4.7 Organic Chemistry

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1 4.7 rgaic hemistry rude oil rude oil is a fiite resource foud i rocks. rude oil is the remais of a aciet biomass cosistig maily of plakto that was buried i mud. Alkaes Most of the hydrocarbos i crude oil are hydrocarbos called alkaes. Alkaes oly cotai sigle covalet bods ad are classed as saturated hydrocarbos rude oil is a mixture of a very large umber of compouds. Most of the compouds i crude oil are hydrocarbos, which are molecules made up of hydroge ad carbo atoms oly. The geeral formula for the homologous series of alkaes is 2+2 Name of Alkae (umber of carbos) Molecular formula Displayed Formula Methae 1 4 Ethae Propae butae Physical properties of hydrocarbos Some properties of hydrocarbos deped o the size of their molecules. These properties ifluece how hydrocarbos are used as fuels. Boilig poits ad viscosity of hydrocarbos icrease as the molecules get bigger (as the itermolecular forces become bigger) Volatility (how easily a liquid vaporises) ad Flammability of the fuels decrease as the molecules get bigger ombustio of ydrocarbos The combustio of hydrocarbo fuels releases eergy. Durig combustio, the carbo ad hydroge i the fuels are oxidised. The complete combustio of a hydrocarbo produces carbo dioxide ad water. (eeds a pletiful supply of air) ydrocarbo + xyge arbo dioxide + Water e.g Fractioal Distillatio of crude oil - how it works The may hydrocarbos i crude oil may be separated ito fractios, each of which cotais molecules with a similar umber of carbo atoms, by fractioal distillatio. o il is pre-heated the passed ito colum. o Some of the oil evaporates o Vapours rise up the colum ad cool o Some vapours codese, separate ad flow out the colum i a pipe o Some vapours stay as gases ad rise out the top of the colum o Each fractio has a differet boilig poit ad codeses at differet levels i the fractioatig colum o The temperature of colum decreases upwards o Boilig poit depeds o size of molecules. o Small molecules codese at the top at lower temperatures o ad big molecules codese at the bottom at higher temperatures N Goalby chemrevise.org 1

$The fractios ca be processed to produce fuels ad feedstock for the petrochemical idustry.$

2 The fractios ca be processed to produce fuels ad feedstock for the petrochemical idustry. May of the fuels o which we deped for our moder lifestyle, such as petrol, diesel oil, kerosee, heavy fuel oil ad liquefied petroleum gases, are produced from crude oil. May useful materials o which moder life depeds are produced by the petrochemical idustry, such as solvets, lubricats, polymers, detergets. The vast array of atural ad sythetic carbo compouds occur due to the ability of carbo atoms to form families of similar compouds. rackig Furace fuel gas (bottled) 20 petrol/gasolie 40 aptha (chemicals) 110 kerosee (jet fuel) 180 diesel oil 250 fuel oil 300 lubricatig oils 340 bitume Larger ydrocarbos ca be broke dow (cracked) to produce smaller, more useful molecules. The crackig process ivolves heatig the hydrocarbos to vaporise them. The vapours are either passed over a hot catalyst or mixed with steam ad heated to a very high temperature Uses of rackig products There is a high demad for fuels with small molecules ad so some of the products of crackig are useful as fuels. Alkees are used to produce polymers ad as startig materials for the productio of may other chemicals. rackig reactios are thermal decompositio reactios. The products of crackig iclude alkaes ad usaturated hydrocarbos called alkees Be able to complete balaced equatios for crackig reactios. Example Decae petae + petee N Goalby chemrevise.org 2

3 Alkees Alkees are hydrocarbos with a double carbo-carbo bod. Alkee molecules are usaturated because they cotai two fewer hydroge atoms tha the alkae with the same umber of carbo atoms. Alkees are more reactive tha alkaes ad react with bromie water, turig it from orage to colourless hemistry oly The geeral formula for the homologous series of alkees is 2 It is the geerality of reactios of fuctioal groups that determie the reactios of orgaic compouds. The first four members of the homologous series of alkees are ethee, propee, butee ad petee. ombustio of Alkees Alkees react with oxyge i combustio reactios i the same way as other hydrocarbos, but they ted to bur i air with smoky flames because of icomplete combustio. Additio Reactios of Alkees Ethee is 2 4 Alkees react with hydroge, water ad the haloges, by the additio of atoms across the carbo-carbo double bod so that the double bod becomes a sigle carbo-carbo bod. Propee is 3 6 butee is Br 2 Br Br ethee + 2 ethae ethee + 2 ethaol + l 2 l l + I 2 I I N Goalby chemrevise.org 3

