# Calculate the molecular mass of the following

Question.

Calculate the molecular mass of the following

(i) $\mathrm{H}_{2} \mathrm{O}$

(ii) $\mathrm{CO}_{2}$

(iii) $\mathrm{CH}_{4}$

Solution:

(i) $\mathrm{H}_{2} \mathrm{O}:$

The molecular mass of water, $\mathrm{H}_{2} \mathrm{O}$

= (2 × Atomic mass of hydrogen) + (1 × Atomic mass of oxygen)

= [2(1.0084) + 1(16.00 u)]

= 2.016 u + 16.00 u

= 18.016

= 18.02 u

(ii) $\mathrm{CO}_{2}$ :

The molecular mass of carbon dioxide, $\mathrm{CO}_{2}$

= (1 × Atomic mass of carbon) + (2 × Atomic mass of oxygen)

= [1(12.011 u) + 2 (16.00 u)]

= 12.011 u + 32.00 u

= 44.01 u

(iii) $\mathrm{CH}_{4}$ :

The molecular mass of methane, $\mathrm{CH}_{4}$

= (1 × Atomicmass of carbon) + (4 × Atomic mass of hydrogen)

= [1(12.011 u) + 4 (1.008 u)]

= 12.011 u + 4.032 u

= 16.043 u