A water treatment works uses several ionic compounds to treat drinking water.
The table shows the names and formulae of some ions.
| Positive ion | Formula | Negative ion | Formula |
|---|---|---|---|
| aluminium | Al3+\mathrm{Al^{3+}}Al3+ | chloride | Cl−\mathrm{Cl^{-}}Cl− |
| calcium | Ca2+\mathrm{Ca^{2+}}Ca2+ | hydroxide | OH−\mathrm{OH^{-}}OH− |
| iron(III) | Fe3+\mathrm{Fe^{3+}}Fe3+ | sulfate | SO42−\mathrm{SO_{4}^{2-}}SO42− |
Calcium hydroxide is added to make the water less acidic. Give the formula of calcium hydroxide.
Aluminium sulfate is added to make small particles of dirt clump together. Give the formula of aluminium sulfate.
The works also uses sodium carbonate, Na2CO3\mathrm{Na_{2}CO_{3}}Na2CO3. Sodium carbonate contains Na+\mathrm{Na^{+}}Na+ ions and CO32−\mathrm{CO_{3}^{2-}}CO32− ions. Calculate the relative formula mass (MrM_{r}Mr) of sodium carbonate. Relative atomic masses: Na = 23, C = 12, O = 16
Calculate the percentage by mass of sodium in sodium carbonate. Give your answer to three significant figures.
Explain why the formula of sodium carbonate contains two sodium ions for each carbonate ion.
56 exam-style questions on Edexcel GCSE Chemistry 2.3 Ionic bonding, covering 2.3.1 Ions and the formation of ionic bonds, 2.3.2 Naming and deducing formulae of ionic compounds, and 2.3.3 Giant ionic lattices. Each one has a worked solution and a mark scheme showing where the marks go.