An environmental chemist monitors the remediation of an acidic wastewater sample. They add solid calcium hydroxide, Ca(OH)2\text{Ca(OH)}_2Ca(OH)2, in small increments to 30.0 cm3 of a dilute nitric acid solution, HNO3(aq)\text{HNO}_3(\text{aq})HNO3(aq), and record the pH after each addition.
The table below shows their measurements:
| Mass of Ca(OH)2\text{Ca(OH)}_2Ca(OH)2 added (g) | pH |
|---|---|
| 0.0 | 1.2 |
| 0.1 | 1.4 |
| 0.2 | 1.6 |
| 0.3 | 2.0 |
| 0.4 | 2.8 |
| 0.5 | 7.0 |
| 0.6 | 11.2 |
| 0.7 | 11.8 |
| 0.8 | 12.1 |
Explain, in terms of the concentration of the ions present in the solution, why the pH has a low initial value, increases as the calcium hydroxide is added, and eventually reaches a high, alkaline value.
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.