Calculate the molar mass of the following substances.

(a) Ethyne, C\(_2\)H\(_2\)

(b) Sulphur molecule, S\(_8\)

(c) Phosphorus molecule, P\(_4\) (Atomic mass of phosphorus =31)

(d) Hydrochloric acid, HCl

(e) Nitric acid, HNO\(_3\)

We know that molar mass of a substance is the sum of the atomic masses of all the elements.

(a) Molar mass of Ethyne C\(_2\)H\(_2\)
= 2 × Mass of C+2 × Mass of H
= (2 × 12) + (2 × 1) = 24 + 2
= 26g

(b) Molar mass of Sulphur molecule S₈
= 8 × Mass of S = 8 × 32 = 256g

(c) Molar mass of Phosphorus molecule, P₄
= 4 × Mass of P = 4 × 31 = 124g

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

(e) Molar mass of Nitric acid, HNO₃
= Mass of H+ Mass of Nitrogen + 3 × Mass of O = 1 + 14 + 3 × 16 = 63g