2. Chromatography

Question 1

A pure substance

Answer 1

1. A PURE substance that contains only one type of element or one type of compound
2. PURE substances have 1 MELTING temp
3. PURE substances have 1 BOILING temp
4. Impure substances are mixtures they melt & boil over a range of temps

Question 2

Chromatography is a ….

Answer 2

Chromatography is a separation technique between coloured substances

Question 3

Stages of Chromatography

Answer 3

1. Draw a start line in pencil of absorbent paper
2. Put a sample of food colourings on the start line
3. Put a sample of unknown substance on start line
4. Dip paper into a solvent (usually water)
5. Wait for the solvent to travel to the top of paper
6. Each moves a different distance up the paper
7. Use Rf to identify the components.
8. distance moved by SUBSTANCE
   Rf = __________________________
   distance moved by SOLVENT

Question 4

How to make sure Chromatography is a fair test

Answer 4

a. use same temperature
b. use same solvent
c. only use pencil to draw start line as it doesn’t move - ink will dissolve & affect results

Question 5

2 phases of Chromatography

Answer 5

Phases of Chromatography

1. Stationary phase - absorbent paper
2. Mobile phase - water/solvent that moves

Question 6

How does Chromatography show that food colouring tested is a MIXTURE and not a pure substance?

Answer 6

A MIXTURE will show two dots. One each for the different components - ie food colouring + substance

Question 7

What can you say about a substance if there is only one dot?

Answer 7

On dot tells you that the substance is pure and not a mixture

Question 8

How does Chromatography separate mixtures?

Answer 8

. Stationary phase mark a line on the absorbent
paper
. Mobile phase the solent moves through the paper
. Different compounds are carried different distances