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8.1 Purity, formulations and chromatography

8.1 Purity, formulations and chromatography

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Question 5

A student investigated a sample of green food dye using paper chromatography.

At the end of the experiment, the following measurements were recorded:

  • The solvent front traveled a distance of 8.0 cm8.0\text{ cm}8.0 cm from the pencil start line.
  • The green dye separated into two distinct spots: a blue spot and a yellow spot.
  • The blue spot traveled a distance of 6.0 cm6.0\text{ cm}6.0 cm from the start line.
  • The yellow spot traveled a distance of 3.6 cm3.6\text{ cm}3.6 cm from the start line.
a.

Explain how this chromatogram shows that the green food dye is a mixture (not a pure substance).

[1]
b.

Calculate the RfR_fRf​ value of the blue spot using the equation:

Rf=distance moved by spotdistance moved by solvent R_f = \frac{\text{distance moved by spot}}{\text{distance moved by solvent}} Rf​=distance moved by solventdistance moved by spot​
[2]
c.

Identify which of the two spots (blue or yellow) has the smaller RfR_fRf​ value.

[1]
Markscheme

8.1 Purity, formulations and chromatography Questions

  1. GCSE
  2. /Chemistry
  3. /8.1 Purity, formulations and chromatography

28 exam-style questions on AQA GCSE Chemistry 8.1 Purity, formulations and chromatography, covering 8.1.1 Pure substances, 8.1.2 Formulations, and 8.1.3 Chromatography. Each one has a worked solution and a mark scheme showing where the marks go.

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