Alkenes and polymers

Question 1

What do long chain hydrocarbons form?

What happens to them because smaller ones are more useful?

Answer 1

Thick and gloopy liquids like tar

They are split through cracking

Question 2

What is the equation for cracking?

What are the products of cracking useful for?

Answer 2

Long chain HC = Shorter alkane and short alkene

for fuels like petrol, or paraffin for jet fuel

Question 3

What is ethene good for?

Answer 3

making plastics

Question 4

What is cracking?
What are the steps? (2)
What is produced because they what?

Answer 4

Thermal decomposition of a long chain HC
1. Heat it to vapourise
2. Pass the vapour over a powdered catalyst of aluminium oxide at a temp of 400-700 degrees
The molecules split apart or crack on the surface of the catalyst and an alkane and alkene is produced

Question 5

What are the properties of an alkene? (3) (1 is the formula)

Answer 5

Unsaturated
Double C=C bond at least once in the chain
The formula is CnH2n

Question 6

How can you test for alkenes? (2 steps) - why?

Answer 6

Add the substance to bromine water
The alkene will decolourise the water by turning it from orange to clear
This is because the double bond has opened up and bonded to the bromine