(a) What is observed when aqueous solutions of potassium iodide and lead nitrate are mixed together ? Name the type of reaction and write the chemical equation for the reaction that occurs.
Generated by claude-sonnet-4-6 · 2026-06-14 10:30 · grounding rag
Model Answer
Observation: A bright yellow precipitate is formed immediately.
Type of reaction: Double displacement reaction (precipitation reaction).
Chemical equation:
$$\text{Pb(NO}_3)_2\text{(aq)} + 2\text{KI(aq)} \rightarrow \text{PbI}_2\text{(s)} + 2\text{KNO}_3\text{(aq)}$$
The yellow precipitate formed is lead iodide (PbI₂).
Source: Chapter 1, Exercises Q.15
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Explanation
- Two marks are split: one for observation + type of reaction, one for the balanced equation.
- Always state the colour of the precipitate (yellow for PbI₂) — examiners specifically look for this.
- Label the precipitate with (s) and aqueous reactants/products with (aq) — state symbols are expected.
- "Double displacement" and "precipitation reaction" are both acceptable names; writing both is safest.
- The equation must be balanced (note the coefficient 2 before KI and KNO₃).