Question

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

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

Answer 1

Answer: (C)

$Be(OH{)}_2$ is amphoteric and the basic strength increases down the group.
Due to small size and high ionisation enthalpy of $Be,Be(OH{)}_2$ is amphoteric.
Therefore, it dissolves both in acid and bases.
$Be(OH{)}_2+2HCl+2H_{2}O\to \left[Be{\left(H_{2}O\right)}_4\right]C{l}_2$
$Be(OH{)}_2+NaOH\to N{a}_{2}Be{O}_2+2H_{2}O$
or $N{a}_2\left[Be(OH{)}_4\right]$ or $Be(OH{)}_2+2\stackrel{\ominus }{\mathrm{OH}}\to {\left[Be(OH{)}_4\right]}^{2-}$
Hence, both reaction are feasible.