Transcript for:
Chemistry Lecture Overview and Concepts

welcome to my ID CSC at Excel all-in-one chemistry video this is for the 91 new specification now as always don't forget that I sell my powerful answer revision guides on my website which is www.hyken.com cannot attending school licenses and private tuition however enough about that let's get started so we're gonna start by looking at solids liquids and gases so when we look at solids liquids and gases be prepared to draw that particle diagrams notice that solids have particles which are in both fixed arrangements and that's because the particles vibrates 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 gas is 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 that 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 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 we see it getting all messed it up on the windows condensation is occurring here touching slightly more on evaporation so how does the evaporation of a puddle or or any liquid happen really so what you find is that the particles have different 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 due 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 or more place they will drift and move across to somewhere some medium which has a lower density or concentration of these particles an example we like to look at in chemistry is you might have seen your teacher go through in class to put this huge glass tube on one end you have ammonia your 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 in the middle of the tube it means that the ammonia and the hydrochloric acid diffused equally quickly across however this isn't true what actually happens is that the ring forms much closer to the hydrochloric hand 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 solutions now to 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's of 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 dissolved 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 in a saturated solution is one way you can't dissolve any more solute into a solvent so it's at its maximum capacity effectively looking at some fundamentals which underpin chemistry we need to look at an atom element mixture in 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 higher 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 the 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 or sugar that's not going to happen and that's due to the chemical reaction that's take taking 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 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 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 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 new Zombo hair 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 as the sands days in the funnel the water flows through into the beaker below so you separated your insoluble so you'd 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 so you two beneath 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 and evaporating based on 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 the oil then you can see this at petrol stations if for some reason it's rained and then Petra'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 will leave the oil behind in the funnel now liquids of different boiling points for example ethanol and water clearly evaporation and filtration weren't working and this is where you use simple distillation and simple distillation and it relies on the fact that liquids have different boiling points because what happens is you use a Bunsen burner 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 mission liquid 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 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 dyes up the paper and you can determine several things from that so first we'll notice that you draw the reference line in pencil why because you don't want the pencil to spread and go flowing up the paper to because that will disrupt it look for matter gram notice that the ink which travels the farthest 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 back to basic chemistry then so we're looking at periodicity I've already told you that an 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 so I think 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 on 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 I tend to say that it has a mass of 1/2 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+ 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 pivot 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 6 and I told you already that atoms are neutral which means their proton number equals their elektra number which means the electron number of we'll 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 total 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 nucleon number and that suggests the total number of particles found within the nucleus of an atom so it's the total of the protons and neutrons ie it's also the mass number so they're very closely linked isotopes now so if you're looking at the other 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 that some chlorine atoms have a high mass number of 37 and other ones have a mass number of 35 and when you work on average you actually find that it's 35.5 and that's because they were far more chlorine-35 compared with chlorine 37 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 you may be asked to calculate the relative abundance of those isotopes and now I will show you how to cut on the iPad now we need to touch on calculating the relative atomic bundles of these various isotopes and this is how you need to do it so the question will look something like this the abundance of chlorine 35 is 75% and the abundance of chlorine 37 is 25% calculate the relative atomic mass of chlorine so 35 is one isotopes mass and 37 is the second isotopes mass so all you have to do is take each isotopes mass so 35 times it's by its percentage which is 75 and add it to the second isotopes mass times it by its percentage and then divide the whole thing by a hundred and when you do that you get the answer 35.5 have three significant figures and that's how you need to do it doesn't matter what the element is you times its mass biased percentage add it to the other mass times it by its percentage and divide by a hundred motive atomic mass of all D 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 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 you 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 period 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 nonmetals appear on the right-hand side with hydrogen appearing by itself at the top because it behaves very differently from all other elements so matters 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 my in Berlin ductile mean reliable 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 will come in to later and they partake in ionic bonding nonmetals now have 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 onto 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 islands and they partake in covalent and ionic bonding so how is an iron formed and what is an ion so ion is a charged particle which is formed from either gaming or losing electrons so clearly if they lose electrons they lose negative charge so therefore they become positive if the gained electrons they gain negative charges that become negative I'm going to show you my favorite method of bouncing 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 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 now we want to do a tally chart to show how many of each element we have so can the hydrogens on the left hand side of the equation so we've got one present in the nitric acid to 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 our days are put together and it's five but