4 Alcohols Alcohols cotai the fuctioal group. Alcohols ca be represeted i the followig forms: 3 2 r Methaol, ethaol, propaol ad butaol are the first four members of a homologous series of alcohols. 3 2 Methaol ethaol propaol hemistry oly butaol Methaol, ethaol, propaol ad butaol: dissolve i water to form a eutral solutio react with sodium to produce hydroge bur i air omplete ombustio I excess oxyge alcohols will bur with complete combustio 3 2 (l) (g) 2 2 (g) (l) Reactios with xidisig agets Alcohols ca be oxidised to carboxylic acids by oxidisig agets (such as potassium dichromate) Ethaol ca be oxidised to ethaoic acid, either by chemical oxidisig agets, or by oxyge i the air Fermetatio Aqueous solutios of ethaol are produced whe sugar solutios are fermeted usig yeast. glucose ethaol + carbo dioxide The coditios eeded are: Yeast No air temperatures o Uses of Alcohols Alcohols are used as a fuels ad solvets, ad ethaol is the mai alcohol i alcoholic driks. The optimum temperature for fermetatio is aroud 38 o At lower temperatures the reactio is too slow. At higher temperatures the yeast dies ad the ezymes deature. Fermetatio is doe i a absece of air because the presece of air ca cause extra reactios to occur. It oxidises the ethaol produced to ethaoic acid (viegar). arboxylic Acids arboxylic acids have the fuctioal group. The structures of carboxylic acids ca be represeted i the followig forms: 3 or arboxylic acids: o dissolve i water to produce acidic solutios o react with carboates to produce carbo dioxide o react with alcohols i the presece of a acid catalyst to produce esters The first four members of a homologous series of carboxylic acids are methaoic acid, ethaoic acid, propaoic acid ad butaoic acid. methaoic acid arboxylic acids are weak acids arboxylic acids do ot ioise completely whe dissolved i water ad so are weak acids Aqueous solutios of weak acids have a higher p value tha aqueous solutios of strog acids with the same cocetratio. ethaoic acid 3 2 propaoic acid butaoic acid Esters Esters are made from the reactio of carboxylic acids with alcohols i the presece of a acid catalyst (sulphuric acid). Esters have the fuctioal group Ethyl ethaoate is the ester produced from ethaol ad ethaoic acid Ethyl ethaoate N Goalby chemrevise.org 4

5 Additio Polymerisatio. Alkees ca be used to make polymers such as poly(ethee) ad poly(propee) by additio polymerisatio. I additio polymerisatio reactios, may small molecules (moomers) joi together to form very large molecules (polymers). hemistry oly I these reactios, the double bods ope up ad may small usaturated molecules (moomers, which are usually alkees) joi together to form very large saturated molecules (polymers). For example: ethee poly(ethee) (the stads for may molecules) 3 3 propee poly(propee) odesatio Polymerisatio I additio polymers the repeatig uit has the same atoms as the moomer because o other molecule is formed i the reactio. l chloroethee l poly(chloroethee) odesatio polymerisatio ivolves moomers with two fuctioal groups. Whe these types of moomers react they joi together, usually losig small molecules such as water, ad so the reactios are called codesatio reactios. The simplest codesatio polymers are produced from two differet moomers with two of the same fuctioal groups o each moomer For example: Moomer 1 Moomer Reacts with ethaediol exaedioic acid 2 May be draw simplified as Polymerise to form a polyester This shows the mai bods preset i the repeatig uit. Lear the ester likage. This is a poly(ester) N Goalby chemrevise.org 5

6 Amio acids ad Proteis Amio acids have two differet fuctioal groups i a molecule. hemistry oly Amio acids react by codesatio polymerisatio to produce polypeptides. For example: the amio acid glycie is 2 N 2 ad polymerises to produce the polypeptide (-N 2 -) ad 2 Differet amio acids ca be combied i the same chai to produce proteis. DNA hemistry oly DNA (deoxyriboucleic acid) is a large molecule essetial for life. DNA ecodes geetic istructios for the developmet ad fuctioig of livig orgaisms ad viruses. Most DNA molecules are two polymer chais, made from four differet moomers called ucleotides, i the form of a double helix. ther aturally occurrig polymers importat for life iclude proteis, starch ad cellulose Moomer ucleotide Amio acid Glucose Glucose Polymer DNA Protei Starch ellulose N Goalby chemrevise.org 6

Organic Chemistry. AQA Chemistry topic 7

Organic Chemistry. AQA Chemistry topic 7 rganic hemistry AQA hemistry topic 7 7.1 arbon ompounds as fuels and feedstock rude il rude oil is a finite resource found in rocks. It s the remains of an ancient biomass consisting mainly of plankton