Question

How are oxides classified? Describe each type of oxide with the help of a chemical reaction.

Answer 1

Definition of oxides

• $\mathrm{Oxides}$ are chemical compounds with one or more oxygen atoms combined with another element.
• They are formed when metal or nonmetal reacts with $\mathrm{Oxygen}\left({\mathrm{O}}_2\right)$ present in the air.

Classification of oxides: Based on the acid-base characteristics $\mathrm{Oxides}$ are classified into 4 types.

• Acidic oxides
• Basic oxides
• Neutral oxides
• Amphoteric oxides

Acidic oxides

• They are the oxides of nonmetals.
• They dissolve in water to produce acids.
• For example acidic $\mathrm{Sulphur}\mathrm{dioxide}\left({\mathrm{SO}}_2\right)$ dissolve in water(${\mathrm{H}}_2\mathrm{O}$) to form $\mathrm{Sulphurous}\mathrm{acid}\left({\mathrm{H}}_2{\mathrm{SO}}_3\right)$.

$\underset{\mathrm{Sulphur}\mathrm{dioxide}}{{\mathrm{SO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}(\mathrm{l}})\to \underset{\mathrm{Sulphurous}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{SO}}_3\left(\mathrm{aq}\right)}$

• Acids generally turn blue litmus to red. Therefore acidic oxides dissolved in water also turn blue litmus paper into the red.

Basic oxides

• They are the oxides of metals.
• They dissolve in water to produce bases.
• For example, basic $\mathrm{Sodium}\mathrm{oxide}\left({\mathrm{Na}}_2\mathrm{O}\right)$ dissolve in water(${\mathrm{H}}_2\mathrm{O}$) to form the base $\mathrm{Sodium}\mathrm{hydroxide}\left(\mathrm{NaOH}\right)$.
• Bases generally turn red litmus to blue. Therefore basic oxides dissolved in water also turn red litmus paper into blue.

$\underset{\mathrm{Sodium}\mathrm{oxide}}{{\mathrm{Na}}_2\mathrm{O}\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}(\mathrm{l}})\to \underset{\mathrm{Sodium}\mathrm{hydroxide}}{2\mathrm{NaOH}\left(\mathrm{aq}\right)}$

Neutral oxides

• Neutral oxides show neither acidic nor basic properties.
• They are unaffected by the litmus paper.
• $\mathrm{Carbon}\mathrm{monoxide}\left(\mathrm{CO}\right),\mathrm{Nitrous}\mathrm{oxide}\left({\mathrm{N}}_2\mathrm{O}\right),\mathrm{and}\mathrm{nitric}\mathrm{oxide}\left(\mathrm{NO}\right)$ are some of the examples of neutral oxides.

Amphoteric oxides

• Amphoteric oxides are the oxides of metal that show both acidic and basic properties.
• $\mathrm{ZnO},\mathrm{PbO},\mathrm{and}{\mathrm{Al}}_2{\mathrm{O}}_3$ are the examples of amphoteric oxides.
• They react with both acids and bases to form salt and water.
• When they react with acids, they form salt and water. Thereby showing basic properties.
• When they react with bases, they form salt and water. Thereby showing acidic properties.

$\underset{\mathrm{Zinc}\mathrm{oxide}}{\mathrm{ZnO}(\mathrm{s}})+\underset{\mathrm{Hydrochloric}\mathrm{acid}}{2\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Zinc}\mathrm{chloride}}{{\mathrm{ZnCl}}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$ [basic in nature]

$\underset{\mathrm{Zinc}\mathrm{oxide}}{\mathrm{ZnO}(\mathrm{s}})+\underset{\mathrm{Hydrochloric}\mathrm{acid}}{2\mathrm{NaOH}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Sodium}\mathrm{zincate}}{{\mathrm{Na}}_2{\mathrm{ZnO}}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$ [acidic in nature]