Question: how many moles of water were lost?
Answer: In our example, 16 grams / 160 grams per mole = 0.1 moles. Divide the mass of water lost when you heated the salt by the molar mass of water, roughly 18 grams per mole. In our example, we lost 9 grams of water; if we divide 9 by 18, we get 0.5 moles of water lost.