Formula for the hydrate copper (II) sulfate ?

[toryn34]

I did an experiment at school to convert the hydrate copper (II) sulfate into its anhydrous form. The initial mass was 1.55 grams, while the final mass was 0.98 grams. Therefore the percent by mass of water would be (0.57/1.55)*100%=36.8 % of H2O. Then, using my observations, I also calculated the percentage composition of the hydrated copper (II) sulfate...(0.98/1.55)*100%=63.2 % of CuSO4.
Question: Do you think it is more useful to have the percent by mass of water in a hydrate OR the percentage composition, assuming that you know the formula for the associated anhydrous ionic compound?

For this question...I think its percentage composition, because you do not need the mass percent of water to determine the number of water molecules attached to a hydrate. The mass percent is only useful when comparing various compounds with one another, however the percentage composition expresses the ratio of elements that make up a compound in which you can assume 100 grams. Therefore, through percentage composition, you can easily determine the amount in moles of each element.

But I'm not sure if this is the correct answer.....

Also,

Question: Would the results have differed if I used more or less hydrated copper (II) sulfate?

For this question, I'm confused between the law of definite proportions and whether the number of water particles present would affect the results. Because, during the experiment, the percent by mass of water that other groups calculated was similar to mine which has to do with the law of definite proportions, because it didnt matter where the CuSO4 came from...the percentage of water was constant. However, the formulas among the groups were different. (the number of water particles attached to the hydrate). I think this was because if the mass in grams of CuSO4 was less, the amount in moles of H2O for every mole of CuSO4 would be smaller. If the mass in grams of CuSO4 was greater, the amount in moles of H2O for every moles of CuSO4 would be larger. In this case, the difference in number of water molecules attached can result in different properties and a shift in the atomic mass of the compound.

But again, I'm not sure if this is the correct answer either...
And Question: Why is it that the formulas for each group were different and the mass percent of water was consistent among all groups?

[emek]

CuSO4