Overview of AQA Chemistry Paper 2

Let's see how quickly we can cover everything you need to know for AQA Chemistry Paper 2. This is good for higher and foundation tier, double combined trilogy and triple or separate chemistry too. That is topic 6 to 10, that's rates, organic, analysis, atmospheric and resources for short. I'll tell you when something is just for triple, we're going to be booking it here so pause the video if you need a bit more time to get your head around something you see. Let's go. How quickly a reaction happens is called the rate of reaction. Any rate is the change in a quantity divided by time. In this case that something can be the quantity of reactant used or product formed. This quantity could be mass or volume of gas that's usually made anyway. They like to stipulate that this technically gives you the mean rate as the rate could be changing over the time you measure but that's true for any measurements over time ever so that's a bit redundant but we'll go with it for now. An experiment on this could be reacting hydrochloric acid and sodium thiosulfate in a conical flask sitting over a piece of paper with a cross on. As the reaction continues the product form turns the solution cloudy. we say that's increased turbidity. We stop the timer when we can no longer see the cross from above the flask. Repeat this at different temperatures and you should see that the hotter the temperature the less time it takes. Another potential experiment is measuring the volume of gas produced by using a gas syringe that fills up when connected to the reaction vessel. A graph to show this would have the quantity on the y-axis and time on the x-axis. It's usually a curve that starts off steeply but then levels out or plateaus which shows that the reaction has completed or we can say reached its end point. To find the rate at any time, you draw a tangent at that point. Pro tip, turn the page so you're drawing the tangent horizontally. That will help you draw it accurately. Then, like the equation says, you can take the change in quantity and divide by time. Up, divided by, across. The rate of a reaction can be increased by the following. Increasing the concentration of reactants that are in solution, increasing the pressure of gas reactants, and increasing the surface area of solid reactants, that is, crushing into a powder. Now these three all have this effect because the reacting particles collide more frequently. They come across each other more often. Increasing temperature does that too due to the particles moving more quickly. But there's the added bonus that they also collide with more energy, meaning they're more likely to react when they collide due to activation energy. Remember your energy diagrams from paper one. Finally, adding a catalyst also increases rate as it reduces the activation energy needed. So particles are more likely to collide successfully and react. Of course, any catalyst is not used up in a reaction, it is not a reactant or product itself. Reversible reactions are pretty self-explanatory, once the products are made they're able to return to their original reactants. The prime example here is the Haber process, hydrogen and nitrogen react to make ammonia which can also break down back into the separate gases again, more on what ammonia is used for later. In a closed system, that is no particles or energy going in or out, both reactions will continually take place. eventually the quantity of particles on both sides will reach a point at which the rates of both the forward and reverse reaction will be the same. So that means there will be no more overall change in the quantities on both sides. Remember that's not saying that the reaction is stopped per se, it's just that there's no more overall change. That is until a condition is changed which will affect these rates. Le Chatelier's principle states if a system at equilibrium is subjected to a change the system will adjust to counteract that change. Sounds awfully vague, so let's see what that means in practice. There are a greater number of moles on the left than the right of this reaction, which means that the reactants take up more space. Therefore, if you increase the pressure of all of these gases, we say this favours the forward reaction. That is, the rate of the forward reaction will increase until equilibrium is once again reached, but that will happen when there's a greater proportion of ammonia than there was before. We could also say that the position of equilibrium is shifted to the right. Reducing the pressure would of course do the opposite by shifting it to the left instead. Concentration follows the same principle when it comes to solutions by the way. Naturally if you remove molecules from one side of the reaction the position of equilibrium shifts in that direction so more is produced. Increasing the temperature in essence means it's harder for a reaction to produce heat. That means that a hotter temperature favours the endothermic reaction. In this case that's the reverse reaction. You could also think of it like this. an endothermic reaction requires energy being put in, so a higher temperature supplies that. A colder temperature will favour the exothermic reaction. In this case, that's the forward reaction. As a rule of thumb, any reaction that involves the breaking down of one reactant, ammonia in this case, that's going to be endothermic. In any reversible reaction, if the forward reaction is exothermic, the reverse reaction must be endothermic, and vice versa. Time for one of the beastiest chemistry topics, C7 is organic. Organic compounds are those that have carbon forming the backbone of the molecules. Crude oil can be found underground and is the result of plankton being buried underwater a long time ago. It consists of mostly hydrocarbons, that is molecules only made up of carbon and hydrogen atoms. Most of these are alkanes, which are chains of single covalently bonded carbon atoms surrounded by hydrogen atoms. As such, there's always twice as many hydrogens as carbons in a molecule, plus another two on the ends. We can therefore write a general formula for alkanes, Cn and then H2n plus 2. All alkane names end with "-ane", whereas the beginning of the name tells you how long the carbon chain length is. Meth is 1, eth is 2, propis 3, butis 4, pentis 5, hexis 6, and so on. Crude oil isn't useful as a mixture of all of these different length alkanes, so we use fractional distillation to separate them out. We heat them so they evaporate and rise up the fractionating column, apart from the very longest ones which stay as liquid, generally