A student tested a red dye using paper chromatography. In the solvent the student used, the dye produced one spot.
The student concluded that the red dye is a pure substance.
Explain why this result does not show that the dye is pure.
Describe how the student could obtain better evidence that the red dye is pure.
40 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.