A student makes a salt by reacting dilute nitric acid with sodium hydroxide solution. Explain why this reaction produces a salt and name the other product formed. Describe how the student could obtain a pure, dry sample of the salt from the resulting solution.

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

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

Model answer (4 marks)

Sodium hydroxide is a base that neutralises the acid.
The reaction produces the salt sodium nitrate and water.
To obtain a pure, dry sample the student should evaporate the solution to concentrate it, then allow it to cool so that sodium nitrate crystals form. Finally, filter the crystals and dry them.

Examiner tips

  • Use the word ‘neutralise’ to show understanding of acid–base reaction. Mention the salt name (sodium nitrate) and the other product (water). Explain the sequence: evaporate → cool → filter → dry.
  • common_mistakes
  • :
  • Saying the salt is ‘sodium hydroxide’ instead of sodium nitrate. Forgetting to mention the water product. Not describing the cooling step before filtration.

Mark scheme (4 marks)

  1. Sodium hydroxide is a base / alkali that neutralises the acid
  2. The other product is water
  3. Evaporate the solution (to concentrate it / to remove most of the water)
  4. Allow the solution to cool so that crystals of the salt form, then filter and dry the crystals

Key terms in this question

salt

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