Formulae for ionic compounds

2 marks · Hard

State the formula for the ionic compound formed between ammonium ions and nitrate ions. Explain your answer.

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

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NH4NO3, and explanation that both ions are singly charged so combine in a 1:1 ratio.

Also accept: NH4NO3, with explanation that total positive (+1) and negative (–1) charges are balanced with one of each ion.

Common mistakes: (NH4)2(NO3)2 or NH4(NO3)2

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Marking points

M1 · 1 mark · Describes that both ammonium and nitrate are singly charged and combine in a 1:1 ratio to balance charges.

A1 · 1 mark · Writes correct formula: NH4NO3.

Worked solution

Ammonium ion: NH4+ has a +1 charge. Nitrate ion: NO3– has a –1 charge.

Because each ion has a charge of 1, the charges balance with one of each ion.

The formula for the compound is NH4NO3.