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Chemguide: Core Chemistry 14 - 16 Answers to Set 6 of the formulae problems ammonium sulfate: (NH4)2SO4 You will need to remember both the ammonium and sulfate ions - ammonium ions are NH4+ and sulfate ions are SO42-. To balance the charges, you need two ammonium ions for each sulfate ion. lead(II) bromide: PbBr2 The Roman numeral tells you the lead ion has a 2+ charge; bromine is in Group 7 and so a bromide ion has a 1- charge. To balance the charges, you need two bromide ions for each lead(II) ion. nitric acid ("hydrogen nitrate"): HNO3 You need to remember both of these ions as well - hydrogen ions are H+; nitrate ions are NO3-. To balance the charges, you need one of each. chromium(III) sulfate: Cr2(SO4)3 The Roman numeral tells you that the chromium(III) ion has a 3+ charge; sulfate ions are SO42- - you have to remember that. To balance the charges, you need equal numbers or pluses and minuses. You can get this if you have 6 of each sort of charge - two chromium(III) ions and 3 sulfate ions. iron(III) hydroxide: Fe(OH)3 The Roman numeral tells you the iron ion has a 3+ charge; hydroxide ions are OH- - you need to learn that. To balance the charges, you need three hydroxide ions for each iron(III) ion. © Jim Clark 2019 |