By hand, rule a pencil base line on chromatography paper, spot an unknown mixture M and four known food colourings with capillary tubes, and stand the paper in a beaker of water with the lid on. Take it out when the solvent front is near the top, mark the front, then measure every distance with a ruler and a magnifier, work out Rf values and decide which colourings are in M. Every attempt uses different colourings, Rf values and mixture. Allow about 25 minutes.
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A base line in pencil about 2 cm from the bottom with all five samples spotted on it, water below the base line, the lid on while the solvent rises, the paper taken out when the front is near the top (but before it reaches the top), and the solvent front marked straight away.
Pencil does not dissolve in the solvent, so the line does not run; the base line is above the solvent so that the spots do not dissolve into the solvent in the beaker.
A column heading with quantity / unit, every distance to the nearest 0.1 cm from the base line (to the centre of each spot) that matches your own paper, Rf values worked out from your own distances to 2 decimal places, and an accuracy mark for Rf values within 0.03 of the true values.
The colourings in M, identified by spots at the same height (the same Rf); the spot that stayed on the base line and why (insoluble in water); and an improvement (a different solvent).
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.