64.60 g of water is how many moles of water H2O

3.586 mol of H2O (correct to 4 sig figs)

Explanation:

Known: 64.60 g water (a. k. a. H2O)

1 mol of H2O = 18.015g

How did I get that mass? Looking at the periodic table and adding atomic mass of 2 hydrogens + 1 oxygen (2 (1.008) + 15.999) = 18.015g

How many of mol of H2O will form?

Solving for the unknown:

64.60g • (1 mol H2O / 18.015g H2O) = 3.58590 mol H2O