[Music] hello and welcome to this revision video this is for AQA alkanes my name is Chris Harrison from Alawis tutors calm and basically we're just going to go through the just a quick overview of the topic of alkanes just to make sure that you've covered the the topic reasonably well like this it is just an overview you do need to practice obviously using your I'm using your past papers and also the the PowerPoint that we're going to use them here and you can purchase it as well so you can use it for your revision and which which could be pretty useful you print it out and annotated add notes etc so then we're gonna you can get access to this on the link in the description box just below the video so if you have a look at the link click on it and then you'll be able to get a hold of the video like I see in this video is specific to the AQA specification and there's the specific point that was taken from the ATR a specification that links in with this PowerPoint okay so let's make a start alkanes okay so they have a general formula cnh2n plus two where obviously n is the number of carbons these are saturated that means they got loads and those two hydrogens as no double bonds in these molecules okay so they are basically hydrocarbons they contain hydrogen and carbon only makes it a little bit obvious and they're saturated each carbon bond is bonded four times no double bonds in here and here's some examples you got methane ch4 ethane c2h6 and and then you got propane there which is four three carbons so and you've got cycloalkanes as well which are a little bit different they actually have the same general formula as an alkene with a double bond with one double bond which is cnh2n they are still a cycle alkane though because they don't have any double bonds they are still our pins but as long as you're aware of that that sort of Quentin nervously these are functional group isomers are Keynes and and they are locus here they're still saturated so they don't have that alkene group okay so um right so that's basically what an alkene is and they make really good fuels that you can burn them which will you'll find out in a minute okay so fractional distillation okay so we need to know obviously these are the kind of practical technique of this so alkanes are found in crude oil okay which is a mixture of different lengths hydrocarbons so crude oil obviously the stuff you dig out from the ground it's got loads and loads of different hydrocarbons and they're all different then and we're going to use a fractional distillation column to separate this so what happens first is the crude oil is vaporized so we heat it up to about 350 degree Celsius and it turns into a gas and this is obviously in the in this bit here and I'm sure the furnace will then heat that up and then the vaporized oil enters the columns is going in through here and and Rises through the trays the longest hydrocarbons don't vaporize and they run to the bottom so your longest hydrocarbons run down into the here and it collecting the slurry this is this bit here where is your ones which are gases because they've been heated remember we'll start to rise up the column okay so now this is really really important because and as we've got to be able to separate these different hydrocarbon lengths and basically the column has a temperature gradient that means as we go up towards the top of the column it's cooler and towards the bottom of the column it's warmer and actually what we get is the vapor rises when it rises it condenses at these different temperatures and then this is because the chain length is different in the in the hydrocarbons that way that we're vaporizing so basically your shorter chains come off at the top they've got the lowest boiling point actually they're still gases at this point where's your longer chain ones like down here will condense to a liquid Maeby's at a lower at a higher temperature and so they would collect on these trays here okay and basically you draw up these fractions you get the fractions that come off that's what I call it fractional distillation and so the shortlist hydrocarbon Lakers they won't even condense these gases at 20 degrees it's about room temperature just under room temperature so these come off at the top of the column okay you can see your different lens hydrocarbons here so 40-plus carbons you look at it about and you're you're lubricating oil in paraffin wax asphalt which is just tarmac and then your gas is obviously meet in beauty anything this these are one to four carbons petrol comes off here and diesel oil is what you would use in fuel oil is what you're using ships okay see they're really heavy oil yeah so the fractions can be used in loads of different ways like I say so gas is used in LPG liquefied petroleum gas stands for and stove gas petrol opportu used in cars kerosene is using jet fuel using heating as well diesel oil use this to fuel a diesel trains and so they need like a heavy one fuel oil is used in ships and power stations are much much higher energy in these and bitumen and which is used or asphalt which is used in roofing and tarmac so this is much much thicker okay air cracking right this is really important in the petrochemicals industry what you get when you dig your oil out of the ground you might find you have lots of heavy fractions of your long-chain fractions but maybe these things are not as popular as your short chain fractions when I say popular I mean they're in lower demand so we're looking