now the calcium is just one now we need to do the same for the product side of the equation so how many hydrogen's 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 in calcium you have one and now we need to have a look at our titles 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 with the oxygen hydrogen aren't so I'm going to put a two in front of water to make that four hydrogen's 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 side two nitrogen eight oxygens and one calcium so that is indeed balanced looking at more calculations now use the formula triangle to help you be arranged and you can see that mass is therefore given by the relative atomic mass which is M R times the 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 do 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's like to pop that into your calculator and you get an mr of 74 grams now looking to find a number of moles in a 5.4 grams of calcium carbonate so I like to write out the equation I'm using it's good practice stops you're making silly mistakes so using my formula triangle I see its mass divided by M R you've been given the mass in the question which is 524 now we need to work out the M R of calcium carbonates are using the periodic tables calcium has a mass of 40 carbon is 12 oxygen is 16 and we need to multiply that by 3 choose 2 this 3 dear so that's 5.4 divided by 100 there 0.05 for now we're looking to find the empirical formula of a compound which contain 22% carbon 4.6 percent hydrogen and seventy three point four percent grow mean I like to lay out these questions always using the tables format so first of all list your three elements and then to a label underneath mass M our moles I don't forget your formula triangle always to be aware so they remember masses at the top and ma and moles and then just substitute what you know from the equation from the question now notice even though it's given percentages because it's a ratio really you can ignore the percentages and pretend those are the masses which is why I'm now going to put the mass of carbon as being 22 hydrogen is 4.6 and berming a seventy three point four now use your periodic table to find that Amar's carbon is 12 hydrogen is one and bromine is 79 and then looking at our formula triangle we see to calculate the moles we simply do mass divided by M R so that's 22 divided by 12 for carbon which is one point eight three recurving four point six divided by one is obviously four point six and I'll send it to you point four / 79 is zero point nine two nine one one three and the note here don't round too early because the numbers are so small your Institute landing others keep them nice and long in your calculator then we want to divide by the smallest number so just have a scan and obviously zero point nine is the smallest number so we're going to divide all of the previous answers by that number and this is so that we have a ratio I wish my iPad would stop deleting stuff that doesn't really make that much of a difference so once you've done that you know that will be one this comes out of four point nine five which I can happily round to five because that's basically what that number is and this comes out of 1.98 so that's basically two so don't be scared to around only if the numbers are very close if one of the numbers had come out at one point five for example so for example one point five versus one what you'd have to do in that case is double both so you have a ratio which is three to two I don't want to show that out now because I want to finish this question so don't forget to actually provide your powerful formula which is c2h5 VR and that is your final answer sometimes they like to extend the question and tell you in Part B that a different compound had a master 216 and then based on this empirical formula you've just calculated work out its molecular formula this is really straightforward all you have to do is work out the mo of the empirical formulas you've just calculated so work that out which would be 2 times 12 plus 5 times 1 plus 79 so that's just a basic mr calculation once you've done that you see that it's a hundred and eight and compare it to the compound you've been given which is 216 so the compounds you've been given must therefore have a molecular formula which is just twice that of the Empowered formula so the actual final answer here is just c4h10 br-2 if the mr of your purple formula had been the same number which is 216 then your answer would just have been the empirical formula which is c2h5 BR now I'm going to show you a water crystallization type of more calculation it's really similar to in Pirkle formula so don't let it freak you out just because it looks more difficult so thirty five point seven five grams of sodium carbonate combined with water are heated strongly and thirteen point two five 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 any two ch3 but instead of listing the elements you're just going to have the various components of the questions which is going to be sodium carbonate on the less water on the right and then math and math and laws as usual so we know that thirteen point two five grams of the same carbonate remain after eating which is why this is the number here you can have to do a small calculation to work out the amount of water that was lost at thirty five point seven five minus thirteen point two five to get twenty two point five the mr used the pivot table so we'll see stadium is twenty three times it by two because of that small two-plus carbons twelve plus three lots of oxygen which is sixteen to get an MRI of 106 and i know off the heart that the ml water is eighteen 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 zero point one two five this is one point two five and then divided by the smallest number which is clearly zero point one two five that will obviously lose one this is tan therefore x equals ten and that's it it's very similar to the empower form of your question now we need to look at reacting mass and gas volume questions so three point three 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 balance 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 super juice of salt which is sodium chloride plus water plus carbon dioxide make sure it's balanced I know I need a two there and a two here and now we need to use the table format in order to help us answer the rest questions so mass em are and malls and don't forget to use your formula you know triangle down here which is mass M are moles and this is how I always set myself up to make sure I'm going to get the a question right so what have you been given in the question well we know three point three 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 thirty five point five equals thirty six point five grams the mi of carbon dioxide is going to be 12 plus two lots of 16 which is 44 using the formula triangle we see that moles is mass divided by M R so we do three point three divided by 36 point five to give us 0.0904 109 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 chrome dioxide which is why in order to carry over the moles we have to actually divide 0.0904 one by two and that becomes zero point zero four five two zero five and now we're ready to work out the unknown mass of carbon dioxide which is mass equals M R times moles so we've already calculated the M R which is 44 moles of zero point zero five four five 205 and that is 2 grams to 3 significant figures 3.2 grams of copper reacted with 0.4 4 moles of nitric acid which region isn't 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 M R and moles down the left-hand side and remember our triangle chocolate here which is mass at the top number of moles and M R 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 Y soon so first of all what is the mo of copper using your periodic table you see it's sixty three point five so using