine 35s compared with chlorine 37s however you just need to know the definition of an isotope which is that is atoms of the same element with the same number of protons but different number of neutrons so how is an ion formed and what is an ion so an ion is a charged particle which is formed from either gaining or losing electrons so clearly if they lose electrons they lose negative charge so therefore they become positive if they gain electrons they gain negative charge so they become negative remember that in an ionic bond you've got both a metal and a non-metal and that's super important because they're what's going to form the ions now the metals always form positive ions whereas the non-metals always form negative ions in our first example we're going to do an ionic bonding diagram of sodium chloride now the first thing you want to do is draw the electronic configuration for both elements so let's start with sodium which is over here now 11 is the atomic number of sodium which is also the same as the proton number and the electron number so we know we need to draw an electronic configuration that contains 11 electrons so i'm going to start by writing the symbol of sodium in the middle now when you're drawing electronic configurations remember that the first shell the first circle can contain a maximum of two electrons and then after that it contains a maximum of eight which we arrange in pairs so we know we need to draw 11 electrons in total there's the 11th now it's time to look at chlorine chlorine is a halogen it's in group 7 so it contains 17 electrons so we'll start by writing the symbol for chlorine in the middle and then add our shells of electrons and now we need to draw 17 electrons and we usually use circles or dots to represent the fact that the electrons come from a different element now with ionic bonding or any type of bonding what you're really looking for is for the atoms to have a full outer shell so let's take a step back and work out what would make sense here so really that sodium needs to lose that final electron and chlorine needs to gain an electron so that it will have eight electrons in its outer shell that electron from sodium transfers itself to chlorine here so in your final answer in the exam you'll be asked to draw the ions which have formed and it always looks like this you want to start with square brackets you want to draw the outer shell you don't need to worry about drawing the inner shells but it's perfectly fine if you want to do that showing that it has a full outer shell because this is the new outer shell for sodium now it's lost an electron remember that an electron has a one minus charge so in effect that sodium is now positively charged which we draw as that now we're going to read your chlorine so we'll add those electrons in the outer shell again making sure that we acknowledge that that final electron has come from a different atom it's come from sodium and that's why i've drawn across because chlorine has gained an electron it's now cl minus so that's why we write that charge that and that is your final answer if you're asked to draw an ionic bonding diagram for sodium chloride this is your final answer now we're going to do a second example now we're going to draw magnesium fluoride so let's have a look at magnesium in the periodic table it has 12 electrons so magnesium has 12 electrons now we need to look at fluorine in the periodic table here it is it has nine electrons so now we're ready to work out what's going to happen well we know that the magnesium needs to lose two electrons so one of those electrons will be transferred to here however fluorine only needs to gain one electron which means we have a spare electron over here so what are we going to do with that well the thing that makes most sense is if we draw another fluorine atom and so that second electron is going to be transferred to here meaning that the magnesium now has a full outer shell here has eight electrons and the fluorine atoms will now have fallout shells so i'll now draw the final answer for you so again we only need to draw that outer shell which is now this one it's nice and full it contains eight electrons notice that it's lost two electrons which remember have a negative charge which means that the magnesium will have a net positive charge which is two plus now we can draw the fluoride ions so label those fluoride ions show those full outer shells with that final electron that's come from magnesium because both fluoride ions have gained an electron they've gained a negative charge and you do want to notice that these charges for the non-metals should equal the charges from the metal and that's your final answer in our third and final example we're going to look at aluminium oxide aluminium sits here it has 13 electrons oxygen has eight electrons now this one's slightly more difficult because if we have a look at what's going to happen we know that aluminium needs to lose these three electrons so it's quite straightforward to know that those two electrons will go here however what's going to happen to this electron well we'll need to draw another oxygen atom to accommodate it but now we have an issue which is that this oxygen outer shell will only have seven electrons so it's missing an electron here which means we need to draw a whole new aluminium atom over here so that electron will go over here we've still got issues which is that we have two spare electrons over here so guess what we need to draw another oxygen atom however at this point we should be done so actually ready to draw our final answer with the square brackets and i'll draw it here on the right hand side quite small so you can see the working together with the answer so here's our aluminiums there's two of them let's label them as we expect they have a full outer shell now in terms of their charge notice that they both lost three electrons which means they have a net positive charge of three now we're ready to draw oxygen so we know we need three of them label them show that they have a full outer shell remember that they each gain two electrons from aluminium they've each gained two electrons so that means they have a two minus charge and double check look six plus on this side six minus on this side so we're sorted and that is your final answer looking at covalent bonding now we can see we're looking at two non-metals so don't be tempted to draw an ionic bonding diagram we're going to take a nice straightforward example to begin with which is water h2o so we're going to have a central oxygen atom two hydrogen atoms coming to the side label the atoms and then have a look in the periodic table and see how many electrons they have in the outer shell and remember that's given by their group number so hydrogen has one electron in its outer shell oxygen has six four five six and now double check and see that they're both full oxygen now has eight electrons in its outer shell hydrogen only has two but that's fine because remember the first shell only needs two to be become full so that is now a perfectly completed covalent bonding diagram let's look at methane now which is ch4 which you need to know for organic chemistry so try and arrange this nice and symmetrically that isn't particularly symmetrical but it will do so again hydrogen has one electron in its outer shell so let's start by filling in those ones carbon is in group four so it has four electrons and actually that's already done because now hydrogen has two in its outer shell her carbon has eight so that is now correct carbon dioxide is trickier and i'll show you that example now so remember that's co2 remember with this one that it has double covalent bonds and that will really help you with your answer so carbon has four electrons in its outer shell but i'm drawing like that because i know it's a double covalent bond oxygen has six so one two three four five six one two three four five six and they both need to have eight electrons two b4 so carbon has eight electrons as two shared pairs and oxygen has eight so that is correct the most difficult example you could be given is ethene c2h4 so i'm going to show you how to do that there's your central carbon atoms here's your four hydrogens label them it's easiest to start with the hydrogens here remembering they have one electron in the outer shells carbon has four so let's make sure that hydrogen is happy first of all so one two three four let's do the other side one two three four and now have a look yes all the hydrogens have two electrons in the outer shell and each carbon now has eight so that is correct let's now take a look at the chemical structures part of the specification and when we're talking about chemical structures we're talking about four main structures that is giant covalent giant ionic giant metallic and simple molecular and you need to know and understand why they have various properties such as either high or low melting points electrical conductivity that sort of thing but we're going to start initially with giant ionic structures so remember these are made up of a metal and a non-metal and what is an ionic bond well it's the electrostatic forces of attraction between oppositely charged ions so remember that the methyl ion is positive and the non-metal ion is negative and therefore they attract so why do giant ionic structures have such high melting and boiling points and that's because they have strong electrostatic forces of attraction between oppositely charged ions and don't forget to qualify this by saying that they require a lot of energy to break why don't they conduct when solid that's because the irons aren't free to move why do they conduct when they're molten or liquid that's simply because the ions are free to move to carry the current why are they brittle and don't forget the brittle means that they smash easily when hit that's because when you hit them or when a force is applied the layers of ions slide so the ions with the same charge end up next to each other so positive charges will therefore repel and the whole structure breaks apart so that's giant ionic done moving on to giant covalent and we are really looking at carbon here so we're looking at diamond and graphite which remember are both forms of carbon so definition of an allotrope is different forms of the same element so why does diamond have such a high melting point and that's because it has a giant tetrahedral structure which really means that each carbon atom is bonded to four others so it has many strong covalent bonds which require a lot of energy to break why does graphite have a high melting point similar argument but this time each carbon atom is bonded to three you still have many strong covalent bonds and it still requires a lot of energy to break but because it's bonded to three rather than four carbon atoms that's why graphite has a slightly lower melting point than diamond why is graphite used as a lubricant that's because the carbon atoms are arranged in layers with weakens molecular forces between the layers these require little energy to break and therefore the layers can slide off each other hence it's used as a lubricant why doesn't diamond conduct electricity and that's because it has no free electrons however graphite does conduct electricity the reason being that each carbon atom as we've already said is only bonded to three others meaning that there's a fourth electron which is free to move and therefore carry the current we should touch on a covalent bond here now remember equivalent bond is a shared pair of electrons if you want to be more complex about it you can say it's the electrostatic attraction between the positive nucleus and the shared pair of electrons why do simple molecular substances have such low melting points and that's because they have weakened molecular forces which do not require a lot of energy to break a small point to note which is why do simple molecular substances have increasing boiling point with increasing mr so remember mr is the relative atomic mass so it's really saying something like why does ethane c2h6 have a higher melting point than methane ch4 and that's because ethane so substances with a greater mr have greater intermolecular forces of attraction between molecules and these require a lot more energy to break and remember when you're boiling these substances you're not breaking apart the individual atoms from the molecule you're simply separating one molecule from another so you're breaking into molecular forces lastly giant metallic structures so these are just the metals you find in the periodic table remember they have high melting points that's because they have strong metallic bonds and a metallic bond is simply the attraction between a positive ion and the delocalized electrons so if you have to draw the structure of a metal keep it nice and simple just draw a rectangle to represent the metal draw some positive ions evenly arranged with a sea of delocalized electrons surrounding them and that will be sorted wire metals or giant metallic structures such good conductors of heat and that's again due to delocalized electrons satellites which are free to move and carry the heat throughout the structure why do metals conduct electricity again that's because they have a sea of delocalized electrons which are free to carry the current lastly two other properties the fact that metals are malleable which remember means that they can be hammered into shape and that they are also ductile which means they can be drawn into a wire the reason for both of these properties is because the layers of ions concide over each other i'm going to show you my favorite method of balancing equation which always works so if you can't actually see straight away how to balance them use this method and you'll be able to balance any equation so start by doing a dotted line and then list the elements present on each side of the equation and obviously they ought to be the same so we've got hydrogen nitrogen oxygen calcium and then just copy that straight over and line that up nicely and now we want to do a tally chart to show how many of each element we have so count the hydrogens on the left hand side of the equation so we've got one present in the nitric acid two present in the calcium hydroxide so that's three the number of nitrogens is one the number of oxygens well three on the nitric acid side and then you've got one inside the brackets but the two after the brackets means that there's two so add those up all together and it's five now the calcium is just one now we need to do the same for the product side of the equation so how many hydrogens do we have well that's two which is present in water oxygen you've got three present in calcium nitrate but remember that small two after the brackets means that's doubled so that's six plus one found in water so that's seven nitrogen you've got two and calcium you have one and now we need to have a look at our tally charts and see what the issue is so the calcium are fine the nitrogen are not fine you've got two on the right hand side one on the left hand side so we're going to add a big two in front of nitric acid remember when we're balancing equations all you're allowed to do is add big numbers and now we adjust your tally so you now have four hydrogens eight oxygens two nitrogens so the nitrogens are happy the calcium is happy but the oxygen hydrogens aren't so i'm going to put a two in front of water to make that four hydrogens and now adjust the oxygens so you now have eight oxygens and look the whole thing is balanced because you have four hydrogens on both sides two nitrogens eight oxygens and one calcium so that is indeed balanced unfortunately there are some ions which you'll simply have to learn off by heart because you can't work them out from the periodic table so let's just go through what all of these are starting with these transition metals along here just going to have to learn them the first one is silver this one is copper pb2 plus is lead and zinc is zm2 plus notice with transition metals like iron that have variable valencies you'll be given it in the question so you can actually see what their charge will be given by the roman numerals so that's not something you need to remember this is the ammonium ion and now looking at the negative ions if it's combined with oxygen it tends to have eight in its name so this is carbonate sulfate and nitrate and that final ion is hydroxide so now we can get started on some examples so starting with magnesium chloride so let's write down the ions we can see from the periodic table that magnesium is in group two hence mg2 plus chlorine is in group seven so eight minus seven is one hence cl minus now have a look they're not balanced obviously you've got two plus and a one minus charge so clearly you need two chlorines remember when you're writing the formula you write a small number after the element in question which is why this is the formula of magnesium chloride so lead hydroxide these are both ions you're going to have to land off by heart so pb2 plus oh minus so we've got the same issue here and that we don't have enough minus so you need two ohs so you're going to write pboh2 however the 2 applies to both the oxygen and the hydrogen which is why you need brackets so insert brackets and that is your formula now lithium lithium is in group 1 so it has an ally one plus charge so it has a one plus charge oxygen is greek in group six eight minus six is two so it's o2 minus this means you need two lithium for every oxygen so li2o magnesium nitrate magnesium is in group two so mg2 plus nitrate you've got to learn from the list above no3 minus you've got a one minus charge with nitrate compared with the two plus charge on the magnesium which explains why you need two lots of that magnesium of that nitrate and you need to insert brackets again don't touch this three here that just remains part of the formula people get confused and start moving it around no that is the final answer lastly aluminium in group three three plus learn sulfates charge which is so4 two minus this is a difficult one now it's not that clear you gotta find a common number that both three and two go into which is six so if i show you my thought process i effectively need two aluminiums and three sulfates to make it equal six because now we have six plus on the aluminium side six minus on the sulfate side so that's therefore ar2 so4 3 not forgetting the brackets as usual now if you don't like the method i just showed you there is a cheats way of doing it where you don't actually have to understand the chemistry what you do is you write out the ions as usual so potassium is in group one hence one plus oxygen is in group six eight minus six is two so two minus and all you have to do here is swap and drop so literally bring down that invisible one to here that two to there and then rewrite the ions so your final answer is k2o and it works with anything really so let's do aluminium nitrate aluminium's in group three nitrate we've run off by half from the list above we're gonna swap and drop so we're gonna bring that three down we're gonna bring that visible one down and so it becomes a l n o three three because you brought that three down relative atomic mass i've already described a little bit but you do need to be able to define it and that is that it's the ratio of the average mass of an element when compared with one atom of carbon-12 looking at more calculations now use the formula triangle to help you rearrange and you can see that mass is therefore given by the