Question

Calculate the molar mass of the following substances.
(a) Ethyne, \(C_2H_2\)
(b) Sulphur molecule, \(S_8\)
(c) Phosphorus molecule, \(P_4\) (Atomic mass of phosphorus= 31)
(d) Hydrochloric acid, \(HCl\)
(e) Nitric acid, \(NO_3\)

Answer 1

(a) Molar mass of \(\bf{C_2H_2}\) = (2 × Atomic mass of C) + (2 × Atomic mass of H)
= (2 × 12) + (2 × 1) = 26 u

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(b) Molar mass of \(\bf{S_8}\) = (8 × Atomic mass of S) 
= 8 × 32 = 256 u

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(c) Molar mass of \(\bf{P_4}\) = 4 × Atomic mass of P 
= 4 × 31 = 124 u

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(d) Molar mass of \(\bf{HCI}\) = Atomic mass of hydrogen + Atomic mass of CI 
= 1 + 35.5 = 36.5 u

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(e) Molar mass of \(\bf{HN0_3}\) = Atomic mass of H + Atomic mass of N + (3 × Atomic mass of 0) 
= 1 + 14 + (3 × 16)
= 15 + 48 = 63 u