hello LS in this video we're going to be going through the whole of your Ed EXL gcsc chemistry paper one and this is to really high standard so we're going to go through spec Point by spec Point explaining in detail everything that you need now Charlotte who's made this video has also written predicted papers for this year and she's done walk through through predicted papers for this year you can get those over the website by the boot camps the master classes where you'll find videos to explain all of this step by step LS free questions three flash cards all waiting for [Music] [Applause] you here we're going to have a look at the development of the model of the atom through time so we started off with Dalton's model Dalton's model told us that the atom was a solid sphere cannot be created destroyed or divided into any smaller parts now different types of spheres made up different elements but this sphere did not contain any protons neutrons or electrons now over time JJ Thompson came along and proposed a new model called The Plum Pudding model here he said that the atom is not actually a solid sphere what it actually is is a cloud of positive charge with negative electrons embedded within it next came along the nuclear model and the experiment that determined this was Rutherford and his students Alpha scattering experiment now what Rutherford and his students did was he fired alpha particles at a thin sheet of gold foil now if the plum pudding model was true we would expect all of these alpha particles just to bounce back however most of them passed straight through some of them were a little bit deflected and very very few came straight back now what this told us was that the mass of an atom was actually concentrated in a central nucleus which had to have been positively charged to have repelled this positive alpha particle and most of the atom actually was empty space completely contradicting the plump hooding model and we know this because most of these atoms went straight through the gold foil with no deflection so over time or came up with the electron shell model and the electron shell model told us that rather than just randomly floating around the nucleus the the electrons were actually found in fixed distances from the nucleus orbiting it in shells later experiments found that the positive charge of any nucleus can actually be subdivided into a whole number of smaller particles of equal charge these were named protons finally James Chadwick carried out some experiments that provided evidence to show the existence of neutrons in the nucleus and this more or less brings us to our up to-date understanding of the atom what is an atom an atom is the smallest part of an element that can exist atoms of an element are represented by a chemical symbol and these symbols will always start with a capital letter and consist of one or two letters as you can see here oxygen is just represented with a capital O and helium is represented with a capital h followed by an e now we need to know how small an atom actually is atoms have a radius of about 0.1 nanom which is 1 * 10- 10 m and the radius of their nucleus is less than 1 10,000 of that of the Aton so it's about 1 * 10-4 M we've already mentioned this word element we need to know though what is an element what is its definition so we need to know going into your exam that an element is a substance made up of only one type of atom if we look at our periodic table which we will be given in the exam you can see that we've got over a 100 different elements all of these different letters or pairs of letter within the periodic table that you can see here is representing a different element and each of those different elements will have their own unique set of properties now if we link this back what we said an atom was the smallest part of an element that can exist we can see that we can represent an element by showing a substance made of only that type of atom so here for instance I've got an atom of carbon and the element of carbon is just shown as lots and lots of these atoms in a structure so now we're going to look at compounds what is a compound we should know that a compound is a substance which contains two or more different elements which are chemically combined in fixed proportions so an example of this could be the chemical reaction that occurs between ion and oxygen to form ion oxide here we should should recognize that ion and oxygen are both elements because they're only made up of one type of atom whereas ion oxide is a compound you can see it's made up of two different elements the ion and the oxygen which have become chemically combined now it's important that we know that compounds actually have different properties from the elements that made them so the properties of ionx oxide are actually very different to the properties of ion and of oxygen now we also need to know that compounds can only be separated into Elements by chemical reactions we aren't able to Simply separate them using filtration or distillation or some other physical process we have to use a chemical reaction now chemical reactions will always involve the formation of one or more new substances such as this example here where ion and oxygen made ion oxide and they will often involve an energy change so quite often we'll observe an increase or a decrease in temperature due to this energy change in chemistry we're often going to be asked about chemical reactions we might be asked to write down the word equation which would look like something like this water goes to hydrogen plus oxygen however sometimes we'll be asked to write down the symbol equation now this involves writing down the chemical names for each of these substances so we know that water is H2O hydrogen is H2 and oxygen is O2 now when we're asked to write down the symbol equation we will need to balance it and this is a certain skill when we want to balance a symbol equation we need to make sure that we have the same number of each type of atom on each side of the arrow so on both the reactant side on the left and the product side on the right now let's use this as a perfect example to show you how to do this the first thing I like to do is to separate the reactants from the products by drawing a little line and then on the left hand side on the reactant side let's count up how much of each type of atom we have I can see I have two h's and one oxygen if I do the same on the other side I can see that I have two hydrogens and I have two oxygens as well now looking at this I can see I have the same number of H's on the left and the right however I only have one oxygen on the left and I have two on the right now the way we can balance this this is by having more waters on our reactant side so let's write another H2O there now here I can clearly see that I have the two oxygens so I would cross out that one and replace it with a two however by introducing another water we now have more hydrogens as well so we cross out the two and we replace it this time with four because I have two of these H2S so now although the oxygen are balanced the hydrogen's are now not balanced so what we need to do is we need to have more hydrogens on the right hand side so let's introduce another H2 now I can see H2 plus an H2 is going to give me four hydrogens so now the hydrogens will all also be balanced I have four on the left and I have four on the right so this means that our equation is balanced now let's write this in the way that the examiner would want it I can see I have one two waters on my left hand side so I'm going to put a big number two in front of the H2O that means that we have two waters so now let's look over on the right hand side here I can see that I have one and two hydrogens which means I want to put a big number two in front of the H2 and there we have it we have our balanced symbol equation now in order to write down all of these balanced equations there's some formula that we really need to know and this is going to hold throughout the whole of chemistry we need to know that carbon dioxide is co 2 we need to know that water is H2O we need to know oxygen is O2 hydrogen is H2 nitrogen is N2 ammonia is NH3 hydrochloric acid is HCl and sulfuric acid is h2so4 if we learn these off by heart we will have such an easier time in our exam the atom is made made up of three different types of particle so we have protons which are positively charged particles found within the central nucleus of the atom then we also have neutrons which are also found inside the nucleus of the atom neutrons however have no charge now we might see this referred to as being neutral now that third particle found within an atom is the electron now electrons are negatively charged particles and we don't find them in the nucleus this time we find them in shells which orbit the nucleus so you can see all this in our little diagram here and we have to get very used to these diagrams and being able to label them accurately this table here summarizes all of the facts that we need to know about the protons neutrons and electrons we need to know that the relative charge of a proton is is + one the relative charge of a neutron is zero and the relative charge of an electron is minus one we also need to know that the relative mass of both the protons and the neutrons so both particles found within that nucleus is equal to one however the electron's relative mass is really tiny compared to this we might see it referred to in several different ways but essentially the relative mass of an electron is approximately 1 over 2,000 we may then sometimes see it referred to is just very small now it's important that we know a few key facts relating to this information so atoms of different elements will all have different numbers of protons this is part of what gives them different properties however all atoms of a particular element actually have the same number of protons now finally if we have a think about the mass of an atom we can see that the relative mass of the protons and the neutrons is so much more than that of the electrons and this is why almost all of the mass of an atom is found within the nucleus in chemistry we will often see Isotopes coming up now we need to know what is an isotope Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons here you can see I've got two different isotopes of helium the helium 4 isotope has two protons two neutrons and two electrons however the helium 3 isotope has two protons only one Neutron and two electrons so notice here the thing that makes these isotopes of each other is that they still have the same number of protons however they have a different number of neutrons now let's have a think about the ion what is an ion an ion is a charged particle which forms when an atom or a molecule gains or loses an electrons so here I've got a diagram of a buril atom I can see that it has four electrons now the burum atom can lose the two electrons within its outer shell to become a burum ion now because it's lost two of these negative electrons it has become more positive think about it like if you lose a negative4 and you become more positive and happy that's exactly what this pilion has done so because it's lost two electrons it now has a 2+ charge and this is how we would represent this in an [Music] exam electrons are found within shells now shells can also be referred to as energy levels so use whichever one you prefer when we're adding our electrons to an atom we start by adding them to the innermost Shell First now we need to know that in the first shell that innermost shell we can only add up two electrons then in the second shell we can only add up to eight electrons and the third shell we only add up to eight electrons again now this is going to be really really important when we're in the exam if we're asked to add the electrons to an atom so let's use carbon as an example here carbon has six electrons now if we want to add this to the shells we can remember that we start with the inner most shell first so with the inmost shell we know that we can add up to two electrons so we add our one two electrons to the innermost shell of this carbon atom then if you think we have six electrons in total that we need to add on if we do six minus that two we're left with four more electrons and we know that in the second shell we can add up to eight electrons so we can fit all of those four in that second shell and that's what I've done here I've got one 2 3 four electrons in its second shell now we can represent this using this diagram however we might also see it using this system here where in Brackets we do 2 comma 4 that represents two in the first shell and four in the second shell now let's have a look at how the atom is represented on the periodic table now the biggest number is known as the mass number the mass number is very important because it represents the sum of the number of protons and the number of neutrons now the smallest number of the two is the atomic number and the atomic number gives us the number of protons within that atom so so much information given just from this periodic table so it's important that we know atoms have no overall charge now that then leads us on to the fact that in an atom the number of protons those positive particles must be equal to the number of electrons those negative particles and that's how they can have no overall charge now we could be asked in the exam to work out the number of protons neutrons and electrons in a certain atom so if we look at Florine here as an example I know that that smallest number is the atomic number which gives me the number of protons therefore I know that the number of protons is equal to 9 now then we can think about the mass number which is the biggest number and remember we said that the mass number was the sum of the protons and the neutrons so as we now know how many protons there are we can work out the number of neutrons by doing 19 minus 9 and that ends up giving us 10 now finally we can work out the number of electrons by using the fact that we just said that in an atom the number of protons is equal to the number of electrons so using that fact then we can say that we also have nine electrons and it's as simple as that so let's carry out the same process now for an argon atom I can see here that the mass number is 40 and I know that that mass number is equal to the sum of the protons and the neutrons I can also see here 18 the smallest number of the two is our atomic number and I also of course remember that the atomic number is equal to the number of protons so now that I've looked at this I can start to work out how many protons neutrons and electrons we have so because the number of protons is equal to the atomic number I can say that I have 18 protons now I know that the number of neutrons is going to be equal to that mass number minus the number of protons therefore to work out the number of neutrons I can do 40 - 18 which gives me 22 so I know that I have 22 neutrons finally to work out the number of electrons that we have we use the fact that in an atom the number of electrons is equal to the number of protons so in this case I can say that I also have 18 electrons sometimes we'll be asked a similar question but to work out the number of protons neutrons and electrons in an ion instead so here we're asked for br minus ion we should understand that in an ion like this which is negatively charged we must have more negative particles than we have positive particles now remember that electrons are the negative particles and protons are the positive particles so in order for Bromine to have a negative charge in this case we must have one more electron than proton we can only have more or less electrons not protons that's an important fact so if we look at this we can see that that smallest number the atomic number is equal to 35 so using our knowledge from before we know that the number of protons is equal to the atomic number so we have 35 protons now we can see that the mass number here is 80 so to work out the number of neutrons we use the fact that the mass number is the protons plus the neutrons so to work out the neutrons I'm just going to do 80 minus the number of protons 35 which ends up giving me 45 so here I can see that I have 45 neutrons finally we need to write down the number of electrons and in order to do this because we have an iron we have to use the fact that we said that in this case because it's BR minus we must have one more electron than the protons so as we have 35 of these positive protons we must have 36 of these negative electrons to get that overall negative charge what is relative atomic mass we need to know the definition of relative atomic mass is the average mass of all of the atoms of an element when compared to 1 12th of the mass of a carbon 12 at atom it's quite a technical definition so definitely want to add to your flashcards now the importance of relative atomic mass is that this definition explains why the relative atomic mass of some elements on the periodic table are not actually whole numbers what they actually are are averages of several different isotopes now on the periodic table we can look at chlorine and notice that its mass number it's actually 35.5 now that is its relative atomic mass that5 has come about because we've averaged all of the different isotopes that exist for chlorine it doesn't actually have 35.5 protons and neutrons it's different to what we're used to it's not quite the mass number in that case it's just the relative atomic mass now remember when we're talking about Isotopes they have the same number of protons but a different number of neutrons so all of those different isotopes of chlorine are still going to have 17 protons however the number of neutrons that they have will vary a very common type of question that we will see in the exam is being asked to calculate relative atomic mass so here is the formula that we need to use relative atomic mass is equal to the percentage of isotope 1 multiplied by the mass of isotope 1 plus the percentage of isotope 2times by the mass of isotope 2 and we repeat this process for