About Acids, bases and salts in O Level Chemistry
Acids, bases and salts is one of the 12 main topics in our O Level Chemistry (Cambridge (CAIE) 5070) question bank, and about 7% of its real questions come from it. Tayyari Karo has 46 real questions on this topic from 2021 to 2026, from Paper 1, Paper 2, Paper 3, Paper 4; 34 are multiple choice and marked instantly, and the rest are structured questions with a model answer. By difficulty: 41 medium, 4 easy, 1 hard.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
Try 7 real questions
These are real past-paper questions. Think of your answer first, then open the explanation.
May/June 2026 · Paper 1 · Acids, bases and salts
Copper(II) hydroxide is insoluble in water. Rubidium hydroxide is soluble in water.
Which row describes copper(II) hydroxide and rubidium hydroxide?
- copper(II) hydroxide: neither a base nor an alkali; rubidium hydroxide: a base and an alkali
- copper(II) hydroxide: neither a base nor an alkali; rubidium hydroxide: an alkali but not a base
- copper(II) hydroxide: a base but not an alkali; rubidium hydroxide: a base and an alkali
- copper(II) hydroxide: a base but not an alkali; rubidium hydroxide: an alkali but not a base
Show answer and explanation
Answer: C. copper(II) hydroxide: a base but not an alkali; rubidium hydroxide: a base and an alkali
Metal hydroxides are bases. A base that dissolves in water is an alkali, so insoluble copper(II) hydroxide is a base only, whereas soluble rubidium hydroxide is both a base and an alkali.
May/June 2025 · Paper 1 · Acids, bases and salts
Insoluble salt prepared by
- titration
- precipitation
- evaporation
- distillation
Show answer and explanation
Answer: B. precipitation
Precipitation.
May/June 2024 · Paper 1 · Acids, bases and salts
Insoluble salt method?
- titration
- precipitation
- evaporation
- distillation
Show answer and explanation
Answer: B. precipitation
Precipitation.
May/June 2023 · Paper 1 · Acids, bases and salts
Strong acid fully
- ionises in water
- partially ionises
- is insoluble
- is alkaline
Show answer and explanation
Answer: A. ionises in water
Strong acids fully ionise.
May/June 2022 · Paper 1 · Acids, bases and salts
Which turns universal indicator red?
- sodium hydroxide
- hydrochloric acid
- water
- sodium chloride
Show answer and explanation
Answer: B. hydrochloric acid
Acids turn UI red.
May/June 2021 · Paper 1 · Acids, bases and salts
pH of 0.1 mol/dm³ NH₃, HCl, NaCl, NaOH?
- 1,7,13,11
- 7,1,11,13
- 11,1,7,13
- 13,11,7,1
Show answer and explanation
Answer: C. 11,1,7,13
NH₃≈11, HCl=1, NaCl=7, NaOH=13.
May/June 2026 · Paper 2 · Acids, bases and salts
Choose from the following compounds to answer the questions: CH4, C2H4, CO2, KBr, NH2OH, NO, Na2O, SO2, ZnO. Each compound can be used once, more than once or not at all.
State which compound:
(a) is amphoteric [1]
(b) has a molecule with only three atoms [1]
(c) has a molecule with only 18 electrons [1]
(d) has an element with an oxidation number of +2 [1]
(e) is unsaturated. [1]
Show model answer
(a) ZnO (zinc oxide)
(b) CO2 or SO2
(c) NH2OH (hydroxylamine)
(d) ZnO or NO
(e) C2H4 (ethene)
ZnO reacts with both acids and bases; CO2 and SO2 are triatomic; NH2OH has 7 + 2 + 8 + 1 = 18 electrons; Zn is +2 in ZnO and N is +2 in NO; ethene has a C=C double bond.
