Cations naming multiple-cation metal ions

Ionic compounds that contain polyatomic ions are named in the same way used to name binary ionic compounds. Attention must be paid as to whether the cation is a metal that forms a single cation or multiple cations, and the name of the polyatomic ion is that given in the table. Note how these six ionic compounds are named ... 

Fe2(S04)3 This compound contains a multiple-cation transition metal, and the charge on the cation must be determined to write a correct name. There are three sulfate ions in parentheses, giving a total negative charge of 6- (3x2- = 6-). The two iron ions then must be iron(III) ions, Fe3+ (2x3+ = 6+), to balance the negative charge of the sulfate ions. The systematic name of the compound is iron(III) sulfate. 

---