Acidic, Basic, Amphoteric & Neutral Oxides

Understanding Oxides

Oxides are compounds formed when elements combine with oxygen. They can be classified based on their chemical properties into acidic, basic, amphoteric, and neutral oxides.

1. Acidic Oxides

• Formed by non-metals.
• Dissolve in water to form acids. For example, carbon dioxide ( $\text{CO}_2$) forms carbonic acid ( $\text{H}_2\text{CO}_3$).
• React with bases to form salt and water.
• Examples: $\text{SO}_2$, $\text{NO}_2$.

2. Basic Oxides

• Formed by metals.
• Dissolve in water to form bases (alkalis). For example, sodium oxide ( $\text{Na}_2\text{O}$) forms sodium hydroxide ( $\text{NaOH}$).
• React with acids to form salt and water.
• Examples: $\text{MgO}$, $\text{CaO}$.

3. Amphoteric Oxides

• Show both acidic and basic properties.
• React with both acids and bases to form salt and water.
• Examples: $\text{Al}_2\text{O}_3$, $\text{ZnO}$.

4. Neutral Oxides

• Do not react with acids or bases.
• Examples: $\text{N}_2\text{O}$, $\text{CO}$.

pH of Oxide Solutions

The pH of an oxide solution depends on its nature:

• Acidic oxides form acidic solutions with pH < 7.
• Basic oxides form basic solutions with pH > 7.
• Amphoteric oxides can form either acidic or basic solutions depending on the reactants.
• Neutral oxides do not affect the pH significantly.

Examples

Example 1: Reaction of $\text{SO}_2$ with Water

When $\text{SO}_2$ dissolves in water, it forms sulfurous acid:

$$\text{SO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_3$$

This solution is acidic with a pH less than 7.

Example 2: Reaction of $\text{Na}_2\text{O}$ with Water

When $\text{Na}_2\text{O}$ dissolves in water, it forms sodium hydroxide:

$$\text{Na}_2\text{O} + \text{H}_2\text{O} \rightarrow 2\text{NaOH}$$

This solution is basic with a pH greater than 7.