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K324 / 2027
Acid-Base Chemistry

Lesson 2 of 7

Recognise the reaction pattern

Predict the salt and the other products.

O-Level 6092 (2026) / SEC G3 K324 (2027)

  • I can describe acid reaction patterns.Syllabus

    Syllabus K324, 5.1(d). Describe acid reaction patterns

  • I can explain neutralisation.Syllabus

    Syllabus K324, 5.1(e). Explain neutralisation

  • I can describe base reactions.Syllabus

    Syllabus K324, 5.1(g). Describe base reactions

Recognise the reaction pattern

Predict the salt and the other products.

Acid and base reactions
ReactantsProductsBalanced example
Acid + suitable metalSalt + hydrogenMg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g)
Acid + baseSalt + waterCuO(s) + H2SO4(aq) -> CuSO4(aq) + H2O(l)
Acid + carbonateSalt + water + carbon dioxideCaCO3(s) + 2HCl(aq) -> CaCl2(aq) + H2O(l) + CO2(g)
Alkali + ammonium salt, warmSalt + water + ammoniaNH4Cl(aq) + NaOH(aq) -> NaCl(aq) + H2O(l) + NH3(g)

The acid supplies the salt anion: hydrochloric acid gives chlorides, sulfuric acid sulfates, and nitric acid nitrates. The metal or base supplies the cation. Not every metal reacts with dilute acid: copper, for example, does not release hydrogen from dilute hydrochloric acid.

For an acid reacting with an alkali, the reacting ions are H+(aq) + OH-(aq) -> H2O(l). This is neutralisation. The other dissolved ions are spectators. For an ammonium salt and alkali, NH4+(aq) + OH-(aq) -> NH3(g) + H2O(l); warming helps ammonia escape.

Worked examplePredict and confirm the gas

Dilute acid is added to a carbonate and bubbles appear. How should the result be described?

Try it first. Then show the worked stepsHide the worked steps
  1. Predict carbon dioxide from the carbonate reaction pattern.
  2. Report effervescence as the observation.
  3. Pass the gas into limewater: a white precipitate supports carbon dioxide.
Answer

Effervescence alone does not identify a gas. Carbon dioxide turns limewater milky; hydrogen instead gives a pop with a lighted splint.

Check your understanding

What salt forms when zinc reacts with dilute sulfuric acid?

  1. Zinc sulfite, ZnSO3, with oxygen gas given off
  2. Zinc sulfide, ZnS, with water as the other product
  3. Zinc sulfate, ZnSO4, with hydrogen gas given off
Show the answer

Zinc sulfate, ZnSO4, with hydrogen gas given off

Metal + acid -> salt + hydrogen. The salt takes its first name from the metal and its second from the acid: Zn(s) + H2SO4(aq) -> ZnSO4(aq) + H2(g).