[rhiannon]

i need to determine the concentration of a specific element
of a hydrated compound in solution in ppm, do i need to
include the water in the molecular weight?

[Donaldson Tan]

Upon dissolution, the water of crystallisation belongs to the solution. It's no longer part of the salt. You need not include water of crystallisation in the ionic formula mass of the salt for calculation of ppm. But in order to contribute to accuracy, you could add the tiny amount of water from the hydrated salt into the water solvent.

[rhiannon]

i think i may have worded my question wrong.
say i have 5 mg CaCl2(dot)6H2O and i need to
find the concentration of Cl in solution, if i get
the mass percent of Cl from the formula can i
still leave the weight of the water out?

[Mitch]

You still have to include the water.