used as bitumen on roads. The column gets cooler the higher up the gases rise. As different length alkanes have different boiling points, they condense back into liquid at different heights where they're then collected. Longer alkanes have higher boiling points because there are stronger intermolecular forces between them which more energy is needed to overcome. The shortest alkanes remain as a gas even at the top. We call this fraction LPG or liquid petroleum gases because they're put into pressurised containers afterwards to transport and then turn into liquid. LPG contains a range of chain length alkanes like all of the fractions below. In LPG's case it's up to four carbons long. These are the other fractions you need to know. Petrol is the next longest fraction so it condenses just below LPG that's used in cars of course. Kerosene is used for jet fuel then diesel oil cars and lorries and things and heavy fuel oil is used in large ships. As you can see these alkanes can be burned as fuel. You should remember that complete combustion with oxygen produces carbon dioxide and water. You know about their varying boiling points, but you also need to know that longer fractions are more viscous or have higher viscosity. It's just a sciencey word for more thick and gloopy. And shorter fractions are more flammable, easy to burn. But these different fractions can also be used to make solvents, lubricants, detergents and perhaps most importantly, polymers used for plastics. Polymers can be made from alkenes but not alkanes. An alkene is a hydrocarbon that has a carbon-carbon double bond in. By the way, we can call this C double bond C, a functional group. Because of this double bond, we can also say that this molecule is unsaturated, whereas alkanes are saturated, which essentially means that they're full. That's why you can test for an alkene, which is a colourless liquid, by adding bromine water, which is orange. If the mixture turns colourless, that means that the bromine has bonded to the alkene. For example... It bonds to ethene by breaking that double bond into single bonds used to attach the bromines. The proper name of this product, by the way, is 1,2-dibromoethane, and this is saturated, as you can hopefully see. This can't happen with an alkane, as it's already saturated, of course, so it stays orange. Chlorine and iodine react in a similar way, and water can also saturate an alkene by attaching itself as an H and an OH functional group. We've now made an alcohol, by the way. More on this for Triple in a bit. Now there are two more problems with crude oil. One is that the demand for shorter alkanes is much higher than that for longer ones. Also, there aren't enough alkenes in it for our purposes. Cracking solves both of these problems. That is, breaking apart a longer alkane into a shorter alkane and an alkene. Catalytic cracking requires a temperature of around 550 degrees Celsius and a catalyst called a zeolite. If there's no catalyst, you can just use an even higher temperature of over 800 degrees, which makes sense, doesn't it? This is called steam cracking. Let's take butane and crack it. It can split right down the middle, but there must be the same number of all atoms in the products. That means that yes, we make ethane, but there's not enough hydrogen to make another ethane, so instead it makes ethene as well, the alkene, which of course is then useful for making polymers. It could also split here instead to make methane and propene. Cracking allows us to meet the demands for shorter alkanes for fuels, as well as produce alkenes for making other materials. More on polymerisation for triple in a bit. The rest of organic is just for triple, so skip to chemical analysis if you're doing double. Like we mentioned earlier, an alcohol is an organic compound with an OH functional group. Their names always end with O, so this is ethanol. These can react with oxygen, that is combust to make carbon dioxide, and water if it's complete combustion, and carbon monoxide or carbon and water if it's incomplete combustion, when there's less oxygen available. Reacting ethanol with sodium makes sodium ethoxide and hydrogen. Similarly for propanol and butanol. Just one of those random bits you need to know. Short alcohols like these can mix with water to produce a solution, which gets more difficult as they get longer. When an alcohol is oxidised without combustion, that is with an oxidising agent, it makes a carboxylic acid. That's a molecule with, instead of COH, it's COOH, that's the functional group. It still has the hydroxide, the OH group, but it's not an alcohol anymore. The name of this would be ethanoic acid. We can also get propanoic, butanoic acid, etc. Polymers are super long chain alkanes made up of repeating sections made from monomers. Poly just means lots, mono just means one. For example, lots of ethines, the monomer, can be joined together through addition polymerization to make polyethene or polythene. That's the polymer. These monomers must have a double bond in. Note that even though it makes a long alkane, we still use the name of the alkene it's made from. It's polyethene, not polyethane. As you can see, this happens because the double bond splits so a carbon can bond to the next monomer and so on. Thankfully, we only have to draw the repeating unit with... brackets around it and the bonds coming out with an N on the outside showing that there are lots of these joined together. Condensation polymerization is when we join together two monomers that have two functional groups for example an alcohol and a carboxylic acid. First let's look at the reaction between ethanol and ethanoic acid. These can react to produce ethyl ethanoate. This is an ester. Can you see water must also be produced. Now let's react an alcohol with an OH on both ends and a carboxylic acid. with COOH on both ends too. Now this reaction happens on both ends and we can make a chain of this ester. This would then be a polyester. It doesn't matter what's in between the functional groups. We can sometimes just write R as a shorthand for the stuff in the middle or just a wee box. The process is the same every time. Again, water is chucked out, hence why it's called condensation polymerization. You should remember amino acids from biology. They're the building blocks of proteins. They have two functional groups, an amino group, NH2 and a carboxyl group COOH which we just saw hence why it's called an amino acid. These can be polymerized to make polypeptides joining together different amino acids makes a protein. DNA full name deoxyribonucleic acid is the large molecule