for higher demand fractions and luckily we've got a longer chain hydrocarbon we can crack these into more valuable lighter fractions so like say it produces a variety of heavier demand fractions which are kind of lower demand and each fraction varies obviously it is kind of a bit random in some respects you don't know what exactly what you're getting from under the ground so heavier fractions like you say like fuel oil are in lower demands than your life fractions which are petrol leaves a lot more valuable we'd take the heavier ones and we can crack them and basically it just means breaking them into shorter hydrocarbon chains which are more valuable so here's an example of an equation so got dodecane which is c12 h six so that is your long 12 carbon chain that can be broken down into decane and Ethan notice reduce an alkene and alkyne okay you don't produce to our kids so and bases are two types of cracking we have thermal cracking we have catalytic cracking and obviously we need to know and the two different types ok so there's like a thermal cracking first now as the name suggests opps we're going to be using heat so we use a high temperature and pressure for thermal cracking thousand degrees Celsius and 70 atmospheres of pressure in particular and basically the products of thermal cracking are mainly alkenes now it's not so much of a bad thing and because actually these alkenes can be used to make polymers which plastics so for example protein is used to make polypropylene the other type catalytic cracking and if type cracking so here's catalytic cracking and again as the name suggests we're using a catalyst now the difference for this one because we're using a catalyst the temperature is still high but it's not as high as thermal cracking but the pressure is lower okay so we use a zeolite catalyst and the zeolite cast is like a honeycomb structure racially this helps to lower the temperature needed and then have products of catalytic cracking are mainly aromatic hydrocarbons useful in fuels for vehicles okay so that's pretty important and our amount of compounds contain benzene rings which is six carbons in a ring with a delocalized electron system so like I say these things are aromatics which are like benzene's let me say a little benzene rings and but these are really useful and fuels they are actually carcinogenic so you have to be careful with them as are and if we use a zeolite catalyst this base is low temperature and the pressure needed so it's a lower cost and it speeds the reaction up so Khalid Krakens menus for petrels making petrels virbull cracking is pretty good if you're going to make alkenes to make plastics okay let's look at combustion of Arc in such alkanes as we know are used as fuels so alkanes they burn an oxygen completely we get a which means you have a plentiful supply of if on carbon dioxide and water so these are your combustion products and basically they're good fuels and they burn readily they produce lots of energy and that's exactly what you want in the fuel and the use of power vehicles obviously use petrol and diesel and we can make electricity as well so some electricity is made using gas burning air gas or oil power stations as well obviously we can get coal sup yeah so we're going to complete the you may be asked sorry to complete a reaction or an equation to show the complete combustion of a reaction in this case we're going to use butane and all you have to do is just make sure however many carbons you've got here you must have the same number of molecules of carbon dioxide because the only place where the carbon comes from and then if you look at your hydrogen's here just put obviously we've got 10 hydrogens so we need 5 hich - oh and then then what you do want to balance these then you balance your oxygens to make sure it balances but you always produce carbon dioxide and water in these reactions ok incomplete combustion so this is basically when we get an alkane and we burn in limited supply of oxygen now the problem with these is we produce in multitude of different products carbon monoxide and suits are just two of them and obviously these are not very good for your health so and just to show you two examples of these reactions and incomplete combustion we can burn it and we can produce carbon monoxide so the top equation there so is the incomplete combustion of carbon monoxide of a fuel to produce carbon monoxide so we still produce water which is fine sometimes we can get a reaction where we produce carbon monoxide and a bit of carbon dioxide this is this reaction is just shown you and how that would fit as well and now common oxides poisonous bond to hemoglobin in your blood and this prevents oxygen from bonding now this isn't obviously very good can you want the option to be carried by the red blood cells of carbon monoxide sitting there your so you can have an oxygen deficiency and and you can remove that carbon oxide by using a catalytic converter and they put these in the car and it basically reacts for carbon monoxide the oxygen oxidizes it effectively and produces carbon dioxide which is lat armful humans you can also produce such x8 and soot is just carbon just pure carbon so here's the reaction showing that so this is basically again we just got beauty in here burning it to produce carbon and five lots of water as well you can see here we've got really very little oxygen compared to and meeting use them and Sir Thomas Lee makes things dirty okay so it causes breathing