Both calcium sulfate and magnesium sulfate can form hydrates with water. Could white anhydrous CaSO4 or MgSO4 be substituted for anhydrous CuSo4? Why or Why not?

3 answers

It depends upon what you are doing, doesn't it? You need to provide some information about your question/experiment.
If it has to do with the determination of moisture, No, it can not, its used as an indicator to see if hydration is taking place, (or that the chemical is absorbing the moisture) If it turns blue, its indicating that water is present in the substance that you are testing,

(Anhydrous cupric sulphate is used to dry liquids, so if you are testing to see if moisture is present/not present, it cannot be substituted) Hope that helps.
Also MgSO4 is slight acidic and CaSO4 doesn't absorb water as well. So CuSO4 is easier to work with.