I have three questions about waters of hydration, the first two of which I'm really stuck on:
A sample of cobalt(II) nitrate hydrate was heated to remove all the water of hydration. The hydrate was found to be $65.96\%$ oxygen. Calculate the number of water molecules associated with each formula unit of cobalt(II) nitrate.
Epsom salts is $\ce{MgSO4.xH2O}$. The hydrate was found to contain $71.4\%$ oxygen. Calculate the value of $x$.
Zinc nitrate $\ce{Zn(NO3)2.xH2O}$ contains $21.98\%$ zinc by mass. What is the value of $x$?
I have absolutely no idea for the first two questions.
For the third:
- Assume $\pu{100 g}$ of material
- $\pu{21.98 g}$ of Zn = $\pu{0.3284 mol}$ of $\ce{Zn}$
I couldn't get any further than this.