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Acids & Bases — MyGCSEScience
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FreeScienceLessons · AQA ChemistryAcids and Bases
Cognito · AQA ChemistryNeutralisation and salt production
Key facts
pH scale and acids/bases
- pH 0–6 = acidic. pH 7 = neutral. pH 8–14 = alkaline.
- Acid = proton (H⁺ ion) donor. Dissolves in water to produce H⁺ ions.
- Alkali = proton acceptor. Dissolves in water to produce OH⁻ ions.
- Strong acids fully ionise: HCl → H⁺ + Cl⁻. Weak acids partially ionise.
- Strong acids (HCl, H₂SO₄, HNO₃) have lower pH than weak acids at same concentration.
- pH is a logarithmic scale: pH 4 is 10× more acidic than pH 5.
Reactions of acids — salt production
- Acid + metal → salt + hydrogen. E.g. Mg + 2HCl → MgCl₂ + H₂
- Acid + metal oxide/hydroxide (base) → salt + water. E.g. NaOH + HCl → NaCl + H₂O
- Acid + carbonate → salt + water + carbon dioxide. E.g. CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
- Salt name = metal (from base/carbonate) + acid radical (chloride/sulfate/nitrate).
- HCl → chloride salts. H₂SO₄ → sulfate salts. HNO₃ → nitrate salts.
Exam questions — 4 questions · 10 marks
⚡ Extended questions included. Read the hint. Show all working. AI marks against the real AQA mark scheme.
1 markNeutralisationAQA 8462 P1 style
Hydrochloric acid reacts with sodium hydroxide solution. What are the products?
A Sodium chloride and hydrogen
B Sodium chloride and water
C Sodium oxide and water
D Sodium chloride, water and carbon dioxide
1 markSalt namingAQA 8462 P1 style
Calcium carbonate reacts with dilute sulfuric acid. What salt is produced?
A Calcium chloride
B Calcium nitrate
C Calcium sulfate
D Calcium carbonate
4 marksAcid reactionsAQA 8462 P1 Jun 2024 style
Write balanced equations for the reactions of dilute hydrochloric acid with (a) magnesium metal and (b) copper(II) carbonate. (4 marks)
Hint: (a) acid + metal → salt + hydrogen. (b) acid + carbonate → salt + water + CO₂. Balance by adjusting coefficients.
+40 XP
3 marksStrong vs weak acidsAQA 8462 P1 style
Explain the difference between a strong acid and a weak acid at the same concentration. How does this affect their pH values? (3 marks)
Hint: Key words: strong acid = fully ionises. Weak acid = partially ionises. More H⁺ ions → lower pH.
+30 XP
Module complete! 🎉
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