Alkanes

2. Alkanes Alkanes • Alkanes are hydrocarbons in which all carbon atoms are bonded by single covalent bonds • Alkanes are said to be saturated because all the bonds are single bonds. • The alkanes are named according to the number of carbon atoms (methane, ethane, propane, butane, pentane etc.) • Alkanes do not turn bromine water colourless

3. Alkanes Alkanes

4. Alkanes H H C methane, CH4 H H H H ethane, C2H6 C C H H H H H H H propane, C3H8 C C H C H H H H

5. butane, C4H10 H H H H C C C H H C H H H H pentane, C5H12 H H H H H C C C H C C H H H H H H

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

7. Cracking Cracking • Hydrocarbons with long chains have limited use due to their lack of flammability • Large hydrocarbons can be broken down (cracked) into smaller, more useful substances • This process uses heat and a catalyst • It is a type of thermal decomposition reaction

8. Cracking Cracking

9. Cracking Cracking

10. In the catalytic cracker long chain molecules are split apart or ‘cracked’. An example of such a reaction is: Octane Heat pressure catalyst hexane ethene + Catalytic Cracking Ethene is used to make plastics Used as a fuel C8H18 C6H14 + C2H4

11. Alkenes Alkenes • Alkenes are hydrocarbons that contain at least one carbon-carbon double bond • Alkenes are said to be unsaturated because of that double bond – written C=C. • Alkenes can be identified using bromine water. The yellow-brown bromine water goes colourless.

12. Saturated means “full up”. Saturated or Unsaturated? • Alkanes are saturated. • Every carbon atom has already used all four of it’s bonds to join to four other atoms. No other atoms can be added. • Alkenes are unsaturated. • They have a double bond that could instead become two single bonds. This means that other atoms can be added. It is not “full up”.

13. Alkenes Alkenes

14. Alkenes Alkenes

15. Copy the Table and complete the empty boxes. Activity alkene C5H10 alkane C8H18 alkene C4H8 alkane C10H22

16. Polymers Polymers • Alkenes are reactive and are called monomers • Monomers (e.g. ethene) can react together to form polymers (e.g. poly(ethene)) • This process is called polymerisation • Addition polymerisation has taken place if no other products are made • Plastics are polymers

17. Polymerisation Polymerisation

18. Monomers and Polymers Ethene This molecule is called POLYETHENE, and the process that made it is called POLYMERISATION Here’s ethene again. Ethene is called a MONOMER because it is just one small molecule. We can use ethene to make plastics… Step 1: Break the double bond Step 2: Add the molecules together:

19. Another way of drawing it… H H H H C C C C H H H H Ethene Ethene Poly(e)thene H H H H C C C C H H H H n C C n C C C C CH3 CH3 H H e.g. n C C n H H H H Instead of circles, let’s use letters… General formula for addition polymerisation: HIGHER

20. One important reaction of alkenes involves the joining together of alkene molecules. H H H H H H H H H H C C C C C C C H C C C H H H H H H H H H H poly(e)thene Pressure high temperature catalyst n n ethene Poly(e)thene And lots more.. 1 2 3 4 5 thousands HIGHER: This is called addition polymerisation and is written as:

21. Vinyl chloride is another alkene that is made into an important plastic used to make e.g synthetic leather, wellington boots,guttering. n n Poly(tetrafluoroethane) or PTFE tetrafluoroethene PVC

22. Tetrafluoroethane is another alkene that is made into an important plastic used to coat non-stick pans: polytetrafluoroethane or PTFE. n n Poly(tetrafluoroethane) or PTFE tetrafluoroethene PTFE

23. Some uses of plastics Polystyrene packing insulation Ball pens Poly(e)thene Shopping bags Bottles Buckets Washing up bowls Polypropene Milk crates Rope Carpet fibres

24. Uses of Plastics Uses of Plastics • Poly(ethene) is used for making plastic bags and bottles • Poly(propene) is used for making crates and ropes • Most plastics are not biodegradable – they cannot be broken down by microorganisms. They can lead to problems with waste disposal

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26. Which of these is an alkane? C6H14 C4H8 C12H24 C102H204

27. Which of these is a true statement about alkenes? They turn bromine water from colourless to red They contain a double bond The smallest alkene has 1 carbon atom They have names that end in “ane.”

28. Which of these is a true statement about cracking? it is the separation of molecules into fractions of different sizes. it is carried out at low temperatures it uses a catalyst. It produces polymers

29. Which of these is a true statement about polymerisation? it is the joining together of many small molecules. it is the thermal decomposition of plastics it is carried out using saturated molecules it is a multiplication reaction

30. Which of these is an addition polymer? styrene ethene p.v.c. propane

31. How might you test to see if polystyrene still contained some unsaturated monomer (styrene)? Crush it up and burn it. Crush it up and add it to bromine water Crush it up and dissolve it in petrol Crush it up and add hydrochloric acid