that stores genetic code. It's made from two polymers that spiral around each other in a double helix and it's made from four different monomers called nucleotides. Starch is also a natural polymer where the monomer is glucose and cellulose is a polymer that's made from beta glucose and like we've just seen proteins have amino acids as their monomers. C8 now, chemical analysis. How can we tell what chemicals we have in front of us? Obtaining pure substances is very important when it comes to chemistry. One way to tell if a substance is pure or not is by testing to see what its melting point or boiling point is. If it's pure it should be a very specific temperature. A formulation is a mixture that has been specially designed to be useful in a very specific way with very specific quantities of different substances. used to make things like paints, fuels, alloys, fertilisers. Think of George's marvellous medicine as being the ultimate formulation. Chromatography is a way of separating substances in a mixture, for example pigments in inks or drugs in a urine sample. The stationary phase, often special chromatography paper or just filter paper, is what the substances move up with the help of the mobile phase, often just water, which rises up the paper due to capillary action, dragging lighter particles further up the stationary phase. We draw the line at the bottom in pencil so it doesn't move with the solvent, the water, then at the end of the process we measure how far the solvent has moved, and also how far the substance or substances have moved too. And these are both measured from that starting line. We can then calculate an RF value, that stands for retention factor, which is just a ratio of how far a spot has moved compared to the solvent. So that ends up being a number between 0 and 1. We can compare RF values of our spots with known RF values to identify what's in our mixture. We can test for hydrogen by holding a burning splint over the test tube which will produce a squeaky pop. Oxygen will relight a glowing splint. Carbon dioxide will turn lime water cloudy when bubbled through it. Chlorine gas will bleach damp blue litmus paper. That means turn it white. We can test for some metals with flame tests. Lithium will produce a crimson flame, sodium yellow, potassium lilac, calcium orange red and copper green. We can test for other metals in solutions by adding sodium hydroxide. Aluminium, calcium and magnesium in solution will produce a white precipitate. However, the aluminium hydroxide produced will then dissolve if excess sodium hydroxide is added. Copper II ions, that is Cu2 plus ions, form a blue precipitate. Iron II, green precipitate. Iron III, brown. You might have to complete an ionic equation for these. For example, the copper and hydroxide ions making copper hydroxide, and you've got to make sure it's balanced too. Just three quick ones. Carbonates react with acids to make carbon dioxide gas, and we know how to test for that. We test for halide ions, that's halogen ions, by mixing with silver nitrate solution and nitric acid. If chlorine ions are present, silver chloride is made. That's a white precipitate. Silver bromide is cream, and silver iodide is yellow. Finally, sulphate ions will produce a white precipitate when mixed with barium chloride and hydrochloric acid. Of course, All of these are chemical tests we can do in our school labs, but in proper labs with lots of money, they use instrumental methods to determine what substances they have. These instruments are accurate, sensitive and fast. For example, they can do flame emission spectroscopy, flame tests on steroids. The light produced by a flame is passed through a spectroscope, which can identify exactly what wavelengths are being emitted, say on an emission line spectrum, which can then be used to identify these metal ions. Atmospheric chemistry. The composition of gases in the atmosphere has changed over the course of the Earth's history. Of course, records only go so far, so we have to extrapolate to get an idea of what it used to be like. but as per usual historical science can't be tested so it's pretty much just a good guess. To begin with it would have just been a lot of nitrogen and carbon dioxide. This then probably dissolved into the oceans which were themselves probably a result of water vapor from volcanoes condensing. This carbon dioxide could have then been trapped in sediment, rocks and fossil fuels reducing the carbon dioxide in the atmosphere. Algae and plants turn CO2 into oxygen through photosynthesis reducing the levels of CO2 to 0.018% which is what we have today. Water vapour, carbon dioxide and methane absorb longer wavelength radiation and keep the earth warm. Without them we'd freeze. This is the greenhouse effect. CO2 levels have increased since the industrial revolution which some think is responsible for the increase in global temperatures. As it's only responsible for a very small percentage of the greenhouse effect whereas 95% of the greenhouse effect is caused by water vapour I'm not so sure personally. To be fair AQA spec does say that as these are such complex systems that it's incredibly hard to model them. That's why every IPCC model over the last 20 years has been wildly incorrect and any warming has been far lower than predicted. I'm old enough to remember when the term carbon footprint entered the mainstream in the mid-2000s when everybody went mad for it. The idea that everything you do is responsible for carbon dioxide being released into the atmosphere and that we should reduce that or offset it by planting trees, for example. Carbon monoxide is an atmospheric pollutant. It binds to your red blood cells so less oxygen can be transported around your body. It's also odourless and colourless, so it's hard to detect. That can prove fatal. Most fossil fuels release sulphur dioxide when burnt, which causes acid rain. Nitrogen oxide can also be released, which can cause breathing problems. Soot is just particulates of carbon made from incomplete combustion, which can also cause health issues. It's everybody's favourite final topic full of random stuff. Literally, C10 is using resources. We need resources for warmth, shelter, food and transport. Some are natural, like food. wood for building, fuels for burning and materials for making fabrics and clothing. As demands for these increase we're trying to find new materials to use to help meet these. Doing so without compromising future generations abilities to do the same is called sustainability. If you're like me you probably take clean drinking water for granted but many people around the