IGCSE Chemistry · 0620

IGCSE Chemistry: Acids, Bases and Salts Questions

Acid reactions follow reliable patterns, and knowing the general equations earns quick marks. These questions cover the reaction of acids with carbonates, neutralisation and testing for carbon dioxide.

What you need to know

Acids produce hydrogen ions (H+) in solution; alkalis produce hydroxide ions (OH-).
Acid plus metal gives salt plus hydrogen; acid plus carbonate gives salt plus water plus carbon dioxide.
Neutralisation is acid plus base giving salt plus water: H+ plus OH- gives H2O.
Carbon dioxide turns limewater milky; hydrogen gives a squeaky pop with a lit splint.

Practice questions with answers

Question 13 marks

Write a general equation for the reaction of an acid with a metal carbonate, and give one balanced example.

Acid plus metal carbonate gives salt plus water plus carbon dioxide. For example: 2HCl plus CaCO3 gives CaCl2 plus H2O plus CO2.

Mark schemeCorrect general products: salt, water and carbon dioxide (1). Correct example reactants and products (1). Balanced example (1).

Common mistakeForgetting that carbon dioxide is produced, or leaving water out of the products.

Exam tipLearn the three general acid equations. They appear every year and are easy marks.

Question 22 marks

Define neutralisation.

Neutralisation is the reaction between an acid and a base to form a salt and water. In ionic terms, hydrogen ions react with hydroxide ions to form water: H+ plus OH- gives H2O.

Mark schemeAcid plus base gives salt and water (1). Ionic equation H+ + OH- gives H2O (1).

Common mistakeSaying neutralisation always gives a pH of exactly 7. It gives a salt and water; the salt solution is not always neutral.

Exam tipInclude the ionic equation. It reliably gains the second mark.

Question 32 marks

A gas is produced in a reaction. Describe a test to show that the gas is carbon dioxide.

Bubble the gas through limewater. If the gas is carbon dioxide, the limewater turns milky or cloudy.

Mark schemeBubble through limewater (1). Turns milky or cloudy (1).

Common mistakeNaming the wrong indicator, or saying limewater turns blue.

Exam tipGive both the reagent and the result. A test without the observed change scores only half.

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Frequently asked questions

What do acids produce in solution?

Acids produce hydrogen ions, H+, in aqueous solution. This is what gives them their acidic properties and low pH.

What is the difference between a base and an alkali?

A base is any substance that neutralises an acid. An alkali is a base that is soluble in water and produces hydroxide ions, OH-.

What are the products when an acid reacts with a metal?

Acid plus a reactive metal gives a salt plus hydrogen gas. The hydrogen can be tested with a lighted splint, giving a squeaky pop.

How do you test for carbon dioxide?

Bubble the gas through limewater. Carbon dioxide turns the limewater milky or cloudy because insoluble calcium carbonate forms.

More IGCSE Chemistry practice

Stoichiometry Electrochemistry Atoms, elements and compounds