C1 - Separation Techniques

Question 1

What do filtration and crystallisation separate?

Answer 1

They separate solids from liquids

Question 2

What does filtration specifically separate?

Answer 2

Insoluble solids from liquids

(It can be used in purification as well.For example,solid impurities in the reaction mixture can be separated out using filtration)

Question 3

Define soluble

Answer 3

If a solid can be dissolved

Question 4

What are two methods to separate soluble solids from solutions?

Answer 4

Evaporation and crystallisation

Question 5

Explain the steps for evaporation

Answer 5

1) Pour the solution into an evaporating dish

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

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

(You dont have to use a bunsen burner,you could use a water bath or an electric heater)

Question 6

Why would you want to use crystallisation instead of evaporation?

Answer 6

Even though evaporation is a really quick way of separating a soluble salt from a solution,you can only use it if the salt doesnt decompose (break down) when its heated.Otherwise youll have to use crystallisation

Question 7

Explain the steps for crystallisation

Answer 7

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

2) 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

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

4) 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 8

What is rock salt a mixture of?

Answer 8

Salt and sand

(They spread it on the roads in winter)
(Salt and sand are both compounds - but salt dissolves in water and sand doesnt.This vital difference in their physical properties gives a great way to separate them)

Question 9

What are the steps to separate rock salt?

Answer 9

1) Grind the mixture to make sure the salt crystals are small,so they will dissolve easily

2) Put the mixture in water and stir.The salt will dissolve,but the sand wont (You can heat the mixture to help dissolve the salt)

3) Filter the mixture.The grains od sand wont fit through the tiny holes in the filter paper,so they collect on paper instead.The salt passes through the filter paper as its part of the solution

4) Evaporate the water from the salt so that it forms dry crystals
( You could also use crystallisation here if you wanted to make nice,big crystals)