A scientist uses chromatography to check whether a sample of a painkiller is pure.
Which result gives the best evidence that the sample is a single pure substance?
It gives one spot with a large Rf value when water is used as the solvent.
It gives a spot with an Rf value that is less than 1 in water.
It gives a spot that moves the same distance as the solvent front.
It gives one spot on chromatograms run in several different solvents.
51 exam-style questions on OCR GCSE Chemistry 2.1 Purity and separating mixtures, covering 2.1.1 Pure substances and melting point data, 2.1.2 Relative formula mass and empirical formula, 2.1.3 Formulations as useful mixtures, 2.1.4 Techniques for separating mixtures, and 2.1.5 Chromatography and Rf values. Each one has a worked solution and a mark scheme showing where the marks go.