Why is the start line drawn in pencil for paper chromatography?
Pencil lines are easier to rub out if a mistake is made
Ink would react with the paper and change its colour
Pencil does not dissolve and move with the solvent
Pencil helps the solvent to move up the paper evenly
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.