posted by Heather .
How many water molecules are in a 10.0g sample of water?
First you need the molar mass of water(H2O).
Given that oxygen is 16 g mole^-1 and hydrogen is 1 g mole^-1 the molar mass of water is 18 g mole^-1.
Next we need the number of moles of water that 10.0 g represents (N) which we get from
N=10.0 g / 18 g mole^-1
as one mole contains 6x10^23 molecules then
Nx6x10^23 is the number of molecules.