Amphoteric oxides are metal oxides that react with both acids AND bases to produce salt and water. The word 'amphoteric' comes from the Greek word 'amphoteros' meaning 'both.' Common examples include Aluminium oxide (Al₂O₃), Zinc oxide (ZnO), Lead(II) oxide (PbO), and Tin(II) oxide (SnO).
Amphoteric oxides react with BOTH acids and bases to form salt and water.
Examples: Al₂O₃, ZnO, PbO, SnO, BeO.
Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O (reacts with acid).
Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O (reacts with base).
ZnO + H₂SO₄ → ZnSO₄ + H₂O (acid reaction).
ZnO + 2NaOH → Na₂ZnO₂ + H₂O (base reaction).
Contrast: Acidic oxides (CO₂, SO₂) react only with bases; Basic oxides (CaO) react only with acids.
Definition: An oxide that reacts with both acids and bases to form salt and water is called an amphoteric oxide.
Common Amphoteric Oxides:
Reactions of Al₂O₃ (Aluminium Oxide):
With an acid (HCl): Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O (Acts as a base — reacts with acid to form aluminium chloride + water)
With a base (NaOH): Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O (Acts as an acid — reacts with base to form sodium aluminate + water)
Reactions of ZnO (Zinc Oxide):
With an acid (H₂SO₄): ZnO + H₂SO₄ → ZnSO₄ + H₂O (Acts as a base)
With a base (NaOH): ZnO + 2NaOH → Na₂ZnO₂ + H₂O (Acts as an acid; forms sodium zincate)
Types of Oxides:
| Type | Reacts with | Example |
|---|---|---|
| Acidic oxide | Bases only | CO₂, SO₂, SO₃, P₂O₅ |
| Basic oxide | Acids only | Na₂O, CaO, MgO, Fe₂O₃ |
| Amphoteric oxide | Both acid AND base | Al₂O₃, ZnO, PbO, SnO |
| Neutral oxide | Neither acid nor base | CO, NO, N₂O, H₂O |
Why are Metals like Al and Zn Amphoteric? • These metals lie in the p-block (Al) and d-block (Zn) with intermediate electronegativity • Their oxides show both metallic (basic) and non-metallic (acidic) character • They are metalloids or borderline metals
Amphoteric oxides are metal oxides that react with both acids and bases to form salt and water. Examples: Al₂O₃, ZnO, PbO, SnO. Al₂O₃ reacts with HCl to form AlCl₃ (acting as a base) and with NaOH to form NaAlO₂ (acting as an acid). ZnO similarly reacts with both H₂SO₄ and NaOH.
With acid: Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O (Al₂O₃ acts as base). With base: Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O (Al₂O₃ acts as acid, forming sodium aluminate). This dual behaviour makes Al₂O₃ an amphoteric oxide.
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