Question

Metals which form amphoteric oxides.

Answer 1

Hint: Amphoteric compounds are the compounds which react with both acid and bases. Amphoteric oxides of metals dissolve in both acidic and alkaline solutions. In other words, we can say that the oxides which show acidic as well as basic properties are amphoteric in nature.

Complete answer:
Some of the amphoteric oxides are given below :
Aluminium oxide ($A{{l}_{2}}{{O}_{3}}$)
It reacts with acids as well as bases. It is insoluble in water.
Reaction of $A{{l}_{2}}{{O}_{3}}$with hydrochloric acid gives aluminium chloride. The chemical reaction is given below:
     $A{{l}_{2}}{{O}_{3}}+6HCl\to 2AlC{{l}_{3}}+3{{H}_{2}}O$
 Reaction of $A{{l}_{2}}{{O}_{3}}$ with sodium hydroxide to give sodium aluminate is given below:
     $A{{l}_{2}}{{O}_{3}}+2NaOH\to 2NaA{{l}_{3}}{{O}_{2}}+{{H}_{2}}O$

Gallium oxide ($G{{a}_{2}}{{O}_{3}}$)
It is formed by burning gallium in oxygen.
$G{{a}_{2}}{{O}_{3}}$ reacts with hydrochloric acid to give gallium trichloride. The chemical reaction involved is as follows:
     $G{{a}_{2}}{{O}_{3}}+6HCl\to 2G{{a}_{2}}{{O}_{3}}+3{{H}_{2}}O$
It reacts with alkali metals oxides to form compounds of the type $MGa{{O}_{2}}$. Here, M is an alkali metal. It forms a solution of $Ga(OH)_{4}^{-}$ in strong basic solutions.

Zinc oxide (ZnO)
Reaction of ZnO with sulphuric acid to from zinc sulphate is given below:
     \[ZnO+{{H}_{2}}S{{O}_{4}}\to ZnS{{O}_{4}}+{{H}_{2}}O\]
ZnO reacts with NaOH to give sodium zincate. The reaction is given below:
     $ZnO+2NaOH+{{H}_{2}}O\to N{{a}_{2}}\left[ Zn{{(OH)}_{4}} \right]$

Lead oxide (PbO)
Reaction with acid: $PbO+2HCl\to PbC{{l}_{2}}+{{H}_{2}}O$
Reaction with base: $PbO+2NaOH+{{H}_{2}}O\to N{{a}_{2}}\left[ Pb{{(OH)}_{4}} \right]$

Stannous oxide (SnO)
Reaction with acid: \[SnO+2HCl\to SnC{{l}_{2}}+{{H}_{2}}O\]
Reaction with base: \[SnO+4NaOH+{{H}_{2}}O\to N{{a}_{2}}\left[ Sn{{(OH)}_{6}} \right]\]
Scandium Oxide ($S{{c}_{2}}{{O}_{3}}$)

It reacts with acids to give hydrated products. Reaction of $S{{c}_{2}}{{O}_{3}}$ with HCl is given below:
     \[S{{c}_{2}}{{O}_{3}}+6HCl+n{{H}_{2}}O\to 2ScC{{l}_{3}}.n{{H}_{2}}O+3{{H}_{2}}O\]
 $S{{c}_{2}}{{O}_{3}}$ forms scandate salts with base. Its reaction with KOH as follows:
     $3S{{c}_{2}}{{O}_{3}}+6KOH+3{{H}_{2}}O\to 2{{K}_{3}}S{{c}_{3}}{{(OH)}_{6}}$
Some other examples of amphoteric oxides are antimony oxide ($S{{b}_{2}}{{O}_{3}}$), vanadium oxide (${{V}_{2}}{{O}_{5}}$), beryllium oxide (BeO), chromium oxide (\[C{{r}_{2}}{{O}_{3}}\]).

Note: Metal oxides are generally basic in nature. Some metals form amphoteric oxides. Oxides of non-metals are generally acidic in nature.