In a practical investigation, a student adds powdered magnesium oxide to dilute sulfuric acid in a beaker and monitors the pH as the reaction proceeds.
The procedure is as follows:
Step 1: Measure 100 cm3 of dilute sulfuric acid into a beaker.
Step 2: Add 0.2 g of powdered magnesium oxide to the beaker.
Step 3: Measure and record the pH of the mixture.
Step 4: Repeat Steps 2 and 3 until there is no further change in pH.
State one action the student should take immediately after Step 2, before measuring the pH, 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.