relative atomic mass which is mr times number of moles moles is going to be mass over mr and that's a good way of rearranging without too much effort so let's get started and have a look at some examples so first of all we're just finding the mr of calcium hydroxide and that's just a matter of looking at the various masses in the periodic table tends to be the top number and adding them all together so if we have a look we see calcium is 40. oxygen is 16. but we have to times it by 2 due to this small 2 here and then we add hydrogen which is 1 and again times it by 2. pop that into your calculator and you get an mr of 74. now looking to find the number of moles in 5.4 grams of calcium carbonate so i like to write out the equation i'm using it's good practice stops you making silly mistakes so using my formula triangle i see it's mass divided by mr we've been given the mass in the question which is 5.4 now we need to work out the mr of calcium carbonate so using the periodic table calcium has a mass of 40 carbon is 12. oxygen is 16 and we need to multiply that by 3 due to this 3 here so that's 5.4 divided by 100 of 0.0 so the empirical formulae is the simplest ratio of atoms of each element present in a compound and just to make that really clear what that actually means we need to look at the molecular formula at the same time because although they sound very similar and indeed they are very similar they have slightly different definitions so the molecular formula is the actual number of atoms of each element present in a compound so let's take propine as our example here so looking at its molecular formula what is the actual number of atoms of each element present in propine well we know it contains three carbon atoms it obeys the general formula cnh2n which is why its formula is c3h6 that is its molecular formula however if we look back at our definition of an empirical formula we're looking for the simplest ratio so basically we want to cancel this down now we can see by looking at the molecular formula of propine that 3 goes into it so we want to cancel by 3 means we'd have ch2 and that is our empirical formula and that's actually what we're going to be looking at calculating now so in question one a compound contains forty percent carbon six point seven three percent hydrogen and fifty three point two percent oxygen by mass to determine the empirical formula so first of all start by listing your elements so we've got carbon hydrogen oxygen make a table and you want to write mass mr and number of moles down the left hand side so the mass we've been given in the question although it says all the masses and percentages it doesn't matter because effectively they're all ratios so you could have 40 grams of carbon and that would still be 6.73 grams of hydrogen which is why we're allowed to write down the numbers exactly as they are then use your periodic table to look at their atomic masses you'll see that carbon has a mass of 12.01 hydrogen has a mass of 1.01 oxygen has a mass of 16 exactly now using this formula triangle which hopefully you'll be very familiar with we have mass at the top mr and number of moles at the bottom so if we cover the one we're after which is number of moles you can see that that is given by mass divided by mr so when we look at the third row of our table that's the exact calculation we're going to be doing so first of all for carbon divide 40 by 12.01 to get 3.33 to get the number of moles of hydrogen to 6.73 divided by 1.01 to get 6.66 and lastly for oxygen do 53.27 divided by 16 to get 3.33 and now at this point you want to have a look at those three numbers and then choose the smallest one and divide all the values by the smallest number and as we can see that will be 3 3 so we're dividing every single value by 3.33 to get our ratio of 1 to 2 to 1. now don't forget to answer the question we're looking for a formula so we have a final formula which is ch2o now i'm going to show you a water crystallization type of mole calculation it's really similar to empirical formulas so don't let it freak you out just because it looks more difficult so 35.75 grams of sodium carbonate combined with water are heated strongly and 13.25 gram remain after heating calculates x so obviously after you've heated it it will now become anhydrous which means you've driven off the water so lay it out like the table again na2co3 but instead of listing the elements you're just going to have the various components of the question so it's just going to be sodium carbonate on the left water on the right and then mass mr and moles as usual so we know that 13.25 grams of the sodium carbonate remain after heating which is why this is the number here i'm gonna have to do a small calculation to work out the amount of water that was lost so that's 35.75 minus 13.25 to get 22.5 the mr used the periodic table so we'll see sodium is 23 times it by 2 because of that small 2 plus carbon's 12 plus 3 lots of oxygen which is 16 to get an mr of 106 and i know off by heart that the mr water is 18 and you can check that in the periodic table if you don't believe me to work out the number of moles now mass divided by mr it's giving us 0.125 this is 1.25 and then divide by the smallest number which is clearly 0.125 so that will obviously be one this is 10. therefore x equals 10 and that's it it's very similar to the empirical formulae question now we need to look at reacting mass and gas volume questions so 3.3 grams of hydrochloric acid react with sodium carbonate to calculate the mass and volume of carbon dioxide collected now i do imagine that in your question paper they'll give you the balanced symbol equation which is the starting point of this calculation however in another part of the exam paper they could easily expect you to write out your own salt equations and to balance them which is why i'm going to do all of that right now so hydrochloric acid reacts with sodium carbonate to produce a salt which is sodium chloride plus water plus carbon dioxide make sure it's balanced i know i need a 2 there and a 2 here and now we need to use the table format in order to help us answer the rest of the question mass mr and moles and don't forget to use your formula little triangle down here which is mass mr moles and this is how i always set myself up to make sure i'm going to get the question right so what we've been given in the question well we know 3.3 grams of hydrochloric acid reacted and we know we need the volume and mass of carbon dioxide which is why my x goes here now the mr use the periodic table now make sure you're just adding up the hydrogen and the chlorine you're not including the two in this so it's just one plus 35.5 equals 36.5 the amount of carbon dioxide is going to be 12 plus 2 lots of 16 which is 44. using the formula triangle we see that moles is mass divided by mr so we do 3.3 divided by 36.5 to give us 0.0904109 and now remember what we can do here is carry that number across to be the number of moles of carbon dioxide do check the big numbers up here now there's two lots of hydrochloric acid compared with only one lot of carbon dioxide which is why in order to carry over the moles we have to actually divide 0.090 by 2 and that becomes 0.045205 and now we're ready to work out the unknown mass of carbon dioxide which is mass equals mr times moles we've already calculated the mr which is 44. moles is 0.0545205 and that is two grams to three significant figures why is it so noisy in london everywhere now to make sure we're answering the second part of the question which is to do with gas volumes make sure you know that one mole of any gas occupies 24 decimeters cubed so we know the number of moles of carbon dioxide we've already calculated that which is 0.045205 therefore to work out the volume simply times that by 24 becomes 1.08 decimeters cubed so that's the answer to the second part of the question do notice that if they could have asked you it in terms of centimeters cubed and in order to convert decimeters cube two centimeters cubed you just have to times by a thousand so just times that number by a thousand and therefore your answer here is one thousand eighty centimeters cubed to three sig fig three point two grams of copper reacted with zero point four four moles of nitric acid which reagent is in excess don't worry too much about this we're going to use the same method as always which is the table format so we're going to write mass mr and moles down the left-hand side and remember our triangle which i'll put here which is mass at the top number of moles and mr so we know that 3.2 grams of copper reacted and weirdly we're going to put x here because that is important and i'll say why soon so first of all what is the mr of copper using your periodic table you see it's 63.5 so using your formula triangle how do you work out the number of moles you do mass divided by mr so that's 3.2 divided by 63.5 to get 0.0 mol and then have a look at the big numbers we've got invisible one here we have a four here and i've already taught you you just need to pull that number across but instead times it by four so you get 0.2 moles so now we compare we have a look and we have a look at what we were given in the question well we were told we had 0.4 moles of nitric acid but we only need 0.2 so clearly nitric acid is in excess now we're looking at percentage yields so for example in a reaction 11.2 grams of copper sulfate was obtained when theoretically 12.5 should have been obtained calculate the percentage yield so you just need to use this equation here which is percentage yield equals actual yield over theoretical yield times 100 so the actual yield here was 11.2 the theoretical one was 12.5 multiplied by 100 and you get a value which is 89.6 now they can be more difficult than this so i'm going to show you that example now so let me talk you through a slightly more complicated version so a student reacted 2.4 grams of copper oxide with sulfuric acid she made 1.8 grams of copper sulfate calculate the percentage yield so as always we need to start with a balanced symbol equation so that will be copper oxide plus sulfuric acid which is h2so4 forms copper sulfate cu so4 plus water and then step back and double check that it is balanced and it is and we're going to use my favorite table as well obviously because i never do a more calculation without it so let's start with what we know we know that we have 2.4 grams of copper oxide and we have made 1.8 so that is the actual yield and we need to find out the theoretical yield which is why i'm going to put an x here so now it's just a matter of working out the mr of copper oxide so do 63.5 plus 16 so use your periodic table for that to work out that it's mr is 79.5 to work out the number of moles simply do the mass divided by the mr so that's 2.4 divided by 79.5 to give a value which is 0.0302 moles now we need to look at the balanced similar equation and have a look if there are any big numbers that aren't so we can easily just carry that number across to be the number of moles of copper sulfate now work out the mr of copper sulfate so you want to do 63.5 plus 32 plus 4 times 16 so that gives us an mr which is 159.5 and then we work out x by doing 159.5 times by 0.0302 to get four 4.8169 grams and now we can just substitute that into our percentage yield equation because that is the theoretical yield so percentage yield is given by actual yield over theoretical times by a hundred because we're looking for a percent so actual was 1.8 the vertical was 4.8169 times that by 100 and we get a value which is 37 percent let's look at titration calculations now so 25 centimeters cubed of 2 mole dms minus 3 hydrochloric acid reacted with 30 centimeters of sodium hydroxide calculate the concentration of sodium hydroxide you need your balanced symbol equation for this which again i think they'll give you but you do need to be able to do this as a separate skill which is why i'm going to do it now so the salt made is sodium chloride and water is the byproduct double check to see if it needs balancing and it doesn't and then to be clear make sure you use this formula triangle now which is the number of moles goes at the top concentration and volume go at the bottom and therefore titration calculations will be really straightforward so just make sure in your table this time it goes moles concentration and volume and then substituting what you know from the question so your concentration of hydrochloric acid is 2 moles dm minus 2 so that's going to be 2. the volume we've been told is 25 now to make sure you don't screw up these questions make sure you convert that straight into decimeters cube so i do that by just writing divide by a thousand so i know what's put into my calculator we know the volume of sodium hydroxide is 30 so i'm going to do the same here make sure i've divided it by a thousand in order to um account for the fact it needs to be in decimeters cubed and then we're looking for the unknown concentration of sodium hydroxide so the moles is concentration times volume i can see that from the formula triangle so let's work out the number of moles of hydrochloric acid so 25 divided by a thousand times two which is 0.05 have a look at any big numbers there aren't any so that means i can carry that number straight over and that becomes the moles of sodium hydroxide to work out this unknown concentration we have to do moles divided by volume we can see that from the formula triangle so we do 0.05 divided by 30 over 1000 just pop that all into your calculator as it is and you get an answer which is 1.6 recurring so that rounds to 1.67 moles dm to the minus 3 to 3 sig fig so here's an example of the sort of questions you might be asked in the exam a student does a titration to find the concentration of a solution of hydrochloric acid the student titrates 25 centimeters cubed of hydrochloric acid with sodium hydroxide solution of 0.2 moles the equation for the erection is the student added 28.6 centimeters cubed of sodium hydroxide to neutralize the acid calculate the concentration of hydrochloric acid so what i would do is do exactly what i was just doing in my talk through so make sure you have the balanced equation here make sure it's balanced just double check that the elements are the same on each side and then remember your triangle is ncv and then i'm going to write that down the side here and remember i like to do it in like a table format next up i'm going to write an x over the thing that i'm looking for which is the concentration of hydrochloric acid so the x is going to go here then i'm going to include what i've actually been told in the question so i've been told that 25 centimeters cubed of hydrochloric acid reacts and remember in these calculations i need to convert it into decimeters cubed so i'm just going to write it divide by a thousand there i've also been told the volume of sodium hydroxide solution so that's 28.6 so that's going to go here and i'm going to divide it by a thousand for the same reason okay i've now looking back i've been told the concentration of sodium hydroxide so that's going to be popped in here and now i'm ready to calculate the number of moles i'm using my triangle i can see that number of moles is concentration times volume so into your calculator you need to put 28.6 divided by a thousand times by 0.2 to get 5.72 times 10 to the minus 3. now because there are no big numbers in front of the hydrochloric acid or the sodium hydroxide i know that the number of moles of sodium hydroxide is the same as the number of moles of hydrochloric acid so i'm going to copy that number across here sorry it's so small definitely need more space and now i need to find the concentration because that's what x is so concentration using the triangle again is number of moles divided by volume so i'm going to divide that number i've kept it in my calculator display i'm going to divide it by 25 divided by 1000 and x is 0.2288 so there's my answer and i'm going to just write that answer to three significant figures into the answer box yay done now some calculations will want you to convert between the number of atoms to the moles to the mass and i definitely think that using this arrow system at the top of this page is the most straightforward way of doing this if you write it out it basically leads you the right way to the correct calculation the only thing you need to remember is the value of avogadro's constant which is 6.02 times 10 to the 23 and remember that stands for the number of atoms or molecules which are present in one mole of a substance so let's have a look at a few examples and hopefully you'll see that this arrow system really works so in this first example we're calculating the amount in mole of water in a sample containing 2.30 times 10 to the 3 molecules so we're looking for the amounts in mole we have been given the number of molecules so we're looking for moles which is in the middle of this arrow set up we've been given the number of molecules and now we just need to follow the arrow head to work out what we need to do and so clearly we need to take the number of molecules and divide by avogadro's constant now let's make sure we lay out your work nicely so i've written number of moles of water equals we know it's the number of molecules given and we need to divide that by avogadro's constant 6.02 times 10 to the 23. this gives us a value which is 0.382 moles so for question two we're calculating the number of oxygen atoms contained in three moles of glucose which is c6 h12 oh so this time we're calculating the number of oxygen atoms containing three moles of glucose c6h12o6 this one's trickier because it's o6 but we'll only start making sure that we haven't made a mistake with that towards the end of this working out so we're looking for the number of oxygen atoms so looking at my diagram above what i need to do that is put number of i'm going to write molecules because we've actually got a molecule here c6h12o6 equals the number of moles times avogadro's constant let's substitute in the values so it's 3 times 6.02 times 10 to the 23. work that out and it's 1.806 times 10 to the 24 but crucially that's the number of molecules of glucose but we need the number of atoms of oxygen and you can see within that one molecule of glucose there are six atoms of oxygen which is why we need to multiply that number by six to get a value which is one point zero eight times ten to the twenty-five and in electrolysis remember you have your giant tonic structure it needs to be molten or in solution why to allow ions to be free to move so they can carry current that is essential so if you have solid sodium chloride and you attach the electrodes to it you're not going to be able to conduct electricity through that sodium chloride we've just discussed this in chemical structures because the ions aren't free to move pudding in solution means that the ions are free to move so we can carry a current so those two electrons electrodes dip into the substance now remember the electrodes are made out of an inert substance and that means an unreactive one which makes sense you don't want it getting involved in the reaction so they can be made out of things like platinum or graphite as these are unreactive in terms of naming things properly you've got to remember what an anion and a cation is so cations are positive ions anions are negative ions so remember opposites attract so anions which are negative will be attracted to the anode which is positive and the cation which is positive will be attracted to the cathode which is the