as many Isotopes as we have adding them all together and then divide through by 100 because all of these percentage abundances will of course total 100% so the three steps we're using are one multiply the percentage abundance of each isotope by its mass to add all of these together and finally three divide by that total abundance so if we're using percentages that is of course going to be 100 let's have a look at an example here so lithium is found to have two isotopes lithium 6 has a 7% abundance and lithium 7 has a 93% abundance here we're asked to calculate the relative atomic mass of lithium so first things first let us remind ourselves of the equation so we know relative atomic mass is equal to the percentage of isotope 1 time the mass of isotope 1 plus the percentage of isotope 2 times the mass of isotope 2 and then we add those together divide by 100 so summarizing the information we have here we know the mass number of lithium 6 is six and its percentage abundance is 7% lithium 7 has a mass number of seven and a percentage abundance of 93 so if we substitute these into our equation we find that the relative atomic mass is equal to 6 * 7 + 7 * 93 / 100 and that gives us a relative atomic mass equal to 6.93 and so that is the relative atomic mass of lithium here we're going to have a look at a vital part chemistry the periodic table we're going to use this so much throughout the course so periodic table why is it called a periodic table it's because similar properties occur at regular intervals or periodically now let's have a look at this periodic table then we should know that the columns are called groups and the periods are the rows so we start with period one which is our first row then the next one is our period two period 3 four and so on now we need to know that all of the different groups have elements with similar properties within it now all of the elements within a group have the same number of electrons in their outer shell this is such useful information so for example all of the elements in group one have just one electron in that alter shell all of the elements in group two have two electrons in the outer shell and so on another great fact to now is that elements in the same period all have the same number of electron shells so hydrogen and helium in Period one just have one shell all of the ones in Period two have two shells and so on early periodic tables like the ones here by newand were incomplete as many of the elements were unknown before the protons neutrons and electrons were discovered scientists arranged elements in order of their atomic weights however this meant that some elements were placed into incorrect groups as their chemical properties were ignored the Mel tried to solve this problem he arranged elements in columns based on their similar properties he arranged elements horizontally in order of atomic weight that left gaps to allow for elements that may have been undiscovered up to that point in some places he changed the order of atomic weights to maintain the patterns in the columns now the time elements with the properties predicted by Mel were discovered filling the gaps now Isotopes explained why the order of atomic weight was sometimes Incorrect and that is how we got to the periodic table that we use today now we need to know that elements that react to form positive ions are metals and elements that react to form negative ions are non-metals now on our periodic table we need we need to know where we find our metals and where we find our non-metals so let's have a look at it if we look at this little staircase that we have here where the staircase starts just above aluminium and goes all the way down we can see that the metals are on the left hand side of the periodic table and the non-metals are on the right hand side of the periodic table there are three types of strong chemical bonds we have ionic bonds calent bonds and metallic bonds we need to know that we find ionic bonds in substances that have metals and nonmetals bonded together an example of that is sodium chloride calent bonding however is found when we have non-metal atoms bonded together an example of that is Diamond which is made up of just carbon atoms now finally we've got metallic bonding now that's found in metals an example of that is ion let's take a closer look at ionic bonding so we've said that ionic bonds form between metals and nonmetals when a metal atom reacts with a non-metal atom electrons from the outer shell of the metal atom are transferred the metal atoms lose electrons and become positively charged ions also known as cattin because they're positive so here if we have a look at burum which has two electrons in its outer shell now burum wants to get a full outer shell this means it needs to lose its two electrons by losing two electrons it ends up as a positive ion with a two plus charge and what we find is that all of the group one Metals form ions with a one plus charge the group two metals form ions with a two plus charge where the group six non-metals form ions with a two minus charge and group seven nonmetals form ions with a one minus charge well we've looked at what happens to the methyl atom but what happens to the non-metal atom non-metal atoms are going to gain electrons and they're going to become negatively charged ions or anion let's have a look at oxygen as an example here I can see here that oxygen has six electrons in its outer shell now to get a full outer shell it needs to have eight electrons in its outer shell and the easiest way that oxygen can do that is by gaining two electrons if it gains two electrons it becomes a negatively charged Ion with a 2 minus charge well all this leads us to the question what is an ionic bond what an ionic bond is is the strong electrostatic attraction between these oppositely charged ions of course we're going to end up with that positive methal ion and the negative non-metal ion after reacting both that metal and non-metal ion are going to have a full outer shell and they now have the same electronic structure as a noble gas in group zero now we can show the electron transfer during the formation of an ionic bond using a dot in Cross diagram and when we draw a DOT cross diagram we generally only draw the outermost shell of electrons well let's have a go at looking at the formation of an ionic bond between burum and oxygen so we know that burum has two electrons in its outer shell in fact its electronic configuration is 22 oxygen as well we just said earlier that we have six electrons in its outer shell so it has a 26 electronic configuration now what's going to happen is the burum is going to give its two electrons to the oxygen we end up with a burum 2 plus ion and an oxygen 2 minus ion and we're going to write them just like this with square brackets around their full shells and the charges up on the top right hand side let's have a look at another example here draw a DOT and cross diagram to show the bonding in sodium chloride well sodium's in group one so we know it has one electron in it it outer shell chlorine on the other hand I know is in group seven so it has seven electrons in its outer shell I'm representing sodium's electrons with a cross and chlorines with a DOT you can do it the other way around and it still works so the sodium is going to give up its electron to get its F out to Shell that leaves us with a one plus charge ion whereas the chlorine is going to gain that electron and it's going to therefore become a negative ion with a one minus charge so I just put a little minus in the top right hand corner for chlorine we need to be able to name ionic compounds we should realize that when a name ends in ey it's because the compound only contains two elements an example of this is sodium sulfide which just has sodium and sulfur in it or calcium oxide which just has calcium and oxygen now if we have a name ending in eight however this means that the compound contains three or more elements including oxygen so examples of this are sodium nitrate which has the formula N3 or calcium sulfate which has the formula cao4 now we also need to know how to write these formulas and to be able to do this we really have to know the formulas of these ions so we need to know that the carbonate ion is CO3 2 minus but enables us to write the formula of things such as calcium carbonate so we know calcium is ca2+ so we've got a balance between the charges there we've got the ca2+ and the co32 minus so we can just smush them together and we get ca3 then we've got the nitrate ions which are NO3 minus this means if we want to write the formula of something calcium nitrate for example we've got ca2+ for the calcium NO3 minus for the nitrates which we don't have a balance there we need an extra nitrate we need two of these negative nitrates to balance with the ca2+ so in that case the formula will be C3 in Brackets with a two so the other two that we need to know are the sulfate ion which is 42 minus and the hydroxide ion which is O minus and the same rules will apply when we want to work out the formulas of different sulfates and hydroxides what is an ionic compound an ionic compound is a giant ltis structure of ions held together by strong electrostatic forces of attraction between oppositely charged ions now these electrostatic forces of attraction act in all directions within the L stce and they can be represented in several different ways they can be represented in a 3D structure or using a ball and stick approach instead let's have a look at calent bonding what is a calent bond we need to know that a calent bond is a bond formed when electrons are shared between non-metal atoms calent bonded substances can have different structures we can see them as small molecules for example H2O or or O2 or CO2 or as giant calent structures for example diamond and silicon dioxide we can use Dot and cross diagrams to show coent bonding when drawing Dot and cross diagrams remember we only draw the outermost shell of electrons now the electrons of one atom are represented by dots and the electrons of the other atom are represented by crosses and we show Dot and cross diagram with calent bonding we have overlapping regions and these overlapping regions show the sharing of a pair of electrons this is a calent bond sometimes two pairs of electrons are shared and this would be a double calent bond and occasionally we even get three pairs of shared electrons which would be a triple bond and here you can see this example of chlorine Each of which have seven electrons in that outer shell they both need to gain one so what they do is they share one of their own electrons and therefore gain one from the other as well resulting in our calent bond let's have a go at another example let's draw a DOT and cross diagram to show the bonding in CH4 but we should know that carbon's in group four so it has four electrons in its outer shell and we should also know that hydrogen has one electron in its outer shell well if each of these hydrogens shares electron with the carbon then that means each of the hydrogens end up with two electrons and get a full outer shell and the carbon ends up with eight electrons and that also has a full outer shell so here we can see that there are four calent bonds in the bonding of CH4 substances with giant coent structures are solids with very high mounting points now all atoms in a giant coent structure are bonded to atoms by these strong coent bonds now some examples of giant coent structures include Diamond graphite and silicon dioxide we need to know that giant coent structures have very high melting points we need to know why this is we need to know that this is because the many strong calent bonds between atoms must be broken in order to melt or boil it this requires a lot of energy we also need to know why most giant coent structures do not conduct electricity this is because there are no delocalized electrons or ions that are free to move to carry charge through the structure with the one exception of graphi which we will learn about in more detail later small molecules are usually gases or liquids and therefore they have relatively low melting and boiling points so some examples of small molecules include water cl2 oxygen anything that you're used to being a gas or a liquid at room temperature so when boiling or melting substance is made up of these small molecules the weak intermolecular forces between the molecules get overcome we're not actually breaking those strong coent bonds just these weak intermolecular forces now relatively speaking this doesn't require much energy at all and this explains the relatively low melting boiling points now we need to know that as the molecules get bigger they have stronger intermolecular forces so as a result bigger molecules have higher melting and boiling points now we should also know that small molecules do not conduct electricity and the reason for this is the fact that they have no charge let's describe the structure and bonding in Diamond this is a very common question we should know that diamond is a giant calent structure and every carbon atom forms Four Strong Co valent bonds with other carbon atoms make sure you include the number of calent bonds and the fact that they're strong so a very common question asks us why is Diamond so hard to answer this we're going to say that it's a giant coent structure that every carbon atom forms four strong calent bonds with other carbon atoms and therefore it requires a lot of energy to break another very common question is why does diamond not conduct electricity and the answer to this is similar every carbon atom forms four strong calent bonds with other carbon atoms and so as a result there are no delocalized electrons or ions free to move and carry that charge we need to be able to describe the bonding and structure in graphite so we should know that graphite is made of only carbon atoms we should know that it forms hexagonal Rings arranged in layers and we need to know that each carbon atom forms strong coent bonds with only three other carbon atoms not the four that it potentially could with its four electrons in its outer shell now this as a result leaves carbon with one spare electron and this electron gets delocalized and is free to move through the layers a very common question we're going to get is why does graphite conduct Electric electricity so the answer we want to give is that each carbon atom has one spare electron which is delocalized and free to move and carry electrical charge through the layers another question we need to be able to answer is why is graphite slippery and so why can it be used in lubricants the reason for this is that it has layers which have weak intermolecular forces between them now these weak intermolecular forces don't require much energy to over come therefore making them slippery now let's have a look at graphine what is graphine graphine is a single layer of graphite and its properties make it useful in electronics and Composites so let's have a look at those properties then so it's got strong coent bonds between the carbon atoms a result of this is that graphine is going to be very strong and it's going to have high melting and boiling points now this is because it's going to take a lot of energy to break those strong calent bonds if we look at the diagram we can see that each carbon atom in graphine is only bonded to three other carbon atoms we should know that as carbon has four electrons in its outer shell it can form four bonds and the fact that graphine only forms three bonds per carbon atom shows that we're going to have a delocalized electron which is free to move and carry charge meaning that graphine is a conductor of electricity what are ferin ferin are molecules of carbon atoms which have hollow shapes the structure of ferin is based upon hexagonal Rings although we can sometimes have rings with five or seven carbon atoms at this level there'll generally be hexagonal rings so ferin can be arranged as a tube for instance a nano tube or as a ball such as Buckminster ferine C60 carbon nanot tubes are cylindrical ferin with very high length to diameter ratios this means that they have a high tensile strength and so are difficult to break and they're useful for nanotchnology electronics and materials Buckminster ferine however is a molecule made of 60 carbon atoms coal bonded into a spherical shape they have weak intermolecular forces between the molecules which gives it a low melting point and making it slippery now that makes it perfect for use as a lubricant and for drug delivery what are polymers so we need to know that polymers are very large molecules made up of many repeating units joined by calent bonds now the polymer chains themselves are held together by intermolecular forces and of course because polymers are such long molecules those intermolecular forces are relatively strong now the result of this is that polymers have higher melting points compared to smaller molecules and therefore they're generally solids at room temperature now a good use of polymers is to make Plastics now an example of a polymer is polyethene and we can represent this in different ways that we need to be able to recognize so it can be represented in this very long way here which shows a short section of the polyethene polymer it actually contains thousands of these atoms but of course we're just showing a short section which still looks pretty long notice those open ends to show that it's continuing onwards or instead we can do it in this abbreviated form where the little n represents how many of these repeated units we have and N is going to be a very large number now we can represent ionic compounds in many different ways and they itations to these different types of diagrams that we used to represent them for DOT and cross diagram is very helpful because it shows the transfer of electrons the disadvantage is that it doesn't show how the ions are arranged in 3D space and it also doesn't show the relative sizes of the ions with a 3D balling stick an advantage is that it shows the arrangement of ions in 3D space however the disadvantages includes