hello and welcome to this revision Monkey video on what's going to be in the combined chemistry paper 2 exam this is for people studying the higher tier of the AQA combined specification let's run through what to expect on the chemistry paper 2 I'll do a quick recap of evaluate explain and compare questions we'll have a look at calculations that you need to know cuz 20% of the paper will still be calculations and we'll have a look at required prac which are 15% of the exam and don't forget also look lots of skills that we've covered before things such as surface area to volume ratio uncertainty averages including mean median mode and tables and graphs are likely to come up as well so have a look through the previous videos and paper one for those skills as well quick recap of what evaluate questions want you to do they want you to give advantages disadvantages and a Justified conclusion to your answer so these are often between four and six marks so they won't tell you that they just have the word evaluate so you need to remember to put pros and cons of each thing and give your reason as to which is best and why for compare again it won't tell you but it expects you to write similarities between two things as well as differences and also explain questions they want you to say say why so include as much scientific detail as possible when you're answering explain questions so having a look at calculations 20% of paper 2 is calculations what you may or may not be aware is the equations that come up in topic C3 of chemistry paper 1 may also come up in chemistry paper 2 so it is worth looking over those calculations again so the calculations that you'll need to remember for higher moles equals mass / Mr concentration equals mass over volume and concentration equals moles over volume remembering if you have a volume in cenm cubed to convert it to decimet cubed you divide by a th and uncertainty can come up on any paper and that is equal to the range divided by two so brain dump those as you go in the exam because you might need them for paper 2 as well as paper 1 the required practicals that you need to be aware of are rate of reaction analysis and purification of water and paper chromatography paper chromatography required practical we use paper chromatography to separate colored substances so in this practical you may be asked a question similar to the one above that says do food dyes A and B contain chemicals that are in band Dy X so in this practical we're going to separate three dyes a b and another one called X and we're going to compare the patterns at the end of the Practical in your exam they might not talk about food dyes they might be talking about inks or another random colored substance but the process is exactly the same what you need to do to start off with is draw a horizontal pencil line around 2 cm from the bottom of a piece of chromatography paper do not use pen as this will smudge and spread up the paper pencil is insoluble so will not dissolve in the solvent so this line here that we draw on must be drawn in pencil on the pencil line put a small dot of the dieses that you want to separate and label these with pencil underneath so I've labeled them a b and X place the chromatography paper in a solvent for example water the solvent must be below the pencil line put it in a be with a lid to prevent the solvent from evaporating then we leave until the solvent front nearly reaches the top of the paper then remove the chromatography paper and leave to dry so the process of separating a substance through chromatography has two different stages the paper itself is called the stationary phase and when the inks are dissolved in the solvent that is called the mobile phase and within the inks that you've put on the paper you will have different compounds and they will interact differently with the paper and they will have different solubilities so they will spend different times attached to the paper in the stationary phase and different amounts of times dissolved in the solvent in the mobile phase so you'll end up separating the substance as it moves up the paper and to do that what happens is the solvent moves up the paper and when it hits the dyes it dissolves any of the soluble compounds in the dyes that will then they will then be carried up the paper in the mobile phase and depending on their solubility they will stop at different distances up the paper I mentioned earlier the solvent front that is where the solvent finishes as it goes up the paper so if the solvent is moving up and it gets close to the top of the paper where it reaches here is called the solvent front and when it gets near to the top we would then remove the paper and leave it to dry so the pattern left on the chromatography paper is called a chromatogram so after we've left it to dry we will see several dots of different colors on the piece of paper we would then compare the chromatograms of dyes A and B with the chromatogram of the band d x in your exam you're likely see a chromatogram in black and white like this rather than it being printed in color and each dot just shows how one of the colors is separated as it's gone up the page so you can see here die a has two dots and so has d x and this top dot here is in exactly the same position as the one on X suggesting it could be the same compound now you'd want to investigate this further to see if d a does contain one of the chemicals that is in the baned food d x because we've only tested this so far on one solvent we chose the solvent as water but to be absolutely sure that our food D contains a ban chemical we would need to repeat this in different solvents for example maybe ethanol and if this compound in a matched X in different solvents it's highly likely that it is containing that band compound we can't just be sure if we just use one solvent we must repeat it with different solvents to be absolutely sure in different solvents different compounds will spend different amounts of time in the mobile and stationary phases and what we'll talk about later is the fact that they can have different RF values the position of this color on D a does not match that of d x and you can see for D B it only has one color here and it doesn't match at all with d x now because d b's got one color and one color only this tells us that D B is a pure substance because it only contains one compound in the exam you might be asked to calculate an RF value you do this by calculating the distance traveled by a substance divided by the distance traveled by the solvent this top line here is representing the solvent front which is where the solvent got to before we took the paper out of the beer and I'm just going to show you an example using one compound here that we found on our chromatogram now the important thing is when you're calculating the RF values you must calculate it from the center of the dot on your chromatography paper not at the top not at the bottom but right in the middle of the dot that you're using and the Bas line that we're using is our pencil line where the die started so we need to measure the distance traveled by the substance so this distance here and then the distance traveled by the solvent so let's say for example