Question

What are amphoteric oxides? Give two examples of amphoteric oxides.

Answer 1

An amphoteric compound is a molecule or ion that can react both as an acid as well as a base. Many metals (such as copper, zinc, tin, lead, aluminium, and beryllium) form amphoteric oxides or hydroxides. Amphoterism depends on the oxidation state of the oxide.

Zinc oxide $\left(ZnO\right)$ reacts with both acids and with bases:

In acid: $ZnO+2H^{+}\to Z{n}^{2+}+H_{2}O$

In base: $ZnO+H_{2}O+2O{H}^{-}\to \left[Zn\right(OH{)}_4{]}^{2-}$

Aluminium oxide

with acid:$A{l}_2{O}_3+3H_{2}O+6H_3{O}^{+}\left(aq\right)\to 2\left[Al\right(H_{2}O{)}_6{]}^{3+}\left(aq\right)$

with base: $A{l}_2{O}_3+3H_{2}O+2O{H}^{-}\left(aq\right)\to 2\left[Al\right(OH{)}_4{]}^{-}\left(aq\right)$