Question

Calculate the molecular mass of the following in u :

i. H₂O 

ii. C₆H₅Cl 

iii. H₂SO₄

Answer 1

i. Molecular mass of H₂O = (2 × Average atomic mass of H) + (1 × Average atomic mass of O)

= (2 × 1.0u) + (1 × 16.0 u)

= 18 u

ii. Molecular mass of C₆H₅Cl = (6 × Average atomic mass of C) + (5 × Average atomic mass of H) + (1 × Average atomic mass of Cl) 

= (6 × 12.0 u) + (5 × 1.0 u) + (1 × 35.5 u) 

= 112.5 u

iii. Molecular mass of H₂SO₄ = (2 × Average atomic mass of H) + (1 × Average atomic mass of S) + (4 × Average atomic mass of O) 

= (2 × 1.0 u) + (1 × 32.0 u) + (1 × 16.0 u) 

= 98 u

∴ i. The molecular mass of H₂O = 18 u

ii. The molecular mass of C₆H₅Cl = 112.5 u

iii. The molecular mass of H₂SO₄ = 98 u