"No precipitation reaction can occur without exchange of ions between the two reactants." Justify this statement giving a balanced chemical equation for the reaction.
Generated by claude-sonnet-4-6 · 2026-06-14 10:28 · grounding rag
Model Answer
In a precipitation reaction, two soluble ionic compounds react by exchanging their ions, forming an insoluble precipitate. Without this exchange of ions (double displacement), no precipitate can form.
Example:
$$\text{Na}_2\text{SO}_4(aq) + \text{BaCl}_2(aq) \rightarrow \text{BaSO}_4(s)\downarrow + 2\text{NaCl}(aq)$$
Here, $\text{Ba}^{2+}$ and $\text{SO}_4^{2-}$ ions exchange to form insoluble barium sulphate (white precipitate).
Source: Chapter 1, Section 1.2.4 Double Displacement Reaction
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Explanation
- Examiners expect you to link precipitation with double displacement — both concepts appear together in NCERT.
- The key phrase is "exchange of ions": Ba²⁺ from BaCl₂ combines with SO₄²⁻ from Na₂SO₄ to form the precipitate BaSO₄.
- Always include state symbols (aq), (s) and the ↓ arrow for the precipitate — these earn marks.
- 1 mark for the justification/explanation + 1 mark for the correct balanced equation.