Describe what happens when a metal oxide reacts with a dilute acid, and explain why the product formed is called a salt.

WJEC GCSE Chemistry (Wales) — 2.2 Acids, bases and salts · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Metal oxides are bases. When they react with acids, two products are formed.

Model answer (4 marks)

A metal oxide reacts with a dilute acid in a neutralisation reaction, giving a salt and water.

The metal ion from the oxide becomes the cation of the salt, while the anion comes from the acid.

The product is called a salt because it is an ionic compound formed from the combination of a metal cation and a non‑metal anion produced in the neutralisation.

For example, ZnO + 2HCl → ZnCl₂ + H₂O, so the salt is zinc chloride.

Examiner tips

  • Use the word ‘neutralisation’ to show understanding of the reaction type.
  • Show that the salt contains the metal ion from the oxide and the anion from the acid.
  • Give a clear example linking the acid to the anion of the salt.
  • Mention that water is the other product.

Common mistakes

  • Writing the reaction as a single step without showing the formation of water.
  • Calling the product simply an ‘ionic compound’ without explaining the metal and acid origin.
  • Using the wrong acid anion name (e.g. calling ZnCl₂ a ‘chloride salt’ but not linking it to HCl).

Mark scheme (4 marks)

  1. A metal oxide (base) reacts with a dilute acid in a neutralisation reaction
  2. A salt and water are produced / formed
  3. The salt is named from the metal in the base / metal oxide
  4. The salt is named from the acid used — e.g. hydrochloric acid produces a chloride salt / sulfuric acid produces a sulfate salt / nitric acid produces a nitrate salt

Key terms in this question

salt · metal oxide · dilute acid

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