Cracking And Alkanes

Question 1

What is cracking?

Answer 1

A method used to break long chains alkanes into shorter chains alkanes and alkenes

Question 2

What are alkenes?

Answer 2

Same as alkanes but with a double Carbon bond and are unsaturated

Question 3

Why are short chain alkanes and alkenes useful?

Answer 3

Alkanes=used as fuels
Alkenes=used to make polymers (plastic)
More demand for them than fractional distillation can offer

Question 4

What is always formed when cracking?

Answer 4

One alkane (or hydrogen) and one alkene

Question 5

What is the formula for an alkene?

Answer 5

CnH2n

Question 6

What happens in catalytic cracking?

Answer 6

Aluminium oxide or silicon dioxide is inserted as a catalyst in a test tube containing a liquid hydrocarbon soaked in ceramic wool to keep in place and doesn’t mix with the catalyst, both are burned strongly (500°C), the longer chains are broken down into smaller chains, the gas continues down the delivery tube is collected in an upside down tets tube, products will be gaseous (usually) or oily liquid

Question 7

Why might the product be an oily liquid?

Answer 7

The hydrocarbon produced is still large enough to be a liquid at room temperature

Question 8

What is steam cracking

Answer 8

Hydrocarbon mixed with steam and heated to a very high temperature, this breaks larger hydrocarbon molecules into smaller ones

Question 9

How to test for alkanes or alkenes

Answer 9

Hydrocarbon added to test tubes with liquid bromine, it is shaken to mix, if there is alkane then no change in colour and if it is an alkene then bromine turns from orange to colourless, because alkenes are more reactive, you can see separation of oil and bromine if the hydrocarbon was put as a liquid

Question 10

What process is involved in cracking?

Answer 10

Thermal decomposition