Distillation Questions

Question 1

What is the point of the condenser and how does it work?

Answer 1

To cool the vapour down to a liquid so that none of it escapes or is lost.

It has 2 tubes, one inside the other.
Cold water runs through the space between the two tubes, keeping the condenser cold.
The cooling water does not mix with the substance being separated.
Location

Question 2

Why and how does fractional distillation work?

Answer 2

Fractional distillation works because the liquids in the mixture have different boiling points.

• When the mixture is heated the mixture boils up.
• Hot vapour rises up the fractionating column.
• Vapout condenses when it hits the cool surface of the column and drips back.
• The fraction with the lowest boiling point reaches the top of the column first.
• Its vapour passes into the condenser.

If you carry on heating, vapours from fractions with higher boiling points pass to the condenser.

Question 3

What is fractional distillation used for?

Answer 3

Separating a liquid from a mixture of miscible liquids (liquids that mix completely with each other).

For example, you can use this method to separate ethanol from a mixture of ethanol and water.

Question 4

What will be left behind when the water has evaporated?

Answer 4

The solute that was dissolved, salts from the water.

Question 5

How does the fractionating column work?

Answer 5

It has a temperature gradient, hottest at the bottom, coolest at the top.

Hot vapour rises up the fractionating column and condenses when it hits the cool surface.
The fraction with the lowest boiling point reaches the top of the column first and passes into the condenser.

Question 6

Why and how does simple distillation work?

Answer 6

Simple distillation works because the solute in the solution has a much higher boiling point than the solvent.

• When the solution is heated the solvent boils.
• Solvent vapour passes into the condenser.
• The vapour is cooled and condensed back to the liquid state.

The solution becomes more concentrated during simple distillation because the solute stays behind.

Question 7

Explain the function of a condenser in distillation.

Answer 7

To cool the vapour; to turn it from the gas state to the liquid state.
(So that none of it is lost or escapes.)

Question 8

State the physical property that allows substances to be separated by distillation.

Answer 8

(different) boiling points

Question 9

Describe the temperature gradient in a fractionating column.

Answer 9

hotter at the bottom and colder at the top/gets cooler towards the top