your formula triangle how do you work out the number of moles you do not mass divided by M R so that's three point two divided by sixty three point five to get zero point zero five mole and then have a look at the big numbers we've got invisible one here we have a four here and I've already told you you just need to pull that number across but instead times it by four so you get zero point two 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 zero point four moles of nitric acid but we only need 0.26 so clearly nitric acid is in excess now we're looking at percentage yields so for example in a reaction eleven point two grams of copper sulfate was obtained when theoretically twelve point five 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 eleven point two the theoretical one was twelve point five multiply it by a hundred and you get a value which is eighty nine point six percent 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 student reacted two point four grams of copper oxide with sulfuric acid she made one point I ate two 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 cuso4 plus water and then step back and double check that it is balanced and it is and we're going to use my favorite tables 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 two point four grams of copper oxide and we have made one point eight so that is the actual yield and we need to find out that the theoretical yield which is what 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 sixty three point five plus sixteen so use your periodic table for that to work out that it's mr is seventy nine point five to work out the number of moles simply do the mass divided by the mr so that's two point four divided by seventy nine point five to give a value which is zero point zero three zero two moles now we need to look at the balance similar equation have a look at any big numbers there 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 sixty three point five plus 32 plus four times 16 so it gives us an Emma which is 159 point five and then we work out X by doing one hundred fifty nine point five times by zero point zero three zero two to get four point eight one six nine 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 percentage so actual was one point eight C reticle was four point eight one six nine times that by hundred and we get a value which is thirty seven percent unfortunately there are some islands which will simply have to learn off by heart because you can't wipe them out from the periodic table so let's just go through what all of these are starting with these transition muscles along here just gonna have to learn them the first one is silver this one is copper PB 2 plus is lead and zinc is there a 2 plus notice with transition metals like iron that have variable valence ease 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 iron I'm now looking at the negative ions if it's combined with oxygen it tends to have 8 in its name so this is carbonate sulfate a 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 2 hence mg 2 plus chlorine is in group 7 so 8 minus 7 is 1 hence CL minus now I have a look they're not balanced obviously you've got 2 plus and a 1 minus charge so clearly you need 2 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 are going to have to learn off by heart so PB 2 plus it's H minus so we've got the same issue in that we don't have enough - so you need to OS so you're going to write PB o h2 however the two applies to both oxygen and the hydrogen which is why you need racquets so insert brackets and that is your formula now lithium lithium is in Group one so it has an ally 1 plus charge so it has a 1 plus charge oxygen is in group 6 8 minus 6 is 2 so 2 minus this means you need to lithium for every oxygen so Li - Oh magnesium nitrate magnesium missing group - sir mg 2 plus nitrate he's got to learn from the list above no.3 - you've got a 1 - charged with nitrate compared with the 2 plus charge on the magnesium which explains why you need to lots of that mag needs of that nitrate and you need to insert brackets again don't touch this 3 here that just remains part of formula people get confused and start moving it around no that is the final answer lastly aluminium in group 3 3 + learn sulfates charge which is so4 2 - this is a difficult one now it's not that clear you've got to find a common number that both 3 and 2 go into which is 6 so if I show you my thought process I effectively need two aluminium and three sulfates to make it equal six because now we have six plus on the aluminium side 6 - on the sulfate side that's therefore AR 2 s so for three I'm 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 1 hence 1 plus oxygen is in group 6 8 minus 6 is 2 so 2 minus and all you have to do here is swap by drop so literally bring down that invisible one to hear that - - that and then rewrite the ions so your final answer is K - oh and it works with anything really so let's do aluminum nitrate ala minions things Lutz three nitrate we've run off by heart from the list above we're going to swap and drop so we're going to bring that three down we're going to bring that invisible one down and so it becomes Al and those three three because you brought up three down let's look at ionic bonding now so it's ionic which means it has to be a metal and a nonmetal use your periodic table to double-check that the two things you've been given are metals and nonmetals if they're not they're probably asking you about covalent bonding so let's have a look at magnesium oxide for example now magnesium has an atomic number of 12 and oxygen has an atomic number of eight so let's work out their electronic configurations so two electrons go into the first shell then they fill up to eight so that's why magnesium is 2 8 2 and oxygen is 2.6 we only need to draw the outer electrons here so don't worry about those whole atom so there's magnesium's two electrons on the outer shell here's oxygens make sure you use crosses and dots to distinguish between the two atoms there's six so we can clearly see where those two electrons will be deposited and now we can actually draw the answer there because magnesium's lost its two electrons I'm not going to show any elections here electrons have a minus charge which is why it's net charge will now be two plus because it's lost two electrons now oxygen will have gained two electrons it's fine draw them a bit more secular than that into shopping and I'm going to use two dots to represent the electrons that came from magnesium because it's gained two electrons that's why the charge is now two minus and therefore we can see the formula of magnesium oxide is mg o let's look at a different example now which is magnesium chloride so magnesium still has an atomic number of 12 chlorine has an atomic number of 17 so drawing out their electronic configurations again you can see to be honest the outer shell electrons from the group number so it's up to you which way you do it so magnesium again two electrons chlorine has seven electrons in its outer shaft so we can see where that first electrons going to go but there's still a second electron here that needs to go somewhere which is why we need a second chlorine at them in terms of your final answer your magnesium it has lost two electrons which is why it's two plus chlorine has gained an electron from magnesium which is why it is one - so there are two chlorine atoms that's why draw a second one keeping it identical the first one - the first one I've already drawn and that's your final answer looking our aluminium oxide which is the most difficult example so aluminium has an atomic number of 13 so it's electronic configuration is 283 oxygen has an atomic number of eight so it's two point six so aluminium also shell will have three electrons on it oxygen will have six electrons so we can see where the first two