Question

Predict the feasibility of the given reactions in aqueous solution
(i) $Be ( OH )_{2}+2 OH ^{-} \rightarrow\left[ Be ( OH )_{4}\right]^{2-}$
(ii) $Be ( OH )_{2}+2 H ^{+} \rightarrow\left[ Be ( OH )_{4}\right]^{2+}$

• 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.
$Be ( OH )_{2}+2 HCl +2 H _{2} O \rightarrow\left[ Be \left( H _{2} O \right)_{4}\right] Cl _{2}$
$Be ( OH )_{2}+ NaOH \rightarrow Na _{2} BeO _{2}+2 H _{2} O$
or $Na _{2}\left[ Be ( OH )_{4}\right]$ or $Be ( OH )_{2}+2 \overset{\ominus}{ OH } \rightarrow\left[ Be ( OH )_{4}\right]^{2-}$
Hence, both reaction are feasible.