world don't have that. Potable water is what we call water that has low enough levels of salt and microbes that it's safe to drink. In most countries water is taken from a fresh water source so little salt is dissolved in it. is passed through filter beds to remove large insoluble particles, then sterilised to kill microbes, usually using chlorine, but we can also use ozone or UV light. In some countries, there are few or no fresh water sources, so they must get seawater and remove the salt. This is called desalination, which can be done through distillation, but also by using special membranes that employ reverse osmosis. However, both of these require a huge amount of energy. Potable water isn't pure water, of course. In fact, pure or distilled water is dangerous to drink in large amounts as there being nothing dissolved in it water will move into your cells due to osmosis and then become turgid. Going to the toilet creates waste water as do industrial processes. It therefore needs to be treated before being released back into the environment which requires removing organic matter, microbes and harmful chemicals. We can do this with screening and grit removal, sedimentation to produce sludge and effluent, we can then treat them separately. Sludge is the solid stuff that sinks to the bottom which needs to be removed. anaerobic digestion to treat whereas the liquid effluent from the top requires treatment with aerobic respiration. Extracting metals from the earth is a huge industry as we use them for electrical appliances, batteries, for building and more. Most metals can be obtained from their ore after mining by electrolysis or displacement reactions. A couple of new ways of extracting metals are being developed especially for copper as we need a lot of it for say electrical wiring. Phytomining uses the fact that plants absorb minerals from the soil into their roots, grow a crop in an area with copper-rich soil, then burn the plants to be left with copper in the ash. Bioleaching uses bacteria that make leachate solutions that contain metal compounds. And we can get the metal from those. Both of these ways are pretty terrible though, as they yield incredibly small amounts of the metal. An LCA or life cycle assessment is the thought process carried out in order to produce Predict a new product's impact on the environment. You need to consider a few things. Extraction and processing of raw materials. Manufacturing and packaging. Its use over its lifetime. Disposal at the end of its life. Then transportation at each of these stages too. We can reduce our impact by reducing the use of products in general. We can reduce the materials needed to make them, the energy required, and also the waste produced. We can recycle materials to reduce our impact too. Glass and metal can be recycled pretty much infinitely, although energy is required to do this. But the impact on the environment is less than what it would be if we just obtained these raw materials from the earth. Corrosion is when materials are destroyed slowly over time by chemical reactions. For example, iron and steel rust when the iron reacts with oxygen and water. Other metals corrode in a similar fashion like the copper statue of liberty, now green copper oxide on the outside. We just reserve the term rust exclusively for iron. We can coat a metal with a more reactive metal that corrodes before the other. We then call that a sacrificial metal. Zinc is an example. Coating a sheet of another metal with this is called galvanising. Alloys are mixtures of different metals. Bronze is an alloy of copper and tin, brass, copper and zinc. Even gold jewellery isn't usually pure gold, it would be too soft. It's combined with silver, copper and zinc. 24 carat is 100% gold, 18 carat being 75% etc. Steel is an alloy of iron and carbon which makes it stronger than pure iron. If it contains chromium or nickel it's a stainless steel which is more resistant to corrosion. Alloys are usually stronger than pure metals because the different size atoms disrupt the regular lattice, which means the layers cannot slide over each other as easily. Aluminium is used in an alloy when we need a low density. Most glass we use is soda lime glass made from heating sand, sodium carbonate and limestone. Borosilicate glass on the other hand has a higher melting point. Ceramics like pottery and bricks are made from clay which are then heated in a furnace. Composites are materials made from two materials. Usually that involves fibres of one material being binded or bound together with another. An example of this is carbon fibre, very strong yet light. Polymers can be high density or low density. For example, you might see HDPE or LDPE on plastics. They stand for high and low density polyethene. The difference depends on the conditions used when making them. Thermosoftening polymers melt when heated, whereas thermosetting polymers do not melt no matter how hot they get. The difference is that there are these cross links between the polymer chains that are formed when a thermosetting plastic is made. That increases the forces between them holding them together. Like we saw at the start, the harbour process is used to make ammonia, which can be used for fertilisers. Nitrogen can be easily taken from the air, whereas hydrogen can be obtained from electrolysing water. The gases are passed over a catalyst at around 450 degrees Celsius and a pressure of 200 atmospheres. Like we saw with Le Chatelier, a high pressure favours the forward reaction. However, we can't have too low a temperature, otherwise the rate of reaction will be too slow. So that 450 degrees is a compromise. balance yield and rate of reaction. The ammonia produced is removed and the unreacted nitrogen and hydrogen are recycled ready to make more ammonia. Plants need nitrogen to grow which is why we use ammonium fertilizers but they also need phosphorus and potassium. Therefore many fertilizers are NPK fertilizers. The ammonia is first used to make ammonium salts to go in the fertilizer. Potassium chloride and potassium sulfate are obtained by mining as is phosphate rock which needs to be treated with an acid first to produce a salt. before going into the fertilizer. That's it. I hope you found that helpful. Leave a like if you did. Pop any questions or comments below. And hey, after you've done the exam, why don't you come back here and tell us how you found it? We'd love to know. Click on the card to go to the playlist for all six papers. If you need some extra help, follow the link in the description to join our discord. I'll see you in the next video. Good luck.

