Chemguide: Core Chemistry 14 - 16

Answers to Set 5 of the formulae problems

barium sulfate: BaSO₄

Barium is in Group 2 and so its ion has a 2+ charge; sulfate is an ion whose formula and charge you have to remember. Sulfate ions are SO₄^2-.

To balance the charges, you need one of each.

zinc nitrate: Zn(NO₃)₂

Zinc is an ion you will have to remember - its ion has a 2+ charge; nitrate ions are NO₃^- and you have to remember this as well.

To balance the charges, you need two nitrate ions for each zinc ion.

If you forgot the brackets, it is wrong.

ammonium chloride: NH₄Cl

The ammonium ion is another one you need to remember - ammonium ions are NH₄⁺; chlorine is in Group 7 and so a chloride ion has a 1- charge.

To balance the charges, you need one of each.

sulfuric acid ("hydrogen sulfate"): H₂SO₄

You have to remember that hydrogen ions have a 1+ charge; sulfate ions are SO₄^2- - you have to remember that as well.

To balance the charges, you need 2 hydrogen ions for each sulfate ion.

lead(II) sulfide: PbS

The Roman numeral tells you the lead ion has a 2+ charge; sulfur is in Group 6 and so its ion has a 2- charge.

To balance the charges, you need one of each.

If you confused sulfide with sulfate in the last two questions learn from your experience!

Return to the problems . . .