elections will be deposited which is here but unfortunately we've still got a left over aluminium electron so we need a second oxygen atom which I'm going to draw here you don't need these intermediate steps by the way if you can go straight to the arms I'm just showing you how I found my answer out so that's where that aluminium is electrons gonna go but that leaves oxygens still missing an electron because now it only has seven electrons in its outer shell so we need a second aluminium atom still with three electrons in its outer shell so there's one of those electrons but unfortunately we've still got two electrons to give away which is why we need a third oxygen atom and finally it's happy because you can see where those two electrons go and now let's actually work out what our answer will look like I hope I've got space for this probably won't house so aluminium has lost three electrons - that's why it's three plus we need two of them which is why I'm doing them twice and then oxygen will bear form it like this is three of them let's label them as oxygen let's show their outer electrons so basically they're clones of each other they're all the same and each oxygen gained two electrons which is why then that charge is to minus so actually the formula value minimum side as we can see is al2o3 looking at covalent bonding now because they were looking at two nonmetals so don't be tempted to draw an ionic bonding diagram we're gonna take a nice straightforward example to begin with which is water h2o so we're gonna have a central oxygen atom two hydrogen atoms telling us aside label the atoms and then have a look in the periodic table to see how many electrons they have in that outer shell I 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 symmetrical eight that isn't particularly symmetrical but 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 no hydrogen has two in its outer shell carbon has 8 so that is now correct carbon dioxide is trickier and I'll show you that example now remember that 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 itself to show but I'm drawing it 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 to before so carbon has 8 electrons as two shared pairs and oxygen has eight so that is correct the most difficult example you could be given is eat bean c2h4 so I'm going to show you how to us there's your central carbon atoms here's your four hydrogen's label them it's easiest to start with the hydrogen's 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 while we're talking about chemical structures we're talking about four main structures that is giant covalent giant ionic giant metallic and semi 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 nonmetal and what is an ionic bond well it's the electrostatic forces of attraction between oppositely charged ions so remember that the metal 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 ions 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 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 one two 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 by des graph I have a high melting point similar argument but this time each carbon atom is bonded to three you still have many stronger and 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 that diamond why is that 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 for knots 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 having the current a third allotrope we need to know about is c60 fullerene now this is really different from diamond a graphite is actually a simple molecular structure which means it has a low melting point and that's due to weakens molecular forces which do not require a lot of energy to break it doesn't conduct electricity and that's because even though each carbon atom is only bonded to three others the fourth electron isn't free to move it has to stay within that molecule so it can't carry the current we should touch on a covalent bond here now remember covalent 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 lost because they have weekend's molecular forces which do not require a lot of energy to break a small point to note which is wider simple molecular substances have increasing boiling point with increasing mo so remember M R is the relative atomic mass so it's really saying something like why does ething c2h6 have a higher melting point than methane ch4 and that's because Ethan so substances with a greater mr have greater in specular 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 or molecule you'll simply set one molecule from another so you're breaking intermolecular forces OOP one elements now so remember that is the first column of the periodic table it is the alkali metals they all have the same chemical properties because they have one electron in their outer shell now remember as you descend that group the elements become more reactive that all extremely reactive as it is as you descend the group they get more 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 oxidize very quickly on exposure to other properties they have is they have low mounting of 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 other 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 fit and what 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 some intrusive flame however sodium produces an orange flame when added to water our potassium reduces our lovely lilac flame learn the word equation so when they're added to cold water Sarah go to touch 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 it produces very characteristic flame colors so lithium bonds to form a red flame the crimson flame potassium again produces a lilac flame and sodium produces a yellow flame in terms of making predictions about Group one metals the low 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 want to describe the atoms are larger more shells of electrons the electron from the nucleus so just be prepared to talk about the fact that there'll be more violence but you'd still see the same set of observations fizzing for example a flame moving around floating melting etc right so the halogens were looking at group seven so these are the elements including fluorine chlorine bromine and iodine now don't forget there states are 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 to the sublimation which is when it turns directly from a solid to a gas and in the case binding it goes from a gray solid to a pop or 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 mentally into hydrochloric acids that's HCl aqueous on addition with water you need to share 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 the most reactive towards the bottom there at their least reactive 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 cried because there'll be no reaction if you try and displace a potassium chloride for example using iodine that wouldn't happen because iodine is less reactive so just rely on the walls 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 moving on to the components of gas in air so let's look at what does it consist of well it's 21% oxygen 78% nitrogen naught point nine percent argon 0.04 percent carbon dioxide and everything else is other noble gases we might need to look at proving that the percentage of oxygen in air is 21% and you can use lots of different methods including the copper method so in this what you have is you have two syringes joined by a tube and in the to be placed copper now one of the syringes contains a hundred centimeters cubed about the other syringe is empty you heat the copper strongly and you pass the earth and one syringe over that copper to the other and what happens is the copper reacts with the oxygen in the air forming copper oxide and then as you can repeatedly pass that air over the copper you will see the syringe alter its volume and it will go from being 