Q38 · CSIR NET Chemistry, June 2015
Paper: CSIR NET June 2015 · Subject: Inorganic Chemistry · Chapter: Acids and Bases · Topic: Acids & Bases – General · Marks: 2 · Difficulty: Medium
Water plays different roles in the following reactions.
\[ \begin{array}{l} \text{(i) } 2\mathrm{H}_2\mathrm{O}+\mathrm{Ca} \rightarrow \mathrm{Ca}^{2+}+2\mathrm{OH}^{-}+\mathrm{H}_2 \quad \text{(ii) } n\mathrm{H}_2\mathrm{O}+\mathrm{Cl} \rightarrow [\mathrm{Cl}(\mathrm{H}_2\mathrm{O})_n]^{-} \\ \text{(iii) } 6\mathrm{H}_2\mathrm{O}+\mathrm{Mg}^{2+} \rightarrow [\mathrm{Mg}(\mathrm{H}_2\mathrm{O})_6]^{2+} \quad \text{(iv) } 2\mathrm{H}_2\mathrm{O}+2\mathrm{F}_2 \rightarrow 4\mathrm{HF}+\mathrm{O}_2 \end{array} \]
The correct role of water in each reaction is,(a)(i) oxidant, (ii) acid, (iii) base and (iv) reductant
(b)(i) oxidant, (ii) base, (iii) acid and (iv) reductant
(c)(i) acid, (ii) oxidant, (iii) reductant and (iv) base
(d)(i) base, (ii) reductant, (iii) oxidant and (iv) base
Answer
Answer: A ✓ checked by 4AB · confidence high
The source book printed C; on checking, A is correct — see the explanation.
Printed C; water cannot be the reductant towards Cl⁻ or the oxidant towards Mg²⁺.
Explanation
(i) Ca reduces water (H⁺ → H₂): water is the oxidant. (ii) Water solvates Cl⁻ through its H atoms: Lewis acid. (iii) Water donates its lone pair to Mg²⁺: base. (iv) F₂ oxidises water to O₂: water is the reductant.
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