Transcript for:
GCSE Chemistry Key Content

hello lovies in this video we're going to be going through everything that you need for your AQA GCSE chemistry paper 2 and this is in a Grade n standard so we're going to go through Point by Point explaining everything that you need now anything sear can marks or you can use the time stamps and the description down below also in the description you'll find link to our Mas class our boot camps and our projected papers for this year where Charlotte is make this videos thinks like what's going to come up and then the video walk through is to the predicted papers where she shows you how to answer the questions so that you can probably show off to the examiners exactly what you [Music] [Applause] know the rate of reaction tells us how quickly reactants are used up or products are made now we can calculate the rate of that reaction using one of two equations we can say that the mean rate of reaction is equal to the quantity of reactant used divided by the time taken or alternatively If instead of measuring the amount of reactant that's used If instead we're using the quantity of product made we can say that the mean rate of reaction equals the quantity of product made divided by time taken now the quantity of the reactant or product made can be measured in a few different ways it can be measured in terms of grams if we're measuring a mass it can be measured in terms of C cubed if we're measuring a volume or we can even measure it as moles now dependent on how we measure the quantity of reactant or product we'll determine what the rate of reaction is measured as so the rate of reaction could either be measured in grams per second in ctim cubed per second or as moles per second however I do want to say that check what your answer line wants because sometimes you'll even see it as grams per minute or centimet cubed per minute or maybe even something different so we have to be aware of what the question want and make sure that we use the correct units for the question however if they don't specify something unusual it will be gram per second ctim Cub per second or moles per second graphs can tell us a lot about the rate of a reaction so if we look at a curve of amount of substance against time if the curve is steep then that tells us that we have a high rate of reaction which means that the reaction is happening quickly however if our curve is comparatively more shallow then this tells us that we have a low rate of reaction and this tells us that our reaction is happening slowly if we want to experimentally determine the rate of reaction we have two different methods first if we're using the mass we can measure the change in mass of our reaction mixture to do this we would use a balance and we would use a stopwatch the stopwatch is very important because that measures the time taken now we'll use this method if a gas gets produced as the mass of our reaction mixture will eventually decrease with time however if we want to measure the volume of gas produced instead then we would use this setup here and we could either use our reaction mixture connected to a syringe or we could connect it to an upturned measuring cylinder we would also always need to have a stopwatch whenever we're working out the rate of anything in science we need a stopwatch to measure our time now this method is perfect if a gas is produced as well this time though we're going to measure the volume of gas produced let's have a look at these experiments in a little bit more detail let's have a look at the method of measuring the change in mass so firstly you put your reaction mixture on a balance you can see here that we have some cotton wall on the top of our conical flask the reason why we use this cotton wall at the top is it will allow gases to escape however it won't allow any other substances to escape so what we're going to see is as this reaction takes place if a gas is produced the mass will decrease we're going to measure the mass of the mixture on the balance and record it at regular time intervals the rate of the reaction can then be determined using rate equals change in mass which we measure using our balance divided by the change in time which we measure using our stopwatch now this particular method because we're using a balance to measure a mass the rate would have the units of grams per second now let's have a look at the method that looks at the volume of gas produced so in this case our reaction mixture is connected either to a gas syringe or to an upside down measuring cylinder as the reaction takes place if a gas gets produced the apparatus of our measuring cylinder or our gas syringe is going to collect the gas we can record the volume of the gas at regular time intervals using our stopwatch to determine those and then finally we can calculate the rate of reaction using the equation that rate equals the volume of the gas produced divided by the change in time and the units in this case will be cm cubed per second because of course we're measuring of volume in this case we're expected to be able to calculate the rate of reaction using graphs so to work out the mean rate of a reaction between two points in time on a graph firstly we're going to use the graph to find the amount of substance at each time next we're going to find the change in the amount then we're going to find the change in the time and finally we can now calculate the mean rate of the reaction it's going to be equal to the change in the amount divided by the change in time so let's put this into practice then let's work out the mean rate between 0 seconds and 30 seconds for this particular graph here first thing that we would need to do is to have a look at the point at zero and then have a look at 30 seconds so that's just here so now that we've done this let's have a look at what the volume of gas is at each of those points and of course what the time is too we can use this to work out the change in the amount so the change in the amount is going to be 60 minus 0 and the change in time is 30 minus 0 now that we know this we can work out what the mean rate of reaction is we can say that the mean rate is going to be equal to 60 / 30 and that simplifies down to give us 2 cm cubed per second make sure that you're always careful of the units by looking at what the axes on the graph are in we might also be asked to use the tangent to work out the rate of reaction at a specific point on a graph now to do this if we want it at a specific time say 30 seconds you would need to start off by drawing a tangent to the curve at that specific time required we would then need to find the gradient of the tangent and the gradient would of course be that mean rate so the mean rate is the change in amount over the change in time it's important that you remember that the tangent is just a straight line that just touches the curve at the point you're being asked to find and of course we also need to remember how to calculate the gradient so once you draw that tangent you're going to draw a little triangle as big a triangle as you can and the gradient will be the change in the Y divided by the change in the X but let's put this into practice this okay let's have a go at working out the rate of reaction at 30 seconds so in order to do this first off we're going to need to take that tangent see I've used a ruler and use a pencil as well in the exam to just touch the curve at 30 seconds now that I've done this I'm going to draw a little triangle out of this and although it's good to just find a nice easy triangle you need to also make sure that it's big the big bger the more accurate your answer so here I can see that my triangle at the bottom it hits at a volume of gas of 20 cm cubed and at a point that I've chosen at the top of it it's 88 cm cubed this means the change in the amount or that change in y is 88 minus 20 now if we look at the base of that triangle that we've made the change in time or the change in x is 50us 0 so now we can go straight in and put this into our calculator so we can see that the rate at 30 seconds is equal to 68 ided 50 and that ends up giving us if we put that into the calculator 1.38 cm cubed per second again make sure that you get your units right by looking at the axis of the graph and there we have it that's how we do it different factors can affect the rate of a reaction and there are five main factors that we need to be able to talk about for this exam firstly we need to know about temperature then pressure concentration surface area and catalysts before we look at all those individual factors let's have a think about Collision Theory because we're going to need to describe how those factors affect the rate of reaction in term terms of something called Collision Theory now Collision theory is what we useed to explain how different factors affect the rate of a reaction Collision theory states that chemical reactions can only occur when reactant particles collide with each other with sufficient energy so there's two key facts there for a reaction to take place we need a collision and that Collision needs to have sufficient energy now when we say sufficient energy we mean that it has at least the minimum amount of energy needed for a reaction to take place and the name for this amount of energy is the activation energy so let's get started with looking at how temperature affects the rate and we're going to explain this in terms of collision Theory well if we increase the temperature those particles will have more energy and therefore they're going to move more quickly as a result of them moving more quickly we're going to have more frequent collisions and because they're going to have more energy there's going to be a higher proportion of successful collisions now those are collisions which exceed the activation energy therefore because we have more frequent collisions and those collisions also have more energy the rate of the reaction will increase if we look at this graph here of amount of substance again against time we can see that when we have a higher temperature the rate is faster we can see that because it's steeper and we make the maximum amount of products quicker than we do at a lower temperature and the graph shows this because it flattens out earlier for a higher temperature than it does for a lower temperature now let's have a look at pressure if we increase the pressure of a system the particles will become more crowded the result of this if they're more crowded a bit like you're on a busier Street compared to a less busy street is there are more frequent collisions you're banging into everyone more and therefore the rate of reaction will increase again if we look at the graph of amount of substance against time we can see the exact same pattern at higher pressures we've got this steeper curve than the lower pressures and it also reaches that maximum amount of substance faster than a lower pressures and we can see that because it plate at an earlier time than at the lower pressure now let's look at concentration concentration and pressure are very similar except concentration is referring to Solutions whereas pressure is really referring to gases well as you can see in these diagrams if you increase the concentration the particles are more crowded and therefore there are more frequent collisions and the rate of reaction ction will again increase now this again you can see on our graph of amount of substance Against Time the exact same pattern again for higher concentrations you can see that we have a steeper curve therefore we've got a faster rate of reaction and it plate at an earlier time than for lower concentrations and this means that we've made our maximum amount of substance earlier than we do at lower concentrations now let's look at that surface area increasing the surface area would mean taking something which maybe is a lump and grinding it down into a small powder a good analogy here for our everyday life would be if you had like a sugar cube versus some powdered sugar if we put the sugar cube in a drink it's going to dissolve much more slowly than our powdered sugar and the reason for that is that we have a bigger surface area when it's a powder versus a lump now the reason for this is if we increase the surface area like we have when we have this powder we increase the number of reactant particles exposed now as a result of that because there's more exposed there's going to be more frequent collisions again and therefore the rate of reaction will increase again here you can see with this