What is the difference between a strong acid and a concentrated acid?
A strong acid fully dissociates in water; a concentrated acid has a high amount of acid per volume — these are independent properties. Learn it step by step →
Chemical Changes is a core part of GCSE Chemistry. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
pH scaleRuns from 0 to 14 — measures acidity or alkalinity
AcidA solution with pH below 7 — releases H⁺ ions
Base / alkaliA base neutralises an acid to form a salt and water; an alkali is a soluble base that releases OH⁻ ions in solution (pH above 7).
NeutralpH exactly 7, like pure water
Universal indicatorChanges colour through the rainbow with pH
Strong vs weak acidStrong fully ionises; weak only partly ionises
NeutralisationAcid + base reaction making salt and water
SaltIonic compound from an acid where H⁺ is replaced
Acid + baseAcid + base → salt + water
Acid + carbonateAcid + carbonate → salt + water + CO₂
Acid + metalAcid + metal → salt + hydrogen gas
Salt namingHCl → chloride; H₂SO₄ → sulfate; HNO₃ → nitrate
Reactivity seriesK Na Ca Mg Al C Zn Fe H Cu Ag Au — most to least
DisplacementMore reactive metal kicks out a less reactive one
What your exam board covers
Where Chemical Changes sits in each exam board's specification. Tap a board to see what it lists.
Questions where students often pick the tempting wrong answer — make sure you know the right one:
What is the difference between a strong acid and a concentrated acid?✗ Strong and concentrated mean the same thing for acids.✓ A strong acid fully dissociates in water; a concentrated acid has a high amount of acid per volume — these are independent properties.
When an acid neutralises an alkali, what is the pH of the resulting solution?✗ Neutralisation always produces a solution with pH exactly 7 regardless of the acid and base used.✓ Approximately 7 if equivalent amounts of strong acid and strong alkali react — but it varies with strength.
What are the products of acid + metal carbonate?✗ Salt + water + hydrogen✓ Salt + water + CO₂
Practise Chemical Changes — free games
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