Filtration and Crystallisation

Question 1

When is filtration used?

Answer 1

If your product is an insoluble solid that needs to be separated from a liquid reaction mixture - can also be used in purification.

Question 2

How do you filter?

Answer 2

Fold the filter paper into a cone shape and pour the solution through it.

Question 3

What 2 methods can you use to separate a soluble salt from a solution?

Answer 3

Evaporation and crystallisation

Question 4

Evaporation

Question 5

1

Answer 5

Pour the solution into an evaporating dish. Using a bunsen burner, water bath or electric heater, slowly heat the solution.

Question 6

2

Answer 6

The solvent will evaporate and the solution will get more concentrated. Eventually, crystals will start to form.

Question 7

3

Answer 7

Keep heating the evaporating dish until all you have left are dry crystals

Question 8

When can you use evaporation as a quick way of separating a soluble salt from a solution?

Answer 8

If the salt doesn’t decompose when it’s heated. If this happens, you have to use crystallisation.

Question 9

Crystallisation

Question 10

1

Answer 10

Pour the solution into an evaporating dish and gently heat the solution. Some of the solvent will evaporate and the solution will get more concentrated.

Question 11

2

Answer 11

Once some of the solvent has evaporated or when you see crystals start to form (the point of crystallisation) remove the dish from the heat and leave the solution to cool.

Question 12

3

Answer 12

The salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution

Question 13

4

Answer 13

Filter the crystals out of the solution and leave them in a warm place to dry. You could also use a drying oven or a desiccator.

Question 14

Filtration and Crystallisation

Answer 14

to separate rock salt

Question 15

What is rock salt?

Answer 15

A mixture of salt and sand

Question 16

salt dissolves in water

Answer 16

sand doesn’t

Question 17

A

Answer 17

Grind the mixture to make sure the salt crystals are small so will dissolve easily

Question 18

B

Answer 18

Put the mixture in water and stir - the salt will dissolve but the sand won’t. You can heat the mixture to help dissolve the salt.

Question 19

C

Answer 19

Filter the mixture. The grains of sand will stay in the filter paper. The salt passes through as it’s part of the solution.

Question 20

D

Answer 20

You could evaporate the water from the salt so it forms dry crystals or you could use crystalisation.