the distance traveled by the substance was 400 MM and the distance traveled by the solvent was 500 mm then we do 400 / 500 to get us an RF value of 0.8 as I alluded to previously RF value will be different depending on the solvent used so this could be for example the RF value for water for this particular compound but if the solvent was ethanol then this number here would be different rates of reaction required practical when wanting to calculate the rate of a reaction you might need to use one of these two equations the first one says the rate of reaction can be calculated by the amount of reactant used up over time and the second one is the amount of product made over time so we're going to design some investigations using these two equations now there are several factors that you may be asked about in the exam that affect the rate of reaction those include temperature concentration and surface area so you may well be designing experiment and changing any one of these three things so that would be your independent variable and if you change temperature for example you need to keep concentration and surface area of your reactants the same and the same goes if you selecting a different independent variable one of them you change and the other two you have to keep the same there are several different practical that you can do to calculate rate of reaction and any one of these may come up in the exam so this first one focuses on the amount of product made over time and the independent variable that we're going to change is concentration so we'd measure 50 m of 0.1 M hydrochloric acid using a measuring cylinder and pour it into a chicle flask we'd place for example 1 cm of magnesium into the chicle flask attach a gast syringe and start a timer so in here we'd have our acid and our piece of magnesium which you should know is going to create hydrogen gas to calculate the rate of reaction in this experiment we could record the volume of gas produced at regular intervals for example every 30 seconds for 5 minutes and as gas is produced by the reaction the gas syringe will move outwards and you can measure the volume of gas produced do not write amount you must use the word volume then we would plot the volume of gas produced Against Time on a graph and we can use this to calculate the mean rate of reaction and I'll go through how we do this later on we then repeat the experiment for the following concentrations of acid so this will be our independent variable the concentrations of acid the dependent variable would be our volume of gas which we then turn into our rate of reaction down here and important control variables are things such as the volume of acid that we are using the length of magnesium that we're using and things such as temperature as well as in all experiments it's also really important to talk about the fact that you're going to repeat The Experiment three times and calculate a mean for each concentration of acid that you're using so a different practical setup now but still looking at how concentration affects the rate of reaction this time this focuses on the equation the amount of reactant used over time so we start off by placing a chicle flask on a balance and zeroing the balance we then measure 50 Ms of 0.1 M hydrochloric acid and pour this into the chicle flask and we then Place one cm of magnesium into the chicle flask and start a timer we take the initial reading on the balance as well so we're starting off with a mass of 25 G now again we're using magnesium and acid so we're producing a gas and because we have no bung on the chical flask that gas is going to be allowed to escape out of the conle flask and in doing so because mass is escaping from the system the reading on the balance is going to go down so to calculate the rate of reaction we can record the mass on the balance every 30 seconds so we wait 30 seconds write down the new Mass another 30 seconds again writing down the mass and so on and so on and then we plot the mass Against Time on a graph and we can calculate the mean rate of reaction we'd repeat this experiment for the following concentrations of acid 0.5 M 0.7 mol and 1 m and as always is good practice right at the end that you're going to repeat it three times for each concentration and calculate a mean a third practical that you might see in your exam again answering the same question with changing concentration and measuring the rate of reaction is when you draw a black cross on a white tile or piece of paper and place a conical flask on top we'd measure 50 Ms of 0.1 M hydrochloric acid using a measuring cylinder and pour that into the flask and we'd also measure 50 m of sodium th sulfate using a measuring cylinder and pour that in the flask as well so you can see at the moment when we've put the acid and sodium th sulfate in we can still see the cross because the solution is colorless however gradually over time a precipitate will form to make the solution go cloudy and at that point point we will no longer be able to see the cross so you can see now when the solution has gone cloudy we can no longer see the cross and we then record the time it takes for the cross to completely disappear obviously this is subject to error because different humans will have a different opinion on the exact time that the cross has disappeared we' repeat the experiment for the following concentrations of acid 0.5 0.7 5 and one Moler and for this one because we're not measuring the amount of reactant used or the amount of product made over time we're simply looking for the time it takes for a color change we could use the equation rate equals th000 divided time to calculate a rate of reaction for each concentration that we're using so with the results of a rate of reaction experiment you may well be asked to draw a graph or do some calculations us using a graph that's provided to you so let's look at this graph here first of all this might be a graph that we might have drawn from the first experiment whereby we're measuring the volume of gas produced over time a few things about rate of reaction graphs to start off with then the steeper the gradient the faster the rate of reaction so you can see this first section here is really steep then a shallower gradient here so the rate of reaction is slowing down and at this point here where the graph starts start to level out the reaction has actually stopped and we know that because if you read off the graph here no more gas is being produced so here are some common questions that you're asked one here says what is the mean rate of reaction so to calculate this from the graph you would find out the point where the reaction stopped draw a line from the x-axis up to that point and then a line across to the y axis and you would read off from the bottom the time that it took so 15 seconds cuz from zero to here is 15 seconds and the volume of gas produced in that time from the zero up to here so 34 approximately and then we would calculate that by doing 34 / 15 giving us an answer of 2.3 cm cubed per second we always do the Y / the X in our calculations and we get the units for rate by reading them off the graph cm cubed / seconds is what we've done so those are our units they could also ask