Cambridge IGCSE · Chemistry 0620
IGCSE Chemistry: Acids, bases and salts — Practice Questions & Answers
Master acids, bases and salts: the pH scale, indicators, neutralisation, oxide types, salt preparation methods and the full set of ion and gas tests.
886 practice questions available for this topic — here are 10 with full answers and explanations.
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Practice questions with answers
1
Multiple choice · Easy
Which colour does litmus paper turn when placed in an acidic solution?
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WhyAcids turn blue litmus red. Litmus is red in acid and blue in alkali.
2
Multiple choice · Easy
What is the approximate pH of a neutral solution such as pure water?
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WhyA neutral solution has a pH of 7. Below 7 is acidic and above 7 is alkaline.
3
Multiple choice · Easy
Which ion is always produced when an acid is added to water?
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WhyAcids release hydrogen ions (H+) in aqueous solution, which gives them their acidic properties.
4
Multiple choice · Easy
Which gas is produced when a reactive metal such as magnesium reacts with dilute hydrochloric acid?
- Hydrogen
- Oxygen
- Carbon dioxide
- Chlorine
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WhyAcids react with reactive metals to give a salt and hydrogen gas, which pops with a lighted splint.
5
Multiple choice · Easy
What is the name given to a soluble base that is dissolved in water?
- Alkali
- Salt
- Oxide
- Indicator
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WhyA base that dissolves in water is called an alkali and produces hydroxide ions (OH-) in solution.
6
Fill in the blank · Easy
In the universal indicator colour scale, a strongly acidic solution gives a colour, while a strongly alkaline solution gives a purple colour.
Answer:
red
WhyUniversal indicator turns red in strong acid and purple/violet in strong alkali, allowing pH estimation.
7
Multiple choice · Medium
Which of the following is the correct word equation for a neutralisation reaction between an acid and an alkali?
- acid + alkali -> salt + water
- acid + metal -> salt + water
- acid + salt -> base + water
- acid + water -> salt + hydrogen
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WhyAcid plus alkali (a soluble base) gives a salt and water; this is neutralisation.
8
Multiple choice · Medium
A student adds dilute nitric acid to copper(II) carbonate. Which gas is given off?
- Carbon dioxide
- Hydrogen
- Oxygen
- Nitrogen
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WhyAcids react with carbonates to produce a salt, water and carbon dioxide, which turns limewater milky.
9
Multiple choice · Medium
Which classification best describes magnesium oxide (MgO)?
- Basic oxide
- Acidic oxide
- Neutral oxide
- Amphoteric oxide
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WhyMetal oxides such as MgO are basic oxides; they react with acids to form a salt and water.
10
Multiple choice · Medium
To prepare a sample of the soluble salt copper(II) sulfate, which method is most suitable?
- Add excess copper(II) oxide to dilute sulfuric acid, filter and crystallise
- Mix two soluble salt solutions and filter the precipitate
- Add copper metal directly to dilute sulfuric acid
- Heat copper(II) sulfate crystals strongly
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WhyAn insoluble base (excess copper(II) oxide) is added to warm sulfuric acid, then filtered and crystallised.
Key terms in Acids, bases and salts
Acid: A substance that releases hydrogen ions (H+) when dissolved in water.
Base: A substance that can neutralise an acid, typically a metal oxide or metal hydroxide.
Alkali: A soluble base that releases hydroxide ions (OH-) when dissolved in water.
Hydrogen ion: The positively charged particle, written H+, that acids release in aqueous solution.
Hydroxide ion: The negatively charged particle, written OH-, that alkalis release in aqueous solution.
Hydronium ion: The ion H3O+ formed when a hydrogen ion bonds with a water molecule in solution.
Acidic solution: A solution containing more hydrogen ions than hydroxide ions, with a pH below 7.
Alkaline solution: A solution containing more hydroxide ions than hydrogen ions, with a pH above 7.
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