A student is separating a mixture of synthetic food colorings using paper chromatography. They draw the baseline (start line) using a standard black ballpoint pen. After developing the chromatogram in an aqueous solvent, they find that the baseline has smudged and resolved into multiple colored components, which overlap with and obscure the food coloring spots.
State one modification to the method that would prevent the baseline from interfering with the analysis.
107 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.