for a mean rate of reaction for a particular time point for example what is the mean rate of reaction between 4 and 12 seconds and in that case at time point 4 you draw a dotted line up and across to the Y AIS you do the same for 12 and then you would read off between those two sections so between 4 and 12 we've got a time of 8 seconds and between our two markers on the Y AIS here we have a volume of gas produced of 12.5 cm cubed so to calculate the rate of reaction again we do the Y ided by the X so our y value is our 12.5 ided x value of 8 seconds 12.5 ID 8 gives us for that section of the graph a mean rate of reaction of 1.6 cm cubed per second and finally a calculation for higher tier only this one says what is the rate of reaction at 8 seconds so this is exactly at this time Point here what is the rate of reaction and to do that you need to draw a tangent on your graph which is a straight line as close to the line as possible at that point like the one I've just drawn on there now there will be some leeway in your exam but try and get it as close as possible and following the same pattern as closely as you can and then look on your gradient line where the line crosses the Grid at some sensible points for example here it crosses in the corner and down here then we draw dotted lines to make a triangle between those two and again we're going to do the change in Y which is this bit divided by the change in X to calculate our gradient so we do 15 / 10 to calculate the rate of reaction at that exact point as 1.5 cm cubed per second analyzing and purifying water required practical for this practical there are three different things that you might be asked to write about the first one is testing the pH of water samples to see if they are in the pable range the second one is to test the water samples for dissolved solids do they have a low enough amount of dissolved salt to make them potable and finally if they are not potable how can we use distillation to purify the water sample so the first two relate to analyzing the water and then the distillation refers to purifying the water so looking at the first step then testing the pH of water samples we would use a device called a pH meter or sometimes you may see it called a pH probe but pH meter is best what you do with the pH meter is put it in your sample and then it will give you a reading of the pH digitally so I've got three different samples here I've got some rain water some spring water and some sea water and I put my pH probe in the rain water and I would then record the pH in the table repeat that with spring water and record the ph and finally with sea water and record the pH now are the in the potable range is the question that we're looking at are these safe to drink well the potable range is between pH 6.5 and 8.5 so you can see here that the spring water and sea water in these examples are within that PH range so they could be potable uh but the rain water is too acidic okay it falls below that PH range so it is not considered to be safe to drink but we don't yet know if it's pable or not because it also has to have a low enough amount of dissolved salts and of course a low low enough amount of microbes the second part is then testing the water samples for dissolve solids so we're going to look if they have a low enough amount of dissolved salt to make them potable this is the equipment that we are going to use we have a balance here we've got our bunson burner on a heat prooof mat with a tripod and GS and then we have a beaker and this Beaker is just acting as a water bath it's just fill up with tapat water and on top of that you've got an evaporating dish and that is where you are going to put your water sample in your evaporating dish all this water is doing is just acting as a water bath that will gently heat the evaporating dish it's much better and much safer to do it this way rather than putting the evaporating dish straight upon the guse you can also get electronic um water baths that will do this as well which you may see in an exam so the method for this we are testing to see if this water sample has dissolved solids in it so we're going to record the mass hence the balance of an empty evaporating dish we are then going to measure 5 ml of one of the water samples for example rain water using a measuring cylinder and add this to the evaporating dish so we pop our small amount of water in our evaporating dish like so we then heat gently over a water bath until all the water evaporates from the evaporating dish now to do it safely in the lab what you might do is allow most of the water to evaporate and then leave the rest to evaporate slowly but once the water evaporates you'll be left with none in your evaporating dish and you allow that to cool and then reway the evaporating dish you would then record any Mass change of the evaporating dish if there is any and observe any salts left on the evaporating dish so once the water evaporated if your sample contains salts it would likely that you would see salt deposits building up on the size of the evaporating dish so when you were to put that dish back on the balance and reway it you'd expect it to be heavier because it now has salt on it you would then repeat steps 1 to six with the other water samples for example if we used salt water and spring water so when you look at your results just because one of the samples may have a low amount of dissolved solids a low amount of dissolve salt in this case that we're looking at it might not mean that it still pable even if it passes the pH test and the low amount of solids you would have to make sure that it has a low enough amount of dissolved microbes so if your water samples are not potable you can use a process called distillation to purify the water sample I've just used a different color here just so we can make it obvious but let's suggest that in here we put our salt water because this is what many countries such as Saudi Arabia would do because they don't have much rain water and this will allow them to access drinking water from their normally non-potable salt waterer so the flask that we put this in is called a round bottom flask and you would heat that flask normally using a water bath or perhaps using a bunson burner if you're doing it in the lab you have a thermometer at the top here which you'd want to make sure for pure water was reading 100° C so that you know that in your Beaker over here you are getting pure water so as you heat the salt water the water will evaporate and it should leave any salts behind in the round bottom flask the water will evaporate and it will turn into water vapor and it will go up the tube here this piece of equipment here is called the condenser or you might see it written as the condensing tube so the condenser is kept cold by this cold water going in and around the glassware it doesn't mix with what's in the middle it just goes around the glassware to keep it cool and as the water vapor comes in here it is then condensed into a liquid and then it will collect as pure water in the beaker so in this pure ification process we would test the pH of the water using a pH meter we neutralize it if we needed to by adding Alkali if it's acidic or adding