problems makes and buildings dirty clogs of engines because these particulates get stuck in the engine you have filters and a car to help try to remove or stop this sub from causing too many problems okay right and so on the topic of burning fuels obviously will burn a fuel either more mainly completely obviously we do produce complete combustion and it's very rare to get a hundred percent complete but we we can get reactions richer and produce large amounts of this carbon dioxide and this obviously needs to global warming and so burning fossil fuels produces carbon dioxide it's a greenhouse gas and and these basically work by absorbing infrared radiation from the Sun and and which is obviously heat and heat from the Sun and but what does the emit some of this radiation back into the earth and we call this a greenhouse effect it's like a warming effect and this is basically infrared or heat not being able or not being allowed to escape from the earth because the carbon dioxide is trapping it so most scientists do argue that the increase in amounts of carbon dioxide in is leading to an increase in global temperatures and this is obviously what they call global warming and they monitor things like in this picture this is a glass yet obviously retreating or melting you can see you've got snow melt here and some melting into this into this pool of water here so this could be evidence for warming earth and and most scientists argue that it's carbon dioxide that's causing it photochemical smog and ozone can cause this photochemical smog at lower levels and so basically again this is linked to the burning of fossil fuels such as alkanes absorbs own occurs in the lowest level of the atmosphere and this exists as Sonlight hydrocarbon and nitrogen dioxide mixed to form the ozone at the lower level okay now your hydrocarbons obviously is the fuel that were burning a nitrogen dioxide is formed when we burn a fuel so we've got the heat and pressure so we can form nitrogen dioxide so a great deal of hydrocarbons and nitrogen dioxide that come from cars and factories and when these solid particulates an ozone mix we create this thing called photochemical smog and this picture here and take the show some footage of smog in China in particular this is a picture taken in shine height and see the obviously the skyscrapers of Shanghai there and just missed it over with photochemical smog and ever see this there's quite a few cities not just Shanghai as few cities globally but have this problem with photochemical smog and obviously this this there's rules and regulations and politicians trying to come up with strategies to plan reduce air pollution okay so chemical smog what it does the harm is a respiratory system which isn't any good there's an animals and and humans as well as you work with your class as an animal so and an ozone is toxic as well we don't want a zone in the lower atmosphere want it in the upper atmosphere so ozone is not very good for his either like I say the oxides of nitrogen like I said here before these are caused by nitrogen oxygen it's naturally found in the air and reacting under high pressure and temperature of the engine and they produces nitrogen dioxide gas and obviously this isn't very good either acidic and we don't want to breathe this stuff in but thankfully catalytic converters they can help remove or reduce the amount of unburned hydrocarbons that haven't quite burnt in the engine and they can prevent the oxides of nitrogen from going into the atmosphere because we can react them and try and reduce the levels of them but it's really difficult cuz obviously producing loads of different gases here and obviously these engines get better and better and we even now looking at electric cars and in the UK in particular and it's a way of trying to reduce the harmful emissions from from car vehicles okay so from vehicle cars today acid rain right we talked a little bit about this so when we're burning a fossil fuel and we release sulphur dioxide nitrous oxides of nitrogen as well can cause acid rain and now obviously this is going to cause a problem because it damages trees as you can see in this picture this is a forest that's be damaged by acid rain as you can see the Bark's been stripped off and the leaves there's no leaves on the trees so these cause harm to plants and fish as well then obviously a road buildings that we knew it and so yeah some fossil fuels that contain these sulfur based impurities and when we burn this fossil fuel the sulfur reacts with the oxygen and it forms sulfur dioxide and obviously this sulfur dioxide is an acidic gas rises up into the atmosphere if it gets up there mixes with the water and forms sulfuric acid which then falls as acid rain again oxides of nitrogen do the same so if we can remove this sulfur dioxide a particular from things like chimneys and factories and we can use a process called wet scrubbing and this is basically where we're using an arc I to neutralize the sulfur dioxide in the flue gases and by doing that see we could inform and compounds was actually we can use we can use it past the board etc okay so basically how it works is we just dissolve the calcium carbonate which is just an alkaline solution and alkaline solid and we dissolve it in water or an oxide to be honest it can work with either and we just spray it onto the acidic gases leaving the chimney and and it effectively reacts with the soft dark side neutralize it and it's removing the soft oxides or reducing