1. In a Stock system name such as iron(III) sulfate, the Roman numeral tells us (a) how many atoms of Fe are in one formula unit
. (b) how many sulfate ions can be attached to the iron atom. (c) the charge on each Fe ion. (d) the total positive charge of the formula unit. 2. Changing a subscript in a correctly written chemical formula (a) changes the number of moles represented by the formula. (b) changes the charges on the other ions in the compound. (c) changes the formula so that it no longer represents the compound it previously represented. (d) has no effect on the formula.
1) The formula of the compound is Fe2(SO4)3. There are two ion atoms in any formula unit as we can see here. Three sulphate ions are attached to iron. Each iron ion carries a +3 charge as we saw in the formula. The total positive charge in each formula unit is +6.
Changing a subscript in a correctly written chemical formula changes the formula so that it no longer represents the compound it previously represented. Hence FeSO4 is a different compound from Fe2(SO4)3.