acid if it's an alkaline and we use pH meter not an indicator to determine when it's neutral because if you're trying a Purify sample there's no point adding an indicator like Universal indicator in there because you're just contaminating it and a pH meter is going to give you a much more accurate result so then we pour the salty water into the distillation Apper ators and we said specifically it's the round bottom flask it goes in and we heat it and the distillation process as discussed will leave us with pure water in our Beaker and we would then just retest the pH at the end to check that it is neutral okay moving on to some content then for chemistry paper 2 topics 6 to 10 little bit more on rate of reactions first just looking at these graphs like we did before you might have massive product over time um the time might not be in M uh seconds you might have it in minutes or hours depending on how quickly the reaction takes and you might need to identify which is the fastest rate so we said before the area on the graph with the steepest gradient is the fastest rate of reaction so if you're describing it let's look at line a here this is the fastest rate of reaction at section one then the rate of reaction slows down as the rate gradient gets shallower and then it's a much slower rate of reaction and then it stops again so you could describe how the rate of reaction changes or you might be asked to select the fastest rate of reaction out of three lines in this case that would be a we said we come back to the Catalyst we said before that it provides an alternative pathway with a lower activation energy that's the GCSE bit you won't get all the marks if you just say that it speeds up a reaction remember remembering reaction profiles from paper one they may well creep into paper two as well because you might need to show on there how a catalyst is providing an alternative pathway if you remember four the activation energy is this line here from the bottom of the reactants to the peak so if we're drawing a line with a lower activation energy you would draw a line on like so lower than the previous line so whether it's Endo or EXO you do exactly the same thing reversible reactions are reactions whereby the reactants make products and then the products can react again to make the reactants the symbol for reversible reaction is here and you will have to um be able to draw that in the exam and one example that they talk about is in the specification is hydrated copper sulfate that's got water in it so think to yourself the one that's hyd ated with water is blue and then that will break down into anhydrous copper sulfate that's a posh word of just saying the water's gone okay and hydr copper sulfate which is white and water is released so this reaction here if you've just got one substance which you heat up and break down to form two the forward reaction here is called a thermal decomposition reaction and if you ever see this kind of reaction it means it's not reacting anything it means you need to take in heat to break it down so this one is endothermic going in this direction because it's taking in heat in a thermal decomposition reaction and in a reversible reaction if One Direction is endothermic the reverse has to be exothermic look at at organic chemistry then let's start off with this general formula this says CN h2n + 2 this is the general formula for an alkane what the N means you probably use this in maths it just means for any number of carbons you will have double that plus two hydrogens so for example if we had two carbons C2 we would have two * 2 + 2 which would be six hydrogens and that would be one formula of an alkane let's look at the ones you need to know then you need to know methane that's CH4 ethane propane and butane so monkeys eat peanut butter is one way to remember the order methane has one carbon ethane is c2h6 and that has two carbons propane has three carbons so that's C3 h8 and butane if you were asked to draw one think to yourself monkeys eat peanut butter so that has four carbons start in the middle there and every single bond is a single Co valent bond in these molecules and they are full up of hydrogen ions and this has got hydrogen atoms sorry apologies hydrogen atoms and this has a special word if it all has single bonds and is full up of hydrogen this means these are saturated molecules think to yourself s saturated s all single bonds let's finish this one off then butane if you ask to write the formula for it C4 h10 now these formulas here are called the displayed formula so if they start talking about displayed formula in the exam that's just the one that shows all the bonds in between them so these are called hydrocarbons because they are just made up of carbon and hydrogen and nothing else and we can burn these in a combustion reaction let's take methane for example when we burn methane we're reacting it with oxygen in the air and the products are always carbon dioxide and water and obviously this can link to global warming so ethane and oxygen would still make carbon dioxide and water and propane and oxygen would still make carbon dioxide and water if there wasn't enough oxygen in our um reaction we would do something called incomplete combustion which is not very good it produces a really Smoky flame and let's say methane and oxygen we'd still produce carbon dioxide and water as before but with incomplete combustion we'd also produce carbon which is s so solid black carbon and carbon monoxide Co carbon monoxide and that's bad as well so the S we'll talk about later causes global dimming and the carbon monoxide is toxic and can kill you okay so that's the alkanes fractional distillation then this is where we are separating different sub substances by their boiling point so when we dig down for crude oil that has taken millions of years to make it will be a mixture of hydrocarbons you'll have some short ones some very long hydrocarbons and it will be a complete mixture and it's not useful whilst it's a mixture so the point of fractional distillation is to separate these you heat the crude oil with um a fossil fuel probably so coal or something used to to heat the fossil fuels and then you are going to separate them by their boiling points so the shortest ones have the lowest boiling points and they go to the top then you get your longer ones until you get right to the bottom where you got very long chains the ones at the bottom have a really high boiling point so they come out of the bottom of the chamber because they're still next to the heat they're still heating up but they're not quite at that stage where they've boiled and Rise risen up the tank so you don't need to know the names of the products that come out of here or the order but they're things such as petrol and Diesel um and gases so gases come out the top then you got things like petrol and Diesel petrol is slightly higher than diesel we'll talk about this in a minute because if you needed petrol but only had lots of diesel available you could crack that diesel because it's a longer chain and produce petrol to meet the demand of the population wanting petrol so what can these be used as well they're really useful fuels the ones at the top that come out