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KS4: Useful Products from Organic Sources

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1 KS4: Useful Products from Organic Sources
ORGANIC CHEMISTRY

2 Crude Oil Crude oil is a mixture; it contains hundreds of different compounds, some small and some extremely large. Nearly all these compounds contain carbon and hydrogen only and are called hydrocarbons. Hydrocarbons are molecules that contain carbon and hydrogen only. The compounds present in crude oil are separated, processed and purified in an oil refinery. These processes are covered in the following slides.

3 Composition of a typical crude oil
Crude oils from different parts of the world have different composition

4 It is difficult to obtain pure compounds from
crude oil so instead, crude oil is separated into groups of compounds called fractions. Each fraction contains compounds of similar boiling point. A description of each fraction is shown below:

5 Fractional distillation
Crude oil is split into fractions using fractional distillation. Here crude oil is heated and pumped into the bottom of a tall tower containing trays. Compounds with low boiling points rise towards the top of the tower where they condense. Compounds with higher boiling point condense lower in the column. Thus each tray contains liquids (fractions) of different boiling point. The liquid on each tray is continuously pumped away. A fractional distillation tower works continuously, unlike distillation in the laboratory.

6 How fractional distillation works 40°C 70°C Liquid out 180°C
Very small molecules do not condense and come out of the top How fractional distillation works 40°C Small ones condense 70°C Short ones condense Liquid out 180°C Medium ones condense Getting cooler 250°C Long ones condense 340°C Very large molecules do not vaporise and fall to the bottom Crude oil preheater

7 Uses of each fraction on next slide
What fractional distillation produces Fuel gas Petrol Fractional distillation separates crude oil according to boiling point. Uses of each fraction on next slide Naphtha Kerosine Getting more volatile Diesel fuel Fuel and lubricating oil Crude oil Bitumen preheater

8 Uses of each fraction Fuel gas Petrol / gasoline Naphtha Paraffin /
Burned in the refinery to fuel the distillation process, sold as LPG, purified and sold as bottled camping gas Fuel gas Petrol / gasoline Fuel for cars and motorcycles, also used to make chemicals. Naphtha Used to make chemicals. Paraffin / Kerosine Fuel for greenhouse heaters and jet engines, manufacture of chemicals. Diesel fuel Fuel for lorries, trains. Fuel and lubricating oil Fuel for the heating systems of large buildings, fuel for ships, lubricating oil. Bitumen Roofing, and road surfaces.

9 Fraction Number of carbon atoms Fuel gas 1-4, mostly 1. Petrol / gasoline 5-10 Naphtha 8-12. Paraffin / Kerosine 10-16 Diesel fuel 14-22 Fuel and lubricating oil 20-70 Bitumen More than 65

10 Burning Hydrocarbons The apparatus below is used to test the products of combustion of a hydrocarbon. Suction pump ice- water Cloudiness- indicates carbon dioxide Candle wax is the hydrocarbon here Liquid collected can be tested with anhydrous cobalt chloride paper (bluepink). any hydrocarbon + oxygen  water + carbon dioxide

11 Alkanes Carbon atoms are unusual in that they are able to form strong covalent bonds to each other. Therefore, carbon is able to form chains of atoms of different length and so make molecules of different size. There are many thousands of molecules containing C-C bonds. In this course you learn about two groups of these compounds, alkanes and alkenes. Alkanes are hydrocarbons (molecules containing carbon and hydrogen only) in which each carbon atom is covalently bonded to four other atoms via 4 single covalent bonds. The other atoms can be either carbon or hydrogen.

12 Alkanes: Methane, CH4 It is common in organic chemistry to show covalent bonds as single lines. This makes it easier to show how the atoms are connected. H H H C H C H H H H Displayed formula or graphical formula ‘Dot and cross’ diagram

13 Alkanes: Ethane, C2H6 Ethane is the simplest alkane containing a
C-C bond. H H H C C H H H H H H C C H H H

14 Alkanes H H C H methane, CH4 H H H ethane, C2H6 H C C H H H H H H H C
propane, C3H8 H H H H

15 butane, C4H10 C H pentane, C5H12 C H

16 hexane, C6H14 H H H H H H H C C C C C C H H H H H H H and so on…………
Notice the carbon chain is not straight and so on…………

17 General Formula, CnH2n+2 Alkane series of molecules methane, CH4
propane, C3H8 General Formula, CnH2n+2 butane, C4H10 pentane, C5H12 hexane, C6H14 This is called a homologous series . Since all these molecules contain only single covalent bonds, alkanes are called saturated.

18 Increasing melting and boiling point.
Physical Properties of the Alkanes The alkanes show a gradual change in melting and boiling points. Increasing melting and boiling point.

19 Cracking The demand for some hydrocarbons is high
and cannot be supplied from fractional distillation alone. To boost the amount of some smaller hydrocarbons produced some of the high boiling point fractions are converted to more useful hydrocarbons. This process is called cracking. Cracking involves breaking C-C bonds. ethene pressure catalyst Distillation tower Heat to vaporise Long alkane smaller alkane

20 Cracking On the surface of the catalyst, long chain molecules are split apart or ‘cracked’. The reaction is: Octane Heat pressure hexane catalyst ethene + Ethene is used to make plastics C8H18  C6H14 + C2H4

21 CHEMICAL REACTIONS OF ALKANES
Alkanes are generally unreactive. This is because they only contain C-H and C-C bonds. However, the lower members of the series readily combust in air. With plenty of air, the products are water and carbon dioxide only. Methane + oxygen  water + carbon dioxide CH O  2H2O CO2 Combustion with limited amounts of air, however, produces carbon monoxide and water. Carbon monoxide is a poisonous gas.

