A student tests solutions for chloride ions by adding dilute nitric acid and silver nitrate solution. The test tubes were rinsed with tap water. A faint white precipitate forms even when distilled water is tested in one of these tubes. What is the most likely reason?
Tap water contains dissolved chloride ions, left in the tube
Tap water contains microorganisms that react with silver nitrate
Tap water contains fine insoluble particles not removed by filtration
Tap water is slightly acidic, and acids react with silver nitrate
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.