are really flammable so they catch fire easily they're easily they're easy uh they're very sorry volatile trying to say both things at the same time which means they easily turn into a gas so those the ones at the top low boiling points flammable and volatile the ones at the bottom have high boiling points they're the long chains and they are described as being very viscous that means they are thick and gloopy and don't flow easily whereas the ones at the top flow easily they can be further processed to produce things such as solvents lubricants and polymers which we'll come on to later but in their raw sauce they're best used as fuels so we said before if you wanted to produce a shorter chain like petrol from a longer chain like diesel you could go through the process of cracking cracking takes place using a heat I'll just get rid of that writing using heat and a catalyst to break up a larger molecule now it could break absolutely anywhere could break here and make two molecules or it could break here and two make two molecules it doesn't matter where on the Chain it actually breaks so let's say we started with a long molecule like C8 h18 when you crack it you produce another alkane with single bonds and something called an alen that has a double carboncarbon bond so the alkane let's say for for instance you could put any products here in the exam let's say the alkane that we produced had um five hydrocarbons so it' be C5 H we need to double that up and add two so 12 so we use five of these leaving three and we've used 12 of these leaving six the product that you make will be an alen so that would be C3 because we've got three left H six and this time you can see that it's just double the number of carbon not double plus two so this is what cracking makes alkanes and alenes and alkenes have a double bond so this one would have one double bond between two of the carbons and then the rest of them are single bonds like so for foundation you won't be asked to draw these alkenes you'll just need to know that cracking produces an alkane and an alkine so C3 H6 so you could have cracked that another way okay you could have three carbons here and five over here it doesn't matter what the products are as long as they all add up to C8 h18 the test for alkenes we need to know about is bromine water and that goes from Orange to colorless in the presence of alkenes in alkanes it will just stay stay orange so you'll know where your alken is because it will go colorless so there's two types of cracking one of those is steam cracking so for this process you would vaporize your hydrocarbon so turn them into a gaseous vapor and mix them with steam and heat them up and that will then crack your hydrocarbon or you may well see something called catalytic crack ing it's got the word nearly Catalyst in here and this is where you vaporize the Hy hydrocarbons again but this time pass them over an aluminium oxide Catalyst and it will do the same process of cracking the molecule so chemical analysis you need to know the test for some different gases hydrogen is one if you put a lit splint in the sample and hear a squeaky pop that means you've got hydrogen present for oxygen if you place a glowing splint in a sample so you've lit it up and then blown it out so it's glowing slightly it will relight if oxygen is present carbon dioxide we should hopefully know this one you bubble it through lime water and if carbon dioxide is present the lime water will turn cloudy and again like previously because a precipitate is has formed a solid precipitate potate has made it go cloudy the final one chlorine to get this correct bleaches damp lpmos paper Okay so that's the test for chlorine you might have touched upon that when you did electrolysis in paper one let's talk about different compounds then some compounds are pure okay so some materials are pure they only contain either one element or one compound nothing else others are specific formulations now this is a definition you'll need to know it's a useful mixture made from a a recipe or a formula you could write for a specific purpose so for example paint is an example of a formulation in paint you've got the pigment in there you've got the resin in there the binder in there and they are all in specific spefic um amounts to make that particular useful purpose pure substances you will recognize because they have very specific melting points and boiling points for example you'll know if a substance is pure copper because it will have an exact melting point of 1,83 De it will have an exact boiling point of 2567 de you find these data tables um online and they are um they tell you the exact um melting and boiling point of a pure substance if you had a mixture or something that was impure or a formulation for example you would not have an exact melting point for copper so let's say you had a particular sample and the Sam tells you that the melting point for copper was 1080° even though that looks very close that is not accurate is not close to the True Value so this would be an impure sample of copper it would contain some impurities perhaps a little bit of sulfur or something like that so only if they are exactly what the table matches can we class them as pure accuracy if that comes up in terms of these constant values here they are accurate if your value is exactly the True Value so chemistry of the atmosphere then scientists believe that the Earth began around 4.6 billion years ago at that time there was lots of volcanic activity releasing Gases such as nitrogen carbon dioxide ammonia which is NH3 um carbon dioxide methane into the atmosphere and the early atmosphere was very much like that of Mars and Venus today so we went for an atmosphere that had lots of carbon dioxide in it to an atmosphere that now contains comparably to everything else very little carbon dioxide loads of nitrogen and some oxygen as well so how did it do that well some water vapor was released from the volcanoes as well that water vapor condensed to form the oceans as the earth started to cool down the water vapor that was in the air condensed to form the oceans and when that happened a lot of the carbon dioxide from the early atmosphere dissolved in into the oceans and there it made the shells of early Marine organism so it made um the shells of we call them calcium carbonate shells of lots of different marine organisms it also um as whilst it was being dissolved in the ocean over millions of years it would have also been crushed down into fossil fuel so these calcium carbonate animals that died would have been crushed down and locked up in fossil fuels as well as that because the this rock type occurs at the bottom of the seabed they would have also been locked up in sedimentary rocks so you had a situation where you've got lots of carbon dioxide in the early atmosphere but as it's getting dissolved in the oceans it is getting locked up in fossil fuels sedimentary rocks and in the production of calcium carbonate shells as well as that before the animals came along really we had algae around 2.7 billion years ago 2.7 sorry am my writing billion years ago we had algae forming and plants a little bit later on and they took in the carbon dioxide in a process called