Any rate is the change in a quantity divided by time. In this case that something can be the quantity of reactant used or product formed. This quantity could be mass or volume of gas that's usually made anyway. They like to stipulate that this technically gives you the mean rate as the rate could be changing over the time you measure but that's true for any measurements over time ever so that's a bit redundant but we'll go with it for now. An experiment on this could be reacting hydrochloric acid and sodium thiosulfate in a conical flask sitting over a piece of paper with a cross on.

As the reaction continues the product form turns the solution cloudy. we say that's increased turbidity. We stop the timer when we can no longer see the cross from above the flask. Repeat this at different temperatures and you should see that the hotter the temperature the less time it takes.

Another potential experiment is measuring the volume of gas produced by using a gas syringe that fills up when connected to the reaction vessel. A graph to show this would have the quantity on the y-axis and time on the x-axis. It's usually a curve that starts off steeply but then levels out or plateaus which shows that the reaction has completed or we can say reached its end point. To find the rate at any time, you draw a tangent at that point. Pro tip, turn the page so you're drawing the tangent horizontally.

That will help you draw it accurately. Then, like the equation says, you can take the change in quantity and divide by time. Up, divided by, across.

The rate of a reaction can be increased by the following. Increasing the concentration of reactants that are in solution, increasing the pressure of gas reactants, and increasing the surface area of solid reactants, that is, crushing into a powder. Now these three all have this effect because the reacting particles collide more frequently. They come across each other more often. Increasing temperature does that too due to the particles moving more quickly.

But there's the added bonus that they also collide with more energy, meaning they're more likely to react when they collide due to activation energy. Remember your energy diagrams from paper one. Finally, adding a catalyst also increases rate as it reduces the activation energy needed.

So particles are more likely to collide successfully and react. Of course, any catalyst is not used up in a reaction, it is not a reactant or product itself. Reversible reactions are pretty self-explanatory, once the products are made they're able to return to their original reactants. The prime example here is the Haber process, hydrogen and nitrogen react to make ammonia which can also break down back into the separate gases again, more on what ammonia is used for later. In a closed system, that is no particles or energy going in or out, both reactions will continually take place.

eventually the quantity of particles on both sides will reach a point at which the rates of both the forward and reverse reaction will be the same. So that means there will be no more overall change in the quantities on both sides. Remember that's not saying that the reaction is stopped per se, it's just that there's no more overall change. That is until a condition is changed which will affect these rates. Le Chatelier's principle states if a system at equilibrium is subjected to a change the system will adjust to counteract that change.

Sounds awfully vague, so let's see what that means in practice. There are a greater number of moles on the left than the right of this reaction, which means that the reactants take up more space. Therefore, if you increase the pressure of all of these gases, we say this favours the forward reaction.

That is, the rate of the forward reaction will increase until equilibrium is once again reached, but that will happen when there's a greater proportion of ammonia than there was before. We could also say that the position of equilibrium is shifted to the right. Reducing the pressure would of course do the opposite by shifting it to the left instead.

Concentration follows the same principle when it comes to solutions by the way. Naturally if you remove molecules from one side of the reaction the position of equilibrium shifts in that direction so more is produced. Increasing the temperature in essence means it's harder for a reaction to produce heat.

That means that a hotter temperature favours the endothermic reaction. In this case that's the reverse reaction. You could also think of it like this.

an endothermic reaction requires energy being put in, so a higher temperature supplies that. A colder temperature will favour the exothermic reaction. In this case, that's the forward reaction. As a rule of thumb, any reaction that involves the breaking down of one reactant, ammonia in this case, that's going to be endothermic.

In any reversible reaction, if the forward reaction is exothermic, the reverse reaction must be endothermic, and vice versa. Time for one of the beastiest chemistry topics, C7 is organic. Organic compounds are those that have carbon forming the backbone of the molecules. Crude oil can be found underground and is the result of plankton being buried underwater a long time ago.

It consists of mostly hydrocarbons, that is molecules only made up of carbon and hydrogen atoms. Most of these are alkanes, which are chains of single covalently bonded carbon atoms surrounded by hydrogen atoms. As such, there's always twice as many hydrogens as carbons in a molecule, plus another two on the ends. We can therefore write a general formula for alkanes, Cn and then H2n plus 2. All alkane names end with "-ane", whereas the beginning of the name tells you how long the carbon chain length is.

Meth is 1, eth is 2, propis 3, butis 4, pentis 5, hexis 6, and so on. Crude oil isn't useful as a mixture of all of these different length alkanes, so we use fractional distillation to separate them out. We heat them so they evaporate and rise up the fractionating column, apart from the very longest ones which stay as liquid, generally used as bitumen on roads.

The column gets cooler the higher up the gases rise. As different length alkanes have different boiling points, they condense back into liquid at different heights where they're then collected. Longer alkanes have higher boiling points because there are stronger intermolecular forces between them which more energy is needed to overcome. The shortest alkanes remain as a gas even at the top.

We call this fraction LPG or liquid petroleum gases because they're put into pressurised containers afterwards to transport and then turn into liquid. LPG contains a range of chain length alkanes like all of the fractions below. In LPG's case it's up to four carbons long. These are the other fractions you need to know.

