Question

What are the amphoteric oxides? Choose the amphoteric oxides from amongst the following oxides.

• ${\mathrm{Na}}_2\mathrm{O},\mathrm{ZnO},{\mathrm{Al}}_2{\mathrm{O}}_3,{\mathrm{CO}}_2,{\mathrm{H}}_2\mathrm{O}$

Answer 1

Amphoteric oxides

• Amphoteric oxides: Amphoteric oxides are the type of oxides that reacts with both acid and base.
• This means amphoteric oxides possess both the properties of acid and base.

Sodium oxide$\mathbf{\left(}{\mathbf{Na}}_{\mathbf{2}}\mathbf{O}\mathbf{\right)}$

• The formation of oxides occurs by the combination of Oxygen and other elements.
• Bases are formed by the gain of electrons or by donating a pair of electrons in the solution.
• Sodium oxide contains Oxygen ions$\left(O_2^{-}\right)$ which act as a strong base and therefore, it easily combines with Hydrogen.
• Thus, Sodium oxide is basic in nature.

Zinc oxide$\mathbf{\left(}\mathbf{ZnO}\mathbf{\right)}$

• The amphoteric oxide when reacts with acid and base to form salt and water.
• Chemical reaction to show acidic characteristics of Zinc oxide: $\underset{(\mathrm{Zinc}\mathrm{oxide})}{\mathrm{ZnO}\left(\mathrm{s}\right)}+\underset{(\mathrm{Sulphuric}\mathrm{acid})}{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}\to \underset{(\mathrm{Zinc}\mathrm{sulphate})}{{\mathrm{ZnSO}}_4\left(\mathrm{s}\right)}+{\mathrm{H}}_2\mathrm{O}$
• Chemical reaction to show basic characteristics of Zinc oxide: $\underset{(\mathrm{Zinc}\mathrm{oxide})}{\mathrm{ZnO}\left(\mathrm{s}\right)}+\underset{(\mathrm{Sodium}\mathrm{hydroxide})}{2\mathrm{NaOH}\left(\mathrm{s}\right)}\to \underset{(\mathrm{Sodium}\mathrm{zincate})}{{\mathrm{Na}}_2{\mathrm{ZnO}}_2\left(\right)}+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$
• Thus, Zinc oxide behaves as amphoteric in nature.

Aluminium oxide $\mathbf{\left(}{\mathbf{Al}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{3}}\mathbf{\right)}$

• Oxygen combines with other elements to form oxides and the oxide can be acidic, basic and amphoteric in nature.
• Chemical reaction to show acidic characteristics of Aluminium oxide: $\underset{\left(\mathrm{Aluminium}\mathrm{oxide}\right)}{{\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)}+\underset{(\mathrm{Hydrogen}\mathrm{chloride})}{6\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{(\mathrm{Aluminium}\mathrm{chloride})}{2{\mathrm{AlCl}}_3\left(\mathrm{aq}\right)}+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$
• Chemical reaction to show basic characteristics of Aluminium oxide: $\underset{\left(\mathrm{Aluminium}\mathrm{oxide}\right)}{{\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)}+\underset{(\mathrm{Hydrogen}\mathrm{chloride})}{2\mathrm{NaOH}\left(\mathrm{aq}\right)}\to \underset{(\mathrm{Sodium}\mathrm{aluminate})}{2{\mathrm{NaAlO}}_2\left(\mathrm{s}\right)}+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$
• Therefore, Thus, Aluminium oxide behaves as amphoteric in nature.

Carbon dioxide$\mathbf{\left(}{\mathbf{CO}}_{\mathbf{2}}\mathbf{\right)}$

• Acids are formed by the loss of electrons or by accepting a pair of electrons in the solution.
• As Carbon dioxide itself is not an acidic compound but when dissolved in water it forms an acidic compound called Carbonic acid.
• The chemical reaction occurs as follows: $\mathrm{CO}\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \underset{(\mathrm{Carbonic}\mathrm{acid})}{{\mathrm{H}}_2{\mathrm{CO}}_3\left(\mathrm{g}\right)}$
• Thus, Carbon dioxide is acidic in nature.

Water$\mathbf{\left(}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{\right)}$

• Water has a neutral pH$\left(7\right)$ solution, the concentration of hydroxide ions is equal to Hydrogen ions(With no disturbance in its equilibrium state).
• Thus, water also behaves as an amphoteric in nature.

Hence, we concluded that amphoteric oxides behave in both acidic and basic nature.

The amphoteric oxides are: Zinc oxide$\left(\mathrm{ZnO}\right)$, Aluminium oxide$\left({\mathrm{Al}}_2{O}_3\right)$, and water.

Basic oxide: Sodium oxide$\mathbf{\left(}{\mathbf{Na}}_{\mathbf{2}}\mathbf{O}\mathbf{\right)}$

Acidic oxide: Carbon dioxide$\mathbf{\left(}{\mathbf{CO}}_{\mathbf{2}}\mathbf{\right)}$