graph when we have this greater surface area which actually means smaller particles we have this steeper curve whereas the smaller surface area which would be our lumps has a shallower curve now I also want to mention here and this is our little top tip instead of seeing it referred to a surface area we might see it referred to as the surface area to volume ratio now bigger particles such as our lumps are going to have a smaller surface area to Vol INE ratio than small particles such as powders so make sure you're comfortable with either language another final factor that affects the rate is a catalyst and whereas all these other factors were very similar in how we talked about them catalysts are going to be a little different so catalysts are substances that can speed up the rate of a reaction without actually getting used up they provide an alternative reaction pathway with a lower activation energy remember we said that the activation energy was the minimum amount of en needed for the reaction to take place so if we lower this activation energy more particles will have this energy so this means that we're going to have more successful collisions and therefore the rate of reaction will increase when a catalyst is present now this graph here we need to be able to recognize and we need to be able to sketch really here we've got energy against progress of reaction and you can see here this particular reaction is an exothermic reaction however you could see this for EXO or endothermic reactions the activation energy is the bump that goes up from the reactants reaching a peak before it goes down to the products and that activation energy is the difference between the reactants and that Peak you can see here that the activation energy with the catalyst is lower than the activation energy without a catalyst just like we said we know that Catalyst provide an alternative reaction pathway with a lower activation energy so make sure that you can draw this graph or label one that they give you reversible reactions are shown using this symbol here a reversible reaction is one in which the products can react to form the original reactants so the reactants can make the products but then the products can go back and make the reactants again now an important thing about a reversible rea ction is that we can actually change the direction of some reversible reactions by changing the conditions one example of this is the thermal decomposition of ammonium chloride ammonium chlorides will make ammonia and hydrogen chloride however this is a reversible reaction now the special thing about this is when we heat the ammonium chloride it will break down to ammonia and hydrogen chloride however if we were to call all that reaction mixture the ammonia and the hydrogen chloride would react back together to form ammonium chloride again so that shows here that the conditions can affect the direction of this reaction now taking this a step further if a reversible reaction is endothermic in One Direction it will be exothermic in the opposite direction and importantly equal amounts of energy will be transferred in each Direction so if it took in a certain amount of energy in One Direction when it goes in the other direction it will give out that exact same amount now there's a specific example we need to know here we need to know that hydrated copper sulfate breaks down to anhydrous copper sulfate and water now that process in that direction is an endothermic reaction so it's going to take in heat energy whereas if we go the other way the anhydrous copper sulfate and water can become hydrated copper sulfate and that is an example of an exothermic reaction now that means that when we heat the hydrated copper sulfate we will remove water and that blue hydrated copper sulfate will end up becoming the anhydrous copper sulfate and water water where the anhydrous copper sulfate is white in color so we will actually observe a color change here likewise though if we cool down the conditions here then we would see that the anhydrous copper sulfate and the water would go in the exothermic Direction and make hydrated copper sulfate so we would see the color change from white to Blue so the next thing we need to know about is what is meant by equilibrium we need to know that we have equilibrium when in a reversible reaction forward and the backward reactions are both happening at the same rate now this is assuming of course that there's no Escape of reactants or products so this is only assuming that we have a closed system yeah so make sure that you learn that we have equilibrium when our reversible reaction has forward and backward reactions happening at the same rate so reversible reactions can reach an equilibrium now the position of this equilibrium can be controlled by three different factors a change in the concentration a change in the temperature and a change in pressure one thing that doesn't change the position of equilibrium however is adding a catalyst this has no effect it simply speeds up the rate of reaction now this whole process of changing the position of equilibrium can be very useful for industrial processes where we're trying to make a certain product the reason for this is if we can shift the equilibrium in the position of that product that we desire we're going to be able to make our process more profitable now we need to consider how each of these factors will affect the position of equilibrium and to do this we're going to consider something called l il's principle so lillia's principle states that if a system at equilibrium is subjected to change the system will adjust to counteract that change let's have a look to start with the effect that changing the concentration has on an equilibrium well first thing we need to know is when we increase the concentration of a substance there's just more of it and the whole point of this equilibrium is it wants to get things back to how it was so if we add more of a substance the equilibrium wants to get rid of it so it's going to shift to the other side so if we increase the concentration of a substance the equilibrium will shift to the opposite side of that substance to get rid of it now if we decrease the concentration of a substance the equilibrium will actually shift to the side of that substance the reason being is if there's less of it we need to make more so if we look at this particular reaction this Harbor process and we ask ourselves what will happen if we increase the concentration of nitrogen well if there's more nitrogen the equilibrium wants to get rid of it so it is going to shift towards the right and it's going to make more ammonia so that's how we always want to think about them when we're looking at changing concentration now let's have a look at the effect that changing the temperature has on the position of equal ibrium of course we know that the equilibrium is going to shift to minimize any changes in the temperature however when looking at temperature we need to think is the forward reaction exothermic or endothermic and the question will tell us this now in this case the forward reaction is exothermic in a reversible reaction that means that the backwards reaction is endothermic now if we increase the temperature equilibrium wants to call things back down again so it's going to shift to the endothermic side if we decrease the temperature the equilibrium wants to heat things back up again and so it's going to shift to the exothermic side what's going to happen then if the temperature is increased in the harbor process as we mentioned we know that that forward reaction is exothermic this means that the equilibrium is going to shift to that endothermic direction to decrease the temperature that means that less ammonia will be made if we increase the temperature in the harbor process now let's have a look at the effect that changing the pressure has on an equilibrium when we're looking at this we always need to look at how many gas moles we have on the reactant side and on the product side so here I can see that in the harbor process we have four moles of reactants and two Ms of products now the equilibrium always wants to shift to minimize any changes so if we want to increase the pressure then the equilibrium wants to decrease the pressure now the way that it can do this is to shift to the side with a fewer moles now the reason for this the example I like to think of is imagine you're in a room with some people and the walls have started to close in what you would want to do is to move into a room with less people because it's going to then feel relatively speaking more spacious and that's exactly what this does here so if we increase the pressure the equilibrium will shift to the side with a fewer moles and if we decrease the pressure then the equilibrium will shift to the side with the more moles so what happens if we increase the pressure in the harbor process well as we said we know we have four moles of reactants and two moles of products so the equilibrium is going to shift to the side with a fewer moles which is that product side it's going to shift to the right and we're going to end up making more ammonia [Music] [Music] [Music] crude oil is a finite resource which is found in rocks and is composed of the remains of an ancient biomass that was buried in the mud crude o ends up being a mixture of a large number of different compounds most of which are hydrocarbons hydrocarbon this is a really important definition we need to know is a molecule made up of carbon and hydrogen only make sure you remember that word only because that's critical to get in your marks so two examples of hydrocarbons we need to learn about are alkanes and alkenes a word we're going to see described a lot throughout this topic is homologous Series so we're going to learn about alkanes alenes alcohols and carboxilic acids and all of these are examples of homologous series now homologous series all have the following properties in common they all have the same general formula the molecular formula of successive compounds differs by ch2 they have similar chemical properties and they have a gradual change in their physical properties most of the hydrocarbons found within crude oil are alkanes the homologous series of alkanes has the general formula cnh h2n + 2 so make sure you remember that we need to know the names of the first four members of the alkane homologous Series so these are methane this one has one carbon then we have ethane which has two carbons then we have propane which has three carbons and finally butane which has four carbons we only need to know these first four and notice that for the alkanes all of the names end in a and the beginning is the same too and this carries for all of the different homologous series that we will see so we've got a little top tip of how to remember these if you remember the phrase monkeys eat peanut butter then you will remember the correct order of the me eth prob and but and therefore you'll be able to write down the correct name for the number of carbons that you need so now let's look at this summary so here we've got methane which has the formula CH4 ethane has the formula c2h6 all of these formulas are aying that rule of cnh h2n +2 propane is c3h8 and butane is C4 h10 crude oil is a mixture of different hydrocarbons or different lengths we can separate crude oil into fractions each of these conin molecules with a similar number of carbon atoms and we can do this using a process called fractional distillation now this process is really important because the different fractions can be processed to produce fuels and feed stock for the petrochemical industry so this fractural distillation of crude oil produces many fuels that get used in Modern Life For example petrol and diesel oil and these fractions can also be used to produce materials that are useful for Modern Life such as Sol ANS polymers to make Plastics detergents and lubricants now let us look at this really important process of fractional distillation now the crude door is going to pass into a furnace when it's in this furnace of course it gets heated up and it's going to evaporate it's vaporized by the furnace now this vapor is going to pass on into this fractionating Colum now in this fractionating column because it's being heated from below the bottom is hotter than the top now this vapor is going to rise up the column and because it's cooler at the top the vapor is going to cool down as it rises this separates out these different fractions the boiling point of the substances at the top