Molecular mass is the sum of atomic masses of the elements present in a molecule. It is obtained by multiplying the atomic mass of each element by the number of its atoms and adding them together. For example, molecular mass of methane which contains one carbon atom and four hydrogen atoms can be obtained as follows:
Molecular mass of methane,
(CH4) = (12.011 μ) + 4 (1.008 μ) = 16.043 μ
Similarly, molecular mass of water:
(H2O) = 2 atomic mass of hydrogen + 1 atomic mass of oxygen
= 2 (1.008 μ) + 16.00 μ = 18.02 μ
Problem: Calculate molecular mass of glucose (C6H12O6) molecule.
Solution
Molecular mass of glucose (C6H12O6)
= 6 (12.011 μ) + 12(1.008 μ) + 6(16.00 μ)
= (72.066 μ) + (12.096 μ) + (96.00 μ)
= 180.162 μ
