1. Cracking Hydrocarbons L.O: To understand what cracking is and why it is useful A food packaging company is low on ethene to make polythene (cling film), the have plenty of hexane (C 6 H 14 ) could they turn this into cling film? Discuss

2. What is a hydrocarbon? How can you separate different hydrocarbons? What is an alkane? What are the differences in properties between different alkanes? What are the formulas for methane, ethane, propane and butane?

3. Catalytic Cracking Large hydrocarbons are broken into smaller molecules using heat and a catalyst. This process is known as catalytic cracking. The small molecules produced are then separated by distillation. Catalytic cracker Heat to vaporise Distillation tower pressure Big Molecules Smaller molecules Molecules break up

4. Cracking This is a THERMAL DECOMPOSITION reaction, with clay used as a catalyst Long chain hydrocarbon Heated catalyst Liquid hydrocarbon Gaseous hydrocarbon Make a drawing of the apparatus and describe what is happening.

5. What is the evidence to show that long chain hydrocarbons can be broken into smaller ones by cracking?

6. Using the molymods make pentane. Can you now crack this into two hydrocarbons? You cannot change the number of atoms and you must also remember to fill all of the bonds.

7. An example of cracking C 10 H 22 (decane) 800°C + catalyst C 5 H 12 (pentane) C 3 H 6 (propene) C 2 H 4 (ethene) + + Long chain alkanes → shorter chain alkanes + alkenes

8. Alkenes Each carbon atom always has 4 bonds but the atoms can form double bonds rather than single bonds. Less hydrogen atoms are needed to fill up carbons 4 bonds. Alkenes have the general formula C n H 2n (Remember the general formula for an alkane is C n H 2n+2 ) hydrogen carbon n= 1 n=2 n=3 n=4 Alkenes none = = = Single covalent bond C C Double covalent bond C C

9. What will be the formula for alkenes containing the following numbers of carbons? Can you draw them? Number of carbonsFormula 11 13 32 21 C 11 H 22 C 13 H 26 C 32 H 64 C 21 H 42 Activity

10. Saturated or Unsaturated? Saturated means “full up”. 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”. unsaturatedAlkenes are unsaturated. Every carbon atom has already used all four of it’s bonds to join to four other atoms. No other atoms can be added. saturatedAlkanes are saturated.

11. Alkenes are unsaturated and so extra atoms can be added to alkene molecules. This forms the basis of a test to distinguish between alkanes and alkenes. When bromine water is added to an alkane nothing happens but when bromine is added to an alkene the red colour of the bromine disappears. + Br 2  Gas red colourless Bromine loses this red colour Predict what will happen when bromine water is added to the hydrocarbons from fractional distillation

12. Which fractions are more useful? And in more demand? Shorter chain hydrocarbons are more useful E.g. petrol Long chain hydrocarbons can be broken apart to make more useful fractions