Question

Calculate the molecular mass of- ${\mathrm{NH}}_3,{\mathrm{CO}}_2,\mathrm{HCl},{\mathrm{Cl}}_2$

Answer 1

1. Molecular mass is the sum of the atomic masses of all the individual atoms present in a molecule or compound.
2. Molar mass is the mass of a substance that consists of one mole of the atom.

The molecular mass of ammonia.

• The chemical formula of ammonia is${\mathrm{NH}}_3$
• Atomic mass of Nitrogen( $\mathrm{N}$ ) = 14
• Atomic mass of hydrogen( $\mathrm{H}$) = 1 .

Molecular mass of NH₃ = ( Atomic mass of nitrogen ) x 1 + ( Atomic mass of hydrogen ) x 3

= $$\begin{gathered} =(14\times 1)+(1\times 3) \\ =17\mathrm{g}/\mathrm{mol} \end{gathered}$$

The molecular mass of carbon dioxide

• The chemical formula of Carbon dioxide is ${\mathrm{CO}}_2$
• The atomic mass of Carbon = 12
• The atomic mass of Oxygen = 16

The molecular mass of CO₂ = ( Atomic mass of Carbon ) x 1 + ( Atomic mass of Oxygen ) x 2

$$\begin{gathered} =(12\times 1)+(16\times 2) \\ =44\mathrm{g}/\mathrm{mol} \end{gathered}$$

The molecular mass of hydrochloric acid

• The chemical formula of Hydrochloric acid is $\mathrm{HCl}$
• The atomic mass of Chlorine = 35.5
• The atomic mass of Hydrogen = 1

The molecular mass of hydrochloric acid = ( Atomic mass of hydrogen ) x 1 + ( Atomic mass of chlorine ) x 1

$$\begin{gathered} =1+35.5 \\ =36.5\mathrm{g}/\mathrm{mol} \end{gathered}$$

The molecular mass of chlorine

Chlorine exists as a diatomic molecule that is Cl₂

.Atomic mass of Chlorine = 35.5

.Atomic mass of Hydrogen = 1

Molecular Mass of ${\mathrm{Cl}}_2$ = (Atomic mass of chlorine) x 2

$$\begin{gathered} =35.5\times 2 \\ =71\mathrm{g}/\mathrm{mol} \end{gathered}$$

Hence

Molecular mass of ${\mathrm{NH}}_3$ = 17g/mol

Molecular mass of ${\mathrm{CO}}_2$ = 44 g/mol

Molar mass of $\mathrm{HCl}$ = 36.5 g/mol

Molecular mass of ${\mathrm{Cl}}_2$ = 71 g/mol