CC2C Paper Chromatography

Question 1

What process can be used to identify substances in a mixture

Answer 1

Chromatography

Question 2

How does paper chromatography work to separate a mixture

Answer 2

The mobile phase (solvent) moves through the stationary phase (paper) so anything dissolved in the mobile phase will move with up the paper
Compounds interact differently with each phase so will move different distances through the stationary phase meaning they will be separated

Question 3

How can chromatography show the composition of a mixture

Answer 3

Different coloured substances in the mixture will separate as they have different solubilities in the solvent and will travel at different rates

Question 4

Why should pencil be used to draw the line along the bottom of the chromatography paper

Answer 4

It will not affect the experiment as it is insoluble in the solvent

Question 5

Why should the water (solvent) in the beaker for paper chromatography be no deeper than 1 cm deep

Answer 5

If it is deeper it will wash away the substance placed on the line on the chromatography paper

Question 6

Why should you use a lid when carrying out paper chromatography

Answer 6

To prevent the solvent evaporating

Question 7

How many spots will a pure substance produce on a chromatogram? How would this be different for an impure substance

Answer 7

Pure substances produce one spot
An impure substance contains more than one compound so will produce more spots (one spot for each chemical)

Question 8

What is an Rf value

Answer 8

The Rf value is the ratio between the distance travelled by the dissolved substance ( the solute) and the distance travelled by the solvent

Question 9

How do you calculate Rf values

Answer 9

Rf = Distance travelled by substance
——————————————
Distance travelled by solvent

Question 10

When measuring the distance moved by a substance on the chromatography paper where should you measure between

Answer 10

Measure from the pencil baseline to the middle of the spot of the substance

Question 11

How can you use chromatography to see if a certain substance is present in a mixture

Answer 11

Run a pure sample of this substance alongside the unknown mixture
If the Rf value of the pure substance matches the value of one of the spots from mixture it is likely to be present