Petrol is the next longest fraction so it condenses just below LPG that's used in cars of course. Kerosene is used for jet fuel then diesel oil cars and lorries and things and heavy fuel oil is used in large ships. As you can see these alkanes can be burned as fuel. You should remember that complete combustion with oxygen produces carbon dioxide and water. You know about their varying boiling points, but you also need to know that longer fractions are more viscous or have higher viscosity.

It's just a sciencey word for more thick and gloopy. And shorter fractions are more flammable, easy to burn. But these different fractions can also be used to make solvents, lubricants, detergents and perhaps most importantly, polymers used for plastics. Polymers can be made from alkenes but not alkanes.

An alkene is a hydrocarbon that has a carbon-carbon double bond in. By the way, we can call this C double bond C, a functional group. Because of this double bond, we can also say that this molecule is unsaturated, whereas alkanes are saturated, which essentially means that they're full.

That's why you can test for an alkene, which is a colourless liquid, by adding bromine water, which is orange. If the mixture turns colourless, that means that the bromine has bonded to the alkene. For example... It bonds to ethene by breaking that double bond into single bonds used to attach the bromines. The proper name of this product, by the way, is 1,2-dibromoethane, and this is saturated, as you can hopefully see.

This can't happen with an alkane, as it's already saturated, of course, so it stays orange. Chlorine and iodine react in a similar way, and water can also saturate an alkene by attaching itself as an H and an OH functional group. We've now made an alcohol, by the way. More on this for Triple in a bit. Now there are two more problems with crude oil.

One is that the demand for shorter alkanes is much higher than that for longer ones. Also, there aren't enough alkenes in it for our purposes. Cracking solves both of these problems.

That is, breaking apart a longer alkane into a shorter alkane and an alkene. Catalytic cracking requires a temperature of around 550 degrees Celsius and a catalyst called a zeolite. If there's no catalyst, you can just use an even higher temperature of over 800 degrees, which makes sense, doesn't it?

This is called steam cracking. Let's take butane and crack it. It can split right down the middle, but there must be the same number of all atoms in the products. That means that yes, we make ethane, but there's not enough hydrogen to make another ethane, so instead it makes ethene as well, the alkene, which of course is then useful for making polymers. It could also split here instead to make methane and propene.

Cracking allows us to meet the demands for shorter alkanes for fuels, as well as produce alkenes for making other materials. More on polymerisation for triple in a bit. The rest of organic is just for triple, so skip to chemical analysis if you're doing double.

Like we mentioned earlier, an alcohol is an organic compound with an OH functional group. Their names always end with O, so this is ethanol. These can react with oxygen, that is combust to make carbon dioxide, and water if it's complete combustion, and carbon monoxide or carbon and water if it's incomplete combustion, when there's less oxygen available.

Reacting ethanol with sodium makes sodium ethoxide and hydrogen. Similarly for propanol and butanol. Just one of those random bits you need to know. Short alcohols like these can mix with water to produce a solution, which gets more difficult as they get longer.

When an alcohol is oxidised without combustion, that is with an oxidising agent, it makes a carboxylic acid. That's a molecule with, instead of COH, it's COOH, that's the functional group. It still has the hydroxide, the OH group, but it's not an alcohol anymore.

The name of this would be ethanoic acid. We can also get propanoic, butanoic acid, etc. Polymers are super long chain alkanes made up of repeating sections made from monomers. Poly just means lots, mono just means one.

For example, lots of ethines, the monomer, can be joined together through addition polymerization to make polyethene or polythene. That's the polymer. These monomers must have a double bond in.

Note that even though it makes a long alkane, we still use the name of the alkene it's made from. It's polyethene, not polyethane. As you can see, this happens because the double bond splits so a carbon can bond to the next monomer and so on. Thankfully, we only have to draw the repeating unit with... brackets around it and the bonds coming out with an N on the outside showing that there are lots of these joined together.

Condensation polymerization is when we join together two monomers that have two functional groups for example an alcohol and a carboxylic acid. First let's look at the reaction between ethanol and ethanoic acid. These can react to produce ethyl ethanoate.

This is an ester. Can you see water must also be produced. Now let's react an alcohol with an OH on both ends and a carboxylic acid.

with COOH on both ends too. Now this reaction happens on both ends and we can make a chain of this ester. This would then be a polyester.

It doesn't matter what's in between the functional groups. We can sometimes just write R as a shorthand for the stuff in the middle or just a wee box. The process is the same every time.

Again, water is chucked out, hence why it's called condensation polymerization. You should remember amino acids from biology. They're the building blocks of proteins.

They have two functional groups, an amino group, NH2 and a carboxyl group COOH which we just saw hence why it's called an amino acid. These can be polymerized to make polypeptides joining together different amino acids makes a protein. DNA full name deoxyribonucleic acid is the large molecule that stores genetic code. It's made from two polymers that spiral around each other in a double helix and it's made from four different monomers called nucleotides. Starch is also a natural polymer where the monomer is glucose and cellulose is a polymer that's made from beta glucose and like we've just seen proteins have amino acids as their monomers.

C8 now, chemical analysis. How can we tell what chemicals we have in front of us? Obtaining pure substances is very important when it comes to chemistry.

