Question

Calculate the molar mass of the following:
(i) $\text{H}_2\text{O}$ (ii) $\text{CO}_2$ (iii) $\text{CH}_4$

Answer 1

(i) $\text{H}_2\text{O}$:
The molecular mass of water, $\text{H}_2\text{O}$
$= (2 \times \text{Atomic mass of hydrogen}) + (1 \times \text{Atomic mass of oxygen})$
= [2(1.0084) + 1(16.00 u)]
= 18.016
= 18.02 u

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(ii) $\text{CO}_2$:
The molecular mass of carbon dioxide, $\text{CO}_2$
$= (1 \times \text{Atomic mass of carbon}) + (2 \times \text{Atomic mass of oxygen})$
= [1(12.011 u) + 2 (16.00 u)]
= 12.011 u + 32.00 u
= 44.01 u

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(iii) $\text{CH}_4$:
The molecular mass of methane, $\text{CH}_4$
$= (1 \times \text{Atomic mass of carbon}) + (4 \times \text{Atomic mass of hydrogen})$
= [1(12.011 u) + 4 (1.008 u)]
= 12.011 u + 4.032 u
= 16.043 u