How do I do this stoichiometry problem?

Question

I am given a 1.205 g sample of Pb(C2H3O2)2·x H2O. It is heated to drive off the water. The anhydrous compound is cooled and has a mass of 1.032 g. What is the integer value of x in the hydrate?

Answer 1

The way to solve these is to realize that the lost weight is the weight of the water and the residual weight is the weight of the anhydrous lead compound. You just need to determine moles of each and check the ratio.

1.205 - 1.032 = 0.173g

0.173g/[(2 x 1.01) + 16.00] = 0.0096 mole water

1.032 g/[207.2 + (4 x 12.01) + (6 x 1.01) + (4 x 16.00) = 0.00317 mole lead acetate

Now compare the ratios:

0.0096/0.00317 = 3.03

So. 3 waters to each lead acetate (x = 3).