A student investigates the neutralisation of acid in a model wastewater sample. They add 0.15 g portions of solid magnesium hydroxide, Mg(OH)2\text{Mg(OH)}_2Mg(OH)2, to 30 cm3 of dilute sulfuric acid, H2SO4\text{H}_2\text{SO}_4H2SO4, recording the pH after each addition.
Explain why the mixture must be stirred continuously for a short time after adding each portion of magnesium hydroxide before the pH is measured.
276 exam-style questions on Edexcel GCSE Chemistry 4.1 Acids, covering 4.1.1 Acids, alkalis and the pH scale, 4.1.2 Hydrogen ion concentration and pH, 4.1.3 Dilute and concentrated, weak and strong acids, 4.1.4 Bases, alkalis and the reactions of acids, 4.1.5 Chemical tests for hydrogen and carbon dioxide, 4.1.6 Neutralisation as a reaction of acids with bases, 4.1.7 Preparing soluble salts, and 4.1.8 Solubility rules and preparing insoluble salts. Each one has a worked solution and a mark scheme showing where the marks go.