Some Basic Concepts Of Chemistry – Solutions

1) Calculate the molecular mass of the following:
i) H₂O ii) CO₂   iii) CH₄
Solution
The molecular mass of a compound is the sum of the atomic masses of the atoms present in the compound.
(Atomic mass of H, C and O are 1, 12 and 16 amu respectively)
Molecular mass of H₂O = 2 x atomic mass of H + 1 x atomic mass of O
= 2 x 1 + 1 x 16 = 18 amu
Molecular mass of CO₂ = 1 x atomic mass of C+ 2 x atomic mass of O
=1 x 12 + 2 x 16 = 44 amu
Molecular mass of CH₄ = 1x atomic mass of C + 4 x atomic mass of H
=1 x 12 + 4 x 1= 16amu

2) Calculate the mass percent of different elements present in sodium sulphate ( Na₂ SO₄ ).
Solution
Mass percent of element = ( Mass of element/ Mass of compound) x 100