5.4 Distillation

Question 1

Why is simple distillation used?

Answer 1

Simple distillation is used for separating out a liquid from a solution, or to separate liquids that have very different boiling points.

Question 2

Describe the equipment needed for simple distillation (6)

Answer 2

• A flask: contains the solution or liquid mixture that we are trying to separate
• A bung: seals the flask at the top so that no gas can escape
• A thermometer: goes through the bung to measure the temperature inside the flask
• A condenser: consists of a main pipe, surrounded by a water jacket (which contains a stream of continually flowing cold water, with the water being fed into the water jacket at the bottom and coming out at the top)
• A beaker: to capture our pure liquid
• A bunsen burner: to heat the solution in the flask

Question 3

Describe how to do the simple distillation practical (4)

Answer 3

• Set up the apparatus. Connect the bottom end of the condenser to a cold tap using rubber tubing. Run cold water through the condenser to keep it cool.
• Gradually heat the distillation flask. The part of the solution that has the lowest boiling point will evaporate. For example, the water.
• The water vapour passes into the condenser where it cools and condenses. It then flows into the beaker where it is collected.
• Eventually you’ll end up with just salt left in the flask.

Question 4

What are two characteristics of a fractionating column used for fractional distillation?

Answer 4

• It is full of little glass rods which provide a very high surface area
• Cooler at the top than the bottom

Question 5

Describe how you would carry out fractional distillation for a solution containing methanol, ethanol and propanol (3)

Answer 5

• Methanol has the lowest boiling point, so you would heat the solution at its boiling point, allowing it to evaporate and then condense in the condenser and fall into the beaker.
• By chance, ethanol and propanol may evaporate as well, however the glass rods in the fractionating column would be cooler than their boiling point and so they would condense back into the flask.
• You should get pure methanol in the flask, so after this you should do the same for the ethanol in the ethanol and propanol mixture. At the end, you will be left with just propanol in the flask or you could evaporate and condense it like the methanol and ethanol.

Question 6

Fractional distillation can separate a mixture of several liquids that each have different:

Answer 6

Boiling points

Question 7

How would you isolate pure water from salt water?

Answer 7

Simple distillation