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Chemistry

Reactions of acids

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# Ionic equations (Credit)

When acids and alkalis react, hydrogen ions and hydroxide ions join to form water.

H+(aq) + OH-(aq) → H2O(l)

When acids and metal carbonates react, hydrogen ions and carbonate ions react to form water and carbon dioxide.

2H+(aq) + CO32-(aq) → H2O(l) + CO2(g)

When acids react with metals, hydrogen ions form hydrogen molecules.

2H+(aq) + M(s) → H2(g) + M2+(aq)

(M represents a metal in the above equation)

## Example question

Now try a typical Standard Grade question. Look at the answer after you have tried the question.

Question

Reactions can be represented using ionic equations.

A: H+(aq) + OH-(aq) → H2O(l)

B: 2 H2O(l) + O2(g) + 4e → 4OH-(aq)

C: 2H+(aq) + CO32-(aq) → H2O(l) + CO2(g)

D: SO2(g) + H2O(l) → 2H+(aq) + SO32-(aq)

E: NH4+(aq) + OH-(aq) → NH3(g) + H2O(l)

Identify the two ionic equations that show the neutralisation of an acid.

Hint: There are two correct answers. Both must be given to be awarded the mark. Look very carefully at each ionic equation given. You could even rewrite each one on paper and put the names of the ions and other substances underneath the formulae. This may help you to work out which equations show neutralisation of an acid.

A: H+(aq) + OH-(aq) → H2O(l)

C: 2H+(aq) + CO32-(aq) → H2O(l) + CO2(g)

In both of the ionic equations H+(aq) ions are reacting to form water. This is neutralisation.

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