is lower than at the bottom so when the boiling point of the different hydrocarbon compounds get reached as it travels up this fractionating column the hydrocarbons will condense once this happens these different fractions are going to be collected as you can see from the diagram the liquid petroleum gases will be collected at the top because they're going to have the lowest boiling point so they get collected up the top whereas things like the bmen and the heavy fuel oil will be collected towards the bottom of this column it's important that we know the prop properties of hydrocarbons with relation to the size of the molecule so we need to know that as the molecules get larger the boiling points increase the viscosity also increases but the flammability decreases this applies to both the alkanes and the alkenes so we should be really familiar with these properties combustions of hydrocarbons release energy during this combustion process hydrocarbons become oxidized we need to know that the general formula for the complete combustion of a hydrocarbon is hydrocarbon plus oxygen makes carbon dioxide plus water let's have a look at an example of this we could be asked to show the combustion of methane which is CH4 in this case we'd write CH4 plus oxygen makes CO2 plus H2O now though we need to balance it we can see that there's four hydrogens in the reactants but only two in the products so in order to balance these let's double those h2os now that we've done this we can see that we have two oxygens in the CO2 and two oxygen in the water of course the carbons are already balanced so those are fine in total this means that we have four oxygens we can balance this now by adding a two in front of the O2 because two o2s gives us four oxygen atoms and so that is our balanced equation for the complete combustion of methane apply that process to whatever hydrocarbon you're given during fractional distillation the mixture of hydrocarbons in the crude oil are separated but some of these hydrocarbons end up being much more useful than others the shorter chain hydrocarbon are often used as fuel and as a result there's really a great demand for these shorter chain hydrocarbons when we compare them to the longer chain hydrocarbons this means that we end up having too much of the longer chain hydrocarbons and not enough of the shorter chain ones to meet demand we can solve this problem using cracking cracking is a process which we use to break up longer hydrocarbons into to smaller more useful hydrocarbons so here we've got a little general formula here and this is very very loose because we can see it in lots of different formats all that matters is that we have a longer hydrocarbon which gets broken down to a shorter alkane and an alken and what you're going to see here is this also needs to balance so long as these rules are applied and it balances then it is a valid equation for cracking now we need to know that the longer hydrocarbon has lower demand and is less useful and the whole point of why we're cracking it is because we can make a shorter alkane which can be used as a high demand Fuel and an Aline which we can use to make polymers and we can also use it as a starting material to make other chemicals so with cracking we can use one of two methods we can use catalytic cracking using this method we vaporize the hydrocarbons and then the vapors get passed over a hot Catalyst we can also use steam cracking when we do steam cracking the hydrocarbons get mixed with steam at high temperatures now alkenes are more reactive than alkanes are this means that alkenes can react with bromine water whereas alkanes cannot this is our test for alenes if we add alkenes to bromine water we will observe a color change bromine water is normally orange but when it's mixed together with an alkine the alen will decolorize the bromine water so the bromine water will now become colorless now here's a little top tip which is really important never describe this decolorized bromine water as clear it is not clear it is colorless you can have a color and still be clear so we never want to use the word clear to describe this we either want to describe it as colorless or decolorized alkenes are hydrocarbons that have a double carboncarbon bond within them the homologous series of alkenes have the general formula of cnh2n now alkenes are saturated molecules this means that they have a carbon carbon double bond which in turn means that they have two fewer hydrogen atoms than an alkane would have if it had the same number of carbon atoms now this table here summarizes the names of the first four alkenes and the formulas and the structures of these we can see that Ethan is actually the first of these alkenes not methan and that's because we need to have two carbons to have this CC double bond so we have Ethan which has two carbons so it's formulated c2h4 tropine has three carbons so the formula is C3 H6 see here that we're obeying that general formula of CN h2n buttine has four carbons so buttine has the formula C4 h8 and finally penene is C5 h10 now you can see the structures drawn here remember that every carbon can only have four bonds attached and every hydrogen just one bond this will help you when drawing these structures alkenes have the functional group C double bond C and because of this bond this functional group we can see that alkenes react differently to alkanes and it's this fact that enables us to identify alkenes compared to alkanes so first let's look at one of the reaction that alkenes do the combustion of alkenes now alkenes are more likely to combust via incomplete combustion then alkanes that means that when they do burn they're likely to burn with a smoky flame when alkenes react with hydrogen water and halogens an addition reaction takes place now addition reactions take place where atoms are added to that carbon carbon double bond so we break the double bond and add on new atoms this means that we're going to form some new bonds with the reactant atoms also that carbon carbon double bond will now become a carboncarbon single Bond let's start off by looking at the addition reaction of alkenes with hydrogen so an alken reacts with hydrogen to make an alkane an example of this is the reaction of Ethan with hydrogen H2 to make Ean same and if we have a look now at the actual symbol equation we have C2 H4 + H2 makes c2h6 and we can draw this and see what it actually looks like so here I'm drawing Ethan with its two carbons and it CC double bond that's going to react with hydrogen and what's going to happen is that double bond is going to break open there's now a single bond between the carbon atoms and the carbons are now able to bond to those hydrogen atoms within the hydrogen molecule now let's have a look at the addition reaction of alkenes with water steam in this case an alken plus water makes an alcohol this is an example of a hydration reaction and this reaction is carried out using a temperature of 300° c and a catalyst so an example of this is the reaction of Ethan with water to make ethanol that gives us c2h4 plus H2O makes C2 H5 now let's have a go at writing this reaction showing its structure let's start by writing ethine which has two carbons and that couble c bond we're reacting it with water in its gaseous form and what's going to happen is again that double bond is going to break open leaving us with a c single c bond and the H and the O from the h to O bond to each of those two carbons now let's have a look at the addition reaction of alkenes with a hogen so what we see is an Aline plus a hogen makes a halogeno alane this reaction is the same regardless of the hogen so these reactions can take place with chlorine bromine and iodine so let's look at an example ethine reacts with chlorine to make D chloro eth let's have a look at the structure of this let's start off by drawing out the structure of Ethan which is a c double bond C and we want to add on cl2 now we know that to do this we're going to break open that double bond leaving us with a c single c bond and attaching to each of those two carbons a CL coming from that chlorine molecule alcohols contain the functional group O now the homologous series of alcohols can be represented in the form of something like ch3 o or we can draw out its structure now we also need to know the names of the first four members of the alcohol homologous series now this follows the exact same pattern as all of these other homologous series when we have a one carbon alcohol it's called methanol when we have a two carbon alcohol it's called ethanol three carbon is propanol and four carbon is butanol again we can prompt ourselves with our monkeys eat peanut butter now we'll notice here that when we have an alcohol the name ends in anol so make sure that you learn that that is our ending of these names this table here summarize es the names of the first four alcohols their molecular formula and their structure and we can also see some of their uses so let's run through these methanol can be used as chemical feed stop and it's also added to Industrial ethanol to stop people drinking it because it's toxic ethanol on the other hand is the alcohol used in alcoholic drinks it's also used as a fuel and as a solvent now propenol and butanol can also be used used as both fuels and solvents we need to know a series of different reactions that alcohols can undertake the first one is combustion reactions we need to know that an alcohol plus oxygen makes carbon dioxide and water so in this case we could look at ethanol plus oxygen makes carbon dioxide and water now complete combustion occurs when we have an excess of oxygen if we have a limited supply of oxygen then incomplete combustion will take place instead during incomplete combustion we still make our water that carbon and or carbon monoxide will get made instead of that carbon dioxide we need to know that shorter alcohols will combust more easily and this makes the more efficient fuels our shter alcohols will combust with a blue flame and will release lots of energy the next reaction that we need to know for alcohols is that if an alcohol reacts with sodium we will make sodium alide and hydrogen so if we look at an example here if we had ethanol plus sodium we'd make sodium ethoxide and hydrogen now when we add sodium to an alcohol we will observe bubbles of gas forming or we might call it effervescence and that's due to the hydrogen gas that gets formed in that reaction alcohols get oxidized by combustion however we also need to know that they can also be oxidized using an oxidizing agent alcohols will react with oxidizing agents to form carboxylic acids an example of an oxidizing agent that we use in chemistry is potassium dichromate so this is our general equation here alcohol plus an oxidizing agent makes a carboxilic acid and water water if we look at a specific example if we had ethanol plus an oxidizing agent we would make ethanoic acid plus water looking at the balanced equation here you can see that when it comes to writing an oxidizing agent we just use a square brackets o that's important that we know that that represents our oxidizing agent we also need to know about the solubility of alcohols short chain alcohols such as methanol ethanol and propanol are all soluble in water however as the length of the alcohol chain increases alcohols become less soluble so we need to make sure that we know this trend finally we need to know that we can make ethanol by fermenting glucose ethanol of course is an alcohol it's found in alcoholic drinks like wine and beer and it can also be used as a fuel for vehicles for these reasons it's something that we often want to make industrially we need to know that fermentation uses yeast and anerobic conditions so without oxygen to make ethanol from glucose so the overall equation here is that glucose will be fermented to make ethanol plus carbon dioxide now we need to know that we need the following conditions to carry out fermentation to make ethanol we need sugar or glucose dissolved in water we need to have some yeast we also need anerobic conditions so we need an absence of oxygen and we need temperatures between 25 and 35° C now the reason why these temperatures are so important is because yeast contains enzymes if the temperature was too low and it was very cold then fermentation will happen very slowly to the point it might even stop however if the temperature are too high then we have a different problem the enzymes will denat and this will also stop fermentation so we need to make sure we stay within