Question #85cd9

1 Answer
Feb 18, 2016


We will use just relation between molecular mass and molar mass for water.


First of all, let us consider the molecular mass of water:
- Each atom of hydrogen has a mass equal to 1 AMU (atomic mass unit).
- Each atom of oxygen has a mass equal to 16 AMU.
- Hence, a water molecule (#"H"_2 "O"#) has:

#2 cdot 1 + 1 cdot 16 = 18 "AMU"#

For any molecule (and also for every atom), its molecular mass in AMU equals to the mass of a mole in grams.
For example, for water: 1 molecule has a mass of 18 AMU, and this implies that 1 mole has a mass of 18 grams. Molecular mass in AMU equals to molar mass in grams. Always, atoms included.

Thus, the number of moles contained in 60 grams of water is:

#{60 " grams"}/{18 " grams/mole"} = 3,33 " moles"#