Can someone explain to me how to write the equation for the decomposition of a hydrate?

Question

I know they produce salt and water. I have to start, MgCl2 * xH2O. I need to find x and the entire equation with this as a product. I'm not only looking for the answer but an explanation so I can do problems like this in the future.

Answer 1

Some links below should help. In general a hydrate decomposes to form an anhydrous salt (the ionic compound part) and water. For example:

CuSO4*7H2O --> CuSO4 + 7 H2O

where CuSO4 on the right is the anhydrous salt.

Usually you can find x by calculating the ratio of moles of water to moles of anhydrous salt. Experimentally, this usually involves heating the hydrate to remove all of the water. The anhydrous salt is left in the crucible, and we can get a mass which we'll convert to moles. The water the mass lost from the crucible, and we'll convert that to moles. Then we'll use those experimental values to find the mole ration between the water and salt, usually rounding to the nearest whole number. That whole number is x.