that sweet spot of 25 to 35° C carboxilic acids contain the functional group Co the homologous series of carboxylic acids can be represented in the form of something like ch3 Co so with that Co H at the end of its formula or using this particular structure which shows a c double bond o and then an O also attached to that carbon we also need to know the names of the first B members of the carboxilic acid homologous Series so the names of the carboxylic acids end with ano acid and they begin with meth eth prob and P just like all the other ones so a one carbon carboxilic acid is called methanoic acid a two carbon carboxylic acid is called ethanoic acid three carbon is propanoic acid and four carbons is butanoic acid this table here perfectly summarizes the first four carboxilic acids together with their molecular formulas and their structures carboxylic acids we know have a pH less than seven when dissolved in water carboxylic acids are weak acids not strong acids and the reason why they're weak acids is because they only partially ionize or dissociate in water now it's important that we know some of the different reactions of carboxilic acids now carboxilic acids actually they're acids aren't they so they will undergo the same reaction as other acids with Metals bases and carbonates so if we had a metal reacting with an acid we'd still make a salt in hydrogen if it was a carboxylic acid if we had a carboxylic acid reacting with a base we would still make a salt and water and if we had a carboxilic acid reacting with a carbonate we'd still make a salt carbon dioxide and water the main difference that we'll see here is that we end up making carboxilate salts when we're using a carboxilic acid for instance if we had sodium reacting with ethanolic acid the salt we would make would be sodium ethanoate finally we need to know that carboxylic acids react with alcohols to form Esters Esters have the functional group Co and the general formula for the formation of an Esther is an alcohol plus a carboxylic acid makes an Esther plus water now the one reaction that they could ask you about is that ethanol plus ethanolic acid makes ethal ethanoate plus water now let me show you what that reaction looks like so let's start off by drawing ethanol remember ethanol has two carbons and it has the O functional group so once we've finished drawing that I'm going to draw ethanoic acid and I'm going to draw it so that the carboxilic acid functional group faces that alcohol all will become clear so again ethanoic acid has two carbons see here that the H from the O and the O from the carboxilic acid can react together to form water now that water gets removed in this reaction and we can Bine these two parts together so this o is going to join together with this cble Bond o and this gives us our ethal ethanoate structure plus the water that got removed in that reaction now Esters like this ethal ethanoate are used as solvents flavorings and perfumes and you'll find that they have a fruity smell alkenes can be used to make polymers using addition polymerization so a couple of examples of addition polymers are polyethene and polypropene as you can see we just stick poly in front of the name of that alkine in an addition polymerization reaction many small small molecules will join together to form a very large molecule that polymer here we can see that reaction taking place so we have ethine here and it will become the polymer polyeth notice here in this diagram we can see that our double bond has broken open and it is now a single bond with two Open Arms now those open arms would be connected to other repeat units okay so it's to show that this just repeats and repeats and repeats and repeats and this is why we call this a repeat unit that little n down here represents a large number of molecules so if we had 100 ethenes then that would be a little 100 to show that we have 100 of these repeat units in a row now The small molecules are called monomers and the large molecules that they form are called polymers now now we'll notice as well that this repeat unit of an addition polymer has the exact same atoms as the monomer that formed it and that's because that polymer was the only product in these reactions this table here shows some examples of addition polymers here we've got the monomer Ethan if we wanted to show the formation of polyethene all we would need to do is open up that double bond open up its arms put the hes above and below those carbons and then do your brackets around it let's do it for propine now propine has three carbons and just the one double bond so here I am drawing it in this particular way and when we have propene forming polypropene again we just open up that double bond open up the arms and put everything else above and below those carbon and then throw in the brackets as well I hope you can notice a pattern here so let's try one that you've not seen before this is chloroethene so here it has and you're not expected to know this it has two h's on the first carbon and an h and a CL on the other but just notice here we can apply the same principles double bond that's in the middle we just open up the arms and we put two h's above and an h and a CL below those carbons and again throw in the brackets at the end condensation polymers are formed using monomers with two different functional groups now these functional groups will end up reacting together and losing a small molecule such as water now this is why we call these reactions condensation reactions so two typical types of molecules that would react together to form condensation polymers include dioles and dicarboxylic acid now all that a diol is is a molecule that has two alcohol groups and a dicarboxylic acid is just a molecule that has two carboxylic acid groups as you can see in these diagrams now we will sometimes see the middle parts of these molecules represented with a simple shape such as a rectangle and the whole point of this is it just simplifies things rather than you at GCSE having to draw these complicated molecules you can just cut out the middle bit and use the shape Now dial and dicarboxylic acids can react together to form polyesters and what will happen is the O group of the Dio will react with the O part of the carboxilic acid group and we will form water see what's happening here we are going to remove the water and this in turn will form this Bond here that is Ester Bond and here you can see we've removed one molecule of water now this is just one reaction we don't yet have a polymer but this reaction would go on and on and on to form a polymer with lots more alternate dial than carboxilic acid dial carboxylic acid repeating and this is what our general equation would look like here we have our dial if we had n of those we could react it with n of the dicarboxylic acid we would make our polyester and we would make 2 N H2O so that would be our general reaction and that is how we make condensation polymers amino acids have two different functional groups as you can see here they have an nh2 group and they also have a carboxilic acid group now amino acids will react together via a condensation reaction to form polypeptides or proteins during a condensation reaction water gets removed and a bond gets formed now one specific type of amino acid is called glycine glycine molecules can react together to form polyglycine a polymer so here this general formula shows this if we had n glycines they would react together via a condensation reaction to form poly Glycine and N Waters now we'll notice there that for every extra monomer added every extra glycine in this case an additional water molecule gets formed now this is one example there are actually many different types of amino acids and different amino acids can all be combined in a chain together to make a protein DNA or deoxy ribonucleic acid is a large molecule which is essential for life now DNA contains genetic instructions these are the codes needed for the development and functioning of all living organisms and viruses DNA molecules consist of two polymer chains which are made up four different monomers called nucleotides arranged in a double helix this table here gives us a great summary of the biological polymers that you need to know about we need to know that DNA is a naturally occurring polymer whose monom are the nucleotides and we need to know that DNA provides the instructions needed for every living organism to stay alive next up we've got proteins we need to know that the polymer of proteins or polypeptides have the monomer of amino acids and proteins have many roles including making enzymes and making hormones next up we've got starch the monomer for starch is a sugar and the role of starch is that it stores energy in Plants finally the last naturally occurring polymer that we need to know about is cellulose cellulose you may remember from biology is used to strengthen cell walls in plant cells the monomer for cellulose just like starch is a sugar [Music] [Music] [Music] [Music] in chemistry we need to understand what is meant by a pure substance so pure substance is a single element or compound which has not been mixed with any other substance now you might find this is a bit different to our everyday language we might use the word pure as we speak about things such as milk may be pure because it doesn't have any additional substances added to it however chemically it is a mixture of different substances is this fat molecules this water all mixed together however in chemistry we park the understanding and we now just think of it as that single element or compound that hasn't been mixed with any other substance so we need to know that pure elements and compounds melt at specific temperatures and we can distinguish between pure substances and impure substances using the following method so we want to measure the melting point pure substances are going to have a sharp very defined melting point for instance water has a melting point of 0° C however impure substances are going to melt over a broader range of temperatures so if you're ever given a range of temperatures for a melting point you know that that substance is an impure substance formulations something that we actually use all the time formulation is a mixture that has been designed as a useful product so examples of formulations include fuels paints medicines Foods fertilizers cleaning agents and Alloys you can see that we have so many uses for these formulations in our day-to-day lives so we need to know how do they get made we need to know that to make a formulation we need to mix together components that have a particular purpose in carefully measured quantities to ensure that the product has the properties required chromatography is a method that can be used to separate mixtures and it can be really useful when we want to attempt to identify certain substances so as you can see in this diagram we often use chromatography paper and a pencil line we put some dyes or whatever substances we're looking to examine along this pencil line and place it into a solvent now chromatography uses two different phases that we'll hear about in the exams that we need to be familiar with so the mobile phase is the solvent which is going to carry the different substances this could be water for example the stationary phase on the other hand is the non-moving phase in this case that could be the chromatography paper so when carrying out this chromatography we can calculate an RF value that will be used to identify unknown substances all different substances will have their own unique RF value so the way that we work out the RF value is we get out our ruler and we measure the distance moved by the substance so that will be from that pencil line up to the point where that dot has moved and then we divide it by the distance moved by the solvent and that again is going to be moving from that line up to the maximum distance that it has moved moved and it should make that clear in the exam where the solvents moveed to so remember we're just going to use our ruler make sure you're consistent with using centimeters or millimeters for both measurements it doesn't matter which one you choose and then pop it into the equation and you'll get the RF value which will always be a number between 0o and one now we need to know that the RF value might change in a different solvent so if we use water one time and say ethanol another time we may get a different RF value so mixtures are going to separate into different spots so here you can see this shows a mixture