When a 0.326 g sample of FeCl2·xH2O is heated to remove all water, a mass of 0.254 g remains. Determine the value of x.

Answer 1

0.326 g = mass FeCl2.xH2O
-0.254 g = mass FeCl2
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0.072 g = mass xH2O

mols FeCl2 = grams/molar mass = ?
mols H2O = grams/molar mass = ?

Now find the ratio of 1 mol FeCl2 to H2O and round to a whole number. That whole number will be x.
The easy way to do that is to divide mols FeCl2 by itself (thereby getting 1.000); then divide the mols H2O by the same number. The resulting answer will be x.