Question

Calculate the molar mass of the following substances: [5 MARKS]

(a) Ethyne, C₂H₂

(b) Sulphur molecule, S₈

(c) Phosphorus molecule, P₄ (atomic mass of phosphorus = 31)

(d) Hydrochloric acid, HCl

(e) Nitric acid, HNO₃

Answer 1

Each point: 1 Mark

(a) Ethyne, C₂H₂
Molar mass of ethyne, C₂H₂ = 2 x 12 + 2 x 1 = 26 g

(b) Sulphur molecule, S₈
Molar mass of sulphur molecule, S₈ = 8 x 32 = 256 g

(c) Phosphorus molecule, P₄ (atomic mass of phosphorus = 31)
Molar mass of phosphorus molecule, P₄ = 4 x 31 = 124 g

(d) Hydrochloric acid, HCl
Molar mass of hydrochloric acid, HCl = 1 + 35.5 = 36.5 g

(e) Nitric acid, HNO₃
Molar mass of nitric acid, HNO₃ = 1 + 14 + 3 x 16 = 63 g