Cracking

Long hydrocarbon are less useful than shorter ones like petrol. We can 'crack' these longer chains into shorter ones. This is done using heat or a catalyst.

When we do this we end up with a mixture of both alkanes and alkenes.

Cracking Paraffin

Method

1. Set up the apparatus as shown in the diagram. Fill four test-tubes with water and invert them in the trough.
2. Strongly heat the catalyst (porcelain chips) for a few minutes.
3. Now flick the flame onto the end of the tube containing the mineral wool and the oil. Try to produce a steady stream of bubbles.
4. Collect tubes of the gas. Discard the first one, which will be mainly air.

Safety

1. Wear eye protection.
2. Be careful to avoid the water in the trough sucking back. When heating stops lift the apparatus out of the water using the stand.
3. Make sure the apparatus is not blocked. If no gas appears check the bung has not melted and that the catalyst has not blocked the delivery tube.
4. Aqueous bromine water is harmful and irritant.

Results

Record:
1. The appearance of the original oil and the gas.
2. The effect of the oil and the gas on aqueous bromine water.