Question

Calculate the molecular mass of the following substances:

(a) Ethyne $\left(C_2{H}_2\right)$

(b) Hydrogen chloride $\left(HCl\right)$

(c) Nitric acid $\left(HN{O}_3\right)$

[3 Marks]

Answer 1

(a) Ethyne $\left(C_2{H}_2\right)$
The molecular mass of ethyne, $C_2{H}_2$=
(2 $\times$ atomic mass of C) + (2 $\times$ atomic mass of H) = (2 $\times$ 12 u) + (2 $\times$ 1 u) = 26 u

[1 Mark]

(b) Hydrogen chloride $\left(HCl\right)$
The molecular mass of hydrogen chloride, HCl =
(1 $\times$ atomic mass of H) + (1 $\times$ atomic mass of Cl) = (1 $\times$ 1 u) + (1 $\times$ 35.5 u) = 36.5 u

[1 Mark]
(c) Nitric acid $\left(HN{O}_3\right)$
The molecular mass of nitric acid, $\left(HN{O}_3\right)$ =
(1 $\times$ atomic mass of H) + (1 $\times$ atomic mass of N) + (3 $\times$ atomic mass of O) = (1 $\times$ 1 u) + (1 $\times$ 14 u) + (3 $\times$ 16 u) = 63 u

[1 Mark]