Question

The IUPAC name of $\left[Co\right(H_{2}NC{H}_{2}C{H}_{2}N{H}_2{)}_3{]}_2(S{O}_4{)}_3$ :

• A. Tris(ethylenediammine)cobalt(III) sulphate
• B. Tri(ethylenediammine)cobalt(III) sulphate
• C. Tris(ethylenediammine)cobalt(II) sulphate
• D. Tris(ethylenediamine)cobalt(III) trissulphate

Answer 1

The correct option is A Tris(ethylenediammine)cobalt(III) sulphate

The sulphate is the counter anion in this molecule. Since it takes 3 sulphate to bond with two complex cations, the charge on each complex cation must be +3.

Since ethylenediammine is a neutral molecule, the oxidation number of cobalt in the complex ion must be +3.

Again, remember that you never have to indicate the number of cations and anions in the name of an ionic compound.