Question

What do you understand by amphoteric oxide? Give the balanced equations for the reaction with three different amphoteric oxides with a caustic alkali. Write your observation if any.

Answer 1

Amphoteric oxides : Amphoteric oxides are those compounds, which react with both acids and alkalis to form salt and water.
For example: Oxides of Aluminium, zinc and lead are amphoteric in nature.

Balanced equations for the reaction of different amphoteric oxides with a caustic alkali :
Amphoteric oxide + Alkali → Salt + Water
(a) \[\ce{\underset{\text{White}}{ZnO} + 2NaOH ->\underset{\text{Sodium zincate(Colourless)}}{Na2ZnO2 + H2O}}\]

(b) \[\ce{\underset{\text{White}}{Al2O3} + 2NaOH ->\underset{\text{Sodium aluminate(White)}}{NaAlO2 + 2H2O}}\]

(c) \[\ce{\underset{\text{Yellow}}{PbO} + 2NaOH ->\underset{\text{Sodium plumbite(Colourless)}}{Na2PbO2 + H2O}}\]