First, change the 39.27grams of water to moles using the molar mass.
Molar mass H2O= 18.02 grams/mole
39.27 grams x (1 mole H2O/ 18.02 grams)= 2.18 moles
The mass of sodium acetate can be calculated by subtracting the mass of the compound minus the mass of water.
84 g - 39.27 grams= 44.73 grams
Now change does to moles using the molar mass
Molar mass of sodium acetate= 82 g/ mol
44.73 g x (1 mole/ 82 grams) = 0.545 mole
Now divide the both value by the smallest .
H2O- 2.18/ 0.545= 4
sodium acetate= 0.545/ 0.545= 1
The formula is NaC2H3O2 • 4 H2O
