MathsGradeUp logoMathsGradeUp
ChemistryInternational GCSEEdexcel & Cambridge IGCSEYears 10–11

IGCSE Chemistry Acids, Bases and Salts Notes

Acids donate H⁺ ions; bases accept them. Combining them neutralises to give a salt and water. Salt preparation is a classic IGCSE practical.

Practise this topic free Ask Study Coach

Key concepts

Acid
Substance that releases H⁺ ions in water; pH < 7.
Base / alkali
Substance that accepts H⁺; an alkali is a soluble base; pH > 7.
Neutralisation
H⁺ + OH⁻ → H₂O; produces a salt and water; pH moves toward 7.
Salt preparation
Acid + metal / metal oxide / carbonate / alkali → salt (+ water / H₂ / CO₂).
  • Common indicators: litmus (red/blue), universal indicator (full colour scale), methyl orange (red/yellow), phenolphthalein (colourless/pink).
  • HCl → chlorides; H₂SO₄ → sulfates; HNO₃ → nitrates.
  • Reactive metal + acid → salt + hydrogen (fizzing).
  • Metal carbonate + acid → salt + water + carbon dioxide (fizzing; limewater turns milky).

Worked example

Describe how to make dry copper sulfate crystals from copper oxide and sulfuric acid.

  1. 1Warm dilute H₂SO₄ in a beaker; add excess CuO until no more dissolves (ensures all acid reacts).
  2. 2Filter off the excess CuO.
  3. 3Heat the filtrate gently to evaporate about half the water — until crystallisation point.
  4. 4Leave to cool; crystals form. Pat dry between filter paper.

Answer: Excess copper oxide → filter → evaporate → crystallise → dry.

Common mistakes

✗ Writing 'salt' instead of the specific salt name.

✓ State the actual salt, e.g. sodium chloride or copper sulfate.

✗ Heating solutions to dryness in crystallisation.

✓ Only evaporate to the crystallisation point, then cool — heating to dryness destroys the crystal shape.

✗ Forgetting water as a neutralisation product.

✓ Acid + alkali always gives salt + water.

Quick check

Try these, then reveal the answers.

What salt is made from HCl and NaOH?Reveal answer

Sodium chloride (NaCl).

What gas is produced when a metal carbonate reacts with acid?Reveal answer

Carbon dioxide.

What is the pH of a strong alkali?Reveal answer

13 or 14.

Practise more questions with Study Coach feedback

Exam tips

  • Remember: acid + metal oxide/hydroxide → salt + water (no gas); acid + carbonate → salt + water + CO₂.
  • Choose the correct method: soluble salt from insoluble base uses excess + filter + crystallise.
  • For titration, add indicator to alkali, run acid from burette until colour just changes.

Related practice

Practise this topic

Exam-style questions with instant Study Coach feedback.

Flashcards

Quick-fire recall to lock in the key facts.

Worksheets

Printable practice you can work through offline.

Past papers

Full papers with official mark-scheme marking.

Study Coach

Ask for a step-by-step explanation any time.

All Chemistry

Every Chemistry topic across every exam board.

Related topics

StoichiometryInorganic Chemistry

Key terms explained

Short, exam-ready definitions with a formula, a worked example and an examiner tip.

What is catalyst?What is concentration?What is covalent bond?What is dynamic equilibrium?What is electronegativity?What is ionic bond?Full glossary

Frequently asked questions

What is neutralisation?+

A reaction in which an acid and a base combine to give a salt and water, moving the pH toward 7.

Why do we use excess base when making a salt?+

So all the acid is used up. The excess base is then filtered off, leaving a pure salt solution.

Create a free account to practise acids, bases and salts with Study Coach feedback

Try 5 questions now, get instant mark-scheme marking and ask the Study Coach to explain anything. Free during our early launch period — no credit card required.

Create free account Try the Study Coach

Related on MathsGradeUp

Keep studying

Practise it

Enquire now