2018 N Level Paper Chromatography Question

A water soluble dye, C, is analysed using paper chromatography. On the same chromatogram, the pattern produced by dye C is compared with those of four other dyes, A, B, D and E.

Chromatogram showing the pattern produced by dye A, B, C, D and E.
Question 1(a)
Dye C is made from a mixture of two of the dyes A, B, D and E. Identify the two dyes.

A and E.

The same dye will have the same spots at exactly the same height. From the chromatogram, dye C contains dye A as it has the yellow and teal green spots. Dye C also contains dye E as they share the pink and purple spots.

Question 1(b)
A dye F is prepared by mixing dyes A and D. On the diagram above, draw the pattern produced by dye F.

Since dye F is a mixture of dyes A and D, it will contain all the spots in the two original dyes. In the exam, there is no need to colour the spots as everything will be printed in black and white.

Tartrazine is an orange dye that can be added to bottled drinks to make them look more appealing.

A food inspector prepares a concentrated solution of drink S and tests it with paper chromatography.

They spotted a drop of concentrated drink S and a drop of tartrazine solution on a piece of chromatography paper. They then placed the paper in a beaker of water for 10 minutes.

The chromatogram obtained from separating drink S and tartrazine.
Question 2(a)
Describe how the inspector can prepare a concentrated solution of drink S.

By evaporating most of the water in drink S.

Question 2(b)
State three conclusions that can be made from the chromatogram.
  1. Drink S contains tartrazine
  2. Drink S is a mixture containing 4 substances
  3. Tartrazine is a pure substance

A pure substance will only give one spot on the chromatogram.

Answers like drink S is separated into 4 spots will not be accepted as the question asks for conclusion and not observation. Instead, you have to infer what having 4 spots means, to draw the conclusion that drink S contains 4 substances.

2016 N Level Paper Chromatography MCQ

A chemist conducted an experiment to separate a mixture of two dyes.

They drew a line on a piece of chromatography paper and placed a spot of the mixture of dyes on it.

They then dipped the paper into a solvent for a few minutes.

Question 3
Which statement about this experiment is correct?

A. The dyes must have different boiling points.
B. The dyes must have different solubilities in the solvent.
C. The line on the paper must be drawn in ink.
D. The paper must be placed with the line below the solvent level.

Answer: B

A is wrong as paper chromatography does not involve boiling. Instead, simple and fractional distillations are the techniques that separate according to the different boiling points.

B is correct. In paper chromatography, a more soluble substance is carried up a further distance by the solvent. Conversely, a less soluble substance travels less.

C is wrong. The line must be drawn in pencil so that it does not smudge. As ink is also soluble in water, it would dissolve and interfere with the results.

D is wrong. The paper must be placed with the line above the solvent level, so that the spot of mixture does not directly dissolve down into the solvent without any separation.

2014 N Level Paper Chromatography Question

A chromatogram obtained from the colouring of three different sweets: A, B and C
Question 4
How many different red dyes are there in total?

There are 2 types of red dyes.

Different compounds can give the same colour. From the chromatogram, spots at 2 different heights are red in colour, suggesting that there are two red dyes.