C5 Chromatography

Question 1

What is chromatography?

Answer 1

An analytical method used to separate the substances in a mixture.

Question 2

Why may we need to separating the substances in a mixture?

Answer 2

To identify the substances.

Question 3

There are different types of chromatography, but they all have two phases. Name the two phases.

Answer 3

A mobile phase.

A stationary phase.

Question 4

What happens in the mobile phase of chromatography?

Answer 4

Where the particles of the phase can move.

Question 5

What state is the mobile phase?

Answer 5

Liquid or gas

Question 6

What happens in the stationary phase of chromatography?

Answer 6

Where the particles of the phase can’t move.

Question 7

What state is the stationary phase?

Answer 7

This can be solid or a very thick liquid.

Question 8

During a chromatography experiment, the substances in the sample constantly move between the mobile and the stationary phases. What is formed between the two phases?

Answer 8

An equilibrium.

Question 9

Different chemicals will have different distributions between the same phase. What does this mean?

Answer 9

They’ll spend different amounts of time dissolved in the mobile phase or attracted to the stationary phase.

Question 10

Complete the sentence

The mobile phase moves through the stationary phase, and anything ……….. in the mobile phase moves with it.

Answer 10

Dissolved

Question 11

How does the amount of time a chemical spends in the mobile phase affect the stationary phase?

Answer 11

The more time a chemical spends in the mobile phase, the further through the stationary phase it’ll move.

Question 12

What will a chromatogram of a chemical with different distributions show?

Answer 12

The different distributions will separate into different spots on the chromatogram.

Question 13

What affect would a different solvent have ?

Answer 13

The number of spots may change in a different solvent as the distribution of the chemical will change depending on the solvent.

Question 14

What will a chromatogram of a pure substance show? Why?

Answer 14

One spot in any solvent, as there is only one substance in the solution.

Question 15

If a chromatogram has more than one spot, what can we say about the substance?

Answer 15

It is a mixture.

Question 16

One type of chromatography is paper chromatography. What are the mobile and stationary phases in this method?

Answer 16

Chromatography paper is the stationary phase (often filter paper)

Solvent is the mobile phase.

Question 17

What does the amount of time the molecules spend in each phase depend on?

Answer 17

How soluble the molecules are and how attracted they are to the paper.

Question 18

Which phase do molecules with higher solubility in the solvent spend more time in? Why?

Answer 18

Mobile phase

They are less attracted to the paper, so spend more time in the mobile phase and are carried further up the paper.

Question 19

See p 60 for chromatography practical.

Answer 19

.

Question 20

Explain how paper chromatography separates mixtures. (4 marks)

Answer 20

During paper chromatography, the molecules of each chemical in the sample move between the stationary phase and the mobile phases. (1 mark)
The mobile phase moves through the stationary phase over the course of the experiment, and anything that’s dissolved in it will move with it (1 mark)
The distance a compound moves through the stationary phase depends on how long it spends dissolved in the mobile phase compared to on the stationary phase (1 mark).
Since different compounds will interact differently with the mobile phase and the stationary phase, they’ll move different amounts through the stationary phase, and so be separated from each other (1 mark).