Question

How many moles are in 10.0 gram sample of water

Answer 1

water is H2O
H=1 gram of moler mass
O=16 grams of moler mass
so you have
2 grams of hydrogen and 16 grams of oxygen
you add those two together you have 18 grams of moler mass.
Then you just do grams of substance divided by the grams of moler mass and you will get your answer. 10.0/18=moles

Answer 2

H2O:
Hydrogen x 2 = 1g mol-1 x 2 = 2g mol-1
Oxygen x 1 = 16g mol-1
H2O total = 18g mol-1

To find the moles of a substance, it is mass of the substance in grams over the molar mass of the substances elements (on the periodic table)

10g/18g mol-1 = 0.5mol

There are 0.5mol in a 10g sample of H2O