Question

Assertion (A):\[Be{\left( {OH} \right)_2}\] dissolves in excess of\[NaOH\].
Reason(R):\[Be{\left( {OH} \right)_2}\] is an amphoteric compound.
Read the above assertion and reason and choose the correct statement regarding it.
A. Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
B. Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
C. Assertion is true but Reason is false.
D. Both Assertion and Reason are false.

Answer 1

Hint: we know that organic molecules are polar and they dissolve in only polar molecules. Such as water molecules because of the hydrogen bonding. Solubility depends on a lot of factors, among which one is the type of solvent itself.

Step by step answer:Barium hydroxide is sparingly soluble in water it will dissociate as shown below.
\[Be{\left( {OH} \right)_2} \to B{e^{2 + }} + 2O{H^\_}\]
This reaction is in equilibrium. If we now add \[NaOH\] to the solution so that \[Be{\left( {OH} \right)_2}\] is dissolved in the \[NaOH\] solution when we produce a high concentration of the \[O{H^\_}\] ions from the complete dissociation of the strong base.
\[NaOH\left( {aq} \right) \to N{a^ + }\left( {aq} \right) + O{H^\_}\left( {aq} \right)\]
This high concentration of \[O{H^\_}\] ions forces the first equilibrium to the left. Less \[Be{\left( {OH} \right)_2}\] is dissolved and dissociated in the solution, and the \[Be{\left( {OH} \right)_2}\] so produced precipitates out of the solution. This is called the common ion effect.
When beryllium hydroxide reacts with $NaOH$ it forms sodium beryllate. It is also water soluble.
$Be{\left( {OH} \right)_2} + 2NaOH \to N{a_2}Be{O_2} + 2{H_2}O$
Beryllium hydroxide is an amphoteric substance because it can dissolve in acid and base both.
When any compound is reacting with acid and base it means, it may be a neutral molecule or an ionic molecule who act both as an acid and a base.

Therefore, the correct answer is B. Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

Note: Amphoteric substances are acid or basic, they are metallic oxides they have metal cation which is usually a transition metal with a variable oxidation state. They tend to behave as both acidic and basic according to the reaction.