4.2 Fractional Distillation

Question 1

What is done to crude oil at refineries?

Answer 1

It is separated into fractions by using fractional distillation

Question 2

What does the boiling point of a hydrocarbon depend on?

Answer 2

The size of the molecule

Question 3

The larger the molecule…?

Answer 3

The higher the boiling point of the hydrocarbon

Question 4

What is done to crude oil?

Answer 4

It is vaporised and fed into a fractionating column

Question 5

What is a fractionating column?

Answer 5

A tall tower that is hot at the bottom and gets cooler going up the column

Question 6

Describe what happens in a fractional distillation column?

Answer 6

There are many trays with holes to allow gases through. The vapours move up the column and get cooler as they go up. The hydrocarbons condense to liquids when they reach the level that is their boiling point. Different liquids collect on different trays at different levels. Then there are outlets to collect the liquids (fractions)

Question 7

Hydrocarbons with the smallest molecules and lowest boiling points are collected at the…?

Answer 7

Top of the column

Question 8

Hydrocarbons with the highest boiling points are collected at the…?

Answer 8

Bottom of the column

Question 9

Fractions with low boiling points have low…?

Answer 9

Viscosity so they are runny liquids

Question 10

What are some properties of fractions with low boiling points?

Answer 10

They are flammable so ignite easily, and burn with clean flames producing little smoke so they are very useful as fuels