Formulae for ionic compounds

3 marks · Normal

Explain how you work out the formula for iron(II) sulfate, using the charges on the ions and their names.

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FeSO4

Also accept: Accept full, correct reasoned answers using correct charges and the right balancing

Common mistakes: incorrect charge for Fe2+; confusing sulfate with sulfide

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Marking points

M1 · 1 mark · Correctly states charge on iron(II) is Fe2+ and sulfate is SO4^2–.

M2 · 1 mark · Explains how charges balance: one Fe2+ and one SO4^2– for neutrality.

A1 · 1 mark · Gives the correct formula: FeSO4.

Worked solution

Iron(II) means Fe2+ ion; sulfate is SO4^2–. To balance the charges, one Fe2+ ion combines with one SO4^2– ion, total charge zero, so the formula is FeSO4.