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.
Practise Edexcel GCSE Chemistry Acids with exam-style questions for Foundation and Higher tier. 276 questions, matched to the Edexcel GCSE Chemistry (1CH0) specification and written in Paper 1 and Paper 2 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.
