Question

Amphoteric hydroxides react with both alkalies and acids. Which of the following Group 2 metal hydroxides is soluble in sodium hydroxides?
a) ${ Be(OH) }_{ 2 }$
b) ${ Mg(OH) }_{ 2 }$
c) ${ Ca(OH) }_{ 2 }$
d) ${ Ba(OH) }_{ 2 }$

Answer 1

Hint: Amphoteric substance is that which can react with both acid or base. It can act both as acid or base e.g. water. It is mostly used with oxides.

Complete step-by-step answer:
Now let us look it the given options

a)Beryllium hydroxide ${ Be(OH) }_{ 2 }$ is amphoteric in nature as it can react with alkalis and acids both.
When beryllium hydroxide reacts with acids and alkalis the following reactions will occur;
When beryllium hydroxide reacts with hydrochloric acid then beryllium chloride will be formed along with water.
${ Be(OH) }_{ 2 }{ +2HCl\rightarrow BeCl }_{ 2 }{ +2H }_{ 2 }{ O }$
When beryllium hydroxide reacts with sodium hydroxide then sodium beryllate will be formed along with water.
${ Be(OH) }_{ 2 }{ +2NaOH\rightarrow Na }_{ 2 }{ BeO }_{ 2 }{ +2H }_{ 2 }{ O }$
b). Magnesium hydroxide ${ Mg(OH) }_{ 2 }$ is a base as it reacts with an acid (like HCl) to form Magnesium chloride along with water.
The following reaction will take place:
${ Mg(OH) }_{ 2 }{ +2HCl\rightarrow MgCl }_{ 2 }{ +2H }_{ 2 }{ O }$
c) Calcium hydroxide ${ Ca(OH) }_{ 2 }$ is a base as it gives hydroxide ions as it reacts with an acid (like HCl) to form calcium chloride along with water.
The following reaction will take place:
${ Ca(OH) }_{ 2 }{ +2HCl\rightarrow CaCl }_{ 2 }{ +2H }_{ 2 }{ O }$
d) Barium hydroxide ${ Ba(OH) }_{ 2 }$ is a strong base as it reacts with an acid (like HCl) to form barium chloride along with water.
The following reaction will take place:
${ Ba(OH) }_{ 2 }{ +2HCl\rightarrow BaCl }_{ 2 }{ +2H }_{ 2 }{ O }$
Hence, Beryllium hydroxide is amphoteric in nature.

The correct option is A.

Note: The possibility to make a mistake is that you may choose option C. But when Calcium hydroxide reacts with a base like NaOH then there will not be any reaction occurring. NaOH is a strong alkali and dissociates to give hydroxide ions. Hence, it is a base, not an acid.