the fact that it uses sticks for bonds which is misleading because instead the forces of attractions act in all directions in the 2D diagram we can see the arrangement of ions in one layer however it doesn't show the different layers of ions and it also doesn't show the 3D arrangement in space finally the 3D diagrams show the 3D arrangement in space which is an advantage however the disadvantages include the fact that it is not to scale and it gives no information about the forces of attraction between the ions we can represent coent compounds in many different ways however there are limitations to using different types of diagrams to represent them so dot and cross diagrams an advantage to this is that we can see the transfer of electrons and we can see which atom the bonding electrons come from however disadvantages include the fact that it doesn't show how the atoms are arranged in 3D space or show the relative sizes of the atoms next up the 3D ball and stick this is good because it shows the arrangement of atoms in space as well as the shape of the molecule however disadvantages include the fact that it uses sticks for the bonds and it doesn't show that the bonds are forces the atoms are placed far apart from each other but in reality the gaps are much smaller so now the 2D diagrams now some advantages to this is that it shows what atoms are in a molecule and how they're connected however disadvantages are that it doesn't show the relative size of the atoms and the bonds and it also doesn't show the 3D arrangement in space finally the 3D diagrams obviously an advantage is that it shows the 3D arrangement in space however disadvantages include the fact that the 3D diagrams aren't to scale and it gives no information about the forces of attraction between the atoms let's have a look at Metals now metals have giant structures of atoms with strong metallic bonding now this means that most metals have high melting and boiling points and this is because it takes a lot of energy to overcome these strong bonds now let's have a think about pure Metals now in a pure metal the atoms are arranged in layers these layers are able to slide over each other and this means that pure metals can be bent and shaped they're malleable now a side effect of this though is that pure metals can be too soft now a way of remedying this is we can perhaps make an alloy an alloy is what we get if we mix pure Metals with other elements now the way that this works is that atoms of different elements have different sizes Now by mixing these together this distorts the layers and the layers can't slide over each other as easily anymore we need much more Force for them to slide over each other now the result of this is that Alloys are harder and stronger than pure Metals making them much more useful for certain jobs than pure Metals we need to know that metals are made up of giant structures of atoms arranged in a regular pattern the electrons in the outer shell of the metal atoms are delocalized forming metal ions now these delocalized electrons are now free to move through the layers of the metal ions so why is it that metals can conduct electricity the reason for this is that the delocalized electrons are free to move between the layers and carry their charge why are metals good conductors of thermal energy this is because the delocalized electrons transfer energy and finally let's ask ourselves what causes metallic bonding this is due to the sharing of delocalized electrons we need to make sure that we can compare the properties of metals and non-metals metals have generally speaking a high melting and boiling point whereas non-metals most of the time have a low melting and boiling point metals on the other hand mostly have high density whereas non-metals most mostly have a low density metals are shiny and non-metals are generally dull metals are good conductors of electricity whereas non-metals are generally poor conductors of electricity with the exception of graphite metals are malleable which mean they can be hammered into shape whereas non-metals are not malleable we need to know why metals are good conductors of electricity and this is because they have delocalized electrons which are free to move through the latice structure we also need to know why metals are malleable the reason that metals are malleable is because when a force gets applied the layers of the ions can slide over each other relative formula mass is the sum of the relative atomic masses of the atoms in the numers shown in its formula now if we had a balanced chemical equation due to the conservation of mass we would expect the sum of the relative formula masses of all of the reactants to be equal to the sum of the relative formula masses of all of the products now the easiest way to explain this is by looking at an example so let's have a look at working out the relative formula mass of sulfuric acid H2 so4 so here I can see I have two hydrogen atoms and the relative atomic mass of hydrogen is 1 so I'm going to do 2 * 1 and then I'm going to do plus and I can see I have one sulfur atom so I'm going to do 1 * 32 which is the relative atomic mass of sulfur and then I can see I have four oxygens so I'm going to add on 4 * 16 where 16 is the relative atomic mass of oxygen now popping that all into the calcul later I find that sulfuric acid has a relative formula mass of 98 in the exam we're often asked how we calculate the percentage by mass now we need to know this formula percentage by mass is equal to the total relative atomic mass of atoms of the element we being asked about divided by the relative formula mass of the compound and then as always to turn it into a percentage we multiply it through by 100 so the easiest way to understand this is to have a look at an example so let's have a look at this question let's calculate the percentage by mass of oxygen in calcium carbonate so the first steps that we need to do is firstly let's calculate the relative formula mass of calcium carbonate so to do this we can see that there's one calcium so we've got 40 plus one carbon that's + 12 and then plus the three ox oxygen so that is 3 * 16 and putting that all together we get 100 now we need to calculate the total mass of oxygen in the calcium carbonate so here because there's three oxygen atoms in calcium carbonate we do 3 * 16 which gives us 48 now finally now that we've got all those parts we just substitute them into the equation above so we're going to do 48 / 100 * Times by 100 and that gives us 48% so the percentage by mass of oxygen in calcium carbonate is 48% and you can do that for anything okay we just repeat the same process and we'll get our marks it's important that we know the difference between molecular formulas and empirical formulas a molecular formula tells us the actual number of atoms in a compound however in an empirical formula this is simply the simplest whole number ratio of atoms in a compound if we look at this example here c2h6 as an example of a molecular formula that is the molecular formula of ethane however the empirical formula we would need to simplify the ratio of atoms we can see that there's a 2:6 ratio between the carbon and the hydrogen we can simplify this to a 1:3 ratio so the empirical formula is ch3 then we can see we've got C6 h126 this is another molecular formula we've got a 6 to 12: 6 ratio now we can simplify this ratio divide them all by six and we get a 1: 2: 1 ratio so the empirical formula of this will be CH H2O we need to be able to describe an experiment to work out the empirical formula of a compound for example magnesium oxide so these are the steps we need to take firstly we want to measure the mass of an empty Crucible and lid then we're going to place a piece of magnesium ribbon inside this Crucible we're going to measure the mass of The Crucible the lid and the Magnesium ribbon all together this time then we're going to place it on a tripod over a bunson burner and we're going to heat it strongly now this is going to oxidize the magnesium and we're going to turn off the buns and burner when the magnesium oxide stops glowing so when that chemical reaction has finished finally now we're going to measure the new mass of The Crucible the lid and its contents so now we should have a set of data so here I can see that the mass of the empty Crucible and the lid was 40 G the mass of The Crucible the lid and the Magnesium ribbon was 40 .19 G and the mass of The Crucible the lid and the magnesium oxide was 4032 G now we can use this information to do some calculations and to work out the empirical formula so first things first let's work out the mass of magnesium we can do this by taking the mass of The Crucible lid and the Magnesium ribbon and subtracting the mass of the empty Cru Sport and lid so that's going to be 4019 Gus 40 0 0 now that leaves us with 0.19 G so now to work out the mass of oxygen we need to take the mass of The Crucible the lid and the magnesium oxide and subtract the mass of The Crucible the lid and the Magnesium ribbon so that's 4032 minus 4019 which is going to give us 0.13 G so the relative atomic mass of magnesium is 24 we can find that in our periodic table and the relative atomic mass of oxygen is 16 again it's in our periodic table so if we do the mass divided by that relative atomic mass 0.19 / 24 we get 0.0079 and doing the same for oxygen I get 0.0081 so here we have actually the ratio between the moles of magnesium and oxygen we want the simp simplest whole number ratio and we get that by dividing by the smallest of the two so we divide each of them by 0.0079 that gives us a one for the magnesium and for the oxygen it gives us a Touch Above one but is close enough for us to round it to one as the nearest whole number now that means that we've got one magnesium and we've got one oxygen so writing its empirical formula will essentially be mg101 but we just don't bother to write the one so that gives us mg and that is our empirical formula the law of conservation of mass is an important one in chemistry we need to know what it is so it states that no atoms are lost or made during a chemical reaction and that the mass of the products is equal to the mass of the reactants and if we had a balanced symbol equation we'll see that the number of atoms of each element is actually the same on both the reactant and the product side of this equation so let's have a look at this in practice we can have nitrogen and then we can add three hydrogen molecules and we end up making two ammonia molecules see here that we have two of those green nitrogen atoms on both the left and the right hand side and you have six of those pink hydrogen atoms on again both the left and the right hand side now that is showing that no atoms are lost or made during that chemical reaction and we can also see this in terms of mass so if we had 14 G of nitrogen and it reacted with three G of hydrogen we would end up making 17 G of ammonia so the mass of the products is equal to the mass of the reactants now we know that mass is always conserved however it might not always look like it is now this is going to depend on if we have an enclosed system like this one on the left hand side or a non-enclosed system so in an enclosed system the mass will be observed to be conserved because everything is contained and nothing escapes whereas in a non-enclosed system gases can enter and leave the system now this may mean that the mass may appear to have changed whereas actually all that's happened is some gases may have escaped from the system so that they can't be measured however it's important to know that that mass is still there and the mass has been conserved so the mass of one mole of a substance in gr is equal to its relative formula mass so if we had one mole of hydrogen atoms that would weigh one gr if we had had one mole of oxygen molecules so O2 that would be equal to a mass 2 * 16 32 G finally if we think about having one mole of water the relative formula mass of water is 18 and so the mass of one mole of water is 18 G too now a lot of people get very confused about moles they think it's something really complicated and fancy but it's just a word to represent a really big number there's a word that we use all the time which has a similar job and that's dozen so we often say oh we've got a dozen eggs or something else and everybody knows that means we have 12 eggs likewise if we had three dozen eggs we know that that's 3 * 12 36 eggs now moles do that same job except it's a really horrible number okay so if we have one mole of a substance we have 6.02 * 10^ 23 particles if we have 2 moles of a substance and we have 2 * 6.02 * 10 23 of those particles so just don't overthink this concept okay so when we talk about this 6.02 * 10 23 let's just talk about particles now that could be atoms it could be ions it could be electrons it could be anything okay it's just representing that much stuff and we call this number avagadro constant so putting this into practice quickly we may be asked how many molecules of water are there in five moles of water well we should know that in one mole of water we have avagadro's number molecules of water we have 6.02 * 10 23 molecules of water in one mole so if we have five moles all we need to do is just times that by five and that ends up giving us 3 01 * 10 24 molecules we can calculate the mass of a substance if we know how many moles there are so let's remember what we said the relative formula mass is equal to the mass of one mole of a substance so we can use this bag to turn it into a little equation we can say that the total mass is equal to the relative formula mass times by the number of moles and we can learn this in shorthand relative formula mass is often referred to as m r and so we can say that mass equals Mr moles it's a short Snappy way of remembering it so we might be asked to find the mass of 0.5 moles of ammonia with a relative formula mass of 17 so in this case we can use that same formula mass equals relative formula mass time moles or mass equals Mr moles so the mass will equal 17 for that relative formula mass times by the 0.5 for the moles and that gives us 8.5 G now when we have a balanced equation it shows us the number of moles that react together and the number of moles of products formed so the balanced equation gives us the ratio of moles in a reaction so this reaction here I can see that I have one mole of nitrogen reacting with three moles of H hydrogen and making 2 moles of ammonia so we can use these balanced equations to work out the mass of one of the reactants or products so long as we know the mass of one of the others let's take a look at this question here how much ammonia can be made if you have 42 gram of nitrogen and an excess of hydrogen so there's three steps to take here first let us work out the number of moles of nitrogen so we should now know that when working out the number of moles moles is the mass divided by the relative formula mass so let's work out the relative formula mass of the nitrogen then N2 is going to be 2 * 14 because the relative atomic mass of nitrogen is 14 so the Mr of nitrogen is 28 so the moles are equal to 42 because that's the mass of nitrogen ID by 28 and that gives me 1.5 moles so now we know this we're on to step two here we want to use the ratio to work out the number of moles of ammonia so here I can see I have one mole of nitrogen for every two moles of ammonia so this is a 1:2 ratio so to work out the number of moles of ammonia we simply need to do 2 * 1.5 and that gives us 3 moles of ammonia so now on to that last step now we need to work out the mass of ammonia let's use the equation that states that mass equals Mr moles so we need to get that Mr or relative formula mass of ammonia of course there's one nitrogen so we've got 14 plus 3 * 1 for the three hydrogens and that gives us an MR equal to 17 so in this case here we're going to say that the mass is equal to that relative formula mass 17 * by 3 that gives us a mass of 51 G so here the answer is 51 G of ammonia can be made if you have 42 G of nitrogen many chemical reactions actually take place in Solutions and therefore concentration is an important measurement because it can really represent the amount of stuff in your solution so the concentration of a solution can be measured in mass per unit volume so how many grams are in that volume that you're looking at maybe grams per decimeter cubed or centim cubed now that's where this equation comes in we can calculate the concentration of a solution by taking the mass of a substance and dividing it by the volume of that solution now let's have a look at that in practice this let's calculate the mass of 25 decim Cub of sodium chloride solution with a concentration of 0.1 G per decim cubed now to solve this we'd need to rearrange the equation above and we'd find that the mass is equal to the concentration times by the volume now if we substitute these numbers in then we find that mass is equal to 0.1 * by 25 which gives us a mass equal to 2.5 gr now an important tip here is that we might find that we need to convert between cm cubed and decim cubed in this equation above we always want to make sure that the concentration and volume units are consistent so they both use decimet cubed or they both use centim cubed and that's where this conversion can come in handy so when we want to go from centimet cubed to decimet cubed we simply divide by 1,000 however when we want to go the other way when we want to go from decimeter cubed to ctim cubed we multiply through by 100 so make sure you learn that little back there now a really useful thing we can do is we can use masses to work out the balancing numbers in an equation so to do this first work out the relative formula mass of all the substances then calculate the number of moles of each substance next work out the simplest whole number ratio by dividing by the smallest and finally use these numbers to balance the equation now let's put this into practice we've got seven grams of nitrogen reacting with 1.5 G of hydrogen to produce ammonia deduce the balanced equation so here I've got a little table first let's work out the Mr of nitrogen so 2 * 14 gives us 28 now let's work out the Mr of hydrogen that's 2 * 1 which gives us two so now let's work out the number of moles and remember we do that by saying moles equals mass over the relative formula mass the m so for nitrogen we have 7 G / 28 which gives us 0.25 and for hydrogen we have 1.5 G ID 2 which gives us 0.75 so finally we divide by the smallest amount the smallest of those two moles is 0.25 so we're going to divide both both of these by 0.25 so 0.25 over 0.25 gives us 1 and 0.75 / 0.25 gives us three therefore we know that one mole of nitrogen reacts with three moles of hydrogen and we can finally use this to balance in the normal way one and two means that we have 2 n's and 3 H2S means we have six hydrogens therefore we must have two NH3 is made to balance this equation so in a chemical reaction that has two or more reactants in all likelihood one of the reactants is going to run out before the others and we call this a limiting reactant and the remaining reactant that hasn't run out yet is said to be in excess now the amount of limiting reactant that we have is going to affect the maximum mass of products that are made because once that limiting reactant runs out the reaction stops let's look at this example here 15 G of nitrogen is reacted with an excess of hydrogen calculate the maximum mass of ammonia made so the first thing we need to do here is to write a balanced equation and they may well give this to you in the exam anyway so here we have N2 + 3 H2 goes to 2 NH3 but like I say they may well give this to you in the exam so we know we have 15 grams of nitrogen and we're looking at the mass of ammonium mate that means that those are the only two bits we care about in this equation I'm going to use my grid method here I've got three rows I've got Mass the relative formula mass or the Mr and the moles and I'm filling in the information I know I know that we have a mass of 15 G of nitrogen to begin with and you may find in the exam they give you the relative formula mass of all of these substances here let's work it out though so nitrogen is 2 * 14 which is 28 so to calculate the moles we've got moles is mass divided by the relative formula mass and I like this grid method because it's just the 15 over the 28 now that gives me 0. 