A student adds a piece of magnesium ribbon to dilute hydrochloric acid. The mixture fizzes and the pH increases from 1 to 3.
Which statement explains why the pH increases?
Magnesium reacts with the hydrogen ions, so the concentration of hydrogen ions decreases.
Hydrogen gas dissolves in the mixture and makes it alkaline.
Magnesium chloride is an alkali, so it neutralises the acid.
Chloride ions are given off as chlorine gas, so the acid is removed.
53 exam-style questions on OCR GCSE Chemistry 3.3 Types of chemical reactions, covering 3.3.1 Oxidation and reduction in terms of oxygen, 3.3.2 Acids, alkalis and neutralisation, 3.3.3 The pH scale and measuring pH, 3.3.4 Oxidation and reduction in terms of electrons, 3.3.5 Dilute and concentrated, weak and strong acids, and 3.3.6 Hydrogen ion concentration and pH. Each one has a worked solution and a mark scheme showing where the marks go.