22 Extension Isomerism Alkanes of the same molecular formula can have different arrangements of atoms These molecules are isomers of butane

23 Alkenes Carbon atoms can also form double covalent bonds to each other. Molecules with a double bond are called alkenes. H H H H C C C or C H H H H Ethene is the simplest alkene. C2H4

24 CnH2n Alkenes Alkenes have the general formula
Alkenes are unsaturated because they contain a double C=C bond. In all alkenes at least two carbon atoms are joined to only 3 atoms.

25 Other alkenes Propene, C3H6 Butene, C4H8

26 CHEMICAL REACTIONS OF ALKENES
The double bond allows alkenes to undergo reactions where atoms are added to the molecule. Thus, alkenes are more reactive than alkanes. An addition reaction: Br2 + If ethene is bubbled through bromine water the solution becomes colourless - this is used as the test for an alkene. Explanation: bromine colours the solution orange, however, this is used up in the reaction and the product is colourless.

27 Polymerisation Alkenes can undergo addition reactions to other alkene molecules. The result is very long chains of carbon atoms called polymers. Pressure high temperature catalyst And lots more.. This is written as: poly(ethene) Pressure high temperature catalyst n n ethene This is called addition polymerisation

28 Examples of addition polymers
Poly(propene) n n propene n n tetrafluoroethane Poly(tetrafluoroethane) or PTFE

29 Three very useful plastics

30 Poly(ethene) Bottles (HDPE) Poly(propene) boxes (PP)

31 REVIEW QUESTIONS

32 1. i) How is crude oil split into fractions ii) Name the seven fractions produced by fractional distillation of crude oil. iii) Give three differences between fractions. 2. i) What is meant by cracking? ii) Complete the formula below: C8H18  C2H4 iii) The starting hydrocarbon is octane, name the two products of this reaction. iv) Describe how you could test for the presence of ethene.

33 3. i) Draw the bonding diagram for methane (show only outer shell electrons, carbon has an atomic number of 6). ii) Draw the graphical formula for methane. iii) Methane is saturated, explain what this means. iv) Draw the graphical formula for another alkane containing five carbon atoms. 4. Propane is used as ‘Calor Gas’. Complete the word and equation for its combustion in the plenty of air Propane + Oxygen  _________ + _________ C3H O2  _____ ___ Why is it necessary to combust hydrocarbons in plenty of air?

34 5. i) In a homologous series the physical properties change gradually in the same direction. Plot a graph of boiling point against number of carbons for the alkanes. Use this graph to predict the boiling point of decane, C10H22. 6. i) Write down the graphical formula for propene. ii) Write down the equation for the reaction of propene with bromine. iii) Predict the reaction of propene with hydrogen and write down the equation. Iv) What type of reaction is this?

35 7. Using the polymerisation of ethene as an example, explain the term addition polymerisation.

36 Harder Questions 8. Draw graphical formula for the three isomers of pentane. 9. Draw graphical formula for three isomers of butene. 10. Write down the equation for the combustion of propene in plenty of air and with a restricted amount of air.

37 ANSWERS TO REVIEW QUESTIONS

38 1. i) Crude oil is split into ‘fractions’ of different boiling point by fractional distillation. Here crude oil is vaporised and passed into a fractionating tower. Towards the top of the tower, where it is cooler, compounds of low boiling point condense and are collected on trays from which they are removed. Lower in the tower, higher boiling point fractions are collected. ii) Refinery gas / Petrol or gasoline / Naphtha / Kerosine or paraffin / Diesel / Oil / Bitumen iii) boiling point / viscosity / colour / size of hydrocarbon molecule

39 2. i) Cracking is the process used to convert long hydrocarbon molecules into smaller ones. The hydrocarbon liquid is vaporised and passed over a catalyst. On the surface of the catalyst the carbon chain is split to produce ethene and a smaller alkane. ii) C8H18  C6H14 + C2H4 iii) C6H14 is hexane, C2H4 is ethene iv) You could pass the gas through bromine water. The bromine water, which is orange, will become colourless.

40 3 i) ii) C H H H C H H iii) Methane is saturated because it contains no double bonds. iv) C H Pentane, C5H12

41 4. Propane + Oxygen  carbon dioxide + water C3H O2  3CO H2O In insufficient air/oxygen, carbon monoxide and water are produced. Carbon monoxide is a poisonous gas.

42 5. 174°C

43 6. propene i and ii) + Br2  C3H6 + Br2  C3H6Br2 iii) propane + H2  iv) Addition reaction

44 7. poly(ethene) n n ethene
Pressure high temperature catalyst n poly(ethene) n ethene This is called addition polymerisation because the molecules of ethene add together without producing any other products.

45 8. Isomers of pentane

46 9. Isomers of butene

47 10. (i) 2C3H6 + 9O2  6CO H2O (ii) C3H6 + 3O2  3CO + 3H2O


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