C2.1.7 - Purification And Checking Purity

Question 1

What can you use to tell if a substance is pure?

Answer 1

Thin-layer chromatography or paper chromatography

Question 2

Which is better at checking pure substances - paper or thin-layer chromatography?

Answer 2

Thin-layer chromatography

Question 3

What are the advantages of using thin-layer chromatography over paper chromatography for checking pure substances?

Answer 3

It is quicker
It is more sensitive, so a smaller substance can be used
There is a larger range of chemical phases to choose from
You can also scrape an individual spot for further analysis from a thin-layer chromatogram by using gas chromatography

Question 4

What do you need to know about the substances in order to use the correct separation method?

Answer 4

The properties of the substances

Question 5

How do you separate insoluble substances?

Answer 5

Dissolving followed by filtration

Question 6

How do you separate solutions?

Answer 6

Crystallisation to obtain the solute

Simple distillation to obtain the solvent

Question 7

How do you separate two or more substances in the liquid state?

Answer 7

Fractional distillation

Question 8

How do you separate coloured soluble solutions?

Answer 8

You use paper chromatography or thin-layer chromatography