the amount that goes into the atmosphere which also should reduce acid rain okay so let's look at some free radical reactions and in the introduction to organic chemistry video if you've seen ABS you we looked at the mechanisms and we said that mechanisms contain curls apart from the free radical reactions which we don't need to do for AQA so basically the chain reaction involves three main stages got an initiation of propagation a termination step and we're just going to show obviously each of these stages so initiation is basically this is where radicals are produced normally using visible light or ultraviolet to use UV and these are called photochemical reactions and basically the bond breaks and we produce two radicals and propagation is like the middle step of this step and I'll show you some reactions in a minute to show you where the fit propagation is basically where we've got a radical meeting with a non radical they react new radicals are formed and these then go on to react with other non radicals so we call this a chain reaction because it literally just keeps going and going and going until we get to a termination step so terminations when we get two radicals that collide and this ends the chain reaction because what you form is a non radical molecule which is more stable than a free radical okay now this is really useful because actually what we can do is you can use alkane the alkanes and you Taurus Li unreactive react with anything so to form to get an alkane to react with something and we really need to either heat it up or we can use free radicals free radicals are super reactive species and these react with the alkane and they form and new products from that so this is where it all fits in okay so particular I'm going to use our kids to make ecology no our kids okay so chloromethane can be made via this reaction so we've got methane reaction to chlorine there's bit of the UV light there as well look this is going to get involved and would produce your chloromethane and hate shell so we can use a free radical mechanism to make this so the initiation step so sunlight breaks the CL bonds okay the CL CL bond this is called photodissociation so support word for breaking a bond using light effectively so the bond breaks equally and we produce two highly reactive radicals so let's have a look though it is there so we've got CL CL is the bond bitter UV and we produce soot two CL radicals now these dots here symbolize a radical or radicals just an atom with an unpaired electron in it in other words it could be just a chlorine atom which is just the same thing okay propagation okay so this is the next stage so basically the CL radical reacts with a methane molecule to make a methyl radical which is ch3 dot then the methyl radical reacts in the co2 molecule and that forms chloromethane a CL radical and then the CL radical can then react with more methane so let's look at them step by step there's the methane there's the CL radical what this does is this reacts with methane and the radical gets passed along onto ch3 dots to form ch3 dot and hate CL now because this is so reactive this is then used in the second propagation step there it is so drag this down here so always the radical the first step is the reactant in the second step this wraps with more chlorine which is unreacted unreacted core in CL 2 and what we form is your product ch3cl and your radical CL dot now the product of step two must be the the radical product of step two must be the radical reactant of step one so these must match okay so the little tricks to make sure you write in the right thing and you can see we've formed our hero alkane which is our halogen alarcon and the final step is termination this is when we get two radicals react and they make a stable non radical molecule so for example form and bromo bromomethane for example and or you can use this one which we're going to use chloromethane instead so it doesn't really matter so this one is obviously and his your methyl group meet I radical and a chloride radical and these are going to collide to form your chloromethane there okay so this is basically just showing a termination you can have a few termination steps don't see any two radicals any radicals that collide they will terminate and they will fall a non radical which is more stable so if there's loads of CL dot though loads of chlorine radicals then what we get is multiple substitution so we get die tri tetra hillock in and and basically we don't get and we don't basically get this pure product but if we don't and then all we get is we just get the single substitution so we've got very little of the chloride radical knockin around and we just get the mono substituted one but if we've got loads of it like an excess then we get die coil try cold tetrachloride it just keeps going and substituting and that's it that's the end of the profit to do with alkanes as you can see it's just a very quick overview there's bits on there too radicals which are pretty important there's a lot in there but green chemistry as well about sulphur dioxide in global warming and all that kind of stuff and so make sure you obviously able to do that and obviously we're looking at things like fractional distillation as well and cracking so which is the petrochemical industry but like say and these powerpoints are available to purchase if you click on the link in the description box below this video and you should be able to get them from there that's it bye bye