negative electrode so do try and remember that and i always use pink to help me remember positive anode negative cathode anodes attract anions cathodes attract cations so the ode ending is the electrode and the ion is the ion in terms of remembering what forms where you need to remember a few rules so if you if you have aqueous solution that makes it more complicated because as well as let's take sodium chloride for example so as well as the sodium and the chloride in solution you've got hydrogen ions and hydroxide ions and remember only one of those ions can move to each electrode so let's take the negative electrode first of all which is the cathode that is obviously going to attract a positive ion because opposites attract now in order to work out which ion attracts remember it is the least reactive element that discharges at the negative electrode so in the case of sodium chloride with hydrogen hydroxide that will be hydrogen so h plus ions will discharge and when you're writing these equations remember you've got h plus you're trying to make it neutral which is why you have to add e minus you have to add electrons to it and it will form h2 because remember hydrogen is diatomic because you've added electrons remember this is reduction so don't forget oil rig oil rig is a way of remembering the difference between oxidation and reduction oil so oxidation is loss of electrons reduction is gain so in the case of hydrogen you've got a gain of electrons so reduction now looking at what discharges at the positive electrode make sure you remember that halogens discharge before anything else we have a halogen in solution here a halide ion it's chlorine so chlorine will discharge so cl minus will have to turn into cl2 the easiest way to see what will happen is because it's minus and you need it to become neutral you need to remove the negativity which is why you need to remove e minus because you've lost electrons you've therefore carried out oxidation and you must practice lots of these questions because this is really quite tricky do notice that both hydrogen and chlorine are both diatomic molecules so you'll be making h2 and cl2 and remember the other elements which are also diatomic is nitrogen chlorine fluorine bromine and iodine and oxygen now do remember this as a list because in case it comes up and you've got to balance equations you've got to remember that they're diatomic and my friend who's also a teacher she told me a way to remember this which is horses need oats for clear brown eyes so hydrogen is horses need is nitrogen oats is oxygen four is fluorine clear is chlorine brown is bromine and eyes split strands because obviously it's not eyes about eyes but iodine going back to our aqueous sodium chloride example so i've already told you that hydrogen discharges chlorine discharges so left over in solution you have sodium hydroxide and this is actually a very important industrial process because all three of these products are very useful why because chlorine is obviously used as a disinfectant it helps to kill bacteria in drinking water and swimming pools for example hydrogen can be used as a fuel it's also used to harden vegetable oils to make margarine and sodium hydroxide is used for making bleach and for making paper so we've looked at electrolysis in a lot of detail now but we're going to go through some various examples and try and work out what is made at the anode and what is produced at the cathode together with some observations so let's do this as a table so don't forget that your anode is positive and your cathode is negative and i've written those there so we know what's going on so we've got molten lead 2-bromide to begin with and remember that's therefore going to be made up of pb2 plus and br minus and that two here has told us that it's two plus bromine is in group seven eight takes seven is one hence why its charge is minus one so remember the opposite subtract which therefore means that at the anode you're going to produce bromine and at the cathode you're going to produce lead the observations here are that the lead collects at the cathode and it literally just drips off in a molten state whereas bromine gas is produced at the anode which bubbles off our next example is going to be concentrated hydrochloric acid what are the ions involved again that's h plus and cl minus again opposites attract which means that at the anode we're going to have chlorine produced at the cathode we'll have hydrogen these are both gases and they'll both be bubbled off next up we've got aqueous sodium chloride this is becoming more complicated now because it is aqueous so we need to list the ions involved so because it's aqueous we have h plus oh minus the sodium well that's in group one so we have na plus chlorine is in group seven eight takes seven is one so it's cl minus and then when we come to look at the product at the anode remember only one product can be formed and at the anode you're gonna find that the halogen wins in every single case the halogen here is group seven which is why chlorine is produced here the product at the cathode where you're looking for the least reactive element out of the positive ions so we're looking at hydrogen and sodium clearly hydrogen is far less reactive than sodium sodium is an extremely reactive group one metal which is why we're going to have hydrogen produced here the chlorine and hydrogen will be bubbled off as with the hydrochloric acid example above electroplating now and that's where you cover an object with another metal you need to know a few things here which is that first of all rather than using platinum or carbon as the anode or cathode what you're going to do here is use the metal that you're coating your object with as the anode object being coated or plated is your negative cathode the electrolytes so the substance undergoing electrolysis is actually a solution of a soluble compound of the metal and when electrolysis occurs what you find is the metal ions are reduced at the cathode so for example if we were coating in copper they would be reduced which means they gain electrons at the cathode to become copper solid and as a result that cathode becomes plated or covered in that ideal metal which in this case would be copper so let's look at some uses of electroplating and really it's because electroplating objects gives them much better properties compared with usual or it means it's cheaper to have a particular object so famously lots of jewelry is electroplated so things if you buy a necklace and it sells says that it's silver plated that has undergone electroplating and you tend to find that the actual necklace itself is made out of copper and then it has a very thin layer of silver over the top so why would we want to do that well because silver is exceptionally expensive it's very rare there isn't very much fun within the ice crust copper is way cheaper so if you make the bulk of the necklace from copper add the silver plate you get the same effect obviously the quality won't be the same we also coat steel bumpers so that's a part of a car with chromium chromium is very hard and very shiny so it's aesthetically really pleasing it's got great properties but it's very expensive hence why we don't make the whole object out of chromium lastly we coat cans or tin cans which are made out of steel so a sausage can that you get baked beans out of or something it will mostly be made out of steel but it'll have a coating of tin on it because tin is corrosion resistant and won't react with the food contents which we really don't want to happen obviously so remember a cell is an object which can produce electrical energy you do need to know that a simple cell is actually made out of two metals and an electrolyte a redox reaction takes place which is where reduction and oxidation occur at the same time and while this is taking place an electric current is formed so we know all about fossil fuels as a method of producing lots of energy but we're looking for cleaner fuels and one particular fuel we're very interested in is hydrogen so the reason we're very keen on this as a possible source of energy is because first of all it's exceptionally available it comes from sea water the reaction that takes place is actually hydrogen reacts with oxygen forming water let's balance this equation this is a great thing to happen because water is not a pollutant we need to drink it every day to keep ourselves alive it's a very clean by-product unlike the carbon dioxide carbon monoxide that comes from burning fossil fuels this process is going to be carried out using a hydrogen fuel cell and what you find is that hydrogen is oxidized at the negative pole which means that it loses electrons and then conversely you find that oxygen is reduced at the positive pole so we're going from oxygen gas to the iron which is o2 minus it's reduced which means it needs to gain electrons and now we need to balance our oxygens because oxygen is diatomic we need a 2 here it's reduced which means it gains and we need a 4 e minus there so with the term exothermic let's define it first of all it means the release of heat energy and remember that more energy was needed to make the bonds in the products than was needed to break the bonds in the reactants so looking at endothermic reactions you'll see the opposite so heat energy in this case is taken in and more energy is required to break the bonds and the reactants than was needed to make the bonds in the products other times we need to know activation energy this is simply the minimum amount of energy required for a reaction to occur how do catalysts work well we know from biology that they speed up the rate of reaction without being used up in terms of how they work it's because they provide an alternative reaction pathway with a lower activation energy and i'll show you some energy profiles so you can actually see that lowered activation energy so i thought the easiest way to talk youtube's energetics topic was to take you through some past exam questions because they're pretty much all the same so the moment you see a polystyrene cup and a thermometer we're looking at enthalpy so be aware of what endothermic and exothermic means here so remember exothermic means gives out heat energy and endothermic means takes in heat energy and with an exothermic reaction you're looking for a negative delta h whereas endothermic you're looking for a positive delta h again in terms of the actual temperature of the beaker or the cup an exothermic reaction will get hot and an endothermic one will get cold and if you bear that in mind hopefully you'll make answering these questions far more straightforward the student uses this apparatus to investigate the heat energy released when nitric acid is added to potassium hydroxide solution so we've got nitric acid inside the buret which is going to be dripped into the polystyrene cup containing potassium hydroxide she uses this method put 25 centimeters cubed of potassium hydroxide solution into the polystyrene cup measure the temperature of the potassium hydroxide solution add five centimeters cubed of nitric acid from the buret stir the mixture and make and measure the highest temperature reached add further five centimeters cubed samples of nitric acid stir and measure the highest temperature reached after each addition name the piece of apparatus that should be used to measure the 25 centimeters cubed of potassium hydroxide solution so you need a fairly precise piece of apparatus here which is why you should state either a pipette over a burette measuring cylinder would not be precise enough the table shows the student's results so here she's got the different volumes of acid and the highest temperature reached and we can see the highest temperature was reached when the largest volume 30 centimeters cubed of acid was added the result for 20 centimeters cubed is anomalous suggest two possible mistakes other than misreading the thermometer that the student might have made to produce this anomalous results so remember anomalous means that it's the odd one out it it isn't quite what you would expect and if we actually look at those results it's 31 which is pretty close to 29 so we're thinking that the temperature is too low so what could have caused the temperature to be too low aside from misfeeding the thermometer well first of all she could have added less than five centimeters cute extra off the acid secondly she might not have waited until the highest temperature was reached and thirdly remember when you're doing this experiment it's really important that you stir the reactants so she might not have stirred them properly suggest a true value for the temperature when 20 centimeters cubed of acid is added so let's have a look you kind of want somewhere that sits between 29 and 37 so i'd probably go in at 33. in another experiment student records these results volume potassium hydroxide solution starting temperature of potassium hydroxide solution total volume of acid added and the highest temperature reached by the mixture and we're calculating the heat energy released using this equation q equals m c delta t so this is really nice they're giving us pretty much all of it so q is what we're after mass of the mixture so you need to add those two volumes together so 25 plus 25 is 50 times the specific heat capacity which we've been given is 4.18 times the temperature change which is we know it goes from 16 to 35 meaning that there has been a 19 degree increase and then when you pop that into your calculator you get a value which is 3970 to 4 significant figures let's have a look at some more questions so explain in terms of making and breaking bonds why some reactions are endothermic draw a labeled energy level diagram for an endothermic reaction so this is what you need to do you need to do your axes here the y-axis is the energy and the x-axis is basically the progression of the reaction so remember with endothermic you're looking at a positive delta h which means that the products by definition must sit at a higher energy level than the reactants so make sure they are and then we label them products we've got our reactants over here and then just draw an arrow from the reactants to the products going upwards so delta h is positive use the bond energy data to calculate the answer we change the reaction below making sure to give a sign in units in your answer draw a labeled energy level diagram for this reaction five marks okay so this is good if they haven't drawn them out for you like this you need to see all the bonds make sure you draw out that diagram otherwise you'll screw up so it's so important that if they give you it looking like this instead like ch4 plus 302 it is essential that you convert it into a picture like this so let's have a look at the bonds broken first of all and so just start by listing the bonds so we've got ch and how many do we have we've got one two three four and i do like to cross the model to make sure i've got more then look into the table and it's four one two then we've got one cc bond which is six one two and then we've got three lots of the oxygen so that's three times four nine six use your calculator to add it all up these questions are just about being accurate more than how difficult they are so you must check your answer that's three seven four eight now bonds made so be careful here we've got an oc bond and count how many there are there one two and then there's a big two there which means there's four times seven four three which i've got from the table again and then again with the oh we've got one two and then the two again so it's four times oh h so four times four six three and that gives us four eight two four and then in order to work out this you need to do three seven four eight take away four eight two four to get minus one zero seven six kj mole to the minus one be careful with your units and that reaction is therefore exothermic because it's a minus just to show you how to draw the energy level diagram really similar to what we did above here are our axes we've got energy or enthalpy on the y-axis now do you remember because it's exothermic that our products therefore have less energy than our reactants which is why it's this way around we know the area is going to go down and it's by minus 1076 kj multiple minus one and then just label your reactants and you can be really precise here because you can actually see what the reactants are so i'm just going to write c2h4 plus 302 as the reactants and then i can see that the products are 2 co2 plus 2 hto h2o now we're moving on to rates of reaction so looking at the effect of temperature surface area and concentration on rates of reaction so what effect does increase in the temperature have on the rate of reaction well clearly it's going to increase it the reason why is because particles have greater kinetic energy so they collide more frequently the collisions are harder and therefore greater proportion of these collisions result in the required energy to overcome the activation energy looking at concentration now so if you increase the concentration of particles that means that there are more particles in the same volume clearly collisions will occur more frequently and therefore the rate of reaction will increase surface area now if you increase the surface area for example by powdering marble chips powdered marble chips have a larger surface area than giant lumps and so by increasing the surface area you're ensuring that you have an increased frequency of collisions and therefore the rate of reaction will increase and do make sure you can argue this from if you decrease the surface area decrease the concentration and decrease the temperature you just need to say the exact opposite remember there are several ways in which you can measure the rates of reaction so rates of reaction are given by for example the change in volume over time the change in concentration over time now if we use the marble chip example remember that marble chips when reacted with hydrochloric acid they will produce carbon dioxide so you can measure how quickly that carbon dioxide is produced either using a top pan balance now remember that needs a high resolution because carbon dioxide doesn't weigh very much so you need at least like 0.00 on your weighing scale in order to measure that difference so when it escapes at the top of a conical flask you'll see the mass decreasing and you can measure that over time equally you could use gas syringes and that will show you the volume of carbon dioxide that's released you can't use this method if you're measuring hydrogen gas because it is too light so you won't actually be able to see a change in the reading on the measuring balance sometimes i have experiments involving crosses being obscured due to a precipitate being formed so you measure the time taken for the cross to disappear but that's obviously fought with difficulties because it's very much human judgment as to decide when that cost disappeared so do be prepared to talk about some limitations related to the methods used so chemical equilibria now we are looking at reversible reactions here so be aware of this special arrow this is your reversible arrow and it tells you that the reaction is happening in both the forward and backwards direction and what that really means is the reactants react to produce the products as we're used to seeing but then the products will fall apart effectively and produce the reactants again so these aren't ideal conditions when we're talking about industrial processes