Chromatography (Cambridge O Level Chemistry)

A student investigated the colours present in a fruit drink. The fruit drink was tested to check that no artificial colours had been added. The apparatus below was used.

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When should the paper be removed from the beaker?

The diagram shows the results of the experiment.

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A mixture of coloured dyes, M, was separated by chromatography. The dyes were insoluble in water.

The chromatogram below shows the result of separating the mixture and the chromatography of three known dyes 1, 2 and 3.

On the diagram, label the base line (origin).

Name a solvent that could be used in this separation.

How many dyes were there in the mixture, M?

What are your conclusions about the identity of the dyes in the mixture, M?

How could the reliability of the results be checked?

The colours present in some fruit sweets can be separated using the apparatus below. The colours are water-soluble dyes. 

Name the process used to separate the colours.

Name the solvent used.

The results obtained for the colours in two different sweets, C and D, are shown below.

What is the name for the line at position B?

What conclusions can you draw about the colours present in sweets C and D?

The diagram shows the results of an experiment to separate and identify the colours present in two coloured mixtures, A and B.

Substances C, D, E and F are single colours.

Name this method of separation.

Draw a line on the diagram to show the level of the solvent at the beginning of the experiment.

Why should a pencil be used instead of a pen to draw the origin line?

State one difference and one similarity between the coloured mixtures, A and B.

difference ....................................................................................................

similarity ....................................................................................................

Which substances are present in mixture A?

The colours present in some blackcurrant sweets can be separated by chromatography.

The colours are water-soluble dyes.

The diagrams show how the colours can be extracted from the sweets. 

Complete the empty boxes to name the pieces of apparatus.

The apparatus below was used to carry out the chromatography.

Sketch, in the box, the chromatogram you would expect if two different colours were present in the sweets.

Chromatography can be used to identify amino acids from a sample of protein.

The diagram shows the chromatogram obtained when four samples of amino acids were analysed. The paper was sprayed with ninhydrin. 

Why is the origin line drawn in pencil?

Which amino acids could possibly be the same?

Which amino acid sample contains more than one amino acid? Explain your answer.

sample ....................................................................................................

explanation ....................................................................................................

The green pigment chlorophyll can be obtained from grass.

Step 1: The grass is crushed with sand.

Step 2: The grass is ground with ethanol until the solution is saturated.

Step 3: The solution is separated from the rest of the mixture.

Step 4: The colours in the solution are separated.

What apparatus is used in Step 1?

Suggest why the grass is ground with ethanol rather than water in Step 2.

Name the separation method in Step 3.

Describe how Step 4 is carried out.

A student extracted and investigated the orange colour in some sweets.
The student followed these instructions:

1. Collect sweets, a watch glass, a beaker, eye protection and 100 cm³ of ethanol.
2. Crush the sweets.
3. Place the crushed sweets in the beaker containing 100 cm³ of ethanol.
4. Boil the mixture with the watch glass covering the beaker.
5. Decant the liquid and concentrate it by evaporation until the colour is dark orange.
6. Investigate which colours are present in the orange solution.

Why should the sweets be crushed?

Why should the experiment be carried out in a well-ventilated laboratory?

State one safety precaution that the student should have taken, other than carrying out the experiment in a well-ventilated laboratory and using eye protection.

State the purpose of the watch glass.

Explain the term decant.

Describe how the student could carry out instruction 6. You may draw a diagram in the space below to help you answer the question.

A fake banknote can be investigated by dissolving the ink off the paper.
You are provided with four different inks from four different criminals.

Describe an experiment to show which one of these inks is the same as the ink from the banknote.
You can use a labelled diagram to help you answer the question.

E numbers identify chemicals which are added to foods.

E210 is benzoic acid. How could you show that a solution of benzoic acid is a weak acid?

test ..............................................................................................................................
result ........................................................................................................................... 

E211 is sodium benzoate. Name a suitable substance that would react with a solution of benzoic acid to form sodium benzoate.

E110 is Sunset yellow.
Outline a method you could use to show the presence of E110 in a food colouring.
A space has been left if you want to draw a diagram to help you answer the question.

Leaves from trees contain a mixture of coloured pigments which are not soluble in water. A student was given these two instructions to investigate the pigments in the leaves.

1.   Crush some leaves to extract the coloured pigments.
2.   Use the liquid extract to find the number of coloured pigments in the leaves.

What would the student need in order to effectively carry out instruction 1?

Describe an experiment to carry out instruction 2.
A space has been left below if you want to draw a diagram to help answer the question.

A sample of orange fruit jam was investigated to check the three colourings present.

Step 1: The jam was boiled with water.
Step 2: The mixture was filtered.
Step 3: The filtrate was concentrated.
Step 4: The concentrate was analysed by chromatography.

What was the purpose of Step 1?

Why was the mixture filtered?

How was Step 3 carried out?

Draw a diagram to show the possible paper chromatogram obtained in Step 4.