Avagadro's Number Example Problem - Mass of a known number of molecules

Avagadro's Number Example Problem - Mass of a known number of molecules

Question: Calculate the mass in grams of 2.5 x 10⁹ H₂O molecules.
SolutionStep 1 - Determine the mass of 1 mole of H₂O
To obtain the mass of 1 mole of water, look up the atomic masses for hydrogen and oxygenfrom the Periodic Table. There are two hydrogen atoms and one oxygen for every H₂O molecule, so the mass of H₂O is:
mass of H₂O = 2 (mass of H) + mass of O mass of H₂O = 2 ( 1.01 g ) + 16.00 g mass of H₂O = 2.02 g + 16.00 g

mass of H₂O = 18.02 g