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Chemistry notebook Cambridge IGCSE 0620

Pupil sheet · Paper chromatography

Can one colour hide several substances? — questions

Name ______________________ Date ____________

Try every question before you use a nudge. Write in full sentences where you are asked to explain.

1. Explain

Choose a valid starting position for the paper and sample spots. Explain how the other position could lose sample into the beaker.

Circle one answer.

  • Baseline and sample spots above the liquid; bottom edge in solvent
  • Baseline and sample spots under the liquid

Explain what would happen to a submerged sample.

Nudge (only if you are stuck): Which part of the paper should touch the reservoir? What happens if the sample itself sits under the liquid?

2. Match

Match each action to the problem it prevents: a pencil line, a cover, and an immediate solvent-front mark.

Write the number of the matching option.

  1. Preserve the solvent-front distance
  2. Avoid adding soluble ink from the line
  3. Reduce solvent evaporation
  • Draw a pencil baseline: ______
  • Cover the beaker: ______
  • Mark the wet solvent front: ______

Nudge (only if you are stuck): What could disappear if the line dissolved, solvent evaporated or the wet edge dried?

3. Explain

Put the last four actions in order. Explain why the pencil mark cannot wait until the paper is dry.

Write the number of each step in order.

  1. Immediately mark the wet front
  2. Dry the removed paper
  3. Develop until the front is below the top
  4. Lift the paper
  • First: ______
  • Second: ______
  • Third: ______
  • Fourth: ______

Why must the mark come before drying?

Nudge (only if you are stuck): Which wet boundary might you lose when solvent evaporates?

4. Explain

A pigment stays at the baseline in water. A pupil calls it a pure substance because it didn't move. Does that observation support the claim? Explain one check of the method.

Nudge (only if you are stuck): Was water a suitable solvent for this pigment? Can a stationary spot tell you how many substances are present?

5. Explain

A food colouring contains soluble dyes and a little insoluble grit. You want the grit removed and the dyes compared with known samples. Choose and justify a method for each goal. Then describe a valid setup and finish for the dye comparison.

Remove grit: method and reason

Compare dyes: method and reason

Chromatography setup and finishing precautions

Nudge (only if you are stuck): Which method retains separate grains? Which gives a pattern of dissolved dyes? What needs to stay above the reservoir?