100 centimeters cubed up to 80 centimeters cubed or approximately and that tells you that 20 centimeters cubed contain oxygen because clearly that reacts with the copper you can also use iron filings in order to prove that the approximate amount of oxygen there is 21% so what you do this time is you get a large glass barrette you place iron filings in it and it's full of air and you dip the end of the direct into a trough containing water so the iron reacts with oxygen in the air and what you will see happen is that water will move into the burette and it should move in about 20% of the volume of the burette which tells you that there contains 20% oxygen looking at various elements reactions in air with oxygen so first rule magnesium fans in oxygen and you see a bright white light form and magnesium reacts with oxygen to form magnesium oxide which is a white solid once you've found that magnesium oxide you can react it with water and remember magnesium is in group two so it is an alkaline earth metal so if you test that resulting solution with universal indicator it will turn blue which is what you would expect because it is alkaline the reaction taking place now is magnesium oxide plus water forms magnesium hydroxide now looking at Sulphurs reaction with oxygen you see a blue flame this time the poisonous and colorless gas sulfur dioxide has formed it's a very strong smelling gas smells like rotten eggs in fact here is the equation you need to learn which is sulfur plus oxygen form sulfur dioxide if you dissolve that sulfur dioxide in water you will form the sulfurous acid and make sure you notice its formula it is different from sulfuric acids formula looking at hydrogens reactions with oxygen you see a pale blue flame water is formed and your summary equation is hydrogen plus oxygen forms h2o which is water moving on to thermal decomposition now so what does that really mean well thermal means to do with heat decomposition means breaking down so it's breaking down a substance using heat and this is what happens when metal carbonates are heated they break down for example copper carbonate when heated it goes from being a green solid which is copper carbonate it's broken down to copper oxide and copper oxide is a black solid all the carbonates respond quite similarly so if we had calcium carbonate now we heated it it would break down to calcium oxide and carbon dioxide although this might seem slightly out of join we now need to look at the effect of excess carbon dioxide on the environment so remember calmed outside is a greenhouse gas so enhanced greenhouse gases so more co2 being released will lead to global warming now global warming causes polar icecaps to melt because they've melted it means that there is a rise in sea level which floods low-lying land this obviously causes the destruction of many habitats it can cause extent extinction of species they get caught up in it and other effects include changes in bird migration patterns so that's why they fly in the summer in the winter and also increased extreme weather the 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 unreactive 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 highly 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 one 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 steam you can try acid and that will produce a salt plus hydrogen and you obviously wouldn't try reacting people metals with acids because they are far too reactive do you notice that when you look at the V Activity 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 HCR 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 busting so rusting is when metals flake away and you only used to work 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 busting process but is not necessary what are the different ways in which we can prevent rusting though 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 link ions and don't and donates electrons and what that means is the electrons can flow to iron and therefore the iron starts to rust and form iron ions this is hardwired got the same name there's electrons which have being donated from zinc can help the iron form it's 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 learned 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 and because we've just talked about the transfer of electrons let's remind ourselves of the definitions of oxidation and 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 indicators so you need to learn various colors of indicator so obviously the most common one is universal indicator that shows the pH scale from 0 to 14 remember 0 to 6 is acidic 8 to 14 is a lie so 7 is neutral universal indicator in a neutral solution is green in an alkali solution is powerful and in an acidic solution if it's a strong acid it will be red and that would be about pH 1 other indicators you may come across have less of a range of colors such as methyl orange na methyl orange is red in acid it is yellow in alkali phenolphthalein which is a very difficult word to spell is colorless in acid and it is a beautiful pink color in alkali and lastly litmus is red in acid and blue in alkali so what makes something an acid well it's the fact it can donate hydrogen ions and what makes something a delight it's the fact that it can donate hydroxide ions 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 well so do you remember your definition of an acid which is that it is a H+ donor a base is there H+ 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 salt so effectively a salt is formed when the hydrogen of an acid is replaced with either metal or ammonium for example say you had how to plug acid you acted it with potassium oxide then you would end up with potassium chloride which is the salt taking soft uric 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 source of a produce now in terms of the reactivity of acids remember the only metals above hydrogen in the reactivity series will react with acids so things like copper silver 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 do 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 a 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 you make sure that whatever is on the products I started 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 formed so make sure you know which one it is oh sorry ability wolves 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 learning exceptions that's a good way to go so let's start by stating that all nitrates are soluble or potassium ammonium and sodium compounds are soluble for sulfates are soluble there are three exceptions and that is led to calcium and barium sulfate or chlorides are soluble except from ledtube 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 would have told you that the sodium ammonium and tascam Kahneman's 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 stops and you need to decide if they're insoluble and soluble so starting with lead nitrate then I saw you more 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 had to learn so that is insoluble and now calcium carbonate that is insoluble because it is carbonate and it is not Shailene potassium or ammonium so 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 reacted with the acid and you form your soluble salt you can also use metals plus our sir so does it need to be combined with an oxide hydroxide or carbonate but do notice that you need a metal which is an 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 though summary for this is that you're going to react comes out of your metal hydroxide with your acid you're going to filter in order to remove any undissolved solid then you're going to evaporate 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 and 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 getting even more detailed now we need to look at the bronsted-lowry theory