photosynthesis which you should be aware of and in the process of photosynthesis they took in the carbon dioxide and they released oxygen so the levels of oxygen in the atmosphere started to rise which sustained other life until we got the composition of the atmosphere as it is today okay which is 80% nitrogen approximately that's round up 20% oxygen again that's rounded because together they make 100% but obviously we've got a few other gases we've got carbon dioxide 0.04% and other gases like argon water vapor and things less than 1% so it's weird but in the exam they will round these figures um up and down normally so it might not add up to 100% altogether so an atmosphere of mostly carbon dioxide dissolved in the oceans made sedimentary rocks fossil fuel F dissolve um made the carbonate shells of animals and then taken in by photosynthesis oxygen released and we end up with the atmosphere like it is today so chemistry of the atmosphere continue then we're going to look at global warming we touched on this iny so hopefully you'll remember my way to remember it which is the S sun produces the S short wave radiation and that can go through the green gases which provide a blanket around the earth so these are things like carbon dioxide the first one methane and the Lesser known one is water vapor so it always writes carbon dioxide first and then methane and water vapor so the short wave radiation goes in but all of the objects on the earth absorb that radiation and reflect it back into the atmosphere but this time as it goes out it is now long wave radiation and that doesn't just go straight through the greenhouse gases some of it does but some of it is absorbed and radiated back to Earth so that is what is causing the global warming the short wave radiation goes in it's reflected off of the earth as long wave radiation and the greenhouse gases absorb and riate that back to Earth causing a warming effect now we need that to some effect to sustain um appropriate temperatures for life on Earth but however carbon dioxide levels are going up as well as other greenhouse gases and that means more longwave radiation is being radiated causing a warming effect this is causing many consequences including increased flooding sea levels Rising changes in species distribution so some animals are becoming extinct um in different areas of the world because they can't um adapt to the changing conditions or they might move places okay so this is meaning they're perhaps migrating away and moving to different areas increased frequency of extreme weather so hurricanes and tornadoes and things like that so there's a few of the consequences and it's important that we all consider our carbon footprint because it's the carbon dioxide levels that are going up our carbon footprint is the amount of carbon dioxide and other greenhouse gases released over the full life cycle of a product so this could be anything from a company making a mobile phone you could be talking about your own carbon footprint in your day-to-day life you could be talking about the carbon footprint of a festival a music festival for example and it's the total CO2 that's released so it's in things such as transport to and from a place it's in things such as fossil fuels and burning fossil fuels to g generate electricity for certain things etc etc and how those can be cancelled down for example many people are reducing um eating meat okay and at the same time they might be eating perhaps vegetables or fruits that come from far away in the world so if you're eating perhaps avocados from somewhere exotic they might be traveling on a plane and releasing lots of fossil fuels so food itself will have its own carbon footprint so that's something important to consider as well let's look at the main pollutants then these are the links and you'll see tables like this in the exam carbon dioxide I want you to always link to global warming as well as the other greenhouse gases solid particulates for example we talked about soot or carbon being produced in incomplete combustion cause global dimming they sit as a layer in the atmosphere and reduce the amount of sunlight going through sulfur dioxide now this is such a common thing in paper two to talk about sulfur might link into the purity of um fuels if you see anything to do with sulfur being an impurity which is making something not pure in a fuel for example if you're trying to burn methane but you realize your sample has got sulfur in it well that is going to react with the oxygen to make sulfur dioxide so whenever you see sulfur link to acid rain and in fact as well as sulfur dioxide nitrogen oxides also cause acid rain but these ones take place within a car engine okay so very specifically always put acid rain but these take place within a car engine at very high temperatures so we said before that 90% of sorry 80% of the atmosphere is nitrogen so if that goes in your car engine and reacts with oxygen it can produce nitrogen oxides it doesn't happen normally like there's loads of nitrogen and oxygen in the air they're not reacting normally but they need really high temperatures both of these two can cause respiratory problems so breathing problems as well carbon monoxide we came across earlier Co just one oxygen that is toxic and it can kill people okay it's called the silent killer because it's odorless you can't smell it and if your boiler at home is doing incomplete combustion because one of the pipes is blocked and it's not getting enough oxygen you will be producing carbon monoxide and that is toxic and can kill you we're going to look at using resources so the first thing we're going to look at is a life cycle assessment you can do this for any product that you are interested in again something like a mobile phone the company might be ask by the government or by the supplier to produce a life cycle assessment for that so first of all there's four factors raw materials so these are things like what are you using to make the phone so it's all of the process involved in for example making the plastic so for this one you might be um extracting crude oil and you need to think about what effect that has on the environment you might be using Machinery to do that which is burning fossil fuels and releasing carbon dioxide as you're doing that you may well have to cut down trees to get to an area to mine it for example for the gold for the connections that you're going to use within the electrical circuit of the phone so there's loads of things that you can think about that will affect the environment when you're looking at the raw materials for the phone the manufacturing and the packaging so in all of these processes they often involve some sort of factory which you need to Power by burning fossil fuels to generate generate electricity again that's going to be releasing carbon dioxide it could also if it's got sulfur impurities be releasing sulfur dioxide causing acid rain and where's the packaging coming from where are you sourcing that from that could link into deforestation again are you cutting down trees to generate your packaging the use of the product so can it be um is it just used once for example and then someone throws it away is it something it's used