Calculate the molar masses of the following substances:
(a) Ethyne, C2H2
(b) Sulphur molecule, S8
(c) Phosphorus molecule, P4
(d) Hydrochloric acid, HCl
(e) Nitric acid, HNO3
The molar masses of all these substances will be equal to the respective molecular masses expressed in g/mol. Now:
(a) Molar mass of ethyne, C2H2 = Mass of C × 2 + Mass of H × 2
= 12 × 2 + 1 × 2
= 24 + 2
= 26 g/mol
(b) Molar mass of sulphur molecule, S8 = Mass of S × 8
= 32 × 8
= 256 g/mol
(c) Molar mass of phosphorus molecule, P4 = Mass of P × 4
= 31 × 4
= 124 g/mol
(d) Molar mass of hydrochloric acid, HCl = Mass of H + Mass of Cl
= 1 + 35.5
= 36.5 g/mol
(e) Molar mass of nitric acid, HNO3 = Mass of H + Mass of N + Mass of O × 3
= 1 + 14 + 16 × 3
= 15 + 48
= 63 g/mol