5357 that's the number of moles of nitrogen we have but in this question we're not being as about nitrogen we're being asked about ammonia and this is where that balanced equation that they will probably give you will help you here we can see we have a one to2 ratios so if we had one mole of nitrogen we have two moles of ammonia if we have 0.535 7 moles of nitrogen we have two times 0.5 357 moles of ammonia I'm putting this into my calculator I find that I have 1714 moles of ammonia so we're nearly there now okay just following through our grid method we need to have the relative formula mass of ammonia now again they may well give this to you in an exam question but let's work it out 14 for the nitrogen plus 3 * 1 for the hydrogen gives us 17 so let's fill that in here so 17 and of course we need to find the maximum Mass made and that's assuming that 1:2 ratio so if we use that number that we found and the fact that mass equals Mr moles or the relative formula masstimes moles we end up getting a maximum mass of ammonia made equal to 18.21% and then use the new moles to calculate the mass of that final substance [Music] [Music] [Music] [Music] the three states of matter can be represented by a simple model which uses small solid spheres to represent the particles you can see that in the solid we've got this regular pattern whereas in a liquid although the particles are still touching they're in a random Arrangement whereas in a gas they are in a completely random Arrangement far apart and not touching so we know that going from a solid to a liquid is the process of melting a liquid to a solid is freezing whereas going from a liquid to a gas is boiling and a gas to a liquid is condensing all of these changes are examples of physical changes they're not chemical changes because no chemical reaction is taking place these are simply physical changes this table here nicely summarizes the difference between solids liquids and gases in a solid the particles are in a regular pattern very close together and vibrating around fixed positions whereas in a liquid the particles are randomly arranged but close together and they move around each other and finally in a gas we have a random Arrangement the particles are very far apart and they move quickly in all directions make sure you can draw all of these diagrams in chemistry we need to understand what is meant by a pure substance so pure substance is a single element or compound which has not been mixed with any other substance now you might find this is a bit different to our everyday language we might use the word pure as we speak about things such as milk may be pure because it doesn't have any additional substances added to it however chemically it is a mixture of different substances this fat molecules this water all mixed together however in chemistry we park the understanding and we now just think of it as that single element or compound that hasn't been mixed with any other substance so we need to know that pure elements and compounds melt at specific temperatures and we can distinguish between pure substances and impure substances using the following method so we want to measure the melting point pure sub substances are going to have a sharp very defined melting point for instance water has a melting point of 0° C however impure substances are going to melt over a broader range of temperatures so if you're ever given a range of temperatures for a melting point you know that that substance is an impure substance what is a mixture we need to know that a mixture consists of two or more elements or compounds which are not chemically combined so this diagram here shows what a mixture looks like you can see we have a mixture here of these green molecules and these blue atoms they are not chemically combined and therefore we have a mixture so we need to know that mixtures can be separated by different physical processes these include filtration crystallization simple distillation fractional distillation and chromatography and the method that we end up using of course depends on what makes up the mixture now these processes do not involve any chemical reactions and no new substances are made so let's start by looking at filtration filtration is used to separate mixtures of insoluble solids for example sand and liquids such as water as you can see from this diagram we will pour a mixture of insoluble solid and liquid through some filter paper which will be sitting in a funnel the insoluble solid will end up staying in that filter paper because its particles are simply too large to pass through and the liquid will pass through the filter paper and end up Gathering inside our conical flask like we said we would use this method whenever we want to separate a mixture of a solid which is insoluble and a liquid now let's look at simple distillation now simple distillation is used to separate a solvent from a solution when we want to keep the liquid so an example of this is we want to produce water from a salt solution let's have a look at this apparatus here you can see that we have a condenser which is an important piece of apparatus which cools down our gas Vapors that will form to condense them back down to a liquid so let's look at the method here so the first thing we're going to do is we're going to heat up our solution you can see we're doing that here using a buns and burner so the liquid part of our mixture will evaporate becoming a vapor and rising up now this vapor is going to pass through the condenser where it's going to get cooled down but when it gets cooled The Vapor will condense back down to a liquid this then separates the liquid from the dissolved solid and we have successfully separated them fractional distillation is another method to separate substances now we use fractional distillation to separate two or more liquids which have different boiling points now this process is very very similar to that of simple distillation with one main difference to the apparatus and that is the presence of a fractionating column it's that fractionating column that is key to separating these two liquids so let's run through the steps here so the mixture is going to get heated to the temperature of the liquid with the lowest Boiling Point now the liquid with the lowest boiling point is going to evaporate first it's going to rise up through the fractionating column and pass through the condenser eventually Cooling and condensing now when all of this substance has evaporated and condensed we've separated the two liquids now let's have a look at crystallization now crystallization is used to separate a dissolved solid a solute for example sodium chloride salt from a solution so we do this when the thing that we want is that dissolved solid so at the end of this process we want to end up with that solid let's look through the steps so the first thing we want to do is to gently heat the mixture in an evaporating Basin now some of the solvent for example water will evaporate away making the solution much more concentrated now we're going to remove this from the heat when the crystals begin to form we're going to leave it to cool and then we're going to filter it to remove any excess liquid that there may be finally we're going to leave those crystals to dry when they've dried we have successfully separated our solid from the solution chromatography is a method that can be used to separate mixtures and it can be really useful when we want to attempt to identify certain substances so as you can see in this diagram we often use chromatography paper and a pencil line we put some dyes or whatever substances we're looking to examine along this pencil line and place it into a solvent now chromatography uses two different phases that we'll hear about in the exams that we need to be familiar with so the mobile phase is the solvent which is going to carry the different substances this could be water for example the stationary phase on the other hand is the non-moving phase in this case that could be the chromatography paper so when carrying out this chromatography we can calculate an RF value that will be used to identify unknown substances all different substances will have their own unique RF value so the way that we work out the RF value is we get out our ruler and we measure the distance moved by the substance so that will be from that pencil line up to the point where that dot has moved and then we divide it by the distance moved by the solent and that again is going to be moving from that line up to the maximum distance that it has moved and it should make that clear in the exam where the solvents move to so remember we're just going to to use our ruler make sure you're consistent with using centim or millimeters for both measurements it doesn't matter which one you choose and then pop it into the equation and you'll get the RF value which will always be a number between zero and one now we need to know that the RF value might change in a different solvent so if we use water one time and say ethanol another time we may get a different RF value so mixtures are going to separate into different spots so here you can see this shows a mixture because we've got two different spots however pure compounds like this one here produce a single spot and that will be true in all of the solvents it will always only produce a single spot potable water is water that is safe to drink and what this actually means is that the water has low levels of microbes like bacteria and also low levels of dissolved salts now both waste water and also groundw must be treated before we can drink them in the United Kingdom most of our potable water comes from fresh water which comes from rain water however in some countries potable water is produced from sea water it really depends on the country how much sea water they have and also how much money they have which we'll see in more detail in a moment how do we treat fresh water well as I mentioned it comes from the rain so the first thing we need to do is remove large objects so this could be branches and leaves and we use a large screen to do this now larger insoluble particles such as grit can be removed using a coarse filter so now we've got rid of those big objects those larg insoluble particles now we're getting to smaller insoluble particles and what we do is we add a substance called aluminium sulfate which does the job of clumping these together now when they Clump together they get heavier and they sink down to the bottom this is called sedimentation so we've done all of that now let's think about the very small insoluble particles now we've removed these using a very fine filter bed so really here we've just used a selection of filter s in addition to of course our sedimentation to remove these particles of varying sizes so the last thing that we do is we add chlorine and we do this to kill bacteria and microorganisms to make sure the water is safe to drink now let's have a think about how we treat seawater now sea waterer has lots of salt in it and that's the main problem to remove that salt from the water we're going to distill the sea water by boiling it and then condensing it back down again now this removes the pure water from the salt we may be asked what is the problem with obtaining potful water from seawater why is it that the United Kingdom doesn't use this method for example and the main reason is that it takes a lot of energy to do this distillation of course distillation means we need to boil the water to remove it from the salt this of course takes lots of energy and it's therefore very expensive and that's why some countries such as the United Kingdom don't use this method but what is the advantage of using distillation to get potable water well the main advantage to this is it does not contain any dissolved ions and if we want to use this water for chemical analysis for example we need to ensure that we remove all of these dissolved ions [Music] [Music] [Music] we need to know what ions the acid produce in aquous solution so this is such an easy Mark if you just learn this one fact so acids produce hydrogen ions we also need to know what ions alkalides produce in aquous solution this is again such an easy Mark so please do learn it it's hydroxide ions we also need to know how we can measure the pH of a solution so we could use one of two methods the first method is universal indicator we should know that when we add Universal indicated to a solution of an acid or Alkali or even a neutral solution we will observe a color change however this is quite an approximate answer you know how you're not going to get a number or anything are you you're just going to get a rough idea if it's an acid or an Alkali or neutral now a pH probe is the other method we could use and this is great because this is an exact method this will tell us the pH of our solution so the pH scale ranges from zero all the way up to 14 and if we were to add Universal indicator we can see this color scale we can see that when we have a strong acid so somewhere around the range of zero or one the universal indicator will change to red when it's neutral the universal indicator will show you a green color and of course when it's very alkaline say 14 pH we will see a dark purple color so we should know of course that in terms of pH a neutral solution has a pH 7 an acid has a pH less than seven and an Alkali will be more than seven so neutralization is the reaction that takes place between an acid and an Alkali and we need to know the ionic equation that takes place when we have a neutralization reaction this is such a simple one when you think about it we've got the H+ from the acid plus the O minus from The Alkali which go together and make water so make sure you learn this we can purify copper by using electrolysis to do this we want to use an impure copper anode pure cathode and an electrolyte which is made up of an aquous copper compound such as copper sulfate now to carry out this process of electrolysis we're going to pass electricity through the Sol solution and what we'll notice is during this process of electrolysis the copper in that impure copper anode is going to dissolve and therefore it's going to over time lose mass now those copper ions in the solution now are going to get attracted to that negative cathode as it gets attracted to it it will pick up electrons and form copper atoms this means that the anode is going to increase in size as more and more pure copper forms and we'll actually be able to see this in the lab if we carry out this experiment different indicators are used to show whether a solution is acidic neutral or alkaline we need to know about three different indicators litmus methy orange and phenoline we need to know that litmus is red in acidic conditions purple in neutral conditions and blue in Alkali condition conditions we need to know that methy orange is red in acidic conditions yellow in neutral conditions and yellow also in Alkali conditions that can cause problems when it comes to distinguishing between neutral and Alkali because we get the same result then for phenoline we get acidic conditions a colorless solution the same for neutral and finally a pink color for alkaline conditions see here phenol filing will also have the issue that can occur if we need to distinguish between an acidic and a neutral solution we're not necessarily going to be able to do that because they will be colorless in both case so a different indicator would be better in that situation concentration tells us how much of a substance is dissolved in water so we need to know the difference between a concentrated acid and a dilute acid what if we have a concentrated acid we've got a lot of acid in a small volume of water so so we could say that we've got a lot of acid per unit volume now a dilute acid on the other hand has a small amount of