How many molecules of H2O are there in 1.0 g of H2O?

Avogadro's number represents the number of units in one mole of any substance. This has the value of 6.022 x 10^23 units / mole. This number can be used to convert the number of atoms or molecules into number of moles. This will be used for the conversion to be done.

1.0 g H2O (1 mol / 18.02 g) (6.022 x 10^23 molecules / mol) = 3.3 x 10^22 molecules