How many moles are in 349.3 g of H2O

19.38 moles

Explanation: When in doubt, use stoichiometry

Molar mass of H2O = 2 (molar mass H) + molar mass O

=2 (1.01) + 16.00 = 18.02

Now, you just convert:

349.3g (1 mol H2O/18.02gH2O)

= 19.384

But the value given has 4 significant figures, so we write it as 19.38

Answer: 19.405 mol

Explanation: 1 mol of H2O is equal TO 18 g/mol

349.3 g of H2O / 18 g/mol=19.405