acid in that same amount of water so we could say that a dilute acid has a small amount of acid per unit volume and these diagrams demonstrate this you can see that there are fewer acid molecules in that dilute acid in that same space compared to the concentrated acid now at any given concentration a stronger acid is going to result in a lower pH now we need to know that as the hydrogen ion concentration increases by a factor of 10 the pH will actually decrease by one unit now this can sound a bit confusing so the best way to see this is to have a look at an example so if we're told that the hydrogen ion concentration of an acid of ph3 increases from 0.01 moles per decim cubed to 0.1 moles per decim cubed and we're asked what is the new pH of the acid here we need to recognize that the concentration is increased by factor of 10 so using our fact above we can say that the pH will decreased by one unit now if it started at three if we subtract one from that we get two so therefore the pH is now two and this is what we mean when we make that statement as the hydrogen ion concentration increases by a fact of 10 the pH decreases by one unit we need to know the difference between strong acids and weak acids so a strong acid is an acid that is completely ionized in aquous solution alternatively we may say that it's an acid fully dissociates in aquous solution so it's examples of strong acids are the classic hydrochloric acid nitric acid and sulfuric acid and we can show the dissociation this ionization using an equation so hydrochloric acid for instance becomes H+ and cl minus now on the other hand a weak acid is an acid that's only partially ionized or dissociated in aquous solution examples of weak acids include ethanolic acid citric acid acid which we find in oranges and other citrus fruit and carbonic acid so we can show this using this equation so here we've got methanolic acid HC and then that becomes H+ and HC minus however we didn't just do our normal Arrow instead we've done this special Arrow which shows that this is a reversible reaction in chemistry it's very important that we know about three main acids hydrochloric acid sulfuric acid and nitric acid we need to know that the formula for hydrochloric acid is HCl and we need to know that when that is put into water into solution it will dissociate to form H+ and cl minus ions with sulfuric acid we should recognize that that has the formula of h204 and again when that's in solution it forms H+ and S so42 minus ions nitric acid on the other hand has the formula H3 and that will dissociate to give the ions of H+ and NO3 minus now you might be wondering why this is so important whenever we need to write formulas for certain things we need to know these ions to get the formula correct we also need to know that acids and metals can react so Metals would generally react with dilute acids to form a salt and hydrogen that's the mash acronym so metal and acid makx a salt and hydrogen we also need to learn about how acids can be neutralized and produce salts so there's a few different reactions that can take place which are neutralization reactions so acids can be neutralized by alkaly which are soluble metal hydroxides like sodium hydroxide by bases such as insoluble metal hydroxides and metal oxides like calcium oxide and metal carbonates like calcium carbonate so it's very important we get memorizing these two reactions so we need to know acid plus the metal carbonate makes a salt plus water plus carbon dioxide and we also need to know that an acid plus a metal hydroxide or an oxide makes a salt and water now different acids are going to produce different types of salt and this is really important we know this so that we name the correct salt in a question so if we ever have hydrochloric acid in our reaction we're going to make a chloride salt sulfuric acid is going to form a sulfate salt and nitric acid is going to form a nitrate salt so let's have a look at what this is like in practice so if we had hydrochloric acid and it reacted with calcium carbonate now we just said that when an acid reacts with a carbonate we make a salt plus water plus carbon dioxide but what salt is it to do that we need to look at what the metal ion is so in this case that's ca2+ the salt I in this case is going to be CL minus because we have hydrochloric acid and so therefore the salt will be calcium chloride now we can work out the formula of this by doing our crisscross method okay so I'm going to crisscross these charges and that is going to give me CA cl2 and the whole reason for this is that we need to have the same charge of both positive and the negative so we need two of the negative cl's to balance with the ca2+ so now if we have sulfuric acid reacting with sodium hydroxide the methyl na+ the salt ion is going to come from the sulfuric acid that's the S so42 minus the sulfate ion and that's going to make us sodium sulfate let's use the crisscross method again and here I can see I have na2 so4 now finally if we have nitric acid with magnesium hydroxide the metalion is mg2+ the salt ion is NO3 minus and the salt in this case is going to give us magnesium nitrate because we have that nitrate ion from the nitric acid let's use our crisscross method again and here I can see the formula will be mg3 and the whole thing is time 2 so it's mg3 in Brackets with a little two down below if we ever need to test for hydrogen gas we want to hold a lit splint at the open end of a test tube containing that gas and if hydrogen's present we will hear a squeaky pop sound we need to know how to test for carbon dioxide gas so what we want to do is to Bubble the gas through an aquous solution of sodium hydroxide or more simply we could say that we need to Bubble it through lime water if carbon dioxide is present then the lime water will turn milky or cloudy in color a common question is them asking us how we make a soluble salt so generally speaking we can make a soluble salt from an acid by reacting them with a solid insoluble substance such as a metal a metal oxide or a carbonate so what we do is we add this solid insoluble substance to the acid and then we should observe a reaction taking place when this reaction stops we're going to take this solution and we're going to filter it and any of that excess solid will be filtered off staying in the filter paper and going through the filter paper into our Beaker or our flask is going to be our salt solution now that we've removed the solid and we just have that salt solution we can do crystallization to remove the water in that solution leaving us just with our salt now let's look at our experiment this is what we want to say if we're asked to describe how to prepare a pure dry sample of a soluble salt from an insoluble base so the first thing we need to do is to choose the correct acid and base required to make the desired salt so maybe the question has asked you to make a pure dry sample of copper sulfate perhaps then because of the sulfate you're going to use sulfuric acid and because we need the copper perhaps we could use copper oxide so now you're going to add some of that dilute acid to a flask we're going to heat it gently using a bunson burner you may have used a water bath to do this and then we're going to add a small amount of the base and stir it we're going to continue to add the base until the reaction is going to stop and the importance of this is that this means the base must be in excess at this point now when the base is in excess because it's a solid we can very easily remove it by using filtration so we filter it and then we're going to pour the remaining Solution that's gone through the filter paper into an evaporating Basin now this solution is going to contain the salt as well as water now we're going to use an electric heater or a water B to gently evaporate this water away this is going to leave us with crystals of the salt and so this is our method make sure that you're familiar with this method you can describe it and most importantly make sure you know that you need to choose the correct acid and base dependent on the salt that the question's asking you about if we want to make a salt from an acid and a soluble reactant for example an Alkali we need to First carry out a titration so this titration is going to enable us to work out exact exactly how much acid and Alkali we need to react together exactly cuz we don't want any leftover acid or Alkali in our solution we just want the salt and the water and we've got no way of separating them because they're both soluble so once we work out those correct proportions of the acid and The Alkali we're going to react them together and that's going to leave us with just that salt solution however we now need to remove the water now to do this we need to leave the water to evaporate and this is going to leave us with pure dry crystals of the salt what is meant by solubility solubility is a measure of the maximum amount of a substance that will dissolve in a given volume of a solvent at a given temperature so something that has high solubility is very soluble however something with low solubility might be considered to be sparingly soluble or insoluble now a precipitation reaction is a reaction that occurs when two solutions react together to form an insoluble substance so something with a low solubility and we name this a precipitate so an example of a precipitation reaction is the reaction that takes place between silver nitrate and sodium chloride to form silver chloride and sodium nitrate so there we've got a displacement reaction taking place and the key thing here is that silver chloride is formed which as you can see from the state symbol and that's why state symbols are so important is a precipitate so that's how we know that this is a precipitation reaction so unfortunately we need to know these solubility rules and this is tricky okay so take it one little chunk at a time if you can just learn for instance one of these facts one day and then another day learn a different fact you will be making really great progress so soluble salts include all common sodium potassium and ammonium salts all nitrates it includes most common chlorides with the exception of silver chloride and lead chloride soluble salts include most common sulfates except lead sulfate barium sulfate and calcium sulfate which are all insoluble however going the other way around now most common carbonates are actually insoluble with three main exceptions which links back to what we said earlier sodium carbonate potassium carbonate and ammonium carbonate are the only soluble carbonates and if we remember that first rule at the top of this table which stated that all common sodium pottassium and ammonium are soluble that is why and finally most common hydroxides are insoluble except again those three that we mentioned earlier sodium hydroxide pottassium hydroxide and ammonium hydroxide we need to be able to describe how to prepare a pure dry sample of an insoluble salt now to do this we're going to mix together two solutions that are required to make that desired salt so for example if we wanted to make silver chloride maybe we'll mix together sodium chloride and silver nitrate so once we mix those together we're going to give it a stir and then we will filter it to remove that precipitate that's formed the insoluble salt that got made then we're going to give that precipitate a bit of a wash with some distilled water and then we're going to place it in a warm oven to dry just to remove any excess water from it electrolysis is a process in which electrical energy from a direct current Supply such as a battery decomposes an electrolyte when an ionic compound for example sodium chloride gets melted or dissolved in water its ions are then free to move through the liquid or the solution now liquids and solutions that can conduct electricity are called electrolytes when an electric current gets passed through this electrolyte the ions will move to the electrodes the positive ions will move to the negative electrode the cathode and the negative ions are going to move to the positive electrode the anode now this is the process of electrolysis we already know about oxidation and reduction we know that oxidation involves the gain of oxygen and reduction is the loss of oxygen however we also need to know about them in terms of electrons we need to know that oxidation is the loss of electrons and reduction is the gain of electrons we've got a great little pneumonic here to help us out so oil rake oxidation is loss of electrons and reduction is gain of electrons so let's have look at this little summary here to help us know the difference between oxidation and reduction so oxidation is the gain of oxygen I always think that kind of makes sense oxidation you're gaining oxygen reduction on the other hand means getting rid of something you're getting rid of that oxygen however in terms of electrons there's nothing about the name oxidation that links with electrons really does it and that's where oil rig comes in oxidation is the loss of electrons reduction is the gain of electrons positive ions end up gaining electrons from the negative cathode now remember oxidation is lost reduction is gained so we can say that those positive ions have been reduced at the cathode now the negative ions lose electrons at the anode again remembering oil rig oxidation is loss of electrons we can see that those negative ions get oxidized at the anode now if we have a look at molten lead bromide as an electrolyte we can see that at that negative cathode the lead ions gain electrons forming lead we can see this using the ionic equation of pb2+ plus two electrons makes PB so we've got a reduction taking place there whereas at the anode the BR minus loses electrons producing bromine again we can see this using our ionic equation so 2 BR minus makes br2 + 2 e minus so here we can see because the BR minus has lost two electrons it has been oxidized so we need to know about electrolysis of aquous solutions too so electrolyzing aquous Solutions can be beneficial over molon substances because less energy is required you don't need to melt down the substance simply dissolve it however working out the products is a bit harder because the water in that solution is also going to break down so that means as well as having the ions from your ionic substance you're also going to have the H+ and the O minus from the water now the products formed is going to depend on the relative reactivity of the elements so over at that negative cathode hydrogen is going to be produced if the metal is more reactive than hydrogen over at the anode though a little bit trickier here if halide ions are present like chloride or bromide the hogen will be produced however if no halide ions are present then oxygen will be produced we need to know the products of electrolysis of the following Solutions so sodium chloride sodium sulfate copper chloride and copper sulfate so let's have a look at how we work out what the products are so with sodium chloride the positive ions in a solution of that substance will be na+ and H+ from the water now the negative ions will be CL minus and O minus from the water now in terms of the products because sodium is more reactive than hydrogen hydrogen will be formed at the cathode whereas over at the anode because halide ions are present here chlorine is going to be produced now in this case we also see the na+ coming together with the O minus to also form sodium hydroxide now let's look at sodium sulfate now again sodium is more reactive than hydrogen so hydrogen will be formed at cathode now in terms of the negative ions there isn't a hogen present as a result because there's no halide ion oxygen is going to form at the anode now for copper chloride we have the positive ions of cu2+ and H+ now copper is actually less reactive than hydrogen therefore we're going to form Copper at the cathode now for the negative ions you can see we have a halide ion present so we're going to make a hallogen at the anode we make chlorine now for copper sulfate again we've got cu2+ versus H+ hydrogen is more reactive than copper so copper is formed and out of the negative ions we have the sulfate and the hydroxide ion neither of those are the halides so therefore we're going to form oxygen at the anode and there we have it make sure that you give those a good practice and that you can recognize what's made in those cases now when doing the electrolysis of acous solutions we also need to know the ionic equation a that happen at the cathode when forming hydrogen and at the anode when forming oxygen so at the cathode when we form the hydrogen this one's quite simple really we take the two H+ ions plus two electrons and you make H2 now here because the H+ ions have gained electrons we have reduction taking place again we're using out oil rake now over at the anode though it's a little bit trickier because this is all about Hy oxide ions so you can learn one of these two reactions you can either learn that 4 oh minus goes to O2 plus 2 H2O plus four electrons or you could simply have those electrons on the other side and instead think of it as 4 oh minus lose four electrons so minus four electrons to make O2 plus 2 H2 and notice these are both the same and here you can see the hydroxide has lost electrons therefore it has been oxidized so make sure that you get learning these ionic equations we can purify copper by using electrolysis to do this we want to use an impure copper anode a pure cathode and an electrolyte which is made up of an aquous copper compound such as copper sulfate now to carry out this process of electrolysis we're going to pass electricity through the solution and what we'll notice is during this process of electrolysis the copper in that impure copper anode is going to dissolve and therefore it's going to over time lose mass now these copper ions in the solution now are going to get attracted to that negative cathode as it gets attracted to it it will pick up electrons and form copper atoms this means that the anode is going to increase in size as more and more pure copper forms and we'll actually