because it basically means you make very little of the products that you're after and we use the word yield to describe the amount of product produced so let's start by looking at what a dynamic equilibrium means now first of all the word dynamic means that the reactions are ongoing which means that the forward and reverse fractions are occurring at the same time because it's equilibrium it means they're occurring at the same rate and that there is no overall change in the concentrations of reactants and products and this is only true if it has within a closed system and a closed system is simply one where nothing is allowed to escape so no gases can leave and no more reactants get added it remains a sealed vessel so looking closer at dynamic equilibria let's look at the effect of a catalyst now you must notice that a catalyst simply increases the rate of reaction we know this i've just said it it does it by providing an alternative reaction pathway with lower activation energy note it does not alter the position of equilibrium so it doesn't increase the yield of the products it keeps the position of equilibrium in the same place it just increases both the forward and reverse reactions equally a summary now of what happens when we choose to alter reaction conditions so remember we can alter the position of equilibria if we change both the temperature and pressure as i've already said the catalyst has no effect remember when a reaction is exothermic the whole reaction gets hotter and when it is endothermic the whole reaction gets cooler so if we start by increasing the temperature we know we need to oppose the change so we're going to favor the reaction which results in a decrease in temperature which is why increasing the temperature favors the endothermic reaction and that means that the position of equilibrium will shift to favor that endothermic reaction so if you have an equation and the delta h says that it is positive we know that the forward reaction is therefore endothermic so increasing the temperature will favor the forward reaction decreasing the temperature will favor the exothermic reaction and the position of equilibrium will shift to favor that and if this is selling home page don't worry because we're going to use the hardware process as an example to help us understand it looking at pressure now if you increase the pressure what happens is equilibrium position will shift to favor a decrease in pressure so it will shift to the side with a fewer moles of gas and you count the number of moles by looking at the big numbers in front of the formula decreasing the pressure will favor the side with increased number of moles of gas so position of equilibrium will again shift so the harbour process this is the manufacture of ammonia and it involves the use of nitrogen and hydrogen delta h is negative which means the forward reaction the reaction which produces ammonia is exothermic so in order to increase the yield of ammonia it makes sense therefore that we decrease the temperature why because the forward reaction is exothermic so the position of equilibrium will shift to the right and therefore more ammonia will be made however the problem with low temperatures is it's all to do with collision theory means that the particles have very little kinetic energy so although when they collide a reaction takes place the likelihood of them colliding is now very low because of the low temperatures which is why we actually have to increase the temperature to 450 degrees celsius and we therefore call these conditions compromised looking at the pressure now if we count the number of moles of gas by looking at the balanced symbol equation you can see that there are four moles of gas on the left hand side and two moles of gas on the right hand side so in order to increase the yield of ammonia we need to increase the pressure because remember increase pressure will favor the side with fewer moles of gas therefore the position of equilibrium will shift to the right meaning that more ammonia is made now again this is a compromised condition because although the high pressure will favor increased yields unfortunately high pressures are expensive and they are dangerous because the vessel reaction vessel needs reinforcing and therefore we used a compromised pressure of 200 atmospheres we do add an iron catalyst when we're talking about ammonia the addition of the iron catalyst increases both the forward and reverse rates of reaction but it has no effect on the position of equilibria and therefore it has no effect on the yield of ammonia let's look at another example now so i'm going to bring up an equation which is showing no2 reversible arrow and n2o4 and do notice their colors no2 is brown and n2o4 is colorless and look at the delta h sign it is an exothermic reaction so let's see what happens when we increase the temperature so what happens when we increase the temperature is the endothermic reaction will be favored which means the reverse reaction will be favored so the position of equilibrium shifts to the left you therefore make more no2 and so therefore the color changes and it becomes brown looking at pressure now and we are going to increase the pressure so let's compare the number of moles of gas on both sides of the equation you can see that there are two no2s and only one n2o4 so increasing the pressure will favor the forward reaction so the position of equilibrium shifts to the right and therefore more n2o4 is produced so the color will change to colorless so be prepared to talk about what effect various changes in pressure and temperature will have and again notice catalysts have no effect let's remind ourselves of the definitions of oxidation reduction so oil rig oxidation is the loss of electrons and reduction is the gain of electrons redox now and that as the name suggests is a reaction where reduction and oxidation occur at the same time a reducing agent is a substance which causes another substance to be reduced so it forces the other substance to gain electrons and therefore by definition reducing agent is therefore oxidized an oxidizing agent causes a substance to become oxidized so it forces the other substance to lose electrons and therefore by definition an oxidizing agent is reduced we're looking at rules for determining oxidation states when we're looking at all station states it all relies on us understanding what oxidation and reduction are so remember oil rig will help you with this so oxidation is the loss of electrons whereas reduction is the gain of electrons and that is key however at this high level it's not always easy to see how electrons have been transferred in redox processes and remember redox processes are ones where oxidation and reduction occur at the same time and therefore oxidation states are a made-up tool made up by us in order to help us identify which species have been oxidized and which have been reduced and basically there's a whole set of rules you need to follow and if you follow those rules you'll be able to first of all work out the various oxidation states and secondly work out what has been oxidized and what has been reduced so to put that into words oxidation states are a useful tool for allowing us to identify which species has been oxidized and which has been reduced so here are oxidation state rules or you could have said our oxidation number rules it means the same thing and our first rule you have to learn is that elements which are not combined with other elements have an oxidation state of zero so let's look at some examples oxygen phosphorus sulfur as elements by themselves have an oxidation state of zero for number two the oxidation state or oxidation number of any young combined ion is the same as its charge so taking sodium ion for example its oxidation state will be plus one calcium its oxidation state will be plus two so its oxidation state or number is the same as the charge on its ion rule three the sum of all the oxidation numbers in a molecule is zero such as water carbon dioxide hydrogen chloride etc so the sum of all the oxidation numbers so that means the individual oxidation numbers here so the oxidation number of hydrogen and the oxidation number of oxygen two lots of hydrogen plus the oxidation number for oxygen will equal zero carbons oxidation number plus two lots of oxygens oxidation number will also be zero and so on nb linked to this point we need to consider ions and we're looking at more complicated ions so ones which contain two or more elements so i'm going to call that in a complicated ion the sum of oxidation numbers is equal to the charge of the ion so taking the ion so42 minus so the sulfate ion what that means is if you add the oxidation number of sulfur to four lots of oxygen you'll still have a net charge of two minus for the nitrate ion if you add the oxidation number for nitrogen to three lots of oxygen you'll have a net charge of one minus next i have a couple of elements which you just have to learn the numbers for so hydrogen try and remember that that always has an oxidation number or state of plus one the exception is hydrogen combined as a metal hydride and here it has an oxidation number of minus one so you must learn that exception fluorine is the second element you need to know the oxidation number off by heart and its oxidation number is always minus one oxygen now this is slightly more complicated it usually has an oxidation number of minus two however there are a few exceptions so firstly in peroxides it has an oxidation number of minus one instead of minus two and secondly when it combines with fluorine it has an oxidation number of positive one in order for this to make more sense let's write the peroxide formula and that's h2o2 so hydrogen will have an oxidation state of plus one and oxygen in this case according to our exception will be minus one by the way guys some teachers might have taught you this in terms of which elements are more electronegative so you treat covalent compounds as ionic compounds obviously that method works too but this for me is the most straightforward thing to do because you just have to learn a load of rules and it will make sure you get the answer right every single time anyway rule seven looking at chlorine now as the element remember that it always has an oxidation number of minus one there is an exception here so when it's combined with fluorine it switches the sign of its oxidation number to being positive and the same is true for oxygen now the number it turns into will very much depend on the compound you find it in and we will look at some examples to make sure that actually makes sense for you guys and then the last rule which is fairly straightforward and hopefully you remember this from gcse and igcse for groups one to three the oxidation number is the same as the group number eg sodium is in group one so its oxidation number is plus one now according to rule three the sum of all oxidation numbers in a molecule is zero we know that overall this charge on the ammonia will be zero and that's helpful because now we need to work out the various oxidation numbers of both nitrogen and hydrogen so according to rule four we know that hydrogen has an oxidation state of plus one we know that there is no overall charge so because we have three hydrogens we have a plus three charge so what must the oxidation number of nitrogen be well it must be minus three following on from our oxidation state rules we need to be able to look at redox reactions and look at the equations and decide what has been oxidized and what has been reduced so we're going to have our rules side by side so we can refer to them because we'll need to know what the various oxidation states are in order to do these questions looking at our first equation therefore we've got sodium which is a solid oxygen which is a gas forming sodium oxide and we need to compare the various oxidation states of the elements on both sides of the arrow so starting with sodium well according to rule one elements not combined with other elements have an oxidation state of zero so here we know sodium has an oxidation state of zero looking at it in sodium oxide so according to rule eight for groups one two and three the oxidation number is the same as the group number so sodium is in group one which is why its oxidation number here is plus one looking at oxygen now now oxygen is an element not combined with any other elements according to rule one its oxidation state is therefore zero and then combined with sodium so as sodium oxide we know according to rule six that it has an oxidation number of minus two and do check that the overall net charge is zero on these things to make sure you're doing it right and now let's just have a look at what's happened with the numbers so sodium has gone from zero to plus one which means that it has lost electrons in order to become positive and because it's lost electrons according to oil rig we know that sodium has therefore been oxidized oxygen has gone from zero to minus two which means it's gained electrons so it has been reduced and then depending on how they ask the question you can add a couple more statements so although sodium has been oxidized it means it has automatically acted as a reducing agent because it has caused oxygen to be reduced so you can write sodium has been oxidized and you can also write sodium acts as a reducing agent concurrently if oxygen has been reduced it means it's automatically acted as an oxidizing agent let's look at a second example where copper oxide reacts with hydrogen to form copper plus water so starting with oxygen let's work out its changes in oxidation state according to rule six it has an oxidation state of minus two there are no exceptions here so we're going to put minus two here and looking on the right hand side again oxygen will have an oxidation number of minus two so here nothing's happened to it it hasn't been oxidized or reduced because its oxidation state has remained the same copper now well we know the net charge of copper oxide is zero so by definition copper must therefore have an oxidation state of plus two and then on the right hand side it exists as an uncombined element according to rule one its oxidation state must therefore be zero hydrogen now hydrogen exists as an uncombined element on the left hand side its oxidation number is therefore zero on the right hand side it exists in water the net charge must be zero so that means that each hydrogen has an oxidation number of plus one and now we can work out what has been oxidized and what has been reduced so copper has gone from plus two to zero which means it has gained electrons in order to become effectively more negative so copper has been reduced and we might as well write the matching statement here which is that it acts as an oxidizing agent looking at hydrogen now hydrogen's gone from zero to plus one in order to become positive it must have lost electrons according to oil rig it's therefore been oxidized and automatically acts as a reducing agent let's look more closely at the topic of acids bases and salts now first of all we need to start by listing the properties of acids now we know an acid donates hydrogen ions it has a ph of less or equal to six because remember ph seven is neutral and because of this low ph remember it turns litmus paper which is a type of indicator to show how acidic or alkaline substances and that will turn red similarly universal indicator will turn red in a strong acid orange in a weak acid like a medium acid and yellow in a weak acid you need to be very clear on the reactions which i'm going to go into in more detail but just to summarize here if you have a metal and an acid you produce a salt and hydrogen i promise i'll show you examples including actual metals if you have either metal oxide or hydroxide plus an acid you produce a salt plus water and then lastly metal carbonates plus acids form a salt plus water and the carbonate indicates that you'll produce carbon dioxide the last indicator i meant to mention which i probably should further up is to notice methyl orange handily also turns red in the presence of acid let's look at bases now remember that these are hydrogen ion acceptors again we need an in-depth knowledge of the color that all the indicators turn remember that bass has a ph greater or equal to eight so they will turn universal indicator blue or purple litmus paper again will turn blue methyl orange unluckily doesn't turn blue it turns yellow now in terms of their reactions you need to remember that a base reacts with an acid to form a salt plus water and lastly notice the difference between an alkali and a base and really the only difference here is that an alkali is a soluble base so if we do a little venn diagram you'll find that all alkalis are bases but that not all bases are alkalized let's look at the difference between strong and weak acids the crucial thing here is that in a strong acid remember it contains lots of hydrogen ions and what you find is that they readily dissociate and what that really means in layman's terms if you have hydrochloric acid that is a strong acid and it will extremely easily give up all of its hydrogen ions or pretty much most of them whereas with a weak acid you find that the hydrogen ions don't readily dissociate they don't enter the solution easily and they stay combined with their other ions so something like ethanoic acid which is a carboxylic acid we call this a weak acid because it doesn't give up its hydrogen ions easily and remember the acids in solution can carry a current and that's due to the presence of the hydrogen ions clearly with a strong acid there are more hydrogen ions so the solution can carry more current than compared with a weak acid and more easy to understand is the fact that you will see a lower ph with a strong acid so approximately two maybe whereas a weaker acid you'll see a much high ph of approximately six looking at the bases now so the strong and weak bases luckily it's incredibly similar to what we've just learned with the acids so you can pretty much say the same thing which is that a strong base will readily dissociate a weak base will not readily dissociate again similarly you'll see that you can carry a much larger current with a strong base and in terms of the ph you're looking at about a ph of 13 for a strong base whereas a ph of around 8 will be seen with a weak base so we've talked a lot about ph's let's quickly chat about it more so the ph of 7 as i've already said is neutral ph of 14 which is one end of the ph scale will be very strong alkali or base a ph of 0 will be a very strong acid and then you have the intermediate value so ph 8 will be a weak alkali or base a ph of 6 will be a weak acid and let's look at the colors so neutral is green you get quite purpley at the very strong alkali end you get red at the acid end and we like universal indicator because that can basically show you what ph you have you add universal indicator to the solution it turns a certain color which you can compare to a scale and work out the approximate ph we're now going to cover the salts topic and when we're talking about salts we need to know a lot about acids and bases because that's where the salt originates from so do you remember your definition of an acid which is that it is a h plus donor a base is a h plus acceptor and it also tends to be a hydroxide donor and examples of bases include metal carbonates metal hydroxides and metal oxides just remember the difference between a base and an alkali they're very similar an alkali