Lesson 3 of 7
Classify an oxide by its reactions
Metal/non-metal character suggests a pattern, but exceptions matter.
O-Level 6092 (2026) / SEC G3 K324 (2027)
I can classify oxides.Syllabus
Syllabus K324, 5.1(h). Classify oxides
Classify an oxide by its reactions
Metal/non-metal character suggests a pattern, but exceptions matter.
| Class | Behaviour | Examples |
|---|---|---|
| Basic | Reacts with acids to form salt and water | CuO, MgO: generally metal oxides |
| Acidic | Reacts with bases to form salt and water | CO2, SO2: generally non-metal oxides |
| Amphoteric | Reacts with both acids and strong alkalis | Al2O3, ZnO |
| Neutral | Does not show typical acidic or basic oxide reactions | CO, NO; being a non-metal oxide does not guarantee acidity |
For example, CO2(g) + 2NaOH(aq) -> Na2CO3(aq) + H2O(l) with excess alkali shows acidic-oxide behaviour. CuO reacting with an acid shows basic behaviour. An insoluble oxide can still be acidic or basic: classification is not determined by whether it dissolves in water.
Check your understanding
An oxide reacts with hydrochloric acid and also with aqueous sodium hydroxide. How is it classified?
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Amphoteric, as it reacts with acids and bases
A basic oxide reacts with acids only, and an acidic oxide with bases only. Reacting with both is the evidence for an amphoteric oxide, such as zinc oxide or aluminium oxide.
Sort these
Sort the oxides by how they behave with acids and alkalis.
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Acidic: SO2 / CO2
Basic: CaO / CuO
Amphoteric: ZnO / Al2O3
Neutral: NO / CO