Question

What mass of cobalt can be extracted from 85.0g of cobalt (Ill) heptahydrate?

Answer 1

You have a cobalt(III) salt, which is a heptahydrate. You'll need to give us the counter-ion

Explanation:

I know there is a `CoSO_4*7H_2O`, but this is a Co(II) salt; I think that the various cobalt halides also form hexahydrates. Anyway, you need to refine your question.