for a long time when they're using it are they needing to charge it up using electricity again burning fossil fuels and all of these things so this is thinking about when the product is being used by the consumer and finally at the end of the life cycle of the product how are you going to get rid of it is it going to fill up landfill has it got toxic chemicals in it which need to be disposed of carefully or can you recycle it so all of this process is showing the effect on the environment of that single product sustainable development um is linking into the resources and the resources that we're using because it is the development that meets the need meets the needs of the present Society without damaging future Generations you can imagine a tick boox type thing in the foundation for this so basically it means making sure that we're not digging up and Mining the whole planet chopping down all the trees and ruining it for future Generations we need to do be sustainable we need to make sure that we're using renewable resources where we can and not just exhausting all of our finite resources which brings us on to those two words in chemistry they use the word finite to describe non-renewable resources like fossil fuels and in terms of making products and things renewable resources would be our things such as wood and Timber that we can replace so if we're looking for sustainable development we're going to want to reduce the finite resources that we're using and try and increase the renewable resources and we want to um try and do recycling as much as we can because recycling means that less energy is used because we're not having to mine and dig for new materials we're conserving the raw materials that we've got which makes it more sustainable and we're sending less waste to landfill so recycling is really good for those three things you need to know specifically about how glass is recycled so you've probably been to the glass bins before so you'll know the first point straight away in that you separate the glass by the different colors of the bottles so for glass recycling the first step is to separate the glass by the color so you put green brown and colorless glass in different bins it's then crushed and melted and then it's reshaped into new products okay so that's specific example you need to know about glass drinking water then final couple of things in relation to water potable water is water that is safe to drink okay so if you see the word potable that means it's safe to drink what that means it h is it has low levels of salt low levels of salt and microbes so you might have a little bit of salt in there a little bit of um microbes or bacteria but they are low enough levels that they are not going to cause any harm it is not the same as pure water pure water would be um ex just H2O nothing else nothing else dissolved in it or anything tainting it it's just H2O so pure water again Ling back to the boiling points would have a boiling point of 100° potable water might not have a boiling point of 100 degrees because it might have a few other bits in it that increase the boiling point water sources so surface water is one in the UK we have lots of surface surface water we have lots of lakes R rivers and reservoirs to collect our fresh water which is our rain water in we could also get water from groundw so underground rocks where water is stored and to get it to make sure it is potable we have to go through a process of filtration so a large wire mesh which will get rid of uh large objects like twigs and I don't know trollies plastic bags bottles whatever else has been chucked in the river then we have to filter out the smallest solid bits so we put that through a gravel and sand bed so the water is filtered through there and other solid bits like smaller twigs and leaves and things will be removed and then finally we need to sterilize it to kill microbes and there are several ways we could do that we could use ultraviolet light that has enough energy to kill the bacteria we could bubble it through with chlorine or bubble it through with with Ozone gas as well so either of those methods or all of them we might use to sterilize the water then it's potable and safe to drink and we can put it through our Taps now in hotter countries um places like Saudi Arabia for example Dubai um where there's not a lot of rainfall there are different um steps you can take if there is not a lot of fresh water and one of those steps is reverse osmosis so normally osmosis would move would mean that the water would move from where there's a dilute solution so a high concentration of water to a low concentration of water so normally I'll just put normally there that's the way the mortar would move but with reverse osmosis what they've done is they've taken salt water which is over this side which is from the sea because they've got lots of sea water available so to taken their Salty Sea water and they've applied a great deal of pressure behind it pushing it through a membrane and that squeezes the water in the reverse direction of Osmosis okay in this Direction that's why they call it reverse osmosis it g goes against the gradient okay so we require a lot of pressure for that the other thing that they can do is distillation like we talked about before they can take their salt water heat it up and make pure water but in this case it requires a lot of energy because you're burning fossil fuels to heat up um the salty water and it's therefore very expensive so a lot of these hotter countries find it more difficult to get their drinking water their potable water treating waste water then we produce a lot of waste a lot of um sewage water and things that we need to recycle because water is precious and we don't want to waste it so we get a lot of um waste from Farmers and also from sewage systems which we need to clear so we first do a screening process which is which is like a filtering process really to start off with whereby we remove large objects from the waste water it then goes through a sedimentation process and in this process our waste water separates into a sludge at the bottom which is really thick and then you get a fluffy layer on the top which is called effluent and you might have seen pictures about that where where this bits really frothy and Foy foamy and really light so it just separates the the products like so then there's two different processes for the sludge we do anerobic digestion to break down all that waste material in the water and for the effluent we do aerobic digestion so you might remember that the effluent is closer to the air CU it's at the top so that might be a good link to think that's the one that has aerobic digestion so for the effluent air is pumped into it and then bacteria break down the effluent in Aerobic conditions for anerobic digestion oh sorry and finally the water is released back into the rivers so the bacteria break down any waste product and then the water is released back into the rivers for anerobic digestion if you are a separate scientist you would have looked at this before in biogas generators so this is where the link is between biogas generators for separate scientists so bacteria break down the sludge but this time