because we've got two different spots however pure compounds like this one here produce a single spot and that will be true in all of the solvents it will always only produce a single spot if we we ever need to test for hydrogen gas we want to hold a lit splint at the open end of a test tube containing that gas and if hydrogen's present we will hear a squeaky pop sound to test for oxygen gas we want to hold a glowing splint inside a test tube containing a gas you want to test now by glowing splint we mean that it was lit then we blew it out and it's still glowing now if oxygen is present then that glowing splint will relight we need to know how to test for carbon dioxide gas so what we want to do is to Bubble the gas through an aquous solution of sodium hydroxide or more simply we could say that we need to Bubble it through lime water if carbon dioxide is present then the lime water will turn milky or cloudy in color to test for chlorine gas we want to put damp blue litmus paper into the gas and if chlorine was present the litmus paper will be bleached and it will turn white sometimes we might need to identify some metal ions in a solid substance to do this we can use a flame test so the method for this is we want to dip a clean wire Loop into a solid sample that we're trying to test and then once we've done that we're going to pick up the loop and we're going to put put it in a blue flame on a buns and burner now what we're going to do is observe the flame color because what we're going to expect to see here is the flame will change color if certain ions are present now these are the results that we need to know so it's only these five different methal ions that you need to know their flame colors so lithium the li+ ion will give you a Crimson flame sod I na+ gives us a yellow flame potassium k+ gives us a lilac flame calcium or ca2+ it gives us an orange red flame and finally copper which is cu2+ gives us a green flame now occasionally a problem will pop up when trying to identify metal ions so there's a good chance that some samples might have a mixture of different ions within them and as you know with paint and so on if you mix together different colors then you can't see the original colors anymore and so this can mask certain flame colors imagine if we had like an orange red calcium ion as well as a crimson lithium ion the orange red and the Crimson they're going to hide each other and we won't necessarily be able to identify them both so we need to know that that's one of the main problems that can arise during a flame test when we have methyls in a solution instead we can't use a flame test instead we're going to use this sodium hydroxide test so to test for methal ions and solutions we add sodium hydroxide to our solution that we're testing and then if a certain metalion is present we will see a precipitate form and the color of that precipitate will enable us to identify it now here there are six different different metal ions in solution that you need to be able to identify here so as you can see here we've got aluminium and when that reacts with sodium hydroxide we form aluminium hydroxide which is a white precipitate now here you can see this ionic equation and all of these reactions have ionic equations I don't want you to freak out that there's so many different ones instead I want to quickly show you the pattern that we see here all of them involve that metal Ion with its relevant charge and then you plus on as many hydroxide ions so o minus ions as you had that charge so aluminium is aluminium 3+ and then we add three o minuses and then you form Al and in Brackets o and again with that three notice all of the rest of these is is exactly the same so actually you don't need to learn six different reactions here just learn the pattern again here we've got calcium 2 plus plus 2 oh minus makes calcium O2 so just spot that pattern and also notice that the state symbols tell us we have an aquous plus an aquous makes that solid for the precipitate calcium also reacts with sodium hydroxide to form a white precipitate this time of calcium hydroxide magnesium also reacts with sodium hydroxide to form a white precipitate this time of magnesium hydroxide now copper 2 and that Roman numerals tells us the charge of the copper ion is going to react with sodium hydroxide to form a blue copper hydroxide solution ion 2+ reacts with sodium hydroxide to form the green Ion 2 hydroxide solution and ion 3 will react with sodium hydroxide to form the brown ion 3 hydroxide now it's very important that you go away and you learn these different colors that are formed as well as these ionic equations now you would have noticed that aluminium calcium and magnesium all react with sodium hydroxide to form a white precipitate now that's going to cause issues when we're trying to do these tests to identify What ions we have present how will we know if it's aluminium calcium or magnesium well there's one key additional fact here that's going to help us if we add more sodium hydroxide so that we have an excess of sodium hydroxide only the aluminium hydroxide precipitate will dissolve again so that's one way that we could positively identify aluminium hydroxide if we had a little sodium Hydrox side we get a white precipitate form and then if we add more we'll notice that it will disappear and dissolve back into the solution whereas calcium hydroxide and magnesium hydroxide won't to test for carbonate ions we want to react the carbonates with a dilute acid now we should know that when carbonates we react with acid we form carbon dioxide gas now this gas we can bubble through l water and if the carbonate was present and carbon dioxide was formed the lime water will turn milky or cloudy in color and this confirms the presence of carbon dioxide and therefore a carbonate in that original solution we need to know how to test for halide ions and in this exam we only need to know about the CL minus the BR minus and the I minus ions to test for these ions we have to First add nitric acid and then add silver nitrate to our solution now if those haly ions are present we're going to get a different precipitate formed dependent on the halide if chloride ions were present they would react with silver nitrate to form silver chloride this is a white precipitate the ionic equation for this is ag+ aquous which is the silver ions plus CL minus those chloride ions which are aquous and they go on to form agcl solid which is the precipitate now if bromide ions were present they would react to form silver bromide which is a cream precipitate the ionic equation is almost exactly the same we just replace the CL minus with BL minus and agcl becomes agbl and then for the iodide ions iodide will react with silver nitrate to form silver iodide which is a yellow precipitate and the ionic equation here is just AG plus aquous plus IUS aquous makes AGI solid but again with those ionic equations don't think that they're three separate equations that makes things so complicated just notice how similar they are and notice the pattern that you can see forming there and just learn that and in addition to that when looking at these observations notice as you go down the group from chloride to bromide to iodide the color is getting kind of grimier it's going from white to cream to Yellow so just remember that Trend in the colors as well as it will help you get them in the right order to test for sulfate ions and solution we want to add a barium chloride solution and dilute hydrochloric acid now if the sulfate ions are present then a white precipitate will form the ionic equation for this is ba2 plus aquous plus those sulfate ions which are s so42 minus aquous will form barium sulfate baso4 solid now it's that barium sulfate that gives us that white precipitate chical tests can be really really helpful however elements and compounds can also be detected and identified using instrumental methods and there's a lot of advantages of using instrumental methods compared with these chemical tests one is that they're very accurate imagine the test for haly ions you've got a white precipitate or a cream precipitate or a yellow precipitate it could be very reasonable to assume you could misjudge those colors however an instrumental method wouldn't do that in instrumental methods are also very sensitive they can detect even very very small amounts which perhaps our chemical tests couldn't pick up on they're also very rapid we just pop them in the machine and they can immediately identify what we have and those are our three advantages that we need to know the instrumental method that we need to know about in a little bit more detail is flame emission spectroscopy now flame emission spectroscopy is an instrumental meth method used to analyze meals in Solutions so we could use it instead of those sodium hydroxide tests we need to know how flame emission spectroscopy works so to start off a sample is put into a flame so the light given off by this flame is passed through a spectroscope and this spectroscope gives a line spectrum that can be analyzed to identify the metal ions in the solution now we can also use this data to work out the concentrations of the metals in solution 2 so we get extra information here in addition to that identification so make sure that you've got a good idea of how flame emission spectroscopy works you don't need to know too much detail just what I've said here and then you should be able to answer any question that comes up [Music] [Music] [Music] for the past 200 million years the composition of the atmosphere of the Earth has been roughly the same we have about 80% nitrogen about 20% oxygen and small proportions of other gases including carbon dioxide water vapor and the noble gases as well we need to know about how the Earth's atmosphere has evolved so we need to know what the Earth's early atmosphere was like in the first billion years of the earth so we need to know that initially we had a lot of volcanic activity and as these volcanoes erupted they released gases which ended up forming this early atmosphere nitrogen was released by these volcanoes and it ended up building up in the atmosphere water vapor was released by these volcanoes as well but it ended up condensing and formed the oceans the early atmosphere of the Earth was mostly made up of carbon Dio oxide and there was little to no oxygen present we think that back in those first billion years as well as all these other gases there were also small amounts of methane and ammonia present in the early atmosphere now as the oceans formed when that water vapor condensed the carbon dioxide that was present in the atmosphere ended up dissolving in the water and carbonates formed producing sediments under the ocean now this reduced the amount of carbon dioxide in the atmosphere bringing it down and we're now on the way to forming our modern atmosphere over time the carbon dioxide levels came down and the oxygen levels increased now we need to understand why the oxygen levels increased we should understand that plants and algae began to evolve and as they evolved and grew they produced oxygen by photosynthesis now the algae first starting producing oxygen as far back as 2.7 billion years ago so a really really long time ago the algae were their first and over time plants evolved and as the plant started to grow even more oxygen was being put out into the atmosphere because even more photosynthesis could happen now this continued until eventually the oxygen levels had got so high that we could support evolution of animals which of course need a lot of oxygen to respire to grow and to move So eventually it ended up coming to this 20% of oxygen in the atmosphere which we currently have now now that process of photosynthesis of the algae and the plants also had the knock on effect of decreasing the proportion of carbon dioxide in the atmosphere so this is one of the main ways which carbon dioxide levels went down over time other ways that the proportion of carbon dioxide decreased was due to the formation of sedimentary rocks such as Limestone and also the formation of fossil fuels such as coal crude oil and natural gas greenhouse gases are gases that are actually really important to have in our atmosphere without the presence of greenhouse gases the Earth would actually be too cold to support life however the problem arises when there's too many greenhouse gases present when we have too many greenhouse gases in the atmosphere and they're too abundant what will happen is the temperature of the earth will be