One way to tell if a substance is pure or not is by testing to see what its melting point or boiling point is. If it's pure it should be a very specific temperature. A formulation is a mixture that has been specially designed to be useful in a very specific way with very specific quantities of different substances.

used to make things like paints, fuels, alloys, fertilisers. Think of George's marvellous medicine as being the ultimate formulation. Chromatography is a way of separating substances in a mixture, for example pigments in inks or drugs in a urine sample. The stationary phase, often special chromatography paper or just filter paper, is what the substances move up with the help of the mobile phase, often just water, which rises up the paper due to capillary action, dragging lighter particles further up the stationary phase.

We draw the line at the bottom in pencil so it doesn't move with the solvent, the water, then at the end of the process we measure how far the solvent has moved, and also how far the substance or substances have moved too. And these are both measured from that starting line. We can then calculate an RF value, that stands for retention factor, which is just a ratio of how far a spot has moved compared to the solvent. So that ends up being a number between 0 and 1. We can compare RF values of our spots with known RF values to identify what's in our mixture.

We can test for hydrogen by holding a burning splint over the test tube which will produce a squeaky pop. Oxygen will relight a glowing splint. Carbon dioxide will turn lime water cloudy when bubbled through it. Chlorine gas will bleach damp blue litmus paper.

That means turn it white. We can test for some metals with flame tests. Lithium will produce a crimson flame, sodium yellow, potassium lilac, calcium orange red and copper green. We can test for other metals in solutions by adding sodium hydroxide. Aluminium, calcium and magnesium in solution will produce a white precipitate.

However, the aluminium hydroxide produced will then dissolve if excess sodium hydroxide is added. Copper II ions, that is Cu2 plus ions, form a blue precipitate. Iron II, green precipitate. Iron III, brown. You might have to complete an ionic equation for these.

For example, the copper and hydroxide ions making copper hydroxide, and you've got to make sure it's balanced too. Just three quick ones. Carbonates react with acids to make carbon dioxide gas, and we know how to test for that.

We test for halide ions, that's halogen ions, by mixing with silver nitrate solution and nitric acid. If chlorine ions are present, silver chloride is made. That's a white precipitate. Silver bromide is cream, and silver iodide is yellow. Finally, sulphate ions will produce a white precipitate when mixed with barium chloride and hydrochloric acid.

Of course, All of these are chemical tests we can do in our school labs, but in proper labs with lots of money, they use instrumental methods to determine what substances they have. These instruments are accurate, sensitive and fast. For example, they can do flame emission spectroscopy, flame tests on steroids.

The light produced by a flame is passed through a spectroscope, which can identify exactly what wavelengths are being emitted, say on an emission line spectrum, which can then be used to identify these metal ions. Atmospheric chemistry. The composition of gases in the atmosphere has changed over the course of the Earth's history.

Of course, records only go so far, so we have to extrapolate to get an idea of what it used to be like. but as per usual historical science can't be tested so it's pretty much just a good guess. To begin with it would have just been a lot of nitrogen and carbon dioxide.

This then probably dissolved into the oceans which were themselves probably a result of water vapor from volcanoes condensing. This carbon dioxide could have then been trapped in sediment, rocks and fossil fuels reducing the carbon dioxide in the atmosphere. Algae and plants turn CO2 into oxygen through photosynthesis reducing the levels of CO2 to 0.018% which is what we have today. Water vapour, carbon dioxide and methane absorb longer wavelength radiation and keep the earth warm.

Without them we'd freeze. This is the greenhouse effect. CO2 levels have increased since the industrial revolution which some think is responsible for the increase in global temperatures. As it's only responsible for a very small percentage of the greenhouse effect whereas 95% of the greenhouse effect is caused by water vapour I'm not so sure personally. To be fair AQA spec does say that as these are such complex systems that it's incredibly hard to model them.

That's why every IPCC model over the last 20 years has been wildly incorrect and any warming has been far lower than predicted. I'm old enough to remember when the term carbon footprint entered the mainstream in the mid-2000s when everybody went mad for it. The idea that everything you do is responsible for carbon dioxide being released into the atmosphere and that we should reduce that or offset it by planting trees, for example.

Carbon monoxide is an atmospheric pollutant. It binds to your red blood cells so less oxygen can be transported around your body. It's also odourless and colourless, so it's hard to detect.

That can prove fatal. Most fossil fuels release sulphur dioxide when burnt, which causes acid rain. Nitrogen oxide can also be released, which can cause breathing problems.

Soot is just particulates of carbon made from incomplete combustion, which can also cause health issues. It's everybody's favourite final topic full of random stuff. Literally, C10 is using resources.

We need resources for warmth, shelter, food and transport. Some are natural, like food. wood for building, fuels for burning and materials for making fabrics and clothing.

As demands for these increase we're trying to find new materials to use to help meet these. Doing so without compromising future generations abilities to do the same is called sustainability. If you're like me you probably take clean drinking water for granted but many people around the world don't have that. Potable water is what we call water that has low enough levels of salt and microbes that it's safe to drink. In most countries water is taken from a fresh water source so little salt is dissolved in it.

is passed through filter beds to remove large insoluble particles, then sterilised to kill microbes, usually using chlorine, but we can also use ozone or UV light. In some countries, there are few or no fresh water sources, so they must get seawater and remove the salt. This is called desalination, which can be done through distillation, but also by using special membranes that employ reverse osmosis. However, both of these require a huge amount of energy.