is simply a soluble base so remember all alkalis are bases but not all bases are alkalized so some background about salts so effectively a salt is formed when the hydrogen of an acid is replaced with either metal or ammonium for example say you had hydrochloric acid you acted it with potassium oxide then you would end up with potassium chloride which is the salt taking sulfuric acid now pretend we reacted it with calcium carbonate you'd end up with calcium sulfate which is the salt so now let's look at some common acids and the salts that they produce now in terms of the reactivity of acids remember that only metals above hydrogen in the reactivity series will react with acids so things like copper silver and gold which lie beneath hydrogen in the reactivity series will not react elements at the very top of the reactivity series such as potassium sodium and lithium they will react extremely explosively and i don't recommend that anyone tries this because it would be extremely dangerous so now let's take you through the salt equations so we're going to start with looking at the general equation when you have metal plus an acid that forms salt plus hydrogen and i'm going to show you some examples if you have metal oxide plus an acid then you make salt and water metal hydroxide this time it's the same as metal oxide in that you produce a salt and water and lastly metal carbonates when you react those with acids you produce a salt plus water and then because of the carbonate you produce carbon dioxide so do make sure that whatever is on the product side start it off on the reactant side don't start creating carbon dioxide on the right hand side when there was no carbon on the left hand side and similarly don't have hydrogen and water forming on the right hand side only one of them forms so make sure you know which one it is solubility rules learning which salts are soluble and which are insoluble the reason why i'm smiling is because this is disgusting it's awful i really struggle to remember them now there is a huge table which you can try and learn off by heart but i much prefer to learn the rules and if you assume that most things are soluble and learn the exceptions that's a good way to go so let's start by stating that all nitrates are soluble all potassium ammonium and sodium compounds are soluble full sulfates are soluble there are three exceptions and that is lead to calcium and barium sulfate all chlorides are soluble except from lead ii chloride and silver chloride now we switch and we look at things which are insoluble so we say that all carbonates are insoluble the exceptions will clearly be the sodium potassium and ammonium compounds which makes sense because i've already told you that the sodium ammonium and potassium combines are soluble and similarly all hydroxides are insoluble the exception being sodium potassium and ammonium compounds so let's just do a quick test on that so i'm just going to say a couple of salts and you need to decide if they're insoluble or soluble so starting with lead nitrate that is soluble because it contains nitrates next up potassium carbonate that is also soluble because it contains potassium now we're looking at magnesium sulfate that is soluble because remember all sulfates are soluble with a few exceptions what about barium sulfate well that was one of the exceptions you have to learn so that is insoluble and now calcium carbonate that is insoluble because it is carbonate and it is not sodium potassium or ammonium so i hope you can see you can work it out using these rules so let's look at the different methods for making these salts and we're going to start by looking at soluble salts but do notice these are ones which do not contain ammonium potassium or sodium so what you can do here is you can use metal oxide a metal hydroxide or metal carbonate you react with the acid and you form your soluble salt you can also use metals plus acid so it doesn't need to be combined with an oxide hydroxide or carbonate but do notice that you need a metal which isn't mega reactive because clearly if you're reacting it with an acid you could end up with a dangerous explosion if you're using group one metals so be sensible and use something like magnesium now the method you're going to actually use is crystallization your summary for this is that you're going to react for example your metal hydroxide with your acid you're going to filter in order to remove any undissolved solid then you're going to evaporate so you're going to place that solution in evaporating basin over a bunsen burner with gauze and a tripod and you're going to get rid of excess water so you evaporate some of the water then you're going to allow the mixture to cool and eventually you want to let it dry out in a warm place so on a warm windowsill in a drying oven for example or on paper looking at making soluble salts now ones which do contain sodium potassium or ammonia you're going to use a slightly different method now the reason why you can't use the crystallization method i just described because the sodium potassium ammonium are extremely soluble so if you added them to acid which contains water they would react with both the acid and the water and they would continuously dissolve away meaning that there'd be nothing to filter and therefore nothing to evaporate so that's why crystallization doesn't work in this case so in this situation you have to use the titration method so titration is the method you use when making ammonium sodium or potassium salt the reason you use the titration is because you need to know the exact volumes of acid and alkali you need to add in order to make the salt so for example we set up our burette and it contains the acid we place the alkaline conical floss together with an indicator and then as you know with a titration you keep adding the contents of the buret to the conical flask swirling all the time until you get that indicator to change and when it does that you know you have the exact volume of acid and alkali then you repeat the entire experiment this time without the indicator because obviously that would disrupt your salt and because you know the exact volumes of both the acid and the alkali you can create the exact amount of salt there won't be any excess to dissolve away and therefore you'll have a perfect salt once you've done that your method is the same as we've just described with crystallization because you've got your solution you now need to evaporate off the excess water you need to allow it to cool and then you're going to leave it to dry in a warm place again so it's very similar to the crystallization method you you still use it but unfortunately you have to use the titration method initially in order to obtain the correct volumes lastly we're making insoluble salts in this case you're going to react two soluble salts and obviously make sure you pick the right salts that will create the insoluble salt you're after so if you're after barium sulfate as your insoluble salt clearly the first thing you're reacting has to contain barium so something like barium nitrate the second thing has to contain sulfate so it could for example be potassium sulfate you react them together in order to form barium sulfate and leftover will be potassium nitrate so do be sensible make sure that whatever's going in will make your insoluble salt which is why it's important that you know your solubility rules so you know which salts are soluble and which ones are insoluble by the way this is a disgusting topic um everyone thinks so so don't worry if you'll find it quite tricky so when you're making insoluble salts this is actually the most straightforward method you'll use you're going to react so you're going to mix those two soluble salts together you're going to filter to remove any excess solid you're going to wash again to remove that extra solid and lastly leave to dry and do state where you're drying it don't just stay dry so stay in a warm place or on filter paper or in an oven and this method we describe as being the precipitation method i'm just going to describe an example of the precipitation method to try and show exactly what is going on so in this example we're going to take silver nitrate and sodium chloride notice that they are both soluble because they contain nitrate and they contain sodium so what happens when you place them in solution is all the ions separate so you left with ag plus which is silver chloride ions which is cr minus nitrate ions which are no3 minus and sodium which is na plus now in order to make that insoluble salt remember what we want to happen is for the silver and the chloride to be attracted and indeed they are they are strongly attracted forming silver chloride which is an insoluble salt now the remaining ions the nitrate and the sodium are very weakly attracted so they remain in solution and they're the soluble salt formed we've won elements now so remember that is the first column of the periodic table it is the alkaline metals they all have the same chemical properties because they have one electron in that outer shell now remember as you descend that group the elements become more reactive they're all extremely reactive as it is but as you descend the group they get more reactive the reason for this is because as you descend the group the atoms get larger because if you actually look at their atomic number it's higher for potassium compared with lithium so the atoms are larger this means the outer shell electron is further from the nucleus which means that it's more shielded by the inner shells of electrons this means it's easier to lose the electron and remember when we lose the electron that's when it partakes in chemical reactions so it's more likely to do that so it is more reactive than elements higher up than it in the periodic table i've already touched on the fact that group 1 metals are extremely reactive this means that they must be stored in oil because they'll react with the slightest bit of moisture they're soft and you can actually cut them with a knife and they oxidize very easily so they go from being shiny to oxidized very quickly on exposure to ah other properties they have is they have low melting and boiling points which makes them quite unusual for metals and they also have a low density and we can see this when they're placed in water they actually float on the water so again these are really quite unusual properties for the group one metals now they're very reactive as i've already said and they can react with oxygen to form oxides so potassium oxide for example they can react with cold water to form hydroxides potassium hydroxide for example they can react with the halogens remember those are the elements in group seven of the periodic table to form something like potassium chloride and they can partake in ionic bonding let's now look more closely at observations when they're added to water so this will be true for all group one elements first of all they fizz and what that actually means is they're releasing hydrogen gas they float they move around they form a small ball which eventually dissolves if you were to add universal indicator to that leftover solution you would see that it would turn blue and that makes sense because remember blue indicates alkali and they're called the alkali metals that makes perfect sense in terms of more specific observations remember that lithium doesn't produce a flame however sodium produces an orange flame when added to water and potassium produces a lovely lilac flame learn the word equations for when they're added to cold water so i've already touched on this but a group one metal plus cold water will produce a metal hydroxide plus hydrogen which makes sense due to the fizzing that you witness so taking lithium for example plus water forms lithium hydroxide and hydrogen we don't add them to steam or to acid because that would be incredibly dangerous they also burn in air and they produce very characteristic flame colors so lithium bounds to form a red flame a crimson flame potassium again produces a lilac flame and sodium produces a yellow flame in terms of making predictions about group one metals below potassium so things like francium now you don't need to learn these observations off by heart but do notice that these observations with water will be more violent because obviously for all the reasons we've already described the atoms are larger more shells of electrons the electron feather from the nucleus so just be prepared to talk about the fact that they'll be more violent but you'd still see the same set of observations fizzing for example a flame moving around floating melting etcetera right so the halogens we're looking at group seven so these are the elements including fluorine chlorine bromine and iodine now don't forget their states at room temperature fluorine and chlorine are gases at room temperature fluorine is a yellow gas chlorine is a green gas then you have bromine which is a red brown liquid and finally iodine is a gray solid don't forget iodine undergoes process called sublimation which is when it turns directly from a solid to a gas and in the case of iodine it goes from a gray solid to a purple vapor now the halogens react with hydrogen to form hydrogen halides for example hydrogen plus bromine forms hydrogen bromide these are very acidic and poisonous and they're also very soluble in water so something like hcl gas will turn readily into hydrochloric acid so that's hcl aqueous on addition with water you need to know about halogen displacement reactions because more reactive halogens will displace less reactive halogens from their compounds let's quickly look at the reactivity of the halogens so remember at the top of the group that's where they're most reactive towards the bottom they're at their least reactive and we can look at the reason for this so iodine is much less reactive than fluorine because iodine is much larger so it has far more shells of electrons this means that the outer shell electrons are farther away from the nucleus they're more shielded and because of that it's harder to gain that extra electron in order to become full hence they are less reactive and this helps to explain why iodine is solid at room temperature so if we look at the halogen displacement table we tend to only look at the elements chlorine bromine and iodine you'll find that chlorine displaces both iodine and bromine from their compounds you clearly don't react chlorine with itself so potassium chloride because there'll be no reaction if you try and displace a potassium chloride for example using iodine that won't happen because iodine is less reactive so just learn the rules for this and the summary equations in terms of their general properties remember they have low boiling points and low melting points and they are poor conductors of heat and electricity so metals now we're going to start by looking at their properties so remember metals have high melting and boiling points they're good conductors of heat and electricity they are shiny they are sonorous which means when you hit it they make a noise they are malleable and ductile so what does malleable and ductile mean well malleable means that they can be hammered into shape and ductile means they can be drawn into a wire another thing to notice is stuff relating to how they bond so be aware that when they enter into bonding they tend to lose electrons to become positive ions they form basic oxides which we'll come into later and they partake in ionic bonding non-metals now their properties include the following they are dull so they're not shiny they tend to have low boiling and melting points there are exceptions to this which we'll come on to later but that is the general rule they are brittle which means when you hit them they easily break they form acidic oxides they gain electrons in bonding to become negative ions and they partake in covalent and ionic bonding why do we go to such effort to obtain aluminium well it's because it's an extremely useful metal it has really great properties mainly because it has low density so compared with other metals it's light but we can't say light in exam we say low density which means it's good for use in making aeroplanes we've always also seen its use in making drinks cans etc it's also a really good conductor of heat which is why you find a lot of pans are made out of aluminium which is why wiring can sometimes be made out of aluminium now copper copper is commonly used in electrical wiring and that's because it's an excellent conductor of electricity with that is its ability to conduct heat which means it can be used to produce cooking pots and pans so saucepans and touching a bit more on this why do alloys tend to be harder than pure metals remember an alloy is a mixture of metals or something like a mixture of metals and a non-metal so for example steel is an alloy of iron because it contains ion and carbon now wider alloys tend to be harder than pure metals that's because the alloys have irons of different sizes which means the layers can't slide as easily so it's not as easy to distort the layers looking at the uses of iron and you need to know about the different types of iron in terms of how much carbon they contain don't forget that when iron has carbon combined with it it's now formed an alloy and the alloy is called steel so looking at low carbon steel so that's steel containing less than 0.25 carbon you find that this steel is very strong malleable and ductile don't forget the malleable means it can be hammered into shape ductile means it can be drawn into a wire and its use is in car bodies that's to make the outside of a car for making bridges and ship building there are disadvantages with using low carbon steel and that's because it rusts easily and it's very heavy due to its high density stainless steel this is an alloy containing also chromium nickel and obviously iron this is highly resistant to corrosion or rusting which means it makes great cutlery so a lot of your cutlery your knives and forks and spoons will be made out of stainless steel and you'll probably see it written on that it's also used to make saucepans and gardening tools do reactivity series so you need to learn the order of metals in the reactivity series and that is potassium sodium lithium calcium magnesium aluminium then we mentioned carbon because although it isn't a metal it's good to use it as a reference point this is followed by zinc and then iron hydrogen comes next not a metal but still a good reference point and lastly our unreacted metals go copper silver and then lastly the most unreactive is gold and that explains why you find silver and gold native in the earth's crust you can literally just find it in streams and rivers and that's because it's incredibly unreactive even though aluminium looks fairly reactive because it appears quite high in the reactivity series due to its oxide layer it means it's less reactive than you would imagine so we have an unknown metal and we don't know how reactive it is so there are several things we can do to try and determine its position in the reactivity series so first of all we would try to react it with cold water now only very reactive metals such as those found in group one so we're looking at potassium sodium and lithium for example will react with cold water and they'll form metal hydroxide plus hydrogen which we've already met if they don't react with cold water you can then try steam and this will produce a metal oxide and hydrogen and then lastly if it doesn't react with steam you