Reacting acids with bases
3 marks · NormalHydrochloric acid reacts with sodium hydroxide in a neutralisation reaction.
Explain, using what happens to the ions in this reaction, why this process is classified as a neutralisation reaction.
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In a neutralisation reaction, the hydrogen ions (H⁺) from the acid react with the hydroxide ions (OH⁻) from the base to form water (H₂O). The acid and base are neutralised as the ions combine, and no excess hydrogen or hydroxide ions remain. This removes the acidic and basic properties, producing a neutral solution.
Also accept: H⁺ ions from the acid join with OH⁻ ions from the base to make water; this removes the acid and base from the solution; A neutralisation reaction happens because the acid's hydrogen ions and the base's hydroxide ions combine to make water, leaving a neutral solution
Common mistakes: Saying the products are always only salt and water, with no reference to ions or neutralisation; Not mentioning hydrogen or hydroxide ions
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Marking points
M1 · 1 mark · Recognises that hydrogen ions (H⁺) from the acid and hydroxide ions (OH⁻) from the base are involved in the reaction.
M2 · 1 mark · States that these ions combine to form water.
A1 · 1 mark · Explains that neutralisation removes acidic and basic properties, resulting in a neutral solution.
Worked solution
When hydrochloric acid reacts with sodium hydroxide, the reaction is:
The key process is that the hydrogen ions (H⁺) from the acid react with hydroxide ions (OH⁻) from the alkali:
This forms water and no excess hydrogen or hydroxide ions remain, so the solution becomes neutral. This is why the reaction is called a neutralisation reaction: the acid and base have cancelled each other out.