increased too much now we need to know the names of three greenhouse gases we need to know carbon dioxide methane and water vapor we need to be able to explain how the greenhouse effect works and this is exactly the same reason why in a greenhouse it gets hot on a sunny day or if you're in a car and all the windows are up again it gets really hot in there on a hot day so let's understand why this greenhouse effect happens so we need to know that electromagnetic radiation from the Sun radiates out and passes through the Earth's atmosphere now this electromagnetic radiation that's coming from the sun includes a range of wavelength including some shorter wavelength and some longer wavelength now the Earth is going to absorb most of this radiation that comes through the atmosphere and the Earth is going to get warmed up now this warmer Earth is going to radiate a longer wavelength infrared radiation now some of this radiation can go back into space but some of this infrared radiation will get absorbed by the greenhouse gases in the atmosphere now it's this process here that increases the temperature of the atmosphere human activities have a direct effect on the amount of some of the greenhouse gases that get released into the atmosphere so if we first think about carbon dioxide the amount of carbon dioxide in the atmosphere can get increased by several human activities these include the burning of fossil fuels and vehicles and factories and deforestation now let's think about the amount of methane in the atmosphere this is increased by cattle farming and Patty fields or rice farming so we need to be able to answer the question are humans causing climate change most scientists believe that the human activities causing the surface temperature of the earth to increase now the evidence that they've used to form these beliefs have come from peer-reviewed evidence however climate change is very complex so scientists can't be certain of this despite all these peer reviews we need to consider the fact that maybe we're oversimplifying some of the models that we're using to come to these conclusions we need to consider that people's opinions and speculations may cause biases and also we might have certain biases from certain companies that might commission the research we need to always think about where this information has come from who has paid the money for this research and if they actually have an ulterior motive to come to a certain conclusion we also need to think about the quality of the evidence and also some uncertainties that might arise from measurements that have been taken and other factors as well we need to know what is meant by climate now climate refers to the average temperature and weather Cycles over a long period of time climate is different to weather which is talking about the temperature and the weather now so the climate of Earth has always actually been changing this isn't a new thing the climate of Earth has cycled between periods of extreme cold which are the ice ages that have happened in the past and also warm periods as well now these used to just be naturally occurring phenomenon they could have been caused by things such as volcanic eruptions and changes that are occurring on the sun however when we talk about global warming this is different to climate change when we refer to global warming we're referring to the warming of the climate that has occurred due to human activities over the last 200 years so we're just looking at recent times when we're talking talking about global warming this graph here is a very important one and it shows the relationship between the change in carbon dioxide concentration over the last few hundred years and the temperature here you can see that as the carbon dioxide concentration has increased the general trend is that the temperature has also increased we can see here that there's a strong correlation between the Earth's average temperature and the concentration of carbon dioxide in the atmosphere an increase in the average global temperature is a major cause of climate change we need to know some of the effects of global warming so these include glaciers melting droughts sea levels rising and also the loss of habitats a carbon footprint is the total amount of carbon dioxide and other greenhouse gases emitted over the full lifetime of a product event or service we can reduce the carbon footprint by reducing the emissions of carbon dioxide and methane so if you think of some examples of how we can reduce our carbon footprint this can include using solar power instead of fossil fuels cycling or walking to work or school instead of driving we can fly less and holiday more locally and also planting trees is another great way that we can reduce our carbon footprint the combustion of fuels is a major source of the pollutants within the atmosphere we need to know that fuels may contain carbon hydrogen and also sulfur now when we combust these fuels we can release the following gases into the atmosphere so we might release carbon dioxide water vapor carbon monoxide sulfur dioxide oxides of nitrogen and particulates let's have a look in a bit more detail at the process of complete combustion now complete combustion occurs when a hydrocarbon fuel is combusted in an excess of oxygen and the general equation for complete combustion is fuel plus oxygen makes carbon dioxide and water now an example of this is methane fuel plus oxygen makes carbon dioxide and water we need to make sure that we can write the balanced symbol equation for these equations too so make sure you're familiar with the formula of the alkanes make sure you know the formula of oxygen carbon dioxide and water and you're happy balancing these equations now the great thing about complete combustion is that we release the maximum amount of energy downsides though are that we release carbon dioxide which is a greenhouse gas and water now however let's have a look at incomplete combustion now incomplete combustion occurs when a hydrocarbon fuel is combusted this time in a limited supply of oxygen now this releases much less energy than complete combustion and instead of releasing carbon dioxide you're going to find that carbon monoxide and or partic carbon are going to be produced now whether you produce carbon monoxide and carbon or just carbon monoxide or just carbon or some other combination is going to be dependent on how much oxygen we have available so let's have a look here at the incomplete combustion of ethane in oxygen so here we've got ethane plus oxygen and here we're saying will make carbon monoxide and water now again we need to be able to balance this so make sure you know that the formula for carbon monoxide is co and the formula for particular carbon is just see so we need to know that carbon monoxide is a poisonous gas and what makes it so dangerous is it combined to hemoglobin in the blood and prevent oxygen from binding now this will lead to death now the problem with carbon monoxide which makes it particularly dangerous is that it is a colorless and odorless gas which means it's an invisible silent killer so I'm using this as my opportunity to remind you that if you have a little fire or campfire make sure it is well ventilated don't ever put it in a tent or something like that where it would have poor ventilation because there can be tragic consequences so next up we've got partic carbon now that is the carbon or the so that can get released during incomplete combustion this can be seen as a black smoke coming off and the problem with this is it can worsen asthma and it can also cause global dimming so make sure you know the dangers of carbon monoxide and carbon and the fact that we make less energy also during incomplete combustion we need to know where each of these atmospheric pollutants are made so carbon dioxide is made during the complete combustion of a carbon containing fuel carbon monoxide is made during the ink complete combustion of a carbon containing fuel sulfur dioxide is Major on the combustion of a fossil fuel that contain sulfa impurities oxides of nitrogen such as nitrogen monoxide and nitrogen dioxide are major the oxidation of nitrogen in the air inside a vehicle's engine and carbon particulates or S are major in the incomplete combustion of a carbon containing fuel some fossil fuels contain sulfate impurities now when we combust these fuels we're going to find that that sulfur is also going to get oxidized so we're going to have the reaction take place that says that sulfur plus oxygen makes sulfur dioxide now this sulfur dioxide is going to get released into the atmosphere and what we'll find is that it's going to get further oxidized and it will end up making sulfur trioxide and this is because the sulfur dioxide plus oxygen makes sulfur trioxide now it's this sulfur trioxide that can dissolve in the rain water and when that happens we make dilute sulfuric acid which forms acid rain now acid rain is particularly harmful to aquatic plants and animals because that acidic rain will go into these bodies of water such as lakes and change the pH making it more acidic now this upsets that perfect balance of that ecosystem and it can lead to plants and animals dying another issue with acid rain is it can damage buildings and statues if the buildings and statues are made from rocks such as Limestone which is a carbonate calcium carbonate what will happen is that will react with the acid turning to salt water and carbon dioxide this erosion can lead to damage to these statues and buildings we should know that the atmosphere is made up of Approximately 80% nitrogen and 20% oxygen car engines where combustion is taking place can reach very high temperatures and pressures now this can lead to the nitrogen and the oxygen that are present in the air reacting together to form oxides of nitrogen now in car engines we'll find that the most common oxides of nitrogen that are made are nitrogen monoxide and nitrogen dioxide it is common that you'll see these oxides of nitrogen referred using the general formula nox now these oxides of nitrogen can be dangerous they can cause photochemical smog and breathing difficulties in humans such as asthma so it's important that we minimize the presence of these oxides of nitrogen in the atmosphere this table here shows a summary of the problem with the different atmospheric pollutants carbon monoxide is a toxic or poisonous gas and it is colorless and odorless which makes it hard to detect sulfur dioxide causes acid rain oxides of nitrogen cause respiratory problems in humans like aggravating their asthma and it also causes photochemical smog whereas particulates which is that carbon particulates or S they cause health problems in humans and also Global Demming [Music] [Music] [Music] humans use the Earth's resources for many different things these include food shelter transport and warmth and humans also use natural resources that's supplemented by agriculture farming to provide food fuels clothing and Timber there are also many finite resources from the earth the oceans and the atmosphere that we processed to provide energy and materials now we need to know what a finite resource is and a finite resource is a resource which will eventually run out and a good example of this is fossil fuels so we use up fossil fuels at a faster rate than we can form new fossil fuels this means it will eventually run out and it is a finite resource now chemistry has a really important role in improving industrial and agricultural processes to make sure that we can sustainably develop new products we also need to know what is meant by sustainable development this is a word that gets used in chemistry quite a lot and a lot of people don't really realize what it means sustainable development is a development that meets the need of current Generations so it ensures they get what they need but without compromising the ability of future generations to meet their own needs so if we were just to quickly use up all the fossil fuels because we need energy now and we're not thinking about future people then that would not be sustainable development so make sure you know your definition for sustainable development portable water is water that is safe to drink now for humans portable water must have low levels of dissolved salts and microbes and that's what makes it safe now both waste water and groundwater will need to be treated before they're safe to drink now in the UK most of the potable water gets produced from fresh water whereas in other places potable water is produced