# How to choose the correct name for calcium sulfate based on a calculations of the crystallisation water included?

I have a test review question which i really need help on. It states :

A student heated a sample of the hydrate $\ce{CaSO4 * xH2O}$ in an evaporating dish over a bunsen burner to remove all the water and recorded the following data:

Mass of empty evaporating dish: $\pu{19.73g}$
Mass of evaporating dish + hydrate: $\pu{21.50g}$
Mass of evaporating dish + anhydrous $\ce{CaSO4}$: $\pu{20.80g}$

Determine A) the value of $x$ and B) the most likely name/formula of the hydrate.

I already figured out $x$ by getting the mass of water then simplifying the ratio of anhydrous to water.
But the second question which asks to name the formula of the hydrate really confused me. I would appreciate if anyone can guide me how to solve B.

• For the hydrate part, you just add [di, tri, quadra, penta, hexa, etc.] to hydrate. So if x were 2 (I don't know, I didn't calculate it) it would be calcium sulfate dihydrate. – airhuff Mar 22 '17 at 1:59
• It would indeed be straight forward to answer, if you had included your finding of $x$. – Martin - マーチン Jun 27 '17 at 5:51

which gives $\ce{CaSO4* 5 H2O}$, calcium(II) sulfate pentahydrate.