When 6.724 g of one of the hydrates of sodium sulfate (Na2SO4) was heated to drive off its water of hydration, the residue of anhydrous sodium sulfate has a mass of 2.964 g. What is the value of x in the formula for the hydrate, Na2SO4•xH2O?

Answer 1

6.724g hydrate
-2.964g anhdrous Na2SO4
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3.760g H2O driven off.

Convert to mols.
3.760/18 = ? mols H2O
2.964/molar mass Na2SO4= ?

Now find the ratio of the water to 1.00 mol Na2SO4.