of acids don't worry too much about this they were extremely specific over their definitions of acids and bases they really only wanted you to use hydrogen ions when defining them so if bonds did allow acid therefore is a hydrogen ion donor which is fine because we already know that a bolstered lowry base is a hydrogen ion acceptor so don't mention anything to do with hydroxide ions when you're talking about one stat lowry let's look at an example of the bronsted-lowry theory in action so we're going to use the dissolving of hydrogen chlorine in water so we've got h2o and HCL and it's a gas at this point so notice that when they are reactive what you find is a hydroxo neo- pond which is h3o plus and a chloride ion which is a Prius so we have water reacts with hydrogen chloride forming the hydro oxonium ion h3o plus plus the chloride ion so let's try work out which species are acting as one state Larry acids and bases so clearly the hydrogen chloride is acting as a bronsted-lowry acid because it donates a hydrogen ion and the water acts as a bronsted-lowry base because it has accepted that hydrogen ion to become the hydroxo nehemiah HD o+ oh we can move away from that disgusting topic now I just look at generic tests so the test for hydrogen don't say is the squeaking 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 bleach is damp litmus paper and ammonia times damp red litmus paper blue now I've given you the most concise precise definitions for this so make sure you like them every single word matters here so it makes for example damp is worth the mark red litmus paper worth mark so make sure you learn them properly and now we're getting more complex so 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 flame tests 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 city flame that won't work because the yellow will extract the color so hold it in a boring blue flame so in the colors now if we've got lithium ions you will see a lovely red crimson color sodium you'll see a yellow flame and potassium as with when you add it to cold water you will see a lighter flame calcium goes an orange red color or a brick red color and copper goes a blue green color if you don't count flow test you can use a precipitation reaction and you can look at the color precipitate formed once you added sodium hydroxide so if you add sodium hydroxide to something containing copper you will see a blue precipitate formed iron 2 will form a green precipitate and iron 3 will be a brown facilitate and I remember those that kind of muddy ugly colors so goes green for INT brown for iron three testing for ammonium ion Sol which is NH four 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 ok moving over now to test for negative islands who've looked at metal ions and ammonium so we're looking now at the halides which is group stubborn the halogens so first of all you need to add nitric acid you I've got 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 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 some 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 we go from white to cream to yellow and we prepared to write the ionic equation for this which will be for example with chlorine will be AG plus plus CL minus forms AG CL solid 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 substances boiling point if it was 100 degrees Celsius you know you have water and linked to this how do you show that water is pure well I 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 and hydra's copper sulfate and high just 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 so I thought the easiest way to talk uses 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 it 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 I'll make answering these questions far more straightforward a student uses this apparatus to investigate the heat energy released when nitric acid is added to potassium hydroxide solution soaked or nitric acid inside the bureau vats which is going to be dripped into the polystyrene cup containing potassium hydroxide she uses this method for 25 centimeters q2 potassium hydroxide solution into the polystyrene cup measure the temperature of the potassium hydroxide solution add five centimeters cubed of nitric acid from the burette stir the mixture mix and measure the highest temperature reached add further 5 centimeters cube 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 cube of potassium hydroxide solution so you need a fairly precise piece of operators here which is why should state either a pipettes or a burette measuring cylinder would not be precise enough the table shows the students 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 acid was added the result for 20 centimeters cubed is anomalous suggest 2 possible mistakes other than miss reading the thermometer that the student might have made to produce this anomalous result so remember anomalous means that it's the odd one out 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 cause the temperature to be too low aside from miss feeding the thermometer well first of all she could have added less than five centimeters cute actor 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 120 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 and another experiments to record these results volume of 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 MC delta T so this is really nice thinking that's 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 4.1 eight 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 three nine seven oh two four significant figures three an excess of zinc powder five grams was added 250 centimeters cubed of 0.5 maldium to the minus three copper sulfate solution in a glass beaker the initial final temperatures are shown on the thermometers below use the picture of the thermometers to complete the temperature before and the temperature after as well as the temperature change so this is what a cute li reading the thermometer so before you can see that it is eighteen point seven degrees Celsius the temperature after is 25 point three degrees Celsius which means that temperature change once you put that into your calculator is six point six degrees Celsius calculate the energy change cue which occurred during this experiments remember using Q equals MC delta T if the mass is the actual mass of the liquids which have been added not the solid so ignore the five grams if you look here it's here 50 centimeters cube which is why the mass is 50 we know times are specific heat capacity which is four point one eight and that's always true and then times the temperature change which I just calculated is six point six and once once you've put that into your calculator you get a value which is Q's one thousand three hundred and seventy nine point four joules and then hence calculate the entropy change Delta H of this reaction so use this equation which is Delta H equals Q over N so we need to work out the number of moles so number of moles is concentration times volume so look up here again our concentration is zero point five a volume is fifty which we need to divide by a thousand to make sure that it's in DM cubed rather than centimeters cubed which is therefore 0.025 and then lastly make sure that Q is in the correct unit so we need it to be KJ so what we do is we take this number here and we simply divide it by a thousand to get one point three seven nine four and then just pop those numbers in so one point three seven nine four divided by zero point zero two five I'm always running out of space and you get a value which is 55.2 kj/mol now do you have a look at the thermometers now and make sure you're happy that the temperature went up yes it did because it went from being eighteen point seven degrees Celsius to twenty five point three it's got hot which means it's an exothermic reaction which means our Delta