Oxides Exam Questions
Practice IGCSE Chemistry exam questions on oxides. Covers acidic, basic, amphoteric, and neutral oxides, their reactions with acids and alkalis, and classification patterns across the periodic table with mark schemes and examiner notes.
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.
These questions cover oxides. Write full answers before checking.
Question 1 (4 marks, Core)
Classify each of the following oxides as acidic, basic, amphoteric, or neutral:
(a) Calcium oxide, CaO (1)
(b) Sulfur dioxide, SO2 (1)
(c) Aluminium oxide, Al2O3 (1)
(d) Carbon monoxide, CO (1)
Mark scheme
(a) Basic [1]
(b) Acidic [1]
(c) Amphoteric [1]
(d) Neutral [1]
Examiner note: General rule: metal oxides are basic, non-metal oxides are acidic. Exceptions: Al2O3 and ZnO are amphoteric (react with both acids and alkalis). CO and H2O are neutral oxides — they do not react with acids or alkalis.
Question 2 (3 marks, Core)
(a) Write a word equation for the reaction of calcium oxide with water. (1)
(b) Predict the pH of the resulting solution. (1)
(c) What type of oxide is calcium oxide? (1)
Mark scheme
(a) Calcium oxide + water → calcium hydroxide [1]
(b) pH above 7 / alkaline (approximately pH 12-13) [1]
(c) Basic oxide [1]
Examiner note: When basic oxides dissolve in water, they form alkaline solutions (metal hydroxides). CaO + H2O → Ca(OH)2. The resulting calcium hydroxide solution (limewater) is alkaline.
Question 3 (3 marks, Core)
Write balanced symbol equations for the reactions of:
(a) Sulfur trioxide with water. (1)
(b) Sodium oxide with dilute hydrochloric acid. (1)
(c) Carbon dioxide with sodium hydroxide solution. (1)
Mark scheme
(a) SO3 + H2O → H2SO4 [1]
(b) Na2O + 2HCl → 2NaCl + H2O [1]
(c) CO2 + 2NaOH → Na2CO3 + H2O [1]
Examiner note: (a) Acidic oxides dissolve in water to form acids. (b) Basic oxides react with acids to form salt + water. (c) Acidic oxides react with alkalis to form salt + water. These are the defining reactions for each oxide type.
Question 4 (4 marks, Supplement)
Aluminium oxide is described as amphoteric.
(a) Explain what amphoteric means. (1)
(b) Write an equation for aluminium oxide reacting with hydrochloric acid. (1)
(c) Write an equation for aluminium oxide reacting with sodium hydroxide solution. (1)
(d) Name one other amphoteric oxide. (1)
Mark scheme
(a) An amphoteric oxide can react with both acids and bases/alkalis [1]
(b) Al2O3 + 6HCl → 2AlCl3 + 3H2O [1]
(c) Al2O3 + 2NaOH → 2NaAlO2 + H2O [1]
(d) Zinc oxide (ZnO) [1]
Examiner note: Amphoteric oxides behave as a base with acids (forming salt + water) AND as an acid with alkalis (forming a different salt + water). At IGCSE, you need to know Al2O3 and ZnO as amphoteric.
Question 5 (3 marks, Core)
Explain the link between acid rain and non-metal oxides.
Mark scheme
- Burning fossil fuels releases non-metal oxides such as sulfur dioxide (SO2) and nitrogen oxides (NOx) into the atmosphere [1]
- These dissolve in rainwater to form acids: SO2 forms sulfurous/sulfuric acid, NOx forms nitric acid [1]
- This makes the rain acidic (pH below 5.6), which is known as acid rain [1]
Examiner note: Normal rain is slightly acidic (pH 5.6) due to dissolved CO2. Acid rain has a pH below 5.6 because of additional SO2 and NOx. The equations: SO2 + H2O → H2SO3; 2SO2 + O2 + 2H2O → 2H2SO4.
Question 6 (2 marks, Supplement)
Explain the trend in oxide type across Period 3 of the periodic table (from sodium to argon).
Mark scheme
- On the left side (Na, Mg), the oxides are basic because they are metal oxides [1]
- Across the period, the oxides change from basic to amphoteric (Al2O3) to acidic (SiO2, P4O10, SO3, Cl2O7) as the elements become non-metals [1]
Examiner note: This is a transition from metallic to non-metallic character across a period. The oxide type mirrors this: basic → amphoteric → acidic. Al2O3 is the turning point (amphoteric). Noble gases do not form oxides.
Question 7 (3 marks, Core)
A student adds copper oxide (CuO) to dilute sulfuric acid. The black powder dissolves and a blue solution is formed.
(a) Name the blue solution. (1)
(b) Write a balanced symbol equation for this reaction. (1)
(c) What type of oxide is copper oxide? (1)
Mark scheme
(a) Copper sulfate solution [1]
(b) CuO + H2SO4 → CuSO4 + H2O [1]
(c) Basic oxide [1]
Examiner note: CuO is a metal oxide so it is basic. It reacts with acids to form a salt and water (neutralisation). The blue colour is due to Cu2+ ions in solution. This is also the first step in preparing copper sulfate crystals.
What to revise if you scored below 5
If classifying oxides was difficult, memorise: metal = basic (or amphoteric for Al and Zn), non-metal = acidic, CO and H2O = neutral. For equations, practise: basic oxide + acid → salt + water, and acidic oxide + alkali → salt + water. Revisit the oxides notes.
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