Amphoteric substances are special because they can act as either an acid or a base, depending on the environment they are in. Here’s a breakdown:
1. Definition
- An amphoteric substance reacts with both acids and bases.
- Examples: Water (H₂O), Aluminum hydroxide [Al(OH)₃], Zinc oxide (ZnO).
2. Behavior with Acids
- When an amphoteric substance meets a strong acid, it behaves as a base:
- It accepts protons (H⁺) from the acid.
- Example:
- Al(OH)₃ + HCl → AlCl₃ + H₂O
3. Behavior with Bases
- When it meets a strong base, it behaves as an acid:
- It donates protons (H⁺) or reacts with OH⁻.
- Example:
- Al(OH)₃ + NaOH → Na[Al(OH)₄]
4. Key Points
- Amphoteric behavior depends on the other substance in the reaction.
- Many metal oxides and hydroxides of elements like Al, Zn, Pb, Sn are amphoteric.
- This property is very useful in industrial chemistry and analytical chemistry for separating metals or neutralizing chemicals.
In short:
Amphoteric substances are “dual-natured” — they act as a base with acids and as an acid with bases, making them versatile in chemical reactions.