H here is positive and don't forget that for the last month by the way that was a lot of maths especially that number of moles equals concentration times volume that's very much to do with the titrations topic so have a look at that part of the video if you don't understand why I entered the numbering why did the calculation like I did so suggest the biggest source of error in this experiment and how the procedure used could be modified to decrease this error well it's always going to be heat loss to the surroundings so rather than using a glass beaker you could use a polystyrene cup with a lid because that is a better insulator 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 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 in 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 powder 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 form 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 and 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 the 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 means the high resolution because carbon dioxide doesn't weigh very much so you need at least like zero point zero zero 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 mask 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 some types of experiments involving crosses being obscured due to 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 costs dissipated so do be prepared to talk about some limitations related to the methods used now we're looking equilibria I'm very excited I'm going there at the end of this and it's been going well so I'm happy so with the term exothermic let's define it first of all it means the release of heat energy so looking at endothermic reactions you'll see the opposite so he energy in this case is taken in so chemical equilibria now we are looking at reversible reactions here so be aware of this special arrow this is your reversible era and it tells you that the reactions 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 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 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 favour the forward reaction decreasing temperature will favor the exothermic reaction and the position of equilibrium will shift to favor that 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 no.2 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 a more no.2 and so therefore the color changes and it becomes brown 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 look 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 archeins 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 that down the 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 protect particular compound has four carbon atoms and ten hydrogens to make it into an empirical formula just counts all 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 errs and so becomes C 1 and then 2 times 1 is 2 plus 2 is 4 so h4 because it looks a bit strange to write the 1 I'm just going to erase that there's an invisible ones so it's CH for its display formula looks like this which is you draw the carbon in the middle and hydrogen's around the outside and remembering that each carbon atom forms four bonds each hydrogen forms one bond and you must remember that to help you draw them it's named well it contains one carbon which is why it Smith and it's now cane which is why it's methane so looking at the second one this time two carbons so we're going to have C 2 and then according to the general formula 2 times 2 is 4 plus 2 is 6 so it's MACUL formulas c2h6 drawing it out there 4 carbons in the middle then you've got your hydrogens filling up around the edge each having one bond and each carbon has 4 because it's still an alkane ends in Ain so it contains 2 carbons which is why it's Ethan the third one now so it's C 3 2 times 3 is 6 plus 2 is 8 h8 3 carbons in a line ends in Ain it contains 3 carbons so it's propane for 4 carbons I run out of space so it'll be seed 4 H 10 and it contains 4 carbons which is why it's butte 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 our Keens they are unsaturated and that means they contain a double carbon bond I'm going to show you how to draw the first 4 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 alkanes 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 the carbons one carbon alkane does not exist and without the 2 carbon so starting with the two carbon one we know we need to substitute two men as the answer becomes c 2 and then simply H for the dissipate formula we need a double bond and therefore we're going to fill up our hydrogens do you notice again that the carbons have 4 bonds the hydrogen has one contains two carbon atoms which is what begins with with eath it's an alkene so it's easy in looking at three carbon atoms nasco c3h6 again make sure you're filling these up properly double-checking the ones I can't reiterate this enough and this will be three carbons soap rope it's an alkene so protein 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 its butene however you now need to look at the other available isomer remember that isomer is something with the same molecular formula but different structural formula so if we draw that molecular formula out again and 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 hydrogen's making sure you don't draw too many bonds on this 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 named them is according to where you find that double them because the double bond in the black version is between the first and second carbon and call it each one Ian because the double bond is between the second and third carbon atom we call this view to means so let's try and work out the various isomers we can draw for c5h12 which is obviously pentane so let's start by drawing the straight chain isomer straight away because that's the easiest to do because we're drawing isomers is likely we need to draw a branched version now so I'm going to add a methyl group it needs to be on a minimum of this second carbon along because if you draw it on the first one it's just like a straight chain isomer but just going around the corner you to ask what chemistry teacher if you don't I know what I'm talking about that and make sure we've got five carbons so I've joined four here's the fifth and fill up with hydrogen's and just double check them so we definitely got five carbons I've got three six seven eight nine ten eleven twelve yep so that's c5h12 let's work out its name how the longest chain is Beach is four carbons we've got a methyl group on the second one which is why it's two methyl butane try not to capitalize that the I shouldn't have done that and then let's work out where the next isomer will be well we can't go and add the methyl group on to this carbon instead because that would actually be the same isomer as the one I've just drawn because it's still on the second carbon but just looking right to left so I'm just going to have to add another methyl group I think off that second carbon which will look like this and I do have one two three five carbons so that's right just fill up the hydrogen's and count them all up so five carbons three six nine twelve yeah that is correct right this is going to be more difficult to name so the longest carbon chain has three carbons in it which is why it's propane it's propane pain rather than in because it's an alkane there's no double carbon bonds and we've got two methyl groups and they're both off the second carbon which is why it's 2-2 let's choose them so it's die and then we fell food so it's two to dimethyl propane 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 it will arcane have a common what all our kings 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 our canes for example will follow cnh2n plus two where's all our Kings will obey cnh2n and then they show a trend or a gradual change in