can try acid and that will produce a salt plus hydrogen and you obviously wouldn't try reacting group 1 metals with acids because they are far too reactive do notice that when you look at the reactivity series only elements which are more reactive than hydrogen will react with acids and that's because acids contain hydrogen such as hydrochloric acid it's hcl sulfuric acid h2so4 nitric acid hno3 so in order to react with acids they must be more reactive than hydrogen looking at protecting iron from rusting so rusting is when metals flake away and you only use the word rust when you're talking about iron if you talk about any other metal you can't call it rust you have to say it corrodes so you can say that zinc corrodes but only iron rusts so what conditions are needed for rusting to occur you need water and oxygen for this and salt actually increases the rusting process but is not necessary what are the different ways in which we can prevent rusting they're the simplest ways which is just simply painting or using oil and grease to protect the iron and stop it being exposed to water and oxygen or you can become more fancy and use methods such as galvanizing so galvanizing is when you use a more reactive metal such as zinc and it reacts before the iron and so actually what happens is the zinc zinc ions and then and donates electrons and what that means is the electrons can flow to iron and therefore if the iron starts to rust and form iron ions this is hard why they've got the same name those electrons which have been being donated from zinc can help the ion form its iron atoms again so it doesn't rust away try not to worry too much if you're not understanding what i'm saying just learn that galvanizing is using a more reactive metal to protect iron when other metals oxidize and react in preference to the iron through the method of galvanizing don't forget we call this sacrificial protection now we know that metals are incredibly useful they're used as all sorts of building materials in everyday life such as aluminium drinks cans but we need to know how we can extract them and there are two main methods which is either heating with carbon or electrolysis and the method you use very much depends on the reactivity of the metal because you can only use the heating with carbon method if your metal is less reactive than carbon for metals which are more reactive than carbon heating with carbon will have no effect and therefore you have to use electrolysis which is far from an ideal because electrolysis is an incredibly expensive process as it involves the use of electricity for extremely unreactive metals such as gold and silver you find these native so not reacted with oxygen or anything they're not found as oxides they're literally found as gold and silver native in the earth's crust which is why people used to pan for gold in rivers in america about 100 years ago in order to find the gold sitting in the riverbed so let's look at the blast furnace which is all to do with purifying iron and that iron exists as iron oxide in the earth's crust which we call hematite remember that heme means related to iron in the way that hemoglobin found in red blood cells contains iron so try to remember that now we're going to use the heating with carbon method and the reason we can do this is because carbon is more reactive than iron so this is a good process because it's not incredibly expensive so let's start by looking at the raw materials which will enter our blast furnace these are obviously the carbon which is entering in the form of coke the iron oxide and its iron iii oxide and lastly limestone is added to remove acidic impurities and now it's essential that we look at the various equations involved in the blast furnace so our first step is reacting carbon so the coke with oxygen to form carbon dioxide and if they ask you the point of this reaction is to produce the heat needed next up we're going to react that carbon dioxide produced in that step with carbon to produce carbon monoxide and do make sure you balance the equation and remember this is going to be the reducing agent which is all important as that actually is going to remove the oxygen from the iron oxide the next important step is what we're really after which is purifying that iron and it's going to produce iron by itself and carbon dioxide let's do some balancing and our summary here is the iron oxide is reduced to iron now it's important that we look at the limestone steps so this is kind of separate to everything that's gone on before so we have our calcium carbonate which is obviously limestone it's going to undergo a thermal decomposition reaction so make sure you can name the type of reaction to produce calcium oxide and carbon dioxide and it's that calcium oxide that's important because it reacts with the acidic impurities found within the blast furnace producing calcium silicate which we remember the formula of because remember most people have a calculator which is of the brand casio and if you remember that it's casio 3 and making sure that you lower an uppercase the appropriate letters you can therefore remember calcium silicates formula and its colloquial name is slag which is a very strange name but that floats on top of the iron and that is a summary of the blast furnace remember this final reaction here is a neutralization reaction when you now look at aluminium because that's another useful metal that's also too reactive to be found by itself in the earth's crust so it's found combined with oxygen you can't use the blast furnace in order to obtain the aluminium because aluminium is more reactive than carbon so if you try and burn them together nothing happens so this is where electrolysis comes in and we use aluminium oxide we electrolyze it and we have to therefore use huge amounts of electricity and that's why it's a far more expensive process compared with iron's blast furnace the second real expense with aluminium is if we look more closely at the reaction taking place what you find is there are carbon anodes which dip into the solution containing aluminium oxide because they're anodes clearly they will be positively charged this means that they attract the oxygen which is the negative ion and if we look at the summary equation we can see that o2 minus which is the oxygen ion loses electrons so it's oxidized to become oxygen gas but the oxygen gas formed actually reacts with the carbon electrodes forming carbon dioxide which actually burns away the electrode so in a month or so time the whole electrode disappears effectively so it needs replacing really regularly which is why it's such an expensive process we might as well talk about the reaction occurring at the cathode so remember that is the negative electrode so here the aluminium ion will be discharged so aluminium ar3 plus it will be reduced because it has to gain electrons in order to become al so it gains three electrons which is why we say reduction has taken place and have another look at the electrolysis part of this video if you're unclear as to what i'm saying now we need to look at the chemical and physical tests for water so the physical test for water is you just need to check a substance's boiling point if it was 100 degrees celsius you know you have water and linked with this how do you show that water is pure well i've already talked about pure substances having one distinct boiling point and the same is the case with pure water the whole lot should boil at 100 degrees if it's boiling over a range it tells you it's not pure now using a chemical test for water you want to add white anhydrous copper sulfate anhydrous means lacking in water once it's exposed to water it should turn blue and that tells you that the substance you have is water how do we make potable water or water suitable for drinking so first of all we want to find a clean source of water so ideally not one that's full of pathogens so bacteria and dirt and then after this we do need to make sure we clean it a little bit so we use a screen to track any large particles the coagulant is added and a coagulant is a substance which causes particles to stick together next up flotation tanks make these particles float so they can be removed they're literally skimmed off the top then we filter to remove smaller particles add chlorine because chlorine remember it's halogen it's incredibly toxic so that helps to kill the pathogens but obviously we don't want to add too much chlorine because then it would be unsafe for us to drink and then lastly that water needs to be stored in a clean environment let's look at fertilizers now so remember we add these to our fields to help the crops grow a little better so what elements do fertilizers contain well firstly they contain lots and lots of nitrogen and nitrogen is essential because it is needed by plants to produce amino acids and proteins fertilizers also tend to contain a lot of phosphorus which is need in the healthy growing of roots and to help crops ripen and then lastly potassium now notice that lots of fertilizers are called npk fertilizers and we can see that the n stands for nitrogen p stands for phosphorus and k stands for potassium as per their symbols in the periodic table we're going back to potassium why is this needed by plants because they use it to produce proteins and to help them resist diseases so first up air is largely nitrogen gas and 78 of it is nitrogen remember nitrogen is a diatomic gas which is why we write n2 21 is that life-giving gas oxygen again it's diatomic so we write o2 and then we have much smaller amounts of carbon dioxide so co2 little bits of water vapor as well as group zero so noble gases so less than one percent now we're going to touch on various pollutants starting with carbon dioxide carbon monoxide methane oxides and nitrogen and sulfur dioxide now you need to know where these various pollutants come from so carbon dioxide is produced by the complete combustion of fuels so what does that mean is when you burn fuels in a plentiful supply of oxygen now carbon monoxide if we just quickly look at the difference in their formulae carbon dioxide is co2 carbon monoxide is just co so it contains one oxygen and that's because it's produced by the incomplete combustion of fuels and that means that there was insufficient oxygen in the engine methane ch4 comes from the decomposition of vegetation and the waste gases from the digestion of animals and that's how it's worded in your specification you'll probably more commonly have known it from biology so that would be the rice paddy fields in terms of decomposition or vegetation and it would be cattle farming in terms of waste gases from digestion animals when the cattle burp and fart they release methane now the oxides of nitrogen i've just changed color so you can see easily where i'm writing they're produced due to the high temperatures in car engines cause the oxygen and nitrogen which we've already said are present in air to react together and then sulfur dioxide while the sulfur comes from sulfur impurities which are originally in the crude oil used to produce the fuel so that's where these various pollutants originate from now we need to look at the adverse effect that they actually have so carbon dioxide again you may have studied this in either biology or geography it's a greenhouse gas which in larger amounts can cause global warming and we know that that leads to massive amounts of climate change and extinction of species carbon monoxide is a toxic gas why because it combines irreversibly with red blood cells in the blood and therefore lowers oxygen carrying capacity of the blood methane is a greenhouse gas so everything we've written over here relating to carbon dioxide is again applicable for methane now oxides of nitrogen lead to acid rain because those nitrogen oxides dissolve in rainwater to form acid rain with low ph they can cause photochemical smog and respiratory problems and then sulfur dioxide is another form of acid rain one final thing to mention is particulates which again tend to be caused by unclean fuel these lead to increased respiratory problems and also increased cancers now if you're doing the extended paper you need to know quite a lot detail to do with the greenhouse effect and so we're going to use this diagram to help us so the first thing to be aware of is the sun over here emits thermal energy in the form of infrared radiation and that's going to enter the earth's atmosphere now some of this thermal energy is absorbed by the earth but then you find that some of it is reflected back out into space and if we look more closely at that absorption of the thermal energy how's that actually carried out it's carried out by greenhouse gases such as carbon dioxide and methane and this is perfectly normal however due to all the human activities we carry out such as burning fossil fuels deforestation you find that as those levels of greenhouse gases in the atmosphere rise more thermal energy is absorbed and trapped so human activities eg deforestation and combustion lead to increased greenhouse gases meaning that more thermal energy is absorbed and trapped so our earth's average temperature is rising this is known as the enhanced greenhouse effect less thermal energy is lost to space and therefore global warming has taken place now i'm always looking at ways in which we can reduce the effects of these environmental issues so how do we reduce the effects of human activity on the earth so to reduce climate change we can do quite a few different things we can plant more trees because remember carbon dioxide is used by trees in their photosynthesis and then a useful byproduct photosynthesis remember is oxygen which we need for respiration we can decrease our livestock farming make the links here why because fewer cows means a reduction in methane gas which is burped and farted out we can decrease our use of fossil fuels so less complete combustion will lead to less co2 being released less incomplete combustion will lead to less carbon monoxide being released and remember linked with fossil fuels was also nitrogen oxides and sulfur oxides which lead to acid rain so if we burn less fossil fuels then theoretically we'll have less acid rain and then what active things can we do well we can use hydrogen as a fuel because remember that produces water as a waste product which is perfectly fine not at all bad for the environment or ourselves and because of that reason it's a clean fuel so no co2 or carbon monoxide is produced we could also use renewable energies for the same reason fewer polluting gases produced and what kind of renewable energies so touching lots and geography biology and physics here solar wind tidal to name three now we're going to touch more on the acid rain points after how we're going to reduce acid rain through use of catalytic converters we're going to reduce our emissions of sulfur dioxide use low sulfur fuels and then we're going to carry out flue gas desulfurization with calcium oxide so flue gas is just waste gases that come from combusting any fuels so we're saying that we're going to remove the sulfur so desulphurization of those waste gases and the substance we're going to use that is calcium oxide now we're going to look at slightly more detail as to how that catalytic converter works notice that the gases going into the catalytic converter i produced carbon monoxide by the incomplete combustion of fuels nitrogen oxides due to the high temperatures found in car engines oxygen obviously is fine then you have a honeycomb stretcher which increases the surface area the honeycomb actually contains metals such as platinum and that platinum is acting as a catalyst and what you actually find is the carbon monoxide is converted to carbon dioxide yes it's still a greenhouse gas but at least it's not toxic anymore that nitrogen oxides which cause acid rain are converted to nitrogen gas vira and then oxygen remains unchanged you take that carbon monoxide going in as well as the nitrogen oxides and they are turned into carbon dioxide and nitrogen gas and then finally don't forget to balance it and so that's your summary equation strangely we do need to mention photosynthesis at this point which if you're studying biology you'll be very familiar with remember that's a reaction carried out by plants and it's used to produce their food glucose in terms of the equation for this reaction you need carbon dioxide water light energy and that's going to produce the plants food glucose and then oxygen as a byproduct remember that this takes place in plant cells so if we draw a basic plant cell here we have the nucleus cell wall cell membrane vacuole cytoplasm and in terms of where that photosynthesis is carried out it's in the all-important chloroplasts because they contain a photosynthetic pigment known as chlorophyll now for anyone studying extended science you'll need to learn the balanced symbol equation so carbon dioxide is co2 water is h2o glucose is c6h12o6 oxygen o2 and then just remember you need to add a 6 in front of everything apart from glucose and you'll have your balanced symbol equation so let's look at organic chemistry one of my favorite topics so first of all organic chemistry what are we talking about we're talking about hydrocarbons so what is a hydrocarbon it's a compound containing hydrogen and carbon only make sure you say only in order to get that second mark so when we're looking at organic chemistry we're really looking at different families of compounds and the simplest family is the alkanes and i'm going to show you now how to draw out the first four alkanes and we'll have a look at their general formula let's look at how we're going to draw various families of compounds starting with the simplest which is the alkane family do you notice their general formula is cnh2n plus 2 and you must obey that when you're working on the molecular formula if we take c4h10 as an example this is a molecular formula because it shows the actual atoms of each element present in the compound so it shows that this particular compound has four carbon atoms and ten hydrogens to make it into an empirical formula just cancel down those numbers so it becomes c2h5 because you can obviously divide four and ten both by two this is therefore the empirical formula because it shows the actual atoms of each element present in a compound and then just to notice a displayed formula is when you draw out all the ones so something like that so let's start by working out the first alkane so obviously it's going to have one carbon atom according to the general formula cnh2n plus two so substitute in the number of carbon atoms as n so it becomes c1 and then two times one is two plus two is four so h4 because it looks a bit strange to write the one i'm just going to erase that there's an invisible one so it's ch4 its display formula looks like this which is you draw the carbon in the middle and hydrogens around the outside remembering that each carbon atom forms four bonds each hydrogen forms one bond and you must remember that to help you draw them its name well it contains one carbon which is why it's meat and it's an alkane which is why it's methane so looking at the second one this time two carbons so we're gonna have c2 and then according to the general formula two times two is four plus two is six so it's molecular formula c2h6 drawing it out therefore carbons in the middle then you've got your hydrogens filling up around the edge each having one bond and each carbon atom has four because it's still an alkane it ends in ain but it contains