Question #eb1dc

1 Answer
Mar 19, 2016

Divide the mass of hydrated water (moles or mass, depending on the intent) by the mass of the entire compound.


A hydrated compound is usually indicated by a numerical prefix (Greek) in the name, or the written number in the formula. Hydrates are complete water molecules associated with a salt, so they are always indicated as a unit in the formula.

For example, copper (II) sulfate pentahydrate is the copper sulfate molecule with five (penta) water molecules. The formula is

#CuSO_4 o 5(H_2O)#. The mole ratio of water to the entire molecule is 5 moles #H_2O#/1 mole #CuSO_4#. The mass ratio is 90g/159.5g or 0.564 (56.4%). The amount of water in the entire molecule is 90/249.5 = 0.36 or 36%.