Topics 3abc – Alkanes, alkenes and ethanol Topics 5bc – natural oil and gas and synthetic polymers

1. Topics 3abc – Alkanes, alkenes and ethanolTopics 5bc – natural oil and gas and synthetic polymers

2. Crude oil (Petroleum) • A mixture of hydrocarbons (chemicals which contain only hydrogen and carbon atoms)

3. Fractional distillation • Separation of liquids with different boiling points

4. Fractional distillation The mixture can be split into simpler fractions by fractional distillation

6. Welcome to a new family

7. The alkanes

8. Methane (CH4)

9. Ethane (C2H6)

10. Propane (C3H8)

11. Butane (C4H10)

12. The alkanes • Methane CH4 • Ethane C2H6 • Propane C3H8 • Butane C4H10 • Pentane C5H12 • Hexane C6H14 • Octane C8H18

13. General formula The alkanes CnH2n + 2 • Methane CH4 • Ethane C2H6 • Propane C3H8 • Butane C4H10 • Pentane C5H12 • Hexane C6H14 • Octane C8H18 Homologous group – similar chemical properties, structures and functional groups

14. General formula The alkanes CnH2n + 2 • Methane CH4 • Ethane C2H6 • Propane C3H8 • Butane C4H10 • Pentane C5H12 • Hexane C6H14 • Octane C8H18 Homologous group – similar chemical properties, structures and functional groups Generally unreactive, but burn exothermically. Longer chains burn less easily.

15. Structural formulae

16. Alkanes are saturated compounds No double bonds

17. Tetrahedral bonds In alkanes, the carbon bonds are tetrahedral

18. Chlorinated methane Methane can be chlorinated. Trichloromethane is commonly known as chloroform.

19. Isomers Same formula, but different structures We have slighty different physical properties (longer chains have higher boiling points)

20. Combustion

21. Combustion Hydrocarbons burn producing carbon dioxide and water CH4 + 2O2 CO2 + 2H2O

22. Incomplete combustion • When there is insufficient oxygen, carbon monoxide is also formed It reduces the blood’s oxygen carrying capability

23. Another family!

24. The alkenes CnH2n • Ethene C2H4 • Propene C3H6 • Butene C4H8 • Pentene C5H10 • Hexene C6H12

25. The alkenes • Unsaturated (contain a double bond) • More reactive • Can “add” atoms – addition reactions

26. Alkenes - equilateral The bonds on a double bonded carbon in an alkene point towards the corners of an equilateral triangle

27. Test for alkenes • Decolourises bromine water Dibromoethane (colourless) ethene Bromine (brown)

28. Alcohols - ethanol

29. Alcohols • Methanol CH3OH • Ethanol C2H5OH • Propanol C3H7OH • Butanol C4H9OH • Pentanol C5H11OH • Hexanol C6H13OH

30. Ethanol Can be made by the addition reaction of water to ethene – when you have plenty of oil Phosphoric acid

31. Ethanol - Fermentation of sugars You can make ethanol for industry this way when you have lots of sugar cane

32. Ethanol and sodium 2C2H5OH + 2Na 2C2H5ONa + H2 Hydrogen and sodium ethoxide formed

33. Oxidation of ethanol Ethanol can be oxidised to form ethanoic acid (acetic acid = vinegar!)

34. Dehydration of Ethanol

35. Ethanol + carboxylic acids Ethanol + ethanoic acid ethyl ethanoate + water An ester (they normally smell nice!)

36. Polymers

37. Polymers – addition polymerisation Molecules of ethene can be joined together to form polyethene ← monomers ← polymer

38. Polythene

39. Polypropylene – Strong and resistant to chemicals

40. poly(chloroethene) - PVC

41. Condensation polymers - Nylon Reactive ends + + + monomers polymer Small molecules given off (HCl)

42. Cracking!

43. Too many long molecules Crude oil contains too many of the long (and not so useful molecules)

44. Cracking Luckily we can break the long molecules into shorter ones by “cracking” The long molecules are passed over hot broken pot (ceramic) and split up into smaller molecules. A catalyst can also be used

45. Cracking Cracking an alkane produces smaller alkanes and also alkenes.