3.3.1Movement and Interactions

Reactions Of Acids — AQA GCSE Combined Science Synergy 8465 - Physical Sciences Revision Notes & Topical Questions

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Part 1 of 7Common acids and the salts they make

Acid reactions

Acid + metal

Acid + metal Makes a salt and hydrogen gas, for example magnesium + hydrochloric acid gives magnesium chloride + hydrogen.
Mg + 2HCl → MgCl₂ + H₂
The more reactive the metal, the faster the bubbles form; copper does not react with dilute acids at all.

Acid + metal oxide or hydroxide

Acid + metal oxide or hydroxide These bases neutralise the acid to give a salt + water.
CuO + H₂SO₄ → CuSO₄ + H₂O

Acid + carbonate

Acid + alkali

Acid + alkali A neutralisation reaction giving a salt + water.
NaOH + HCl → NaCl + H₂O
Indicator colour changes show when the acid has been exactly neutralised by the alkali.

Hydrogen

Hydrogen Hold a lit splint at the mouth of the test tube; hydrogen burns with a squeaky pop.

Carbon dioxide

Carbon dioxide Bubble the gas through limewater; it turns cloudy (milky) because calcium carbonate forms.

The first part of the name comes from the metal in the base, carbonate or metal, for example copper.

The second part comes from the acid: chloride, sulfate or nitrate.

So copper oxide with sulfuric acid makes copper sulfate.

Write a balanced equation, checking the number of atoms of each element on both sides.

Identify the type of reaction: a metal carbonate reacting with an acid.

Write the word equation: copper carbonate + sulfuric acid → copper sulfate + water + carbon dioxide.

Write the formulae: CuCO₃ + H₂SO₄ → CuSO₄ + H₂O + CO₂.

Check that each element has the same number of atoms on both sides; here the equation is already balanced.

Add state symbols if asked: (s), (aq), (aq), (l) and (g) respectively.

Reaction	What you see	Gas given off
Acid + reactive metal	Bubbles, the metal gets smaller and the tube warms	Hydrogen
Acid + metal oxide	The black or coloured solid dissolves and the solution changes colour	None
Acid + carbonate	Vigorous fizzing as the solid dissolves	Carbon dioxide
Acid + alkali	No visible change unless an indicator is used; the mixture warms slightly	None

Predict the products

Predict the products Identify which of the four reaction types applies,
- then recall the products: salt and hydrogen, salt and water,
- or salt, water and carbon dioxide.

Write the formula of the salt

Write the formula of the salt Balance the charges of the metal ion and the acid ion, for example Al³⁺ and Cl⁻ give AlCl₃,
- then balance the whole equation.

Term	Meaning
Salt	A compound formed when the hydrogen of an acid is replaced by a metal or ammonium.
Neutralisation	The reaction of an acid with a base that forms a salt and water.
Base	A substance that reacts with an acid to neutralise it, such as a metal oxide.
Alkali	A base that dissolves in water, forming hydroxide ions.
Carbonate	A compound containing CO₃²⁻, which gives off carbon dioxide with acid.
Hydrogen ion	H⁺, the ion that makes a solution acidic.

Forgetting that carbonate reactions also produce water.

Naming sulfates and chlorides the wrong way round: sulfuric acid gives sulfates.

Leaving equations unbalanced, such as writing Mg + HCl → MgCl₂ + H₂.

Saying all bases are alkalis; only soluble bases are alkalis.

Writing that copper reacts with dilute hydrochloric acid to give hydrogen; copper is below hydrogen in the reactivity series.

Last updated: 20 October 2026