O Level / IGCSE Chemistry chapter 7: Acids, bases and salts MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
70 exam-style questions on Acids, bases and salts, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. A few drops of methyl orange are added to aqueous sodium hydroxide. Dilute hydrochloric acid is then added until it is in excess. What colour change is seen?
A
red to yellow
B
blue to colourless
C
colourless to blue
D
yellow to red
Show answer
Answer: D. Methyl orange is yellow in alkali and red in acid, so the colour goes from yellow to red once the acid is in excess. Blue to colourless would be thymolphthalein.
2. Zinc oxide reacts with aqueous sodium hydroxide: ZnO + 2NaOH → Na2ZnO2 + H2O. What does this reaction show?
A
zinc oxide is a basic oxide, because it reacts with sodium hydroxide
B
zinc oxide is a reducing agent, because it removes oxygen from sodium hydroxide
C
zinc oxide can behave like an acidic oxide, forming a salt and water with a base
D
zinc oxide is an alkali, because it forms a sodium compound
Show answer
Answer: C. Basic oxides do not react with alkalis. Reacting with a base to give a salt (sodium zincate) and water is acidic behaviour; with its reaction with acids, this shows zinc oxide is amphoteric.
3. A little calcium oxide is shaken with water and universal indicator is added. What is the most likely pH?
A
2
B
5
C
7
D
12
Show answer
Answer: D. Calcium oxide is a basic oxide; it reacts with water to give calcium hydroxide, an alkali, so the pH is well above 7.
4. A farmer spreads ammonium sulfate fertiliser and calcium hydroxide (slaked lime) on a field at the same time. Why is this a poor idea?
A
the two react to form an acid that lowers the pH of the soil
B
calcium hydroxide is an acid and neutralises the fertiliser
C
the two react to form nitrogen gas, which is poisonous to plants
D
the calcium hydroxide reacts with the ammonium salt and ammonia gas escapes, so nitrogen is lost
Show answer
Answer: D. Bases react with ammonium salts to release ammonia, so the nitrogen meant for the crop is lost to the air. Calcium hydroxide is a base, not an acid.
5. Zinc oxide reacts with dilute hydrochloric acid and also with aqueous sodium hydroxide. What type of oxide is it?
A
neutral, because it does not react with acids
B
amphoteric, because it reacts with acids and alkalis
C
acidic, because it reacts with the alkali
D
basic, because it reacts with the acid
Show answer
Answer: B. An oxide that reacts with both acids and bases to form a salt and water is amphoteric. Aluminium oxide behaves the same way.
6. Which method is most suitable for preparing crystals of potassium nitrate?
A
add excess potassium metal to dilute nitric acid, then filter off the excess metal
B
add excess solid potassium carbonate to dilute nitric acid, then filter off the excess solid
C
titrate aqueous potassium hydroxide with dilute nitric acid, then repeat with the same volumes but no indicator
D
mix aqueous potassium sulfate with dilute nitric acid, then filter off the precipitate
Show answer
Answer: C. Potassium compounds are soluble, so an excess of potassium carbonate would dissolve and could not be filtered off; potassium metal is far too reactive to add to acid. Titration finds the exact volumes, so the solution contains only the salt.
7. Calcium oxide is used to remove sulfur dioxide from the waste gases of power stations. Why does this work?
A
calcium oxide is an acidic oxide and reacts with the basic sulfur dioxide
B
calcium oxide is a basic oxide and sulfur dioxide is an acidic oxide, so they react to form a salt
C
both are amphoteric oxides, so they react with each other
D
calcium oxide oxidises sulfur dioxide to sulfur
Show answer
Answer: B. A basic metal oxide neutralises an acidic non-metal oxide, forming calcium sulfite, a salt.
8. Barium carbonate is to be prepared by precipitation. Which pair of reactants should be mixed?
A
aqueous barium chloride and solid calcium carbonate
B
solid barium sulfate and aqueous sodium carbonate
C
aqueous barium nitrate and aqueous ammonium carbonate
D
aqueous barium nitrate and solid magnesium carbonate
Show answer
Answer: C. Precipitation needs two soluble salts: one gives Ba2+ ions and the other CO32− ions. Barium nitrate and ammonium carbonate are both soluble; calcium carbonate, barium sulfate and magnesium carbonate are insoluble.
9. Blue crystals of copper(II) sulfate are heated gently in a test-tube. A white powder is left and droplets of colourless liquid form near the mouth of the tube. What is the white powder?
A
copper(II) oxide
B
anhydrous copper(II) sulfate
C
copper(II) hydroxide
D
hydrated copper(II) sulfate
Show answer
Answer: B. Heating drives off the water of crystallisation (the droplets), leaving anhydrous copper(II) sulfate, which contains no water and is white. Copper(II) oxide would be black.
10. Excess magnesium oxide is added to 50.0 cm3 of 2.00 mol/dm3 sulfuric acid. MgO(s) + H2SO4(aq) → MgSO4(aq) + H2O(l) After filtering, crystallising and drying, 9.0 g of anhydrous magnesium sulfate is obtained. What is the percentage yield?
A
37.5%
B
75.0%
C
133%
D
150%
Show answer
Answer: B. Moles of acid = 0.0500 × 2.00 = 0.100 mol, so the maximum is 0.100 mol MgSO4 = 0.100 × 120 = 12.0 g. Yield = 9.0 ÷ 12.0 × 100 = 75.0%. 133% comes from dividing the wrong way round.
70, each with the answer and a short explanation, across 3 topics: The characteristic properties of acids and bases, Oxides, Preparation of salts. Every chapter test draws ten of them, so you can take it many times.
Is the O Level / IGCSE Chemistry chapter 7 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