be able to see this in the lab if we carry out this experiment [Music] [Music] [Music] [Music] when metals react with oxygen they form metal oxides this is called an oxidation reaction so an example here is when magnesium reacts with oxygen forming magnesium oxide now reduction on the other hand happens when we remove oxygen from a metal oxide for example the reaction between copper oxide with carbon to form copper and carbon dioxide now we can summarize this so oxidation will involve a gain of oxygen and reduction will involve a loss of oxygen now Metals will generally react with water to form a metal hydroxide and hydrogen now this General reaction is one that we need to learn so metal plus water makes a metal hydroxide and hydrogen so if we have a look at an example we could see sodium plus water makes sodium hydroxide and hydrogen it's quite common will be asked about the observations of this reaction and I always find the state symbols of the key to this we will notice the solid metal is going to dissolve and we're going to see a fizzing or effervescence as that hydrogen gas is formed also if we were to add Universal indicated to the solution we will notice it will turn purple and the reason for this is that hydroxides are alkalized and alkaly of course turn Universal indicator purple now generally speaking as the metals get more reactive they will react more quickly and vigorously an example of this is potassium which is a very reactive metal and when we add it to water we're going to see it Fizz move quickly around the surface propelled by all those Bubbles and it's going to heat up to the point where we see a lilac flame and sometimes even a small explosion now of course we've already said haven't we that when a metal does react with water we form a metal hydroxide and hydrogen however we also want to know what that reaction is going to look like so we should recognize that the reaction of potassium and sodium with water is going to be a violent reaction lithium and calcium is not going to be but it's still going to be very quick magnesium on the other hand is very slowly zinc you'll usually see no reaction happen iron is going to rust very slowly and for copper we will see no reaction so what we can deduce from those results is that those violent quick reactions show us the most reactive metals and where we have no reaction we have the least reactive metals now let's look at the reactions of metals with dilute acids so generally Metals will react with a dilute acid to form a salt and hydrogen I really like the aconine mash for this so metal and acid make salt and hydrogen just remember Mash so here's an example if we have sodium plus hydrochloric acid we'll make sodium chloride and hydrogen gas now again we might be asked about our observations here again look at those state symbols we can see that the metal is going to disappear or dissolve and over on the other side you can see the formation of this gas so we're going to see a fizzing or an effervescence observed as that gas is formed again the same rule applies and more reactive metals will react more quickly and vigorously however we've got this extra little fact to know here if a metal is below hydrogen on the reactivity series it will not react with dilute acids and the reason for this is that the metal is going to displace the hydrogen in the acid normally so if the hydrogen is actually more reactive then the metal can't displace it the hydrogen will stay where it is so let's compare the speed of the reaction for these different Metals the potassium sodium and lithium we're going to get a violent reaction with the acid for calcium and magnesium we're going to see a vigorous reaction reaction for both zinc and ion we're going to see a slower reaction take place and for copper we're going to observe no reaction now again the scale of these reactions can tell us the order of reactivity and so potassium is going to be the most reactive of those metals and copper will be the least reactive because it's the only one where there's no reaction the common question we'll see in the exam is we may be asked to place Metals in order of their reactivity based on on experimental results so this could be either looking at the reaction with water or acid so here I'm going to show you the observations when four different Metals a b c and d react with water so see here C has no bubbles D has the most Bubbles and a and b have somewhere in the middle so we can use this information to see that D must be the most reactive as the most bubbles are released a is going to be the second most most reactive as the second most bubbles are released and C must be the least reactive as no bubbles are released at all there must be no reaction taking place so we could use those observations to conclude the order of reactivity so D is the most reactive followed by a b and then C metals can be arranged in order of their reactivity in the reactivity theories we'll often find in included in these tables the elements carbon and hydrogen although they're not Metals it can be very helpful to compare the reactivity of the metals to these two elements the reactivity of a metal is related to how easily it forms positive ions which is how easily it's oxidized the more easily it's oxidized the more reactive the metal we can use what we know about the reactivity series to at displacement reactions so in a displacement reaction a more reactive element can displace a less reactive element in a compound for example we know from the reactivity theories that magnesium is more reactive than ion so as a result magnesium is able to displace ion from an ion compound an example of this is if we had magnesium reacting with Ion 2 sulfate so an ion compound what's going to happen is that magnesium will displace the ion to form ion plus magnesium sulfate so there we have it we have our displacement reaction a common question in the exam is about Metal extraction so we should know that unreactive Metals For example gold or silver will be found in the earth as simply pure Metals however it's not normally that easy most metals aren't just found on their own as pure Metals instead they're found as compounds in rock and we're going to need to extract them from the rock using different chemical reactions and this is where the reactivity series and including something like carbon can be so helpful and this is because Metals less reactive than carbon can be extracted from their oxides by reducing them with carbon when we have a displacement reaction we can instead write them in terms of ions let's have a look at this example where the more reactive ion reacts with copper sulfate a displacement reaction takes place and copper and ion sulfate are formed or this can be written as an ionic equation you might be wondering how we can do this well what we do is if we look at all of the aquous substances in our earlier equation if we break those down into their respective ions that's going to be our first step here so we've got the Fe which was a solid we left that as it was the copper sulfate which was aquous we've broken down into cu2+ and S so42 minus it's important we know the formula for that sulfate ion then on the other side copper which is as solid we just leave as it is but the aquous ion sulfate we're going to break down again into its respective ions in this case into fe2+ and S so42 minus so this is where the clever bit comes in this is our next step when an iron is on both sides of an equation we have a spectator ion and spectator ions are doing absolutely nothing so we can just cancel them so we're just going to strike through the sulfate on each side leaving us with our ionic equation which is Fe solid plus cu2 plus aquous makes c s plus fe2 plus aquous and that is it that's how we get our ionic equations so when we have an ionic equation like this we can actually split it into two half equations let's start off by just looking at ion so here the Fe solid has lost two electrons to become the fe2+ ion so we can write this as f Fe goes to fe2+ + 2 e minus and because the ion has lost two electrons remember oil rig we can say oxidation is the loss of electrons so we know that the ion has been oxidized on the other side if we have a look at what's left here so the copper part of the equation we can see that those copper 2+ ions must have gained two electrons to just become copper so our half equation will be cu2+ plus two electrons makes copper so here we have another half equation and we can see that the cu2+ ion has gained two electrons now this means that the c2+ has been reduced again using our oil rig reduction is gain of electrons we can extract iron from its ore by heating it with carbon now the reason for this is if we look at our reactivity series here we can see that ion is below carbon in the reactivity series now this means that the ion can be displaced from ion compounds such as ion oxide by heating it with carbon now this is a process that gets carried out in a blast Fus and the reaction that we'll see take place is Fe2O3 plus 3 Co so carbon monoxide makes two fe+ 3 CO2 so in this reaction the carbon gets oxidized it goes from carbon monoxide to carbon dioxide and the ion oxide gets reduced as it loses oxygen now the advantage to doing this process compared to electrolysis is of course it's so much cheaper we're not having to use electricity for this to take place now when we look at extracting Metals some metals can be extracted from molten compounds using the process of electrolysis now we generally use electrolysis if the metal is more reactive than carbon or if it's likely to react with the carbon so the classic example that you need to know about is the fact that aluminium is extracted from aluminium oxide by this process of electrolysis so we take the following steps we take out aluminium oxide and we mix mix it with a substance called prolite we heat up this mixture until it melts and this mixture that we get is electrolyzed using graphite electrodes now we're going to see aluminium forming at the negative cathode and oxygen forming at the anode as you can see from the diagram when that aluminium gets made at the cathode it's molten still and what happens is we can simply drain it away via a little tap and remove it from this system and use it for whatever purposes we need it for we need to be able to explain what's happening in terms of the ionic equations so we know that at the cathode aluminium ions gain electrons forming aluminium atoms therefore due to oil rig reduction is gain we can say that the aluminium ions get reduced and the ionic equation here is A3 Plus plus plus 3 e minus makes a l so over at the cathode the negative electrode the oxide ions will lose electrons and they're going to form oxygen gas of course using oil rig oxidation is loss of electrons we can say that those oxide ions have been oxidized so the ionic equation we need to know here is that 202 minus makes O2 plus 4 electrons the overall reaction taking place here is aluminium oxide becoming aluminium plus oxygen now there are a couple of very important questions they can ask us about this electrolysis of aluminium oxide the first question that we'll see come up a lot is why is a mixture used for the electrolyte why do we mix together the aluminium oxide with the cryte so the reason for this is that this process lowers the melting temperature and reduces the cost as less energy is needed to melt this compared to aluminium oxide on its own the second question we'll see a lot is why must the positive electrode the anode be continually replaced so the reason for this is oxygen is formed at the anodes and this will react with those carbon graphite anodes and make carbon dioxide now this means that the anodes are oxidized and will need replacing the availability of metal ores in the Earth are limited this means that scientists have to come up with new methods of extracting the metals from lower grade ores so they've got two methods that they use for this they've got bioleaching and phyto Mining or phyto extraction so let's have a look at bioleaching first what is bioleaching bile leing is using bacteria to produce acidic leachate Solutions which contain metal compounds now once we obtain this metal compound we can process it to extract the metals now let's have a look at phyto mining so phyto mining is using plants to absorb metal compounds so this process of phytoextraction involves growing plants in a soil which contains that low grade oil then as the plants grow they're going to absorb the metalions through their Roots as a result they're going to accumulate the metals within their cells so as they grow and grow and get bigger we will eventually Harvest them and then burn them now when we burn them we're going to have some ash left over and that Ash is going to contain the metal compounds that we can process and extract the metal from we need to make sure we can compare the processes of bile leaching and vitam Mining and know what the advantage ages and disadvantages of them both are so bile leaching has a great advantage of not requiring any high temperatures however it does produce some toxic substances such as sulfuric acid which can be harmful for the environment V mining on the other hand is very useful because it can conserve high- grade ores and it reduces the need for Mining and it also reduces the need to dispose of rock waste however some disadvantages of it is that it's quite slow because of course we need to nurture these plants grow them to a good size before we can then burn them and extract the metal recycling materials we need to take the following steps we need to collect the used materials we need to transport them to the recycling centers and then we need to sort all of the different metals and materials apart and finally we need to remove any impurities what are you advantages then of recycling these Metals firstly less energy is needed to produce the metal so it's going to cost us less secondly it's going to conserve raw materials and finally there's going to be less environmental damage because there's going to be less need for processes such as mining what on the other hand then are the disadvantages of Recycling metals well we need to sort and separate all of the different materials and this can be challenging we then need to collect and transport all these materials and this requires a lot of organization and Manpower finally of course we're going to need to use vehicles to transport these materials to the recycling centers now these vehicles are going to use fuel and there's a chance that this could actually lead to an increase in pollution overall life cycle assessments are assessments that can be carried out to find the environmental impact of a product such as a paper cup a service or an event and life cycle assessments have four different stages so we want to look at the extraction and processing of the raw materials we need to have a look at the manufacturing and packaging process we need to have a look at the use and operation of this product during its lifetime and we also need to look at how it gets disposed of at the end of its useful life if it is indeed a product so at each of these stages our life cycle assessments are going to have a look at what raw materials are used this can include water the amount of energy used along the way and what waste substances have been released into the environment reversible reactions are shown using this special symbol which shows two half arrows one going to the left and one going to the right now reversible reactions are special types of reactions because we could change the direction of the reaction by changing the conditions now one particular reversible reaction that you need to know about is the harbor process in the harbor process we use nitrogen and hydrogen to make ammonia now because this is a reversible reaction this means that some of the ammonia that gets made will also get broken back down into the nitrogen and hydrogen that made it now this process will at some point reach what's called a dynamic equilibrium well what is a dynamic equilibrium this is a reaction where the forward and the backward reactions both happen at the same rate so they're both happening as quickly as each other we also need to know that at dynamic equilibrium the concentrations of the reactants and the products stay the same we need to know about the harbor process in the Harbor process nitrogen and hydrogen gases gets pumped into the system now in this system we're going to ramp up the pressure to 200 atmospheres the temperature is going to get increased to 450° C and these gases of nitrogen and hydrogen are going to be passed over an iron Catalyst now the reaction mixture is going to get cooled the reason for this is that as ammonia gets formed it will be a gas to remove it we want to condense it back down to a liquid so that we can open up a tap and drain it away so now that we've done that and we've removed the ammonia that we've made we're going to recycle any left over nitrogen and hydrogen to summarize the harbor process we need to make sure that we know these key facts so nitrogen plus hydrogen makes ammonia and the balance chemical equation for this is N2 gasius plus 3 H2 Gus goes to make with a reversible Arrow to NH3 Gus we need to make sure that we know these three conditions for the harbor process we need to know that we need an iron Catalyst 450° C temperature and 200 atmosphere pressure we also need to know where we're getting the raw material of nitrogen and hydrogen from nitrogen is coming from the air and hydrogen is coming from natural gas so reversible reactions can reach an equilibrium now the position of this equilibrium can be controlled by three different factors a change in the concentration a change in the temperature and a change in pressure one thing that doesn't change the position of equilibrium however is adding a catalyst this has no effect it simply speeds up the rate of reaction now this whole process of changing the position of equilibrium can be very useful for industrial processes where we're trying to make a certain product the reason for this is if we can