How many molecules in 1.00 grams of water?

Question

How do you solve this? 

Answer 1

(1) Look up the molecular weight of H₂O or compute it from the atomic weights of H and O: 2H + O

(2) Divide the mass of the water by the molecular weight.  That gives the number of moles of water.

(3) Multiply the number of moles of water by Avogadro's number, which is 6.02 x 10²³.  That gives the total number of water molecules in the mass.