Formulae for ionic compounds

2 marks · Easy

Calculate the formula for the ionic compound formed when magnesium ions combine with nitrate ions. Show how the charges are balanced in your answer.

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Mg(NO3)2

Also accept: Mg(NO3)2

Common mistakes: MgNO3; Mg2(NO3); Mg(NO3)2−

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Marking points

M1 · 1 mark · Shows clear method for balancing charges: Mg2+ and 2 × NO3− (or states ions and their charges and need for two nitrate ions per magnesium ion).

A1 · 1 mark · Correct formula: Mg(NO3)2.

Worked solution

Mg2+ combines with NO3−. To balance the 2+ charge on magnesium, you need two nitrate ions:

So the correct formula is Mg(NO3)2.