Question

Of the following oxides, the oxides which are soluble in sodium hydroxide are:

1. $A{s}_2{O}_3$

2. $S{b}_2{O}_3$

3. $SnO$

• A. 1 and 2 only
• B. 2 and 3 only
• C. 1 and 3 only
• D. 1, 2 and 3

Answer 1

The correct option is D

1, 2 and 3

All of these are amphoteric oxides, hence soluble in both acid as well as base.

Arsenic trioxide is an amphoteric oxide, and its aqueous solutions are weakly acidic. Thus, it dissolves readily in alkaline solutions to give arsenites. It is less soluble in acids, although it will dissolve in hydrochloric acid. With anhydrous $HF$ and $HCl$, it gives $As{F}_3$ and the trichloride:

$A{s}_2{O}_3+6HF⟶2As{F}_3+3H_{2}O$

$SnO$ is amphoteric, dissolving in strong acid to give tin(II) salts and in strong base to give stannites containing $Sn(OH{)}_3^{-}$.$S{b}_2{O}_3$, an amphoteric oxide, dissolves in aqueous sodium hydroxide solution to give the meta-antimonite $NaSb{O}_2$, which can be isolated as the trihydrate.

Antimony(III) oxide also dissolves in concentrated mineral acids to give the corresponding salts, which hydrolyzes upon dilution with water. With nitric acid, the trioxide is oxidized to antimony(V) oxide.