A student carried out paper chromatography on four different food colourings, W, X, Y and Z. The chromatogram showed that colouring W separated into three spots with Rf values of 0.25, 0.50 and 0.75. Colouring X produced a single spot with Rf value 0.50. What can be concluded from these results?

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Question

A student carried out paper chromatography on four different food colourings, W, X, Y and Z. The chromatogram showed that colouring W separated into three spots with Rf values of 0.25, 0.50 and 0.75. Colouring X produced a single spot with Rf value 0.50. What can be concluded from these results?

Accepted Answer

W and X both contain the same substance — Award 1 mark for recognizing that the Rf value of 0.50 appears in both W and X, indicating a common component. D is incorrect — W is a mixture (three spots) and X could be pure, but this reverses the relationship. B is incorrect — X does occur in W (same Rf value). C is incorrect — solubility cannot be determined solely from the number of spots or Rf values shown.

Answer

W is more soluble in the solvent than X

Answer

X is a pure substance and does not occur in W

Answer

W and X both contain the same substance

Answer

W is a pure substance and X is a mixture

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