Every time you see molecules, atoms, & particles think of avagadros #. (6.022 x 10^23)
Answer: 13.6 grams of H2O
Solution: (4.56x10^23) x (1 mol H2O/6.022x10^23) x (18 grams H2O/1 mol H2O) = 13.6 grams of H2O
Using dimensional analysis above makes these types of problems easy.