Potable water isn't pure water, of course. In fact, pure or distilled water is dangerous to drink in large amounts as there being nothing dissolved in it water will move into your cells due to osmosis and then become turgid. Going to the toilet creates waste water as do industrial processes. It therefore needs to be treated before being released back into the environment which requires removing organic matter, microbes and harmful chemicals. We can do this with screening and grit removal, sedimentation to produce sludge and effluent, we can then treat them separately.

Sludge is the solid stuff that sinks to the bottom which needs to be removed. anaerobic digestion to treat whereas the liquid effluent from the top requires treatment with aerobic respiration. Extracting metals from the earth is a huge industry as we use them for electrical appliances, batteries, for building and more.

Most metals can be obtained from their ore after mining by electrolysis or displacement reactions. A couple of new ways of extracting metals are being developed especially for copper as we need a lot of it for say electrical wiring. Phytomining uses the fact that plants absorb minerals from the soil into their roots, grow a crop in an area with copper-rich soil, then burn the plants to be left with copper in the ash. Bioleaching uses bacteria that make leachate solutions that contain metal compounds. And we can get the metal from those.

Both of these ways are pretty terrible though, as they yield incredibly small amounts of the metal. An LCA or life cycle assessment is the thought process carried out in order to produce Predict a new product's impact on the environment. You need to consider a few things. Extraction and processing of raw materials. Manufacturing and packaging.

Its use over its lifetime. Disposal at the end of its life. Then transportation at each of these stages too.

We can reduce our impact by reducing the use of products in general. We can reduce the materials needed to make them, the energy required, and also the waste produced. We can recycle materials to reduce our impact too. Glass and metal can be recycled pretty much infinitely, although energy is required to do this.

But the impact on the environment is less than what it would be if we just obtained these raw materials from the earth. Corrosion is when materials are destroyed slowly over time by chemical reactions. For example, iron and steel rust when the iron reacts with oxygen and water.

Other metals corrode in a similar fashion like the copper statue of liberty, now green copper oxide on the outside. We just reserve the term rust exclusively for iron. We can coat a metal with a more reactive metal that corrodes before the other.

We then call that a sacrificial metal. Zinc is an example. Coating a sheet of another metal with this is called galvanising.

Alloys are mixtures of different metals. Bronze is an alloy of copper and tin, brass, copper and zinc. Even gold jewellery isn't usually pure gold, it would be too soft.

It's combined with silver, copper and zinc. 24 carat is 100% gold, 18 carat being 75% etc. Steel is an alloy of iron and carbon which makes it stronger than pure iron.

If it contains chromium or nickel it's a stainless steel which is more resistant to corrosion. Alloys are usually stronger than pure metals because the different size atoms disrupt the regular lattice, which means the layers cannot slide over each other as easily. Aluminium is used in an alloy when we need a low density.

Most glass we use is soda lime glass made from heating sand, sodium carbonate and limestone. Borosilicate glass on the other hand has a higher melting point. Ceramics like pottery and bricks are made from clay which are then heated in a furnace.

Composites are materials made from two materials. Usually that involves fibres of one material being binded or bound together with another. An example of this is carbon fibre, very strong yet light.

Polymers can be high density or low density. For example, you might see HDPE or LDPE on plastics. They stand for high and low density polyethene. The difference depends on the conditions used when making them.

Thermosoftening polymers melt when heated, whereas thermosetting polymers do not melt no matter how hot they get. The difference is that there are these cross links between the polymer chains that are formed when a thermosetting plastic is made. That increases the forces between them holding them together.

Like we saw at the start, the harbour process is used to make ammonia, which can be used for fertilisers. Nitrogen can be easily taken from the air, whereas hydrogen can be obtained from electrolysing water. The gases are passed over a catalyst at around 450 degrees Celsius and a pressure of 200 atmospheres. Like we saw with Le Chatelier, a high pressure favours the forward reaction. However, we can't have too low a temperature, otherwise the rate of reaction will be too slow.

So that 450 degrees is a compromise. balance yield and rate of reaction. The ammonia produced is removed and the unreacted nitrogen and hydrogen are recycled ready to make more ammonia.

Plants need nitrogen to grow which is why we use ammonium fertilizers but they also need phosphorus and potassium. Therefore many fertilizers are NPK fertilizers. The ammonia is first used to make ammonium salts to go in the fertilizer. Potassium chloride and potassium sulfate are obtained by mining as is phosphate rock which needs to be treated with an acid first to produce a salt. before going into the fertilizer.

That's it. I hope you found that helpful. Leave a like if you did. Pop any questions or comments below. And hey, after you've done the exam, why don't you come back here and tell us how you found it?

We'd love to know. Click on the card to go to the playlist for all six papers. If you need some extra help, follow the link in the description to join our discord. I'll see you in the next video.

Good luck.

Transcript for:Overview of AQA Chemistry Paper 2

Transcript for:
Overview of AQA Chemistry Paper 2