Amphoteric Oxide – IGCSE Chemistry Definition
IGCSE Chemistry definition of amphoteric oxide: an oxide reacting with both acids and alkalis. Covers examples, equations, and exam tips for Cambridge 0620.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
Amphoteric oxides are a favourite of examiners because they test whether candidates truly understand the acid–base spectrum. If you only revise basic oxides and acidic oxides, you will lose marks when Paper 4 asks for an oxide that reacts with both acid and alkali.
The 0620 definition
An amphoteric oxide is a metal oxide that reacts with both acids and alkalis to form a salt and water.
The word amphoteric comes from Greek meaning “both” — these oxides behave as a base when added to acid and as an acid when added to alkali.
Key examples
| Oxide | With acid | With alkali |
|---|---|---|
| ZnO | ZnO + 2HCl → ZnCl₂ + H₂O | ZnO + 2NaOH → Na₂ZnO₂ + H₂O |
| Al₂O₃ | Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O | Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O |
| PbO | PbO + 2HNO₃ → Pb(NO₃)₂ + H₂O | PbO + 2NaOH → Na₂PbO₂ + H₂O |
You do not need to memorise the formulae of the sodium zincate or sodium aluminate products — the examiner awards the mark for knowing that a salt and water are formed on both sides.
Where amphoteric oxides sit
Acidic oxides are non-metal oxides (e.g. CO₂, SO₂). Basic oxides are metal oxides that react with acids only (e.g. CuO, MgO). Amphoteric oxides sit in between — they are metal oxides of elements near the boundary between metals and non-metals in the periodic table. Aluminium and zinc both sit close to the metalloid staircase.
Worked exam question
Zinc oxide is described as amphoteric. (a) Define amphoteric. [2] (b) Write the equation for zinc oxide reacting with dilute sulfuric acid. [1]
Mark scheme
(a) Reacts with acids [1] and reacts with alkalis/bases [1] — both marks require the idea of reacting with both.
(b) ZnO + H₂SO₄ → ZnSO₄ + H₂O [1]
Common exam mistakes
- Defining amphoteric as “can act as an acid or a base” without specifying it reacts with both acids and alkalis — examiners want explicit mention of both reaction partners.
- Confusing amphoteric with neutral. A neutral oxide (e.g. H₂O, CO) does not react with either acids or alkalis. An amphoteric oxide reacts with both.
- Listing iron oxide as amphoteric — Fe₂O₃ is a basic oxide, not amphoteric.
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