Q2 · CSIR-NET Chemistry, December 2013

Paper: CSIR-NET December 2013 · Subject: Inorganic Chemistry · Chapter: Acids and Bases · Topic: Acid and Bases – General · Marks: 2 · Difficulty: Medium

Water plays different roles in the following reactions.
\[ \begin{array}{l} \text{(i) } 2\mathrm{H_2O} + \mathrm{Ca} \rightarrow \mathrm{Ca^{2+}} + 2\mathrm{OH^-} + \mathrm{H_2} \\ \text{(ii) } n\mathrm{H_2O} + \mathrm{Cl} \rightarrow [\mathrm{Cl(H_2O)_n}]^{-} \\ \text{(iii) } 6\mathrm{H_2O} + \mathrm{Mg^{2+}} \rightarrow [\mathrm{Mg(H_2O)_6}]^{2+} \\ \text{(iv) } 2\mathrm{H_2O} + 2\mathrm{F_2} \rightarrow 4\mathrm{HF} + \mathrm{O_2} \end{array} \]
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
Explanation
(i) Ca is oxidised to Ca²⁺ and water is reduced to H₂: water is the oxidant. (ii) Water hydrogen-bonds Cl⁻ through its H end: acid. (iii) Water donates a lone pair to Mg²⁺: base. (iv) F₂ is reduced to HF and water is oxidised to O₂: water is the reductant.

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