from sea water we need to know how we obtain potable water from fresh water well our first step is we need to choose an appropriate source of water once we've done that we're going to pass the water through a series of filter beds the purpose of this is it's going to remove any large objects perhaps like branches and other insoluble molecules finally once we've done this we're going to sterilize the water we'll do this either using UV light chlorine or ozone and the reason for this is it's going to kill any microbes that may be present now let's have a little comparison of the different types of water that there are pure water is composed of water molecules only there's nothing else in it except H2O then if we think about sea water or other salty Waters there are water molecules present of course there's also very high levels of salt and potentially high levels of microbes now if we think about fresh water fresh water of course has water molecules it will likely have low levels of salt but it's going to have potentially high levels of microbes finally if we think about potable water it's going to have water molecules in it it's safe for it to have low levels of salts and also it can have safe levels of microbes within it so it's not going to really be water molecules only it's not pure water necessarily but it needs to have safe levels of salt and microbes to be drinkable in certain places like the UAE freshwater supplies might be limited but there might be an abundance of sea waterer now in these cases we may need to desalinate or remove the salt from the sea water to obtain the potable water now desalination can be carried out using either distillation where we heat up the salt water the water will evaporate and then condense and you've separated the water from the salt or we could use reverse osmosis reverse osmosis involves the use of membranes to separate the salts from the water now the problem with desalination is that these processes require a large amount of energy therefore this is an expensive process and it's only really going to be practical if the this is your only option and if you have a lot of money to spend on these processes large amounts of waste water get produced by urban lifestyles and Industrial processes now this waste water needs to be treated before it can be released back into the environment we need to know that with sewage and agricultural Wastewater we need to remove organic matter and harmful microbes whereas with Industrial Waste Water water which comes from factories we need to remove organic matter and harmful chemicals now when we need to treat sewage we have to go through the following steps firstly we need to do screening and grip removal these processes are going to remove large particles next up we've got to do sedimentation now this process allows the solid sediments to settle to the Bottom now this forms sludge and remaining liquid we call effluent now this sewage sludge that's now separated from the effluent can be treated separately the sewage sludge will get anerobic digested so without oxygen by specific anerobic bacteria this forms biogas which we can then use as a fuel and at the same time of course we've broken down that sewage sludge now the air fluent on the other hand is treated with aerobic bacteria so bacteria that will respire using oxygen this breaks down the effluent we will then remove the bacteria and the water is now safe enough to release back into the environment the availability of metal ores in the Earth are limited this means that scientists have to come up with new methods of extracting the metals from lower grade ores so they've got two me methods that they use for this they've got bile leaching and phyto Mining or phyto extraction so let's have a look at bioleaching first what is bioleaching bioleaching is using bacteria to produce acidic leate Solutions which contain metal compounds now once we obtain this metal compound we can process it to extract the metals now let's have a look at phyto mining so phyto mining is using plants to absorb metal compounds so this process of phyto extraction involves growing plants in a soil which contains that low grade oril then as the plants grow they're going to absorb the metalions through their Roots as a result they're going to accumulate the metal iions within their cells so as they grow and grow and get bigger we will eventually Harvest them and then burn them now when we burn them we're going to have some ash left over and that Ash is going to contain the metal compounds that we can process and extract the metal from we need to make sure we can compare the processes of bile leaching and F Mining and know what the advantages and disadvantages of them both are so bile leaching has a great advantage of not requiring any high temperatures however it does produce some toxic substances such as furic acid which can be harmful for the environment vitam mining on the other hand is very useful because it can conserve highgrade ores and it reduces the need for Mining and it also reduces the need to dispose of rock waste however some disadvantages of it is that it's quite slow because of course we need to nurture these plants grow them to a good size before we can then burn them and extract the metal life cycle assess assments are assessments that can be carried out to find the environmental impact of a product such as a paper cup a service or an event and life cycle assessments have four different stages so we want to look at the extraction and processing of the raw materials we need to have a look at the manufacturing and packaging process we need to have a look at the use and operation of this product during its lifetime and we also need to look at how it gets disposed of at the end of its useful life if it is indeed a product so each of these stages our life cycle assessments are going to have a look at what raw materials are used this can include water the amount of energy used along the way and what waste substances have been released into the environment many materials including Metals glass clay Ceramics PL Plastics they're all made from limited raw materials which means that they can eventually run out now obtaining the raw materials from the Earth by Mining and quarrying is problematic because it uses a lot of energy and it can also damage the environment so for these reasons it's really important that we find ways to reduce the use to reuse and to recycle materials now let's think about glass glass and metals and how we can reduce the use of resources for those well with glass we can always recycle it when we recycle glass the glass gets crushed and melted so that we can then reform it into different products with glass we can also reuse it of course if we had a glass bottle or a glass jar we could reuse it and not just throw it away after one use and metals as well we can of course recycle those as well and we would do this by melting them and then recasting them or reforming them into different products metals can oxidize in air and this is because the metal reacts with the oxygen that's of course present in the air to form metal oxides and we can see it happening when we see a formation of a dull layer on top of a metal this dull layer is actually that metal oxide an example of this is when sodium reacts with oxygen to form sodium oxide as we can see here that metal has reacted and oxidized in the air to form sodium oxide which would appear to be a dull layer on That Metal now not all metals will oxidize it does depend on how reactive the metal is for instance gold A Very unreactive Metal won't oxidize so this brings us to corrosion what is corrosion well corrosion is the process when a metal continues to oxidize and it becomes weaker over time now an example of corrosion that we're both familiar with is the process of rusting now this happens when iron or steel reacts with both oxygen and water now this process of rusting can be represented using this equation so ion plus Oxygen Plus water makes hydrated ion 3 oxide it's important that we remember those little Roman numerals don't miss those out and that is what the orange brown substance of rust actually is that is its chemical name hydrated ion 3 oxide so we can investigate these factors that affect corrosion if we have a look at these three different test tubes we can see that test tube a has an iron nail just sitting in some water we can see that test tube B has the same thing it's got an iron nail sitting in boiled water however it's coated with a layer of oil and in test tube C we have an iron nail it's not in water but it is sitting in some calcium chloride what we will observe over time is that only the nail in test tube a will Rust this is because in test tube a we have both air and water present however in test tube B that oil removes the air it stops the oxygen getting through to that nail and in test tube C we have the presence of that desicant calcium chloride which removes water now this shows us that we need both of these to be present not just one of them for rusting to occur now it's important that we think about how we can prevent rusting because rust of course damages materials so if we think about what we need for rust to take place we need oxygen well a great way to stop rusting happen then is to remove the oxygen we could do this by using a barrier method such as painting or we could store the metal in an unreactive gas such as nitrogen now for rust to take place we also need water so another way that we could prevent rusting is by removing the water now again we could use a barrier method such as painting that metal or we could store the metal in a desin this is a substance such as calcium chloride now you might be wondering what this is but I can assure you you've got some everyday experience of this you might know when you open up a shoe box for instance you get that little white packet which says do not eat and that is the desicant that is there to prevent moisture building up and potentially molding happen probably isn't there to prevent rusting in that case but it's the same substance finally we could use sacrificial protection which is putting the metal in contact with a more reactive metal let's have a look now at each of these in a bit more detail there are several different physical barrier methods that we can use we can do painting Coating in oil coating with plastic and electroplating and this applies to the oxidation of all of the different Metals particularly focusing though on rusting of iron or steel if we look at aluminium though aluminium is quite a special metal because it reacts with oxygen and ends up forming a thin layer of aluminium oxide well this acts as its own physical barrier and it protects it from corrosion sacrificial protection is a good alternative method of preventing rusting the way it works is we put iron or Steel in contact with a more reactive metal such as zinc and this prevents rusting the way that this works is the more reactive metal will oxidize instead of the ion it sacrifices itself and we can say that the ion is Galvanized with zinc the good thing about this is we can replace the more reactive metal for instance that zinc as it corrodes and that doesn't affect the iron most metals that we use in everyday use are actually Alloys we need to know a few specific examples for this exam so we need to know that brass is made up of copper and zinc we need to know that it's got some really important properties such as the fact that it's resistant to corrosion and malleable now these properties make it really useful for lots of jobs for instance pins in electrical plugs and musical instruments now bronze on the other hand that is composed of copper and Tin bronze is also resistant to corrosion and we'll often see statues and coins made from bronze now gold for jewelry actually isn't just pure gold well rarely it is anyway 24 garat gold would be 100% gold but anything lower than that such as 18 karat gold it's actually a mixture an alloy of gold silver copper and zinc in varying degrees now gold for jewelry is stronger than pure gold and it's resistant to corrosion and it is shiny all of these things make them great for using for jewelry now we use iron to make steel however we get different types of Steel we get high carbon steel low carbon steel and stainless steel now these different Steels are iron alloyed with different amounts of different elements let's have a look at high carbon seal high carbon seal is composed of iron and 1 to 2% carbon it has the properties that make it strong and brittle