two carbons which is why it's ethane the third one now so it's c3 two times three is six plus two is eight h8 three carbons in a line and zine it contains three carbons so it's propane for four carbons i ran out of space so it'll be c4 h10 and it contains four carbons which is why it's but still an arcane so butane so these are the simplest hydrocarbons and we call them saturated and that's because all the carbon bonds are single if we look at alkenes they are unsaturated and that means they contain a double carbon bond i'm going to show you how to draw the first four alkenes let's now look at the alkenes and remember they have a general formula which is cnh2n let's first of all start by discussing the functional group of the alkenes remember this is the series of atoms or bonds which makes a particular family of compounds special so here we see that the alkenes contain a c double bond c by definition therefore they need a minimum of two carbon atoms to exist which is why a carbon one carbon alkene does not exist and you have to start with the two carbon so starting with the two carbon one we know we need to substitute two in as the n so it becomes c2 and then simply h4 the displayed formula we need a double bond and therefore we're going to fill up our hydrogens do notice again that the carbons have four bonds the hydrogen has one contains two carbon atoms which is why it begins with with eth it's now keen so it's ethene looking at three carbon atoms now so c3h6 again make sure you're filling these up properly double checking the bonds i can't reiterate this enough and this will be three carbons so probe it's an alkene so propene now looking at the four carbons which is when it gets a bit more interesting so we've got c4h8 and therefore we can draw the first version of this like this in terms of its name it's butene however we now need to look at the other available isomer remember then isomer is something with the same molecular formula but different structural formula so if we draw that molecular formula out again c4h8 but we try and work out a different structural formula we can simply shift that double bond along so it now appears in the middle and now just fill in those hydrogens making sure you don't draw too many bonds on those central carbons and you can see this is still c4h8 however the structures are different and therefore these are both isomers and the way in which we name them is according to where you find that double bond because the double bond in the black version is between the first and second carbon we call it but one in because the double bond is between the second and third carbon atom we call this button now these families of compounds we call homologous series and that's just a fancy way of describing a family of compounds so what can we say that all members of the same homologous series have in common so what do all arcanes have in common what do all alkenes have in common well first of all they have the same chemical properties which makes sense they're going to react in a similar way because they have the same functional group they're therefore going to have the same functional group which is good because i just said that they obey the same general formula so all arcanes for example will follow cnh2n plus 2 whereas all alkenes will obey cnh2n and then they show a trend or gradual change in physical properties which again makes sense so ethane has two carbon atoms whereas methane has one so therefore you'd expect ethane to have a higher melting point and boiling point which it does so what is a functional group well it is an atom or a group of atoms which determine the chemical properties of a compound so we've talked about alkanes and alkenes but where do they all come from and they come from crude oil which is a black sticky substance which comes out of the earth's crust and it has made some people billionaires because this stuff is worth a lot why because once it has been sorted once it has gone through fractional distillation and been separated out into various fuels that can be sold for a huge amount of money why because fuels are essential for how we run our lives it's how we heat our homes and how we run our cars so what is a fuel well it's a substance which releases energy when burnt we've talked about crude oil but how is fractional distillation actually carried out so we get our crude oil which we know is a mixture of hydrocarbons we heat it until it evaporates and then we pass that vapor into a fractionating column or tower now that fractionating column has a temperature gradient which means it's hotter at the bottom and cooler at the top so in terms of these various crude oil fractions and a fraction is just a group of compounds with similar boiling points they will condense at different positions within the fractionating tower so the longer chains will condense at the bottom where it is hottest so looking at fractional distillation so we're looking within the fractionating column and we need to know the different fractions starting from the top and various uses so refinery gases this is bottled gas used in central heating and cooking so within our homes basically the next fraction down we have petrol otherwise known as gasoline and as the name suggests it's used as fuel for cars getting slightly longer in terms of our carbon chain we have naphtha main uses to produce chemicals then we have paraffin which is used as jet fuel diesel oil now this is a heavier fuel and it tends to be used in lorries and buses getting longer again with our carbon chain we have fuel oil which is fuel for ships and we also produce lubricants which are slippery and therefore used in waxes and polishes and then the last fraction is bitumen it's black and sticky and we can use it in road surfacing a couple of words to be aware of first of all viscosity so that's how readily a fluid flows be aware that the more viscous the fluid is the less readily it flows so honey is very viscous because it's slow to flow i like the fact that that rhymed and water is very unviscous or not viscous at all because it runs very quickly flammability obviously that's to do with how readily something sets a light volatility is how readily something turns into a gas so if we take the various fractions and we make a few comparisons let's compare the viscosity volatility and boiling points of bitumen compared with refinery gases so clearly bitumen will be more viscous it will be less volatile and it will have a higher boiling point it will also have a darker color because it's a brownish sticky color whereas refined gases are colorless so do be aware and do be willing to make comparisons and make full comparisons so same finer gases are lighter in color have a lower boiling point are less viscous etc cracking now remember that is a process carried out in order to break large hydrocarbon chains into smaller more useful ones and it's all due to demand because effectively the shorter chained hydrocarbons the shorter chain alkanes and alkenes make much better fuels than the long chains which is why we carry out cracking do remember that you need a high temperature which is between 600 and 700 degrees celsius and you need an alumina or silica catalyst in order to speed up the process let's touch on a few reactions that you need to be aware of it could ask you what is the test for an alkene or an unsaturated hydrocarbon that's actually the same question so effectively you're testing for the presence of the c double bond c what you'd write as your answer is that you add bromine water and in terms of your observations what you would say see is they would go from orange to colorless let's actually look at an example so we'll take ethene we're adding bromine water remember bromine is diatomic hence why i'm saying br2 and then what happens is the double bond breaks meaning that there are two available spaces for bromine to join on which is here and here and there's no byproduct because of that and because bromine simply added itself you say that this is an addition reaction so what is the type of reaction addition you add bromine water and it turns from orange to colorless now looking at alkanes reactions with bromine water so alkanes or a saturated compound is basically the same thing what you see this time i'm going to take methane as my example but i could have used ethane or propane we add it to bromine water but what happens this time is one of the hydrogen pops off the bromine joins you complete the rest of the molecule and what you have left over is clearly a hydrogen that's just left methane and another bromine atom which is why this is your equation here because all that's happened is that hydrogen has simply been swapped or substituted for bromine we say that this is a substitution reaction so you can actually see what's happened here looking at the alcohols now notice that their functional group is oh and do remember that each oxygen atom can form two bonds while hydrogen obviously forms only one so we'll bear that in mind now so starting with the most simple version which contains one carbon it's named one carbon so map is an alcohol so it's methanol in terms of drawing it draw your functional group coming off first i've already told you it forms two bonds when you're talking about oxygen and then just fill up with hydrogens and that is methanol two carbons now so two meaning it's f so ethanol this is the alcohol found in natural alcoholic drinks so we need two carbons here's our functional group the oh filling up with hydrogens there's ethanol three carbons three carbon so pro alcohol propanol do notice there is a second isomer of propanol because actually what i've drawn here is propane 1 but there's also propane 2 all so we can actually move the position of that alcohol functional group to be on the second carbon here and then just fill up with hydrogens try and draw your hydrogen is better than i am these don't even look like h's so how can alcohols be oxidized firstly you can burn them in air which we would call combustion because that's burning secondly they just react naturally with the oxygen air and that's due to the action of microbes in the air we call that microbial oxidation and lastly you can heat them with potassium dichromate in the presence of dilute sulfuric acid and that will also oxidize them so if we're taking ethanol for example it will be oxidized to ethanoic acid so we've taken an alcohol we've oxidized it and it has produced a carboxylic acid some uses of alcohol aside from use in alcoholic drinks they can also be used as good fuels and in perfumes and sometimes you'll see on your perfume bottle it might say alcohol-free because many actual perfumes do contain alcohol looking at now at the production of alcohol we need to know the two main ways which is fermentation and hydration of ethene so we need to compare both of these methods for making alcohol so let's first of all look at their raw materials hydration of ethene is obviously ethene so that's going to be from crude oil which means it's a non-renewable resource whereas fermentation involves using sugarcane and using your old-fashioned approach so using yeast in order to ferment that sugarcane to produce the ethanol so obviously that uses a renewable resource in terms of temperature and pressure needed fermentation that's going to use low temperatures and pressures whereas hydration of ethene is a very industrial process so it involves high temperatures and pressures the type of process involved now we say that fermentation is a batch process and that's because you mix together all the reactants and you leave it for several weeks or months you remove the alcohol and then you start again hence why it's a batch process whereas hydration of ethene is a continuous process because it can just carry on endlessly as long as you've got the reactants and the reaction conditions it keeps going let's look at our reaction equations now you've got glucose from the sugar cane so c6h12o6 and it breaks down using anaerobic respiration by yeast into ethanol plus carbon dioxide and we know carbon dioxide can be used in bread making hydration of ethene is as the name suggests adding water to ethene so you've got c2h4 you add h2o to it and that's how you produce your ethanol lastly look at the product produce fermentation obviously makes a pretty impure product it's got lots of other things mixed in with it whereas hydration of ethene makes a pure product so be aware when they give you an exam question and they give you a situation and they tell you what sort of resources are available whether there's lots of electricity available that sort of thing be aware of which method would be better to use right let's look at the carboxylic acids now they have a more complicated functional group which is cooh do notice in the top right corner that this actually looks like a c with a double bond to the o and then a sort of alcohol group coming off the bottom of it so one carbon because it is a carboxylic acid we're going to start with math because it's one carbon but it's methanoic acid in terms of drawing it draw that carbon draw the functional group and now just count up and make sure you've got enough bonds coming off the carbon so far it has three we know it needs four which is why it just needs a single h here looking at two carbons now so that means it's f so it's ethanoic acid two carbons next to each other here's our key functional group fill up with hydrogens where necessary and that is ethanoic acid looking at the three carbon version so pro propanoic acid three carbons in a line there's your functional group fill up with h's this question is about alcohols carboxylic acids and esters the table gives information about some alcohols complete the table by giving the missing information right so we've got c4h9oh so remember your mnemonic is monkeys eat peanut butter to help you remember the names so we're dealing with the fourth one so it starts with butte it's butanol we now need to provide an estimation for the relative formula mass of ethanol so use your periodic table it will tell you that carbon is 12 so we do times two plus five lots of hydrogen which is one plus oxygen 16 plus hydrogen which is one to get an answer which is 46. ethanol can be oxidized to ethanoic acid by heating with potassium dichromate six and another reagent namely the other reagent this is something you just need to learn is sulfuric acid state the color change that occurs during this reaction it turns from orange to green alcohols react with carboxylic acids to form esters namely ester that forms when ethanol reacts with ethanoic acid so remember the first part of the ester name comes from the alcohol which is why it's ethyl the second bit comes from the carboxylic acid so it's ethanoate because remember that's the ending on the ester complete the equation for the reaction between methanol and ethanoic acid and now we need the ester i'm just going to show you how we're forming that ester so here's the alcohol we've been provided with so in order to form that water molecule we lose the oh from the carboxylic acid the h from the alcohol so then you stick the ends together so there's the ester structure so now you can write it out so you can see that it is ch3 co o which is the functional group of an ester followed by ch3 and i do find you're on those display formula really help you out here now a polymer is a large molecule formed for many small molecules known as monomers an addition polymer is formed for many monomers joining together and the reason we say it's an addition reaction is because there are no byproducts you're simply adding those various monomers together let's take an example now eg the formation of the addition polymer polyethylene so because it's addition polymerization you need a monomer which in this case is ethene remember the ethene has two carbon atoms and it is unsaturated there's a very specific way of drawing the equation for how this is formed you then need an arrow and then effectively you break that double bond elongate those side bonds and then add those hydrogen atoms back in and then you have some all-important square brackets and now because you've got a large number of these monomers joining together we're not going to draw them all we're just going to use a small n to show that there's a lot of them and that's how you draw polyethylene formation and if we were to name the monomer we know that that was ethene and our polymer is polyethylene meaning many ethene molecules join together now this is a version of plastic you'll be quite familiar with because it's used to make things like cling film and plastic bags let's take a second example now so what about the formation of polypropylene remember that propene consists of three carbon atoms and i'm going to draw it like this and i'll show you why shortly let's draw that arrow then we're going to break the double bond and add all the other atoms back in place elongate those bonds and then draw square brackets finally add your n and that is the formation of polypropylene now sometimes you might actually be given the structure of a polymer and be asked to deduce what the repeat unit was or which monomer it was made from so for example polystyrene which you see in the example below and so basically you just need to step back and have a look and see where you think that structure is repeating itself so i can see that it takes place here and here and here and here and this one's just chopped in half so you take one of those out effectively and then you just remove those side bonds here and reinstall that double bond and you'll have the monomer or the repeat unit from which the polymer was made from so your answer will look like this we draw it with that double bond add back your hydrogen bonds and don't forget to add that c6h5 check your bond number because remember each carbon atom forms four bonds one two three four one two three four and that is your final answer now we're moving on to condensation polymerization so this is different from addition polymerization that word condensation tells you that a small molecule is lost in the reaction and honestly that tends to be water so the first example we're looking at is the formation of polyester which is an example of a condensation polymerization reaction and just to point out the monomers you need a diol and a dicarboxylic acid now a diol is an alcohol so remember you've got the oh functional group die meaning two so you'll find that that monomer has two oh groups on it the dicarboxylic acid functional group is cooh again die so you're going to have two of them so i'll show you the general equation for forming a polyester so we'll start with our dicarboxylic acid here are the all-important functional groups notice that we're using a block diagram to represent that carboxylic acid please don't worry about this all the block means is that you have a certain number of carbon atoms in the middle we're not that fussed about it because after all they're not going to be involved in the reaction it's only this bit that's important so we just use that block to represent a set number of carbon atoms so there's our dicarboxylic acid here's our alcohol then we're going to have another dicarboxylic acid followed by another dial so i've already told you that in a condensation reaction water is lost but where are those water molecules going to be lost in order to allow our monomers to join together to form our polymer well it's going to happen like this remember that water is h2o so you're going to take the o and the h from the