Q15 / 160 · TS EAMCET 2020 (10 Sep Shift 1) · Chemistry

Predict the feasibility of the given reactions in aqueous solution (i) $\mathrm{Be}(\mathrm{OH})_2+2 \mathrm{OH}^{-} \longrightarrow\left[\mathrm{Be}(\mathrm{OH})_4\right]^{2-}$ (ii) $\mathrm{Be}(\mathrm{OH})_2+2 \mathrm{H}^{+} \longrightarrow\left[\mathrm{Be}(\mathrm{OH})_4\right]^{2+}$

  • A
    Only (i) is feasible
  • B
    Only (ii) is feasible
  • Correct answer
    C
    (i) and (ii) are feasible
  • D
    (i) and (ii) are not feasible

Solution

$\mathrm{Be}(\mathrm{OH})_2$ is amphoteric and the basic strength increases down the group. Due to small size and high ionisation enthalpy of $\mathrm{Be}, \mathrm{Be}(\mathrm{OH})_2$ is amphoteric. Therefore, it dissolves both in acid and bases. $\begin{aligned} & \mathrm{Be}(\mathrm{OH})_2+2 \mathrm{HCl}+2 \mathrm{H}_2 \mathrm{O} \longrightarrow\left[\mathrm{Be}\left(\mathrm{H}_2 \mathrm{O}\right)_4\right] \mathrm{Cl}_2 \\ & \mathrm{Be}(\mathrm{OH})_2+\mathrm{NaOH} \longrightarrow \mathrm{Na}_2 \mathrm{BeO}_2+2 \mathrm{H}_2 \mathrm{O} \\ & \mathrm{Or} \mathrm{Na}_2\left[\mathrm{Be}(\mathrm{OH})_4\right] \text { or Be}(\mathrm{OH})_2+2 \mathrm{O} \mathrm{H} \longrightarrow\left[\mathrm{Be}(\mathrm{OH})_4\right]^{2-} \end{aligned}$ Hence, both reaction are feasible.

Hence, the correct answer is option: 'C'.

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