In an investigation to study neutralisation, a student adds small portions of solid calcium hydroxide, Ca(OH)2\text{Ca(OH)}_2Ca(OH)2, to 50 cm3 of dilute hydrochloric acid, HCl(aq)\text{HCl}(\text{aq})HCl(aq), in a beaker and records the pH after each addition.
The method used is:
Step 1: Measure 50 cm3 of dilute hydrochloric acid into a beaker.
Step 2: Add 0.15 g of calcium hydroxide powder to the beaker.
Step 3: Measure and record the pH of the mixture.
Step 4: Repeat Steps 2 and 3 until the pH remains constant.
State one action the student must perform immediately after adding the calcium hydroxide in Step 2, but before measuring the pH in Step 3, to ensure that the reaction is complete.
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.