ABC26IN0005 · Acids and Bases

Subject: Inorganic Chemistry · Chapter: Acids and Bases · Topic: Acid and Bases – General · Exam: CSIR-NET DEC 2013 · 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 (as printed): A
Explanation
In reaction (i) Water acting as an oxidant oxidizing $\mathrm{Ca}$ to $\mathrm{Ca^{2+}}$ getting itself reduced to $\mathrm{H_2}$. In reaction (ii) Water act as Lewis acid accepting electron from $\mathrm{Cl^{-}}$ which act as a ligand. In reaction (iii) Water act as Lewis base donating electron to $\mathrm{Mg^{2+}}$. In reaction (iv) Water acting as an reductant reducing $\mathrm{F}$ to $\mathrm{F^{-}}$. i) $\mathrm{H_2O + Cl^{-} = [Cl(H_2O)_n]^{-}}$ Where, $\mathrm{Cl}$ = Base, $\mathrm{H_2O}$ = Acid iii) $\mathrm{6H_2O + Mg^{2+}} \rightarrow$ octahedral complex shown below

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