A student measures the pH of two acids using a pH meter. Both acids have a concentration of 0.10 mol dm−3\mathrm{mol\,dm^{-3}}moldm−3.
The table shows the results.
| Acid | pH |
|---|---|
| hydrochloric acid | 1.0 |
| ethanoic acid | 2.9 |
Explain why ethanoic acid is described as a weak acid.
Explain why the hydrochloric acid has a lower pH than the ethanoic acid, even though both acids have the same concentration.
Write an equation to show hydrogen chloride ionising in water. Include state symbols.
Another student says: "A 1.0 mol dm−3\mathrm{mol\,dm^{-3}}moldm−3 solution of ethanoic acid is more concentrated than 0.10 mol dm−3\mathrm{mol\,dm^{-3}}moldm−3 hydrochloric acid, so it is a stronger acid." Explain why this student is wrong.
Equal pieces of magnesium ribbon are added to the two 0.10 mol dm−3\mathrm{mol\,dm^{-3}}moldm−3 acids. Suggest how the observations with ethanoic acid would differ from those with hydrochloric acid.
44 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.