which makes it really useful for cutting tools low carbon steel on the other hand as the name sort of suggests is iron and less than 1% carbon now low carbon steel is easy to shape and it is soft this makes it great for using to make car body parts now stainless steel is iron alloyed with chromium and nickel it's hard and it resists corrosion which makes it really useful for things such as Cutlery now we can also make aluminium Alloys as well and there's many many different types of aluminium alloy we don't need to know about any specific aluminium Alloys however we do need to know that generally speaking aluminum Alloys are low density and that makes them useful for certain purposes such as making aircraft parts we need to know about two types of Ceramics glass Ceramics and Clay Ceramics clay Ceramics are used to make bricks and pottery these are made by shaping wet clay and then heating it in a furnace this causes Crystal to form and join together now clay Ceramics a brittle hard and resistant to corrosion so now let's think about glass Ceramics the main type of glass used is sodal glass however sometimes Boris silica glass is used instead they have different uses these different uses come from the fact that Boris silic glass has a much higher melting point than soda line glass that means that we might want to use Boris silic glass for certain purposes that means it's going to get hot examples of this include laboratory glass glass wear and oven glass wear whereas sodine glass we're just going to use for everyday glass objects like the glasses that we drink out of now soda lime glass we make using a mixture of sand sodium carbonate and Limestone heated together and that gives us this brittle transparent sod lime glass or a silica glass on the other hand is made when we heat sand with Boron trioxide that's what gives us that characteristic high melting point in this topic we need to know the difference between low density polyethene and high density polyethene or low density polyethene is formed when addition polymerization of ethine is carried out under high pressure and with a small amount of oxygen present as a result of these special conditions we make branched polymer chains now these Branch chains cannot pack together and this gives us our low density polye now on the other hand we've got high density polyethene and we make this when we do the addition polymerization of Ethan but under 50° C with a catalyst present using this method we make straight polymer chains and these straight chains comp pack together very closely making it high density we need to be able to compare the properties and uses of low density polyethene and high density polyeth so low density polyeth or ldp is flexible and unreactive that makes it really useful for things such as plastic carrier bags now high density polyethene or hdp is strong it's flexible and it's resistant to chattering that makes it really useful for making plastic pipes and Bottles we also need to know the difference between the thermosoftening polymers and Theros setting polymers we need to know that thermosoftening polymer do not have cross links between the different polymer chains and as a result they will melt when they are heated the M setting polymers on the other hand have strong calent cross links between the polymer chains and because of these strong calent cross links they do not melt when they're heated Composites are made of two materials a main material called a matrix and fibers or fragments of other materials that we add to to this Matrix we call these materials reinforcements everyday examples of Composites include plywood and concrete we need to know about the harbor process in the harbor process nitrogen and hydrogen gases gets pumped into the system now in this system we're going to ramp up the pressure to 200 atmospheres the temperat is going to get increased to 450° C and these gases of night nitrogen and hydrogen are going to be passed over an ion Catalyst now the reaction mixture is going to get cooled the reason for this is that as ammonia gets formed it will be a gas to remove it we want to condense it back down to a liquid so that we can open up a tap and drain it away so now that we've done that and we've removed the ammonia that we've made we're going to recycle any leftover nitrogen and hydrogen to summarize the harbor process we need to make sure that we know these key facts so nitrogen plus hydrogen makes ammonia and the balanced chemical equation for this is N2 Gus plus 3 H2 Gus goes to make with a reversible Arrow 2 NH3 gasius we need to make sure that we know these three conditions for the harbor process we need to know that we need an iron Catalyst 450° C temperature and 200 atmosphere pressure we also need to know where we're getting the raw materials of nitrogen and hydrogen from nitrogen is coming from the air and hydrogen is coming from natural gas now in Industry we have to think of a lot of factors when deciding what conditions to use we need to think about theost cost of energy and the availability of raw materials we need to have a think about the conditions that are needed to get that right balance between getting a good yield also having a good rate of reaction now this is really important because it might seem obvious that we want to get the highest yield however we don't want to get that highest yield if it's going to be so slow it takes thousands of years to get that maximum yield we need to weigh this up so looking at the harbor process and using what we've just said we know to get a maximum yield of ammonia we need low temperatures so that it shifts in that forward exothermic Direction and high pressures so it shifts to that side with a fewer moles however if we break these down we know that low temperatures actually slow down the rate of that reaction a lot so we need to compromise and use a temperature somewhere in the middle so we use 450° C so that we have a fast enough reaction and enough yield now we know that high pressures is good for the har process now that works that well because we know higher pressures increases the rate of reaction however High pressures can be quite dangerous so we're going to slightly lower the pressure to 200 atmospheres we also add an iron Catalyst during the haror process and that's because this will increase the rate of reaction some of the substances needed to make fertilizers get mined from the earth so pottassium chloride is one of these substances this can be used as a fertilizer straight away after mining because it contains these soluble potassium ions now potassium sulfate is also something that can be used as a fertilizer immediately after mining and this is again because it contains those soluble potassium ions then finally we have potassium rot now this is insoluble therefore we can't use it as a fertilizer immediately after mining it we need to process it so that we can use it as a fertilizer now there's three reactions that this phosphate Rock can go through to make it into something that can be used as a fertilizer and we need to know these three reactions so the first reaction is the phosphate bro can be reacted with nitric acid so when this happens we end up making calcium nitrate and phosphoric acid the phosphoric acid can then be neutralized by ammonia to make ammonium phosphate this can be used as a fertilizer then we can take the phosphate Rock and we can react it with sulfuric acid this makes single super phosphate which is actually calcium phosphate and calcium sulfate finally that phosphate Rock we can react it with phosphoric acid by doing this we make triple super phosphate which is simply just calcium phosphate so those are our three reactions that we can put the phosphate Rock through to make something that we can use as a fertilizer we need to be able to compare the industrial and laboratory methods of producing fertilizes this table below summarizes everything we need to know about these processes and how we can compare them so the industrial production of NPK fertilizers is a continuous process we're continually making these fertilizers if we compare this to the laboratory methods this is just a batch process we might decide that today we want to make a certain type of fertilizer so we set it up to make a batch of that next up industrial processes is a very large scale production we're trying to make this on enormous scales whereas in the lab maybe we're just making it for ourselves in a small scale production industrially the production of these mpk fertilizers is an automatic process so that means that the machinery and computers will be used to minimize the labor and running costs everything happens on a little process that is automated however in the lab it's very labor intensive there's going to be someone there doing every step of the way and therefore has high running costs industrial processes have a very fast production speed due to all these automations whereas in the lab it's very slow finally industrially reactants get made from the raw materials because this has been done on such a large scale we can make everything from the raw materials which in the end makes it much more cost effective however in the lab we don't do this we instead purchase the reactants from A supplier so that's our general comparison and this is true throughout chemistry of things made industrially versus in the lab and in an everyday example we can imagine this like you're at the mcfit factory making biscuits on an enormous scale making millions and millions of biscuits a day vers is in a little Home Bakery where we're just making some little cookies and cakes to order it's a completely different process and you can appreciate different differences in the speed the Automation and so on hopefully that will help you relate this to real life now ammonium sulfate is another salt that can be used as a fertilizer we can make this in the lab using the following reaction so ammonia plus sulfuric acid makes ammonium sulfate now in this case because both the ammonia and the sulfuric acid are soluble in order to make ammonium sulfate we must carry out a titration now this process in the lab is a batch process which means that we're just making small amounts of ammonium sulfate at a time and after each process we'll have to clean out all of our apparatus and start again we need to be able to describe an experiment to make this ammonium sulfate in the lab so the first step we're going to take is we're going to put some dilute sulfuric acid into a chronical flas we're then going to add a few drops of methyl orange indicator we'll then add some dilute ammonia drop by drop using a burettes and stir between each drop we're going to continue adding ammonia until eventually we get a color change from red to Yellow we're going to add a few more drops of dilute ammonia solution this is to make sure that this has fully reacted and we're not going to worry about there being excess of ammonia because it will just evaporate off we're then going to pour the mixture into an evaporating Basin and then we're going to heat it using a water barall the reason for doing this is to start the evaporation of some of this water that's in the solution and of course to remove any of that excess ammonia now before all the water evaporates we're going to remove this from the Heat and we're going to leave it until crystals begin to form and at that point we're going to pour away any excess water and then we're going to leave it crystallize in a warm oven now we also make ammonium sulfate in Industry as well on a very very large scale now when making ammonium sulfate in Industry the reactants of ammonia and sulfuric acid are actually made from their raw materials industry uses a continuous process which means that we're never shutting off the machine we're continually making this ammonium sulfate and continually putting in new reactants to then be able to make even more so this flow chart here shows how we make this we can see we're making the nitrogen from the raw material of air hydrogen you can see we get from the raw materials of natural gas and water and the nitrogen and the hydrogen we used to make that ammonia that's needed to make the ammonium sulfate now the sulfuric acid on the other hand that we need we make via making sulfur trioxide so we use sulfur and air to make our sulfur trioxide and then react that with some more water to make our sulfuric acid once we've got that ammonia and sulfuric acid we finish off by making our ammonium sulfate ouch this is why in some videos I explain scratches [Music]