Alkanes - Organic (6)

Question 1

Describe the process of fractional distillation (5)

Answer 1

1. Crude oil is heated in a fractionating column which has a temperature gradient (cooler at the top)
2. Different components of crude oil have different boiling temperatures and so condense at different points to be separated
3. Near the bottom, fractions contain larger molecules with longer chains and higher boiling temperatures
4. Near the top, fractions contain smaller molecules with shorter chains and lower boiling temperatures
5. Some hydrocarbons are dissolved gas (refinery gases) and don’t condense

Question 2

Describe the process of cracking (3)

Answer 2

1. Cracking is used to convert longer chain hydrocarbons into more useful shorter chain ones
2. The large chain hydrocarbon is passed through a ‘zeolite’ catalyst under high temperature and pressure
3. It produces a mixture of shorter chain alkanes and alkenes

Question 3

Give the definition of a free radical (1)

And explain how it is formed (1)

Answer 3

1. A free radical is a chemical species with an unpaired electron
2. It is formed by homolytic fission of a covalent bond

Question 4

Explain the use of catalytic converters (2)

Answer 4

1. Catalytic converters convert harmful pollutants produced in cars into less harmful products
2. A transition metal such as Palladium is used as a catalyst for the reactions and is spread thinly over a honeycomb mesh to increase surface area

Question 5

What is the process of reforming? (1)

Answer 5

1. Reforming is used to convert straight-chain hydrocarbons into branched and cyclic hydrocarbons which combust more rapidly

Question 6

List out the steps of the mechanism for a substitution reaction between an alkane and a chlorine radical. (4) [1 for each step plus further reactions]

Label the initiations, propagation and termination steps (3)

Answer 6

See red Pearson textbook p185