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A forensic scientist is analyzing a black ink sample from a suspected forged signature using thin-layer chromatography (TLC).

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

  • The solvent front traveled a distance of 12.5 cm12.5\text{ cm}12.5 cm from the pencil baseline (start line).
  • The black ink separated into two distinct component spots: a purple spot and a yellow spot.
  • The purple spot traveled a distance of 10.0 cm10.0\text{ cm}10.0 cm from the baseline.
  • The yellow spot traveled a distance of 5.5 cm5.5\text{ cm}5.5 cm from the baseline.
a.

Explain how this chromatogram indicates that the black ink is a mixture rather than a pure substance.

[2]
b.

Calculate the RfR_fRf​ value of the purple spot using the equation: Rf=distance moved by spotdistance moved by solventR_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 (purple or yellow) has the greater RfR_fRf​ value.

[2]

Purity, formulations and chromatography Questions

Practise AQA GCSE Chemistry Purity, formulations and chromatography with exam-style questions for Foundation and Higher tier. 39 questions covering Pure substances, Formulations, and Chromatography, matched to the AQA GCSE Chemistry (8462) specification and written in Paper 1 and Paper 2 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.

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Purity, formulations and chromatography Questions

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