shift the equilibrium in the position of that product that we desire we're going to be able to make our process more profitable now we need to consider how each of these factors will affect the position of equilibrium and to do this we're going to consider something called lilas principle so lelia principle states that if a system at equilibrium is subjected to change the system will adjust to counteract that change let's have a look to start with the effect that changing the concentration has on an equilibrium well first thing we need to know is when we increase the concentration of substance there's just more of it and the whole point of this equilibrium is it wants to get things back to how it was so if we add more of a substance the equilibrium wants to get rid of it so it's going to shift to the other side so if we increase the concentration of a substance the equilibrium will shift to the opposite side of that substance to get rid of it now if we decrease the concentration of a substance the equilibrium will actually shift to the side of that substance the reason being is if there's less of it we need to make more so if we look at this particular reaction this Harbor process and we ask ourselves what will happen if we increase the concentration of nitrogen well if there's more nitrogen the equilibrium wants to get rid of it so it is going to shift towards the right and it's going to make more ammonia so that's how we always want to think about them when we're looking at changing concentration now let's have a look at the effect that changing the temperature has on the position of equilibrium of course we know that the equilibrium is going to shift to minimize any changes in the temperature however when looking at temperature we need to think is the forward reaction exothermic or endothermic and the question will tell us this now in this case the forward reaction is exothermic in reversible reaction that means that the backwards reaction is endothermic now if we increase the temperature equilibrium wants to cool things back down again so it's going to shift to the endothermic side if we decrease the temperature the equilibrium wants to heat things back up again and so it's going to shift to the exothermic side what's going to happen then if the temperature is increased in the harbor process as we mentioned we know that that forward reaction is exothermic this means that the equilibrium is going to shift to that endothermic direction to decrease the temperature that means that less ammonia will be made if we increase the temperature in the harbor process now let's have a look at the effect that changing the pressure has on an equilibrium when we're looking at this we always need to look at how many gas moles we have on the reactant side and on the product side so here I can see that in the harbor process we have four moles of reactants and two moles of products now the equilibrium always wants to shift to minimize any changes so if we want to increase the pressure then the equilibrium wants to decrease the pressure now the way that it can do this is to shift to the side with a fewer moles now the reason for this the example I like to think of is a you're in a room with some people and the walls have started to close in what you would want to do is to move into a room with less people because it's going to then feel relatively speaking more spacious and that's exactly what this does here so if we increase the pressure the equilibrium will shift to the side with a fewer moles and if we decrease the pressure then the equilibrium will shift to the side with the mor moles so what happens if we increase the pressure in the harbor process well as we said we know we have four moles of reactants and two moles of products so the equilibrium is going to shift to the side with a fewer moles which is that product side it's going to shift to the right and we're going to end up making more ammonia now in Industry we have to think of a lot of factors when deciding what conditions to use we need to think about the cost of energy and the availability of materials we need to have a think about the conditions that are needed to get that right balance between getting a good yield also having a good rate of reaction now this is really important because it might seem obvious that we want to get the highest yield however we don't want to get that highest yield if it's going to be so slow it takes thousands of years to get that maximum yield we need to weigh this up so looking at the harbor process and using what we've just said we know to get a maximum yield of ammonia we need low temperatures so that it shifts in that forward exothermic Direction and high pressures so it shifts to that side with a few moles however if we break these down we know that low temperatures will actually slow down the rate of that reaction a lot so we need to compromise and use a temperature somewhere in the middle so we use 450° C so that we have a fast enough reaction and enough yield now we know that high pressures is good for the h process now that works out well because we know higher pressures increases the rate of reaction however High pressures can be quite dangerous so we're going to slightly lower the pressure to 200 atmospheres we also add an iron Catalyst during the harbor process and that's because this will increase the rate of reaction [Music] [Music] [Music] [Music] transition metals are metals that are found specifically in this middle region of the periodic table transition metals are different from other metals like The Alkali Metals in that they have a high density they have a high melting point they can form colored compounds and they can be used as catalysts and example of this is the fact that ion increases the rate of formation of ammonia in the harbor process metals can oxidize in air and this is because the metal reacts with the oxygen that's of course present in the air to form metal oxides and we can see it happening when we see a formation of a dull layer on top of a metal this dull layer is actually that metal oxide an example of this is when sodium reacts with oxygen to form sodium oxide as we can see here that metal has reacted and oxidized in the air to form sodium oxide which would appear to be a dull layer on That Metal now not all metals will oxidize it does depend on how reactive the metal is for instance gold A Very unreactive Metal won't oxidize so this brings us to corrosion what is corrosion well corrosion is the process when a metal continues to oxidize and it becomes weaker over time now an example of corrosion that we're very familiar with is the process of rusting now this happens when iron or steel reacts with both oxygen and water now this process of rusting can be represented using this equation so ion plus Oxygen Plus water makes hydrated ion 3 oxide it's important that we remember those little Roman numerals don't miss those out and that is what that orange brown substance of rust actually is that is its chemical name hydrated ion 3 oxide so we can investigate these factors that affect corrosion if we have a look at these three different test tubes we can see that test tube a has an iron nail just sitting in some water we can see that test tube B has the same thing it's got an iron nail sitting in boiled water however it's coated with a layer of oil and in test tube C we have an iron nail it's not in water but it is sitting in some calcium chloride what we will observe over time is that only the nail in test tube a will Rust this is because in testr a we have both air and water present however in testr B that oil removes the air it stops the oxygen getting through to that nail and in test tube C we have the presence of that desicant calcium chloride which removes water now this shows us that we need both of these to be present not just one of them for rusting to occur now it's important that we think about how we can prevent rusting because rust of course damages materials so if we think about what we need for rust to take place we need oxygen well a great way to stop rusting happen then is to remove the oxygen we could do this by using a barrier method such as painting or we could store the metal in an unreactive gas such as nitrogen now for rust to take place we also need water so another way that we could prevent rusting is by removing the water now again we could use a barrier method such as painting that metal or we could store the metal in a desin this is a substance such as calcium chloride now you might be wondering what this is but I can assure you you've got some everyday experience of this you might know when you open up a shoe box for instance you get that little white packet which says do not eat and that is the desicant that is there to prevent moisture building up and potentially molding happen probably isn't there to prevent rusting in that case but it's the same substance finally we could use sacrificial protection which is putting the metal in contact with a more reactive metal let's have a look now at each of these in a bit more detail let's have a look in a bit more detail about the physical barriers to rusting so we can paint our material that will of course prevent both oxygen and water getting to the material we can coat it in oil we can coat it with plastic or we could electroplate it now electroplating is a process that uses electrolysis to coat an object with a thin layer of metal so the way that we do this is on the anode we use the metal that we want to Plate the other material with the cathode is that material that we want to coat so this could be for instance a spoon and we place these in an electrolyte which contains ions of that plating metal so imagine we want to Plate this spoon with silver make it look all pretty and shiny we would then use the solution such as silver nitrate because that will have silver ions present in it now this process of electroplating provides a barrier to oxygen and water which will prevent the rting and also make it look nice just like a my silver spoon as you can see here the silver ions will be attracted to that negative cathode and form silver on top of that spoon an alternative to Barry methods is sacrificial protection sacrificial protection works by putting out iron or steel that we want to prevent from rusting in contact with a more reactive metal such as zinc now the way that this works is how more reactive metal is going to oxidize more easily than the less reactive ion or steel and therefore it basically sacrifices itself to that oxygen and corrodes instead now the great thing about this then is over time as our zinc for instance corrodes we can simply remove it once it gets too corroded and replace it with some fresh zinc which hasn't corroded yet and so all of this is going to mean that our iron or our Steel does not corrode what is an alloy an alloy is a mixture of two or more elements where at least one of the elements is a metal the reason why Alloys are so useful is because pure metals are often just too soft for a lot of uses and by adding this additional element and making an alloy we can increase their strength let's compare the pure metal with the alloy here I can see that the pure metal has at ATS arranged in layers now these layers are able to slide over each other and this means that the pure Metals if a force is applied they can be bent and shaped they're malleable and this often means that those pure metals are just too soft however if we have a look at the Alloys we can see that by adding those atoms of different sizes from other elements we've distorted those layers now this means that if we apply a force the layers can't slide over each other as easily we're going to need a larger Force to have them move over each other and this is what makes the Alloys harder and stronger than the pure Metals iron can be alloyed to different materials to make a range of different types of Steel all of which are going to have different properties and different uses we need to know these three examples so mild steel is composed of ion and carbon and it's often used in car body parts because it's malleable and it's ductile El T seal on the other hand is made from Iron and tungsten this is hard and it can withstand high temperatures which makes it perfect for using for drill bits stainless steel is made from Iron and chromium it is hard and it resists corrosion now this makes it very useful for cutlery now there's three other Alloys that you need to know about we need to know about brass magnesium and gold for jewelry so brass is composed of copper and zinc we need to know that it's resistant to corrosion it makes a good electrical conductor and it's stronger than copper so if you pick up a plug and look at the pins sticking out at you those are made from brass magnalium is made from aluminium and magnesium see it's like their names have sort of mixed together it's resistant to corrosion it's low density but it's stronger than aluminum this makes it particularly useful for aircraft parts of course it's up in the air so we don't want it to corrode and get weaker and the fact it's low density means it's light and also its strength is going to make it very useful for aircraft Parts finally we've got gold for jewelry now pure gold is actually very very soft to the point it will probably just get damaged just by wearing it so gold for jewelry is generally composed of gold and copper of course it's stronger than pure gold it's resistant to corrosion and it's shiny this makes it perfect for using in jewelry so as well as thinking of concentration as the mass per unit volume we can also think of it in a different way we can instead think of it as the moles per unit volume and commonly we'll be asked to calculate the concentration by dividing the moles by the volume so concentration in moles per decim cubed equals the moles divided by the volume in decim cubed and we might even need to convert between moles per decim cubed and G per decim cubed the way that we do that is if we have GRS per decim Cub we divide by the relative formula mass or the Mr to get moles per desm cubed and if we want to go in the other direction we simply do the opposite so the moles per decim cubed times by that relative formula mass gives us the concentration in ground pedes cubed now if the volume of two solutions react together completely and we know the concentration of one of the two solutions we can calculate the concentration of the other solution let's have a look at this in a calculation in a reaction 50 cm Cub of 0.2 m per decim cubed of sodium hydroxide reacts completely with 25 cm cubed of hydrochloric acid here we asked work out the concentration of hydrochloric acid so we know two volumes and one concentration and we need to find the second concentration so what we need here is a balanced equation now they may give this to us in the exam here it's going to be NaOH plus HCL makes NAC plus H2O so I'm going to use the grid method here I know that we have concentrations volumes and we can use those to calculate the moles so starting off here looking at the sodium hydroxide we're told we have 50 cm cubed now because concentrations in moles per decim cubed we need to convert this to decimet cubed and we do that simply by dividing through by 1,000 so 50 div by 1,000 gives us a volume of 0.05 DM cubed we're told that the concentration is 0.2 moles per decim cubed so we fill that into our little grid and here we can see we've got two out of three things in our grid so we can use that to calculate the third thing the moles now we know that concentration is moles over volume so therefore moles is equal to concentration times the volume and so 0.2 * by 0.05 gives us 0.01 moles of sodium hydroxide now the question wants the concentration of hydrochloric acid so let's put a little question mark there in our grid so we can see here that between that sodium hydroxide and the HCL we have a 1: one ratio means that we have the same number of moles of HCL as we do NaOH so we've got 0.0 0 1 mol of HCL now we're told that we have 25 cm cubed of hydrochloric acid we've got the same problem here we need to convert that to decimeter cubed and we do that again just by dividing by 1,000 so that gives us 0.025 decim cubed now finally we're just going to use the equation that we know for concentration concentration equals the number of moles divided by the volume in this case that's going to be 0.01 / 0.025 and that gives us a concentration for the HCL equal to 0.4 moles per DM cubed and that there is our answer to this question titrations are carried out to work out the concentration of an unknown solution in a reaction between an acid and an Alkali so we need to know how do we carry out titration we acid is added to an alkaline and vice versa as well let's look at it this way first so first off let's use a pet to add an amount of alkali to a conical flask in this case let's say 25 cm cubed now let's add a few drops of indicator to this alkaline let's put our flask on a white tile the reason for this is when we get a color change we can see it much more clearly up against this white tile so now we're going to get a buet and we're going to fill that buet with acid we're going to look at that buet and we're going to record the starting volume of acid on that buet then we're going to turn the tap and we're going to add the acid drop drop drop to that alkaline it's very important that we just do it drop by drop because then we're going to get the closest volume as possible that's needed to neutralize that alkaline so after every drop we're going to SWR the solution to ensure that it mixes and we're going to keep doing those drops until we observe a color change and then we're going to stop we're going to record the final volume and then we're going to repeat until we get concordant tighters so that brings us to a question really doesn't it what is the Tighter and the tighter is the difference between the final and the initial volume reading on the buet and that's why you need to take that reading before you do any drops and after we've had that color change and what are concordant results as well those are tighters within 0.10 