physical properties which again makes sense so Ethan has two carbon atoms whereas methane has one so therefore you'd expect Ethan to have a higher melting point and boiling point which it does so what is the functional group well it is an atom or group of atoms which determine the chemical properties of a compound so we talked about alkenes 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 is 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 again our crude oil which we know is the mixture of hydrocarbons we heat it until it evaporates and then we pass that vape it 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 just make sure you learn my summary if you're not following what I'm saying because you'll get all month anyway now looking at the top then which we need to go through the order in which the fractions are condensed so refinery gas is a car at the top after that you have petrol then you have kerosene followed by diesel fuel oil and lastly bitumen so what are the various uses of these different fractions well refinery gases are often gas which we use in our central heating petroleum or gasoline answers otherwise known as in America is obviously used as a fuel for cars you have kerosene which is a fuel for airplanes diesel is a fuel for lorries and buses set anything big fuel oil is used as ship fuel and lastly bitumen is used for Road surfacing or roof material I don't know if that's a verb or not to be honest but I think it's used to help stick down roots I've no idea couple of words to be aware of first of all viscosity so that's how readily a fluid flows be aware that more viscous of fluid is the less readily it flows so honey is very viscous because it's slow to flow I like the fat that rind and water is very ambitious 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 with finer gases so clearly Bitterman will be more viscous it will be less volatile and it will have a higher boiling point they will also have a darker color because it's a brownish sticky color whereas for finer gases or colorless so do be aware and do you be willing to make comparisons and make full comparisons so saying the finer gases are lighter in color have a lower boiling point are less viscous etcetera so once we've got these fuels what do we need to do to them we need to burn them and that's why complete and incomplete combustion takes place so complete combustion is when you burn something in a plentiful supply of oxygen and that means you produce carbon dioxide and water is a byproduct which is a good thing because neither of these things are toxic although there are obvious environmental with carbon dioxide production due to it being a greenhouse gas incomplete combustion is when you have insufficient oxygen and that means you don't produce carbon dioxide this time you produce carbon monoxide and water so what are the issues relating to carbon monoxide weather well it is extremely toxic and poisonous and that's because it combines with the hemoglobin and red blood cells forming carboxyhemoglobin and that means the red blood cells can no longer transport oxygen around the body acid rain now so we're looking at more environmental issues so acid rain comes from two areas firstly nitrogen and oxygen in car engines reacts due to the high temperatures found forming nitric oxide that reacts with water in the atmosphere forming nitric acid so there's your first acid rain next crude oil can contain sulfur impurities and when burnt they form sulfur oxides that reacts with water forming sulfuric acid so there's your second acid rain and acid rain gets into lakes and rivers making them too acidic there for killing aquatic animals it damages trees and it damages limestone buildings and you must mention that they're limestone 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 you 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 so if we take an unsaturated hydrocarbon so an alkene and we react it with bromine water now you must remember the color change what you'll see is it will go from being orange to colorless and I'll show you the summary equation now we 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 is your answer that you add foam in water and in terms of your observations what you would say see is that go from orange to colorless let's actually look at an example so we'll take Ethan we're adding bromine water remember bromine is diatomic hence why I'm saying BR 2 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 by-product 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 washing it runs from orange to colorless now looking at our Cane's reactions with bromine water so our chains or a saturated compound it's basically the same thing what you see this time I'm going to take methane as my example I could have used ethane or propane we add it to bromine of water well what happens this time is one of the hydrogen pops off the burning joins you complete the rest of the molecule on 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 the hydrogen has simply been swapped or substituted for bromine you say that this is a substitution reaction so you can actually see what's happened here now we're going to look at addition polymerization and they could ask you to show this as an equation so I'm going to show you what's going to happen we are taking a monomer such as e-beam it's got to make sure I can answer probably eat Dean this is your monomer which means it is a small subunit because it is an addition reaction we're effectively going to add lots of them together which is why we write an N here that just means you have lots of them then we know what we saw some big square brackets you want to break that double bond as I've done that extend the bond and now just complete the rest of the structure and you write an N here to show that there's lots of them and this was the polymer formed and if you were to name them we know that that was Ethan because there's many of them joining together we say that the polymer formed is polythene which you've probably heard of before and not realized is polythene and that's used to make cling film and plastic bags etc let's take protein now and I'm gonna draw the protein like this just to make it easier to draw the polymer I hope you can see that that is protein it is the three h6 again that's our monomers we're gonna have any number and hence the and squid supply brackets break that double bond and now just complete the atoms be very careful where you draw your bonds make sure those carbons are joining extend the bonds out draw your N and this is therefore poly protein this is a hardest plastic than polythene so it's used to make pockets windows etc let's take a third example now again stri brackets break that double bond extend the bonds and then just complete and this is poly tetra flooring what does biodegradable mean it means breaking down the substance using microorganisms and everything these days we want it to be biodegradable we don't want plastic hanging around for hundreds of years which is why it's really good if they say that they're biodegradable what poems are associated with the disposal of addition polymers so really problems associated with plastics that is that most of them are non biodegradable they are unreactive which means it's difficult to break them down and when you burn them as a different way of disposing them they produce lots of toxic gases so there's no one good way of disposing of addition polymers or plastics because they just fill up your landfills they don't rot they don't by degrade their unreactive and when they're burnt they give off nasty toxic gases do you notice that bio polyesters are biodegradable thank you so much for watching my video well done if you made it to the end don't forget you can buy my sizes hazal perfect answer vision guides on my website they're available right now at WWI with hazel code or UK [Music]