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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
Answer
Molar mass of C = 12g
Molar mass of H = 1g
Molar mass of S = 32g
Molar mass of P = 31g
Molar mass of Cl = 35.5g
Molar mass of N = 14g
Molar mass of O = 16g
(a) Ethyne, C 2 H 2
Molar mass of C 2 H 2 = 2 x Molar mass of C + 2 x Molar mass of H
= 2x 12g + 2 x 1g
= 24g + 2g
= 26g
(b) Sulphur molecule, S 8
Molar mass of S 8 = 8 x Molar mass of S
= 8x 32g
= 256g
(c) Phosphorus molecule, P 4
Molar mass of P 4 = 4 x Molar mass of P
= 4 x 31g
= 124g
(d) Hydrochloric acid, HCl
Molar mass of HCl = 1 x Molar mass of H + 1 x Molar mass of Cl
= 1x 1g + 1 x 35.5g
= 1g + 35.5g
=
36.5g
(e) Nitric acid, HNO 3
Molar mass of HNO 3 = 1 x Molar mass of H + 1 x Molar mass of N + 3 x Molar mass of O
=1x 1g + 1 x 14g + 3 x 16g
= 1g + 14g + 48g
= 63g
