Question

In hydrated copper sulfate, the chemical formula is CuSO4.5H2O, while that of hydrated cobalt(II) chloride is CoCl2.6H2O. I want to ask how to determine the number of moles of water is needed to hydrate any salt. Is there a pattern or formula?

Answer 1

Often, but not always, it is twice the charge on the metal ion; i.e., for Cu that is +4 and for Co that is +6. For many ions it is +6 regardless. Mostly it's a case of remembering which is which. For Cu, the hydrate for Cu(H2O)4^2+ ion is 4. The extra H2O molecule is associated with the crystal structure as a whole to make it 5 H2O total.