A cosmetics scientist uses paper chromatography to analyse the dyes in a lipstick.
Explain why the different dyes in the lipstick separate on the chromatography paper.
A dye has an RfR_{f}Rf value of 0.45 in the solvent used. The solvent front moves 12.0 cm. Calculate the distance moved by the dye.
One spot from the lipstick stays on the baseline. Suggest why.
The dye extracted from lipstick J gives only one spot. A student says this proves that this dye is a pure substance. Explain why the student may be wrong.
Describe how the scientist could get further evidence that a spot from the lipstick is a particular known dye.
48 exam-style questions on Edexcel GCSE Chemistry 3.2 Methods of separating and purifying substances, covering 3.2.1 Pure substances and mixtures, 3.2.2 Techniques for separating mixtures, 3.2.3 Paper chromatography and Rf values, and 3.2.4 Making water potable. Each one has a worked solution and a mark scheme showing where the marks go.