cm cubed of each other so for example let's find the mean tighter of the following results here we can see in this table we need to work out the tighters we do this by subtracting the initial volume from the final volume and then we fill them in the table now we need to look for which of these results are concordant so within that 0.10 cm cubed so the first thing we need to know is that we ignored the rough Tighter and the reason for this is that we just use that to get a ballp part as to how much we're going to need to add we don't actually use it in our measurements so then if we look at one 2 and three I can see that one and two are concordant they're within that 0 point 1 so the mean tighter is going to be 1935 + 19.45 / 2 and that gives us 19.4 cm cubed now these readings should always be two decimal places and they must always end in a zero or a five so make sure that all of your results are filled in in that way so we can use the results of a titration to work out the concentration of the unknown solution so the way that we do this is we write a balanced equation then we calculate how many moles we have of the known substance the substance whose volume and concentration we know and then we use a balanced equation and the ratios between all of the different substances to work out the moles of the unknown solution finally we use those moles that we just worked out and the mean tighter so that mean volume to work out the concentration of the unknown solution so let's have a look at this example so in a titration 50 cm cubed of 0.1 mole per decim cubed of pottassium hydroxide is exactly neutralized by 25 cm cubed of hydrochloric acid here we need to work out the concentration of hydrocloric acid so the very first thing we need to do is to write a balanced equation so potassium hydroxide is Koh plus hydrochloric acid which is HCl and they'll react together to make potassium chloride KCl plus H2O and that is already balanced actually so we're in Lu so I like to use this grid method so I'm going to do three rows one for concentration one for volume and one for moles now looking at the information for potassium hydroxide I know both volume and the concentration but notice the units are different we've got cenm cubed for the volume let's divide that by 1,000 to get the volume also in terms of decimeter cubed so here I'm going to write it all in into this little grid that I've got the volume of pottassium hydroxide is 0.05 decim cubed and the concentration is 0.1 moles per decim cubed so I need to work out the the moles here I know that moles is equal to the concentration times by the volume so here I'm going to do 0.1 * by 0.05 and that ends up giving me 0.05 moles so now I've got the number of moles of pottassium hydroxide I can use my balanced equation and the molar ratio between potassium hydroxide and hydrochloric acid to work out how many moles there are of hydrochloric acid so here I can see that there's no balancing numbers in front of them which means there's one of each so I've got a 1: one ratio between the two so we have 0.05 moles of HCL so looking back at the information in the question I also know I have 25 cm cubed of hydrochloric acid now let's get that into decimet cubed again as well by dividing through by 1,000 so this means I now also know the volume of hydrochloric acid and I can fill it into my grid again I've got 0.025 decimet cubed of HCL so now I can see I've got two things that I know about HCL and I'm being asked to find the third thing that concentration so how do we do that we just Ed the same equation we did earlier that moles equals concentration time volume but we rearranged this equation to find that concentration equals moles over volume so in this case then substituting in the numbers I have 0.005 / 0.025 and popping that into the calculator I find that I have a concentration equal to 0 .2 and that's moles per decimeter cubed and that there is our answer so really the key thing in a question like this is to lay out all of your information in this grid method is always my favorite way of doing it so that you've got all of the information you need to answer the question the percentage yield is calculated by taking the mass of the product actually made and dividing it by the maximum the theoretical mass of the product I'm timesing it by 100 and when we say maximum theoretical Mass that's if the reaction went perfectly and all of the atoms from the reactants went on into making our product so in reality as you can imagine most reaction don't actually have 100% percentage yield now we need to know why this is the case and this is a very common type of question you may see so one of the reasons is that the reaction may actually be reversible and so it's never actually going to completion another reason is that some of the products may be lost and it's separated from the reaction mixture imagine you're pouring it from one container to another it always be some residue left it's never a perfect process and every time that happens you're losing some of the mixture and therefore you yield the final reason you need to know about is that some of the reactants May react in different ways than you expected so other reactions might be taking place at the same time so let's have a look at what this might look like in practice they may tell us that in an experiment the theoretical yield is 8 gr only 6.2 G is actually made so they may ask us to calculate the percentage yield in this scenario so using our equation the percentage yield will be equal to 6.2 / 8 .0 and timesing it by 100 and that gives us a percentage yield equal to 77.5% atom economy is a measure of the amount of starting materials that end up as useful products we've got this formula here that we can use to calculate it in an exam the atom economy equals the relative formula mass of the desired product divided by the sum of the relative formula masses of all of the products or you might have learned it as reactants but it works out exactly the same and then we times it by 100 to make this a percentage in chemistry we'll see that a high atom economy is very important and we need to know why so there's two reasons you need to be able to talk about the first one is sustainable development now what this means is if we have a high atom economy we're going to have less waste being produced and fewer natural resources being needed another reason is economic reasons imagine the more things you make that you don't want to make you've got to spend money getting rid of disposing of you might even need more reactants in order to make stuff you don't even need so it makes good economic sense to have a high atom economy now top tip here if we have a reaction that only has one product we should know that the atom economy is 100% we don't even need to do a calculation now let's put this into practice with this example so this following reaction is used to make sodium chloride calculate the atom economy of the reaction the first thing we always need to do is to identify what was the useful product and here the question has clearly stated that we're making sodium chloride so that is our useful product let's remind ourselves of the formula for atom economy so atom economy is the rfm of our useful or desired product divided by the rfm of all of the products or you may use the reactant they work out the same either way and then finally we times it by 100 to change it into a percentage so in this question we have said that the useful product the desired product is sodium chloride so in this case you can see that we're given all of the information that we need to be able to work out that relative formula mass of chloride so that's going to be 23 + 35.5 which gives us 58.5 now that of course is our desired product but we want all of the products here we can see we've also got H20 as well so let's work out the relative formula mass of that as well that's going to be 2 * 1 for the hydrogen and then plus the 16 for the oxygen and that gives us 18 for the relative formula mass of water so let's substitute these numbers into our equation here then so atom economy is going to be equal to that 58.5 of that desired product divided by 58.5 + 18 and then we Times by 100 to change it to a percentage so putting that into the calculator I end up getting 76 6.47% and that is our atom economy of this reaction in chemistry when we talk about gases there's a really interesting fact it doesn't matter what gas you have if you have the same amount of it so you have one mole of it it will occupy the same volume under room temperature and pressure now that has a very specific value that you need to learn so at room temperature and pressure one one mole of any gas whatever the gas occupies 24 decim cubed or 24,000 cm cubed now room temperature we say is 20° C and room pressure is one atmosphere pressure now under the same temperature and pressure say one mole of carbon dioxide gas will occupy the exact same volume as one mole of chlorine gas or oxygen gas or ammonia gas or any gas let's look at this example let's calculate the volume of gas produced in decimeter cube when 10 G of sodium reacts with an excess of HCL at room temperature and pressure so we're given this balanced equation here we know two sodiums plus 2 hcls makes two nac's plus H2 now I like to use the grid method here I'm going to draw on three rows I'm going to have the mass the relative formula mass and the moles and the point of this is if I know the mass of sodium 10 G I can work out the number of moles of sodium I have so I know that I have 10 gram of sodium I know that it's relative atomic mass in this case is just 23 and I know the formula that says that moles is mass over the relative formula mass so I can calculate the number of moles of sodium by doing 10 divided by 23 that gives me 0.435 m of sodium so now in this question we're being asked to find the volume of gas now the only gas that's produced here is the hydrogen gas and if I look at the relationship between the sodium and the hydrogen I can see I have a 2:1 ratio that means I have half as many moles of hydrogen than I did sodium so the moles of hydrogen will simply be that 0.435 we just calculated divided 2 now that gives me for the moles of hydrogen 02175 moles now that we know how many moles we can use the fact the one mole occupies 24 decim cubed so in this case 02175 * 24 is going to be the volume occupied in this case that gives me a volume of 5.22 decim cubed so always make sure that you know that you take the number of moles you have and times it by that 24 decim cubed or 24,000 cm cubed if that's what the question wanted a fertilizer is a substance which provides mineral ions required for plant growth over time as a plant grows they'll end up taking all the mineral ions out of the soil and eventually we might find that the soil becomes deficient in these mineral ions so gardeners or Farmers might choose to add fertilizers to the soil to replenish these ions we need to know what elements are found in fertilizers so there's three elements the first is nitrogen which we can find in ammonium ions and nitrate ions we also have phosphorus which is found in phosphate ions and finally potassium which is found in all common potassium compounds which are of course all soluble and they're in the form k+ we need to know how ammonia reacts with nitric acid to make a salt that can be used as a fertilizer well of course ammonia is an Alkali so when we add acid to it we neutralize it forming a salt so if we neutralize it specifically using nitric acid above all the acids will end up making nitrate ions which is like a double whammy in this example because we'll end up with both ammonium ions and nitrate ions being formed which is great of course because they both have nitrogen in them so the reaction that takes place will be ammonia plus nitric acid makes ammonium nitrate or NH3 plus H3 makes nh4 NO3 so the ammonia required for this reaction gets made in the harbor process and the nitric acid is made from ammonia in the following reaction the ammonia reacts with oxygen to make nitric acid and water now ammonium sulfate is another salt that can be used as a fertilizer we can make this in the lab using the following reaction so ammonia plus sulfuric acid makes ammonium sulfate now in this case because both the amonia and the sulfuric acid are soluble in order to make ammonium sulfate we must carry out a titration now this process in the lab is a batch process which means that we're just making small amounts of ammonium sulfate at a time and after each process we'll have to clean out all of our apparatus and start again we need to be able to describe an experiment to make this ammonium sulfate in the lab so the first step we're going to take is we're going to put some dilute sulfuric acid into a chicle flask we're then going to add a few drops of methy orange indicator we'll then add some dilute ammonia drop by drop using a burettes and stir between each drop we're going to continue adding ammonia until eventually we get a color change from red to Yellow we're going to add a few more drops of dilute ammonia solution this is to make sure that this has fully reacted and we're not going to worry about there being an excess of ammonia because it will just evaporate off we're then going to pour the mixture into an evaporating Basin and then we're going to heat it using a water ball the reason for doing this is to start the evaporation of some of this water that's in the solution and of course to remove any of that excess ammonia now before all the water evaporates we're going to remove this from the Heat and we're going to leave it until crystals begin to form at that point we're going to pour away any excess water and then we're going to leave it crystallize in a warm oven now we also make ammonium sulfate in Industry as well on a very very large scale now we're making ammonium sulfate in Industry the reactants of ammonia and sulfuric acid are actually made from their materials industry uses a continuous process which means that we're never shutting off the machine we're continually making this ammonium sulfate and continually putting in new reactants to then be able to make even more so this flow chart here shows how we make this we can see we're making the nitrogen from the raw material of air hydrogen you can see we get from the raw materials of natural gas and water and the nitrogen and the hydrogen we used to make that ammonia that's needed to make the ammonium sulfate now the sulfuric acid on the other hand that we need we make via making sulfur trioxide so we use sulfur and air to make our sulfur trioxide and then react that with some more water to make our sulfuric acid once we've got that amoni and sulfuric acid we finish off by making our ammonium sulfate in chemistry we learn about cells but they're not the cells that we learn about in biology no instead cells in chemistry are devices which contain chemicals which will react to produce electricity now we may be asked how can we make a simple cell and simply all we need to do is connect two different Metals in contact with an electrolite just like this diagram here now the voltage that we end up getting from this cell is going to be dependent on two different things the first one is the type of electrode so what metals or materials we're using for the two different electrodes and also what electrolyte we have as well so what solution do we have connecting these two electrodes so we might hear the term battery as well a lot of people can get confused about the difference between a battery and a cell and actually the batteries that you know in day-to-day life are actually cells but a battery would consist of two or more cells connected in series and the whole purpose of this is that we're going to get a greater voltage from a battery rather than just a single cell we may well be asked to describe the difference between non-rechargeable and rechargeable cells and batteries we need to know that a non-rechargeable cell or battery is one where if the reactants get used up the chemical reactions stop and the battery just stops working and an example of that is the typical alkaline battery that we add to many of our devices around the home now a rechargeable battery is one where the chemical reactions are reversible when an external electric current is applied and we have an example here that we're all using all the time and that is our mobile phone batteries our laptop batteries EX example similar to that where we can just plug it in and recharge that battery fuel cells are cells which are supplied with an external source of fuel for example hydrogen and oxygen we need to know how fuel cells work we should know that in a fuel cell the fuel is oxidized electrochemically within the fuel cell to produce a potential difference now hydrogen fuel cells generate this electricity by reac acting together hydrogen and oxygen and forming water now the type of reaction that we have in this case is an oxidation reaction and the reason why this is oxidation is because the hydrogen gas gains oxygen to produce water therefore we can say that the hydrogen is oxidized finally here let's summarize the advantages and disadvantages of using hydrogen fuel cells so a great Advantage is that the only waste product produced is water we're not having to find suitable places to dispose of these batteries which have dangerous chemicals in them another great Advantage is that they don't need to be recharged however the disadvantages include the fact that hydrogen can be very difficult to store particularly due to the fact that it's highly flammable another disadvantage of using hydrogen is that it's often produced from nonrenewable resources particularly fossil fuels such as natural gas and so although when we use the fuel cell we only make water great in order to get the fuels that we needed for this fuel cell actually other products would probably formed along long the way and that's all while also depleting those non-renewable resources so make sure you know these advantages and disadvantages of hydrogen fuel cells ow this is why in some videos I explain scratches [Music]