in anerobic conditions and the two products are methane which is a biog gas which can be used as a fuel and fertilizer which can be used um by Farmers to put nutrients back into the soil so as you can see there's not a lot of um higher tier content on there there's just three things to have a look at um we've already looked at this one calculating rate use a gr using a gradient so I'm not going to um look at that again but that's where we had our rate graph and we drew a tangent to measure the rate at a particular time point point that is a high only thing so I expect that in the exam equilibrium and chatellier's principle and phyto Mining and bioleaching so let's go through those now so first of all equilibrium and the chatalas principle let's look at this example here you've got an example where you've got two gases reacting so you can think about what things can affect the rate of reaction in gases we've got nitrogen reacting with hydrogen in a reversible reaction to produce ammonia and for separate scientists this is also the equation for the harbor process so lat's principle says that when conditions of a reversible reaction change at equilibrium the system will respond to counteract that change and there's several changes that could happen you could increase the pressure if you're talking about a gasier system you could increase the temperature or you could increase the concentration so just look carefully at the system that you've got if this wasn't involving gases you wouldn't be talking about increasing the pressure let's look at concentration first of all let's think imagine if you're looking at acids or something like that reacting in a reversible reaction if you increase the concentration of reactants so everything on this side of the equation the syst system will respond by making more products because you've increased the concentration of reactants the system wants to decrease the reactants again and in doing so it makes more products so the reactants react together and make more products so if you increase the concentration of these more ammonia would be used for example the equilibrium would shift to the right so you produce more ammonia and would counteract that change because then the concentration of the reactants would go down again if you're looking at temperature this will depend on which way is endothermic and which way is exothermic normally in the exam they will help you out by telling you in the question if not you might need to look out for it and the way to look out for it is if there's one product this side that will be broken down in a thermal decomposition reaction for that one you need to take in energy so that's endothermic in that direction and in the opposite direction it's EXO but if in the exam they had two products here they would give you a hint as to which one was EXO and which one was Endo so for temperature if you increase the temperature it will favor the endothermic reaction because this is a thermal decomposition reaction which which means that heat is taken in to break down this ammonia so in the example above the equilibrium will shift to the left which means that more of the nitrogen and hydrogen will be produced because the endothermic reaction is in this direction if you do the opposite and decrease the temperature that favors the exothermic reaction a little bit more difficult conceptu you to understand but if you understand that increasing the temperature will favor the endothermic reaction then think to yourself the opposite will favor the exothermic so decreasing the temperature will favor the exothermic reaction Shifting the equilibrium to to the right so more ammonia would be produced for pressure if I clear the screen that's all to do with the number of moles in the equation if we remember this equation says that one mole of nitrogen is reacting with three moles of hydrogen to produce two moles of ammonia so we could kind of represent it like that if you increase the pressure it will favor the reaction with the most moles so if you think about Collision theory that kind of makes sense because if you're squashing these closer together you're going to get more collisions between these molecules so in the example above the equilibrium will shift to the right because it will favor an increase in pressure will favor this reaction because it has four moles alog together compared to two so the equilibrium will shift to the right and you will produce more ammonia if you decrease the pressure the opposite will happen the equilibrium will shift to the left and you will produce more nitrogen and hydrogen so phyto mining something completely different now phyto mining p phyto mining is to do with plants now for hi you need to be aware of the problem that many of our finite resources of copper are running out so ores are rocks that contain um metals and many of our highgrade ores that contain copper which contain lots of copper are running out so now we need to use new technologies which will get copper out of low grade ores which are rocks that contain a little bit of copper but it's not very economical to extract it would cost a lot of money to dig this up with mechanical equipment and it would make the copper very expensive and not many people would want to buy it so instead they need to find new technology to try and get the copper out of these low grade OES so this one is to do with plants first of all you'd have your ore and you'd grow plants on your low grade ores the plants would take up up the copper in the leaves and it will build up in the plant you will then burn the plants and harvest them so set fire to them or cut them sorry Harvest them dry them out and then burn them and then you would end up with some ash which contained copper now unfortunately copper is not magnetic so you can't just put a giant magnet here to extract the copper you can't do that you'd have the material and the copper so you might link back to paper one here because what you could do is you could extract bi electrolysis so let's imagine you added some sulfuric acid to make copper sulfate you could then do electrolysis of copper sulfate to extract the copper or again you could add the sulfuric acid to make copper sulfate and a really cheap method is to do a displacement reaction with scrap iron so if you added iron to the copper sulfate you would end up with copper plus iron sulfate okay so that one's phyto mining growing the plants the plants are taking up the Copper from The Ore then you harvest them dry them burn them and then you have to think about either electrolysis or displacement to extract it for bioleaching it's very similar but this time you are using bacteria so B for bacteria B for bioleaching bacteria is grown on a low grade or is very cheap so you can grow lots of it and it will divide rapidly so this is quite um an advantageous process for that respect and the bacteria produces a leate which is a liquid solution containing the soluble copper compounds so they do all the work for you and then again you can extract it by electrolysis or displacement so you don't need to know this process in a lot of detail you just need to know involves bacteria and they produce a leachate containing the copper compounds