Q19 / 160 · AP EAMCET 2021 (25 Aug Shift 1) · Chemistry
Which of the following pairs of reactions give $\mathrm{H}_2$ gas as a product upon hydrolysis?
- A(i) $\mathrm{Ba} \xrightarrow{\mathrm{H}_2 \mathrm{O}}$ Products (ii) $\mathrm{BaO}_2 \xrightarrow{\mathrm{H}_2 \mathrm{O}}$ Products
- Correct answerB(i) $\mathrm{Ca} \xrightarrow{\mathrm{H}_2 \mathrm{O}}$ Products (ii) $\mathrm{CaH}_2 \xrightarrow{\mathrm{H}_2 \mathrm{O}}$ Products
- C(i) $\mathrm{K} \xrightarrow{\mathrm{H}_2 \mathrm{O}}$ Products (ii) $\mathrm{K}_2 \mathrm{O} \xrightarrow{\mathrm{H}_2 \mathrm{O}}$ Products
- D(i) $\mathrm{Na} \xrightarrow{\mathrm{H}_2 \mathrm{O}}$ Products (ii) $\mathrm{Na}_2 \mathrm{O}_2 \xrightarrow{\mathrm{H}_2 \mathrm{O}}$ Products
Solution
When calcium metal is dropped in water, it begins to bubble vigorously and react with the water, producing hydrogen gas and a cloudy white precipitate of calcium hydroxide.
$$
\underset{\substack{\text { Calcium } \\ \text { metal }}}{\mathrm{Ca}}+2 \mathrm{H}_2 \mathrm{O} \longrightarrow \underset{\substack{\text { Calcium } \\ \text { hydroxide }}}{\mathrm{Ca}(\mathrm{OH})_2}+\underset{\substack{\text { Hydrogen } \\ \text { gas }}}{\mathrm{H}_2}
$$
The reaction of $\mathrm{CaH}_2$ with water can be represented by
$\underset{\substack{\text { Calcium } \\ \text { hydride }}}{\mathrm{CaH}_2}+2 \mathrm{H}_2 \mathrm{O} \longrightarrow \underset{\substack{\text { Calcium } \\ \text { hydroxide }}}{\mathrm{Ca}(\mathrm{OH})_2}+\underset{\substack{\text { Hydrogen } \\ \text { gas }}}{2 \mathrm{H}_2}$
The two hydrolysis products, $\mathrm{H}_2$ and $\mathrm{Ca}(\mathrm{OH})_2$ can be readily separated from the dried solvent.
Hence, the correct answer is option: 'B'.