This question is about an experiment to determine the solubility of calcium hydroxide in water at 20 ∘C20\ ^\circ\text{C}20 ∘C.
Calcium hydroxide is slightly soluble in water.
Suggest why the solution must be kept in a stoppered flask with excess solid until no more solid dissolves.
Suggest why it is important to completely remove any undissolved calcium hydroxide by filtration before the titration.
Give the chemical equation for the reaction between calcium hydroxide and hydrochloric acid.
Table 1 shows the results of the titrations with 0.0500 mol dm−30.0500\text{ mol dm}^{-3}0.0500 mol dm−3 hydrochloric acid (HCl\text{HCl}HCl).
Table 1
| Titration | Rough | 1 | 2 | 3 |
|---|---|---|---|---|
| Final burette reading / cm3\text{cm}^3cm3 | 24.1024.1024.10 | 25.3025.3025.30 | 31.8531.8531.85 | 24.2524.2524.25 |
| Initial burette reading / cm3\text{cm}^3cm3 | 0.000.000.00 | 2.502.502.50 | 8.508.508.50 | 1.401.401.40 |
| Titre / cm3\text{cm}^3cm3 | 24.1024.1024.10 | 22.8022.8022.80 | 23.3523.3523.35 | 22.8522.8522.85 |
Use the results in Table 1 to calculate the mean titre. Then, use your mean titre to calculate the solubility of calcium hydroxide, in ggg per 100 cm3100\text{ cm}^3100 cm3 of solution at 20 ∘C20\ ^\circ\text{C}20 ∘C. Give your answer to 3 significant figures. (Assume Mr(Ca(OH)2)=74.1M_r(\text{Ca(OH)}_2) = 74.1Mr(Ca(OH)2)=74.1)
77 exam-style questions on AQA A Level Chemistry Acids and bases (A-level only), covering Brønsted–Lowry acid–base equilibria in aqueous solution (A-level only), Definition and determination of pH (A-level only), The ionic product of water, $K_w$ (A-level only), Weak acids and bases $K_a$ for weak acids (A-level only), pH curves, titrations and indicators (A-level only), and Buffer action (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.