Translate the following word equations into balanced chemical equations, adding state symbols wherever appropriate:
(i) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
(ii) Barium chloride reacts with aluminium sulphate to give barium sulphate and aluminium chloride.
(iii) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
Generated by claude-sonnet-4-6 · 2026-06-26 00:54 · grounding rag
Model Answer
(i) Potassium + Water → Potassium hydroxide + Hydrogen
$$2\text{K}(s) + 2\text{H}_2\text{O}(l) \rightarrow 2\text{KOH}(aq) + \text{H}_2(g)$$
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
$$3\text{BaCl}_2(aq) + \text{Al}_2(\text{SO}_4)_3(aq) \rightarrow 3\text{BaSO}_4(s) + 2\text{AlCl}_3(aq)$$
(iii) Hydrogen sulphide + Oxygen → Water + Sulphur dioxide
$$2\text{H}_2\text{S}(g) + 3\text{O}_2(g) \rightarrow 2\text{H}_2\text{O}(l) + 2\text{SO}_2(g)$$
Source: Chapter 1, Section 1.1.2 (Balanced Chemical Equations)
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Explanation
- Each sub-question is 1 mark: award is for the correctly balanced equation with proper state symbols.
- Key state symbols: metals/solids → (s); gases → (g); solutions in water → (aq); liquids → (l). BaSO₄ is insoluble, so (s); KOH dissolves, so (aq).
- Balancing tip: always check atom count on both sides before writing the final equation.
- Do not forget to write the word equation before the chemical equation — examiners appreciate it, and it helps you set up the formula equation correctly.