dicarboxylic acid and the h from the dial so here and then the same will happen at this point and again at this point it's always the oh from the dicarboxylic acid and the h from the dial and then when those water molecules are lost you're just going to stick together the remaining parts of the molecule and be very careful with how you draw that adjoining bond and we're just going to add some dotted lines around the end of that molecule to show that that molecule continues so here's our polyester and then to show you that ester bond which is formed it's here as you would imagine because it's where the molecules have stuck themselves together and that helps to explain why the functional group of an ester is c o a now very specific examples given in the specification include p e t which is a polyester you don't need to know what p t stands for you could be asked to draw that and it would be more than fine for you to draw what i've just drawn here because after all it is a polyester so i'm just going to write that here e g e-g-p-e-t now one thing i wanted to point out with p-e-t it's just a random part of the spec is that it can be converted back into its original monomers and be re-polymerized we're now going to look at how you would draw a polyamide now polyamides are formed from dicarboxylic acids and diamines so very similar to what we've just done we just need to be very careful as to how we draw those monomers so let's start with our dicarboxylic acid again so that cool functional group we're going to use a block diagram again to show those carbon atoms in the middle then we need the diamine which has an nh2 functional group again using that block diagram and then let's draw the same monomers again so here's our dicarboxylic acid here's our diamine because it's a condensation reaction we're going to lose the water molecules again notice that the oh comes from that carboxylic acid again the h is this time from the diamine so that will happen three times in this particular example and then just stick together the remaining parts of the molecule and again the molecules will continue on either end and we formed an amide bond here where all those joints have taken place now the named example of the polyamide you need to know is nylon if you ask a joint structure you need to draw what i've drawn down here so we spent a large amount of time looking at different plastics now we need to look at issues with their disposal now plastics are difficult to dispose of because they are unreactive they are inert so what methods of disposal exist and what are their various advantages and disadvantages firstly obviously landfill plastics occupy landfill now the advantage of using landfill is first of all it's cheap and that no greenhouse gases or toxic gases are produced disadvantages they're ugly smelly noisy no one wants to live close to one they use large areas of land up and the waste will be there for thousands of years how about if we were to incinerate our plastics so ban them well the advantage is that it requires little space and it can produce heat used by local homes offices as well as being used to produce electricity however many disadvantages first of all it's expensive to build and maintain the plant it produces toxic and greenhouse gases and lots of ashes produced which still needs disposing of in landfill one other thing to point out is that with any of these things which are dumped whether it's ash or just the straightforward plastic as well as being dumped in landfill it could also be dumped in oceans which is obviously going to destroy aquatic organisms now proteins we've talked about polyamides and our proteins are natural polyamides and the monomer from which they're formed is the amino acid so let's draw the structure of an amino acid now it has a central carbon atom a carboxylic acid functional the amine functional group and then importantly it has an r group which is variable and that gives the huge diversity of amino acids that exist within the natural world so the r is different types of side chain if you're asked to draw the structure of a protein again you can use a block diagram so i'm using three amino acid block diagrams to demonstrate this as it's a condensation reaction we're going to lose that water molecule again i'm using three different colors here to show you that we had three different amino acids and now stick those monomers together and here i've just shown some elongated bonds here just to show that that protein molecule continues here's the amide bond again and i'm just going to point out that this was a condensation polymerization reaction again let's do a list of apparatus and be familiar with recognizing them and potentially drawing them so first of all our bunsen burner the easiest way to draw that is with an arrow going upwards with the word heat underneath with chemistry it's not an arc competition it's not about how well you can draw stuff you need to draw in a very scientific way so the tripod remember that's what you heat stuff on will look like this and on top of the tripod often sits a gauze which lots of people pronounce that quite strangely that's how you say it and that's how you spell it and then that often sits on top of a heat proof mat and then while i'm at it i might as well put an evaporating basin on the top so i don't have to draw it later your beaker is very basic hopefully less wobbly than that you have a conical flask which is more triangular at the bottom if you're carrying out a filtration technique remember that's separating an insoluble solute from a solvent you're going to use a filter funnel which tends to sit atop a beaker and you need filter paper in there measuring cylinders remember they're used to measure out inaccurate volumes of liquids something like this is more than adequate scales are used to measure the mass or weight of objects you might use the thermometer if you're needing to find out the temperature and a stopwatch is good when you're looking to measure rates of reaction for example so the time it takes to evolve 100 centimeters cubed of gas for example that's going to look very similar to your scales do notice although i've already pointed out the measuring cylinder is a very inaccurate way of measuring volume you've got far more accurate ways using pipettes so like a glass pipette that you use in titrations that will accurately measure out 25 centimeters cubed of liquid for example and then you have the very long skinny buret i really don't think you'll be asked to draw this remember that has a little tap and that measures out extremely precisely looking at solutions now so be aware of the solution words you need to know and their definitions so we're going to use coffee being dissolved in hot water as our example so you can actually understand the words i'm saying so we're trying to make a nice cup of coffee and we're going to start by looking at what a solute is so a solute is a solid which dissolves in a solvent so in the case of our coffee example the solute is the coffee grounds the solvent is the liquid in which the solute dissolves so in our example that would be the hot water the solution is the mixture of the solvent and solute so that would be the nice cup of coffee that we make and then a saturated solution is one way you can't dissolve any more solute into the solvent so it's at its maximum capacity effectively now there are lots of different reasons why you carry out a titration one could be that you want to produce a soluble salt which contains ammonium potassium or sodium because of the way in which the soluble salts dissolve you need to use the titration in order to work out very accurate volumes of both reactants so that could be one reason why you want to carry out the titration another reason you want to carry out a titration is because you want to carry out the titration calculation in order to find out an unknown concentration now i'm not going to talk about that in too much detail here because the whole point of this video is to show you the method used you need to watch my alternative video on titration calculations to understand the maths involved but what emilia and i are focused on doing today is showing you how to accurately carry out titration and to accurately find the volume of hydrochloric acid needed to neutralize a particular volume and concentration of sodium hydroxide because that's really what a titration is it's adding a very specific volume of one reactant to another causing a neutralization reaction to take place and we use an indicator in order to tell us the neutralization has occurred okay so we're going to put hydrochloric acid in the burette and sodium hydroxide in the flask so i'm going to load the burette with the acid usually you wash it with us two three times but this time we just do once so the top of course must be off close and but it's lonely because it loads very quickly otherwise it will all flow and notice you can carry out a titration in either way you could have the acid in the buret or the acid in the conical flask just depends on which indicator you're using okay because i want to start from zero i'm going to lose a bit of acid in the beaker and also to get rid of the bubbles that sometimes forms in the top that's it perfect in order to avoid parallax errors you need to make sure you read from the bottom of the meniscus because if you look at liquid in a particularly narrow tube you notice that it has a very curved shape so you need to read from the bottom of what's known as the meniscus then you add the sodium hydroxide to the flask which has been previously washed with sodium hydroxide solution multiple russian so this is 25 cubic centimeter of sodium hydroxide this is a glass pipette and it's used to produce very accurate volumes of solution [Music] okay then you add a drop of metal orange so methyl orange is an indicator which as you can see turns orange in an alkaline solution remember that sodium hydroxide is from the alkali and then the places yeah so we're ready to begin our titration notice that the endpoint that's when neutralization occurs is when the methyl orange turns from orange to red the whole point of using these indicators is they have a very sharp endpoint they have a sharp change in colour which is why methyl orange phenolphthalein they're both ideal for use in titrations universal indicator is inappropriate because remember it shows a range of different colors so amelia's going to open the tap and start slowly adding hydrochloric acid to the sodium hydroxide beauty of a buret is that it can add drop by drop so it makes it far more accurate than a measuring cylinder or a beaker she's swirling the flask in order to mix the contents so we place the tile underneath the floss in order to observe the color change when you know when now you have the drop you will see pink and then disappear yeah so it's not ready it doesn't mean that that is the end point because it must be a color that doesn't disappear when you sweep the flowers yeah see pink starting to appear and then disappear so it means that we are close to the end point oh that's it here we are is pink this is the color we want so we've reached our end point the solution although it looks pink in your exam you're going to have to say that it's red and that means that solution is slightly acidic so the essential thing now is that we read the volume of the acid that was added notice that the buret runs from zero centimeters cubed down to 50. so we're really trying to work out what this volume is here yes it's 25 yeah so reading from the bottom of the meniscus we can see that 25 centimeters cubed of acid was added so if you have a discarder it means that you have been further we've already met chromatography earlier remember it tends to be used as a separation technique to look at dyes and inks and food colorings but we can also use it in this topic to look at the hydrolysis products of both carbohydrates and proteins the only thing that makes them slightly tricky is that they're both colorless and remember dyes and inks contain lots of color which is why they're really useful in chromatography so in order to cope with the fact that they're colorless we need something called a locating agent our last separation technique is chromatography remember this is used to separate liquids of different solubilities so that could be food coloring dyes inks for example be prepared to describe how you set up a chromatogram remember you have filter paper which you draw a reference line on in pencil you put a dot the dots of ink along the pencil line and then you dip the paper into water as the water soaks up it draws the dies up the paper and you can determine several things from that so first of all notice that you draw the reference line and pencil why because you don't want the pencil to spread and go flowing up the paper too because that will disrupt your chromatogram notice that the ink which travels the furthest has the highest solubility which kind of makes sense and be prepared to use the formula which is the rf formula and that's the formula whereby the distance traveled by the component is divided by the distance traveled by the solvent we now need to touch on separation techniques so i'm going to give you all the different examples and how you would use each of them so first of all filtration you are going to use this to separate an insoluble solute from a solvent and your example here could be sand and water the reason filtration works so well is you pull the mixture through the filter funnel containing filter paper and what you'll find is the sun stays in the funnel the water flows through into the beaker below so you've separated your insoluble solute from the solvent and be prepared to label all the apparatus involved and be able to draw simple diagrams getting slightly more complicated now we now have a soluble solute that needs separating from a solvent this could be something like salt being separated from water so clearly filtration won't work because the salt will go straight through into the beaker below which is why we need to use evaporation so you have a tripod with gauze on the top an evaporating basin containing the salt solution you boil using a bunsen burner the excess water boils off and you're left behind with salt in the evaporating basin next up we're separating immiscible liquids so these are liquids which do not mix a good example here is oil on water and you will find that oil and you can see this at petrol stations if for some reason it's rained and then petrol's ended up in the puddle you can see the petrol floating on top of the water and that's what happens with oil too so in this case you can just put it into a funnel you can open a tap and the water will drain out first close the tap and you'll leave the oil behind in the funnel now liquids of different boiling points for example ethanol and water clearly evaporation and filtration won't work here and this is where you use simple distillation and simple distillation relies on the fact that liquids have different boiling points because what happens is you use a bunsen banner to boil the mixture of liquids and the liquid with the lower boiling point will evaporate first so that would be the ethanol with a boiling point of 78 degrees celsius leaving behind the water below and if you have a real mixture of liquids with lots of different boiling points such as crude oil this is where you'll use fractional distillation which actually allows you to separate out many different liquids of different boiling points when we look at a pure substance this is a substance which contains only one type of material so that could be for example one element so carbon or it could be one compound such as carbon dioxide but the point is there's nothing else in there contaminating it if you think you have a pure substance and you want to look at its boiling point be aware that a pure substance will have a fixed boiling point and should not boil over a range of temperatures if it boils over a range of temperatures as crude oil would it's a mixture it is not a pure substance so the test for hydrogen don't say it's the squeaky pop test you won't get a mark for that you need to say that you hold a lighted splint over the gas and if hydrogen is present there should be a squeaky pop with oxygen you need to say that it relights a glowing splint carbon dioxide remember turns lime water cloudy chlorine bleaches damp litmus paper and ammonia turns damp red litmus paper blue now i've given you the most concise precise definitions for this so make sure you've learned them every single word matters here so for example damp is worth a mark red litmus paper worth a mark so make sure you learn them properly and now we're getting more complex and we're going to look at flame tests so remember if we have an unknown metal ion a flame test is a good way of working out what that metal was so in terms of carrying out a flame test remember that you're going to use a clean nichrome wire which is you could clean it using hydrochloric acid but the point is you don't want any contaminants on the end of that nichrome wire then you dip it in the sample to be tested and then hold it in a roaring blue flame and that is key you can't be adding it to a yellow flame that won't work because the yellow will obstruct the colour so hold it in a warming blue flame so the colours now if we've got lithium ions you will see a lovely red crimson colour sodium you'll see a yellow flame and potassium as with when you add it to cold water you will see a light up flame calcium goes an orange red color or a brick red color and copper goes a blue green color if you don't want to carry a flame test you can use a precipitation reaction and you can look at the color precipitate formed once you've added sodium hydroxide so if you add sodium hydroxide to something containing copper you will see a blue precipitate formed iron ii will form a green precipitate and iron three will be a brown precipitate and i remember those because they're kind of muddy earthy colours so it goes green for iron ii brown for iron iii testing for ammonium ion sound which is nh4 plus again add sodium hydroxide you won't see a precipitate form in this case you instead a stinky gas will be released which should be ammonia and you test for the presence of that ammonia using the method i've already described which is that it should turn damp red litmus paper blue okay moving over now to test for negative ions we've looked at metal ions and ammonium so we're looking now at the halides which is group seven the halogens so first of all you need to add nitric acid you add that dilute nitric acid in order to remove any carbonate ions which might interfere with your test following that you add silver nitrate and then you'll end up with a range of precipitates so looking at the chlorides if you add chloride ions to silver nitrate you produce silver chloride which is a white precipitate if you add silver nitrate to something containing bromide ions you make silver bromide which is a cream precipitate and lastly adding silver nitrate to something containing iodide ions will produce a yellow precipitate so notice those colors get darker and go from white to cream to yellow and be prepared to write the ionic equation for this which will be for example with chlorine it'll be a g plus plus cl minus forms a gcl solid thank you so much for watching my video well done if you made it to the end don't forget you can buy my science hazel perfect answer revision guides on my website they're available right now [Music] you