Fractional distillation and Cracking

Question 1

Crude oil is a mixture of which hydrocarbons? ​

Answer 1

alkanes

Question 2

How does the size of the hydrocarbon link to its boiling point?

Answer 2

Boiling point depends on size (mass or chain length) of the hydrocarbon

Question 3

Why does the size of the hydrocarbon link to its boiling point?

Answer 3

more electrons means greater intermolecular /van der Waals forces

Question 4

What is a temperature gradient in the fractionating column?

Answer 4

A temperature gradient is where the column is hot at the bottom and becomes colder as the column is ascended. ​

Question 5

Why do the gases in the fractionating column condense at different points??

Answer 5

There is a temperature gradient in the fractionating tower which means that the gaseous mixture of hydrocarbons cools as it ascends the column becoming a liquid from a gas at its specific boiling point based on mass/chain length.

Question 6

Where do heavy/long molecules collect in the fractionating column? Why?

Answer 6

at the bottom. They have strong intermolecular forces and so have high boiling points so will condense first.

Question 7

Where do the smallest molecules collect in the fractionating column?

Answer 7

At the top. They have weak intermolecular forces and so will condense at the lowest temperatures.

Question 8

What do we call the groups of hydrocarbons that condense in the fractionating column at similar temperatures?​

Answer 8

Fractions. Hence, fractional distillation.

Question 9

Why are long molecules cracked?

Answer 9

Small chain molecules are more useful to industry and so have a higher demand and hence value.

Question 10

What is cracking?

Answer 10

Cracking is when long chain hydrocarbons are broken into smaller molecules or compounds

Question 11

Which homologous series are always produced in cracking?

Answer 11

Alkenes and alkanes

Question 12

What does a saturated hydrocarbon mean?

Answer 12

it has single carbon - carbon bonds only

Question 13

Name an homologous series that is unsaturated

Answer 13

alkenes

Question 14

What are the conditions of thermal cracking?

Answer 14

500C

50 atmospheres pressure

Question 15

What are the products of thermal cracking?

Answer 15

short alkanes and alkenes

Question 16

What are the uses of the products of thermal cracking?

Answer 16

plastics and polymers

Question 17

What are the conditions for catalytic cracking?

Answer 17

zeolite catalysts
450°C
slightly above atmospheric pressure

Question 18

What are the products of catalytic cracking?

Answer 18

branched hydrocarbons
cyclic hydrocarbons (e.g. cyclic alkanes)
aromatic hydrocarbons (e.g. benzene)

Question 19

What are the uses products of catalytic cracking?

Answer 19

high demand fuels

Question 20

What is a zeolite

Answer 20

A catalyst made from aluminium silicate with a very high surface area