Fractional distillation of crude oil

Question 1

What are alkanes?

Answer 1

Saturated hydrocarbons

Question 2

What are hydrocarbons?

Answer 2

Compounds made up of hydrogen and carbon only.

Question 3

What does the term ‘saturated’ mean?

Answer 3

Single bonds between carbon atoms

Question 4

What is the general formula of alkanes

Answer 4

CnH2n+2

Question 5

What isomerism do alkanes show when there are branches?

Answer 5

Chain isomerism

Question 6

What are the physical properties of alkanes?

Answer 6

Polarity - how polar something is
- Alkanes are non-polar because the electronegativities of carbon and hydrogen are very similar. This means that the van der waals forces between the molecules in alkanes are very weak.

Boiling point
- Very low, most alkanes are gases at room temperature. This is because of the weak van der waals forces between the molecules.

Solubility
- Alkanes are insoluble in water because water is polar and alkanes are non-polar.

Question 7

Why are larger alkanes liquid?

Answer 7

Because the larger the molecule gets, the more van der waals forces it will have.

Question 8

Do branched alkanes have a higher or lower boiling point than unbranched alkanes?

Answer 8

Lower boiling point because the IM forces are weaker because the surface area is smaller so the van der waals forces are not very effective.

Question 9

Are alkanes reactive or unreactive?

Answer 9

Alkanes are very unreactive because the C-C bonds are strong and the C-H bonds are strong too.

Question 10

What can alkanes be used for

Answer 10

• Starting materials for other compounds e.g alkenes or halogenoalkanes
• For fuels since they are flammable
• As lubricants to reduce friction e.g engine oil

Question 11

What is fractional distillation?

Answer 11

The process of separating crude oil into groups of hydrocarbons with similar numbers of carbon atoms. We call these groups of hydrocarbons “fractions”.

Question 12

What are short-chain hydrocarbons?

Answer 12

Hydrocarbons with few carbon atoms.

Question 13

What are long-chain hydrocarbons?

Answer 13

Hydrocarbons with many carbon atoms.

Question 14

How does fractional distillation separate different hydrocarbons?

Answer 14

According to their different boiling points

Question 15

What are the steps for fractional distillation?

Answer 15

1. Crude oil is heated until it evaporates. Crude oil vapour is put into a fractionating column at the bottom and rises upwards.
2. The temperature is highest at the bottom of the column so long-chain hydrocarbons condense at the bottom and collect as liquids. Short-chain hydrocarbons have low boiling points so they pass up the column and condense at lower temperature at the top
3. The fractions are collected and then processed to make different products e.g. petrol, lubricants, detergents