# Calculate the molecular masses

Question.
Calculate the molecular masses of $\mathrm{H}_{2}, \mathrm{O}_{2}, \mathrm{Cl}_{2}, \mathrm{CO}_{2}, \mathrm{CH}_{4}, \mathrm{C}_{2} \mathrm{H}_{6}, \mathrm{C}_{2} \mathrm{H}_{4}, \mathrm{NH}_{3}, \mathrm{CH}_{3} \mathrm{OH}$.

Solution:

Molecular mass of $\mathrm{H}_{2}=2 \times$ Atomic mass $(\mathrm{H})$

$=2 \times 1=2 \mathrm{u}$

Molecular mass of $\mathrm{O}_{2}=2 \times$ Atomic mass $(\mathrm{O})$

$=2 \times 16=32 \mathrm{u}$

Molecular mass of $\mathrm{Cl}_{2}=2 \times$ Atomic mass $(\mathrm{Cl})$

$=2 \times 35.5=71 \mathrm{u}$

Molecular mass of $\mathrm{CO}_{2}=$ Atomic mass $(\mathrm{C})+2 \times$ Atomic mass $(\mathrm{O})=12+2 \times 16=44 \mathrm{u}$

Molecular mass of $\mathrm{CH}_{4}=$ Atomic mass $(\mathrm{C})+4 \times$ Atomic mass $(\mathrm{H})=12+4 \times 1=16 \mathrm{u}$

Molecular mass of $\mathrm{C}_{2} \mathrm{H}_{6}=2 \times$ Atomic mass of $\mathrm{C}+6 \times$ Atomic mass of $\mathrm{H}=2 \times 12+6 \times 1=30 \mathrm{u}$

Molecular mass of $\mathrm{C}_{2} \mathrm{H}_{4}=2 \times$ Atomic mass $(\mathrm{C})+4 \times$ Atomic mass $(\mathrm{H})=2 \times 12+4 \times 1=28 \mathrm{u}$

Molecular mass of $\mathrm{NH}_{3}=$ Atomic mass of $\mathrm{N}+3 \times$ Atomic mass of $\mathrm{H}=14+3 \times 1=17 \mathrm{u}$

Molecular mass of $\mathrm{CH}_{3} \mathrm{OH}=$ Atomic mass $(\mathrm{C})+4 \times$ Atomic mass $(\mathrm{H})+$ Atomic mass $(\mathrm{O})$

$=12+4 \times 1+16=32 \mathrm{u}$