Question 1.55: Calculate the percentage composition of the following compou......

(i) Urea : $CO(NH_2)_2$

Molar mass of urea = 12 + 16 + 2 (14 + 2) = 60

Mass of carbon = 12

Mass percentage of carbon = $\frac{12}{60} \times 100 = 20 \%$

Mass of oxygen = 16

Mass percentage of oxygen = $\frac{16}{60} \times 100 = 26.67 \%$

Mass of nitrogen = 2 × 14 = 28

Mass percentage of nitrogen = $\frac{28}{60} \times 100 = 46.66 \%$

Mass of H = 4 × 1 = 4

Mass percentage of hydrogen = $\frac{4}{60} \times 100 = 6.67 \%$

(ii) Copper sulphate, $CuSO_4.5H_2O$

Molar mass of $CuSO_4.5H_2O$ = 63.5 + 32 + 4 × 16 + 5 × 18

= 249.5

Mass of Cu = 63.5

Mass percentage of Cu = $\frac{63.5}{249.5} \times 100 = 25.45$

Mass of S = 32

Mass percentage of S = $\frac{32}{249.5} \times 100 = 12.82 \%$

Mass of O = 9 × 16 = 144

Mass percentage of O = $\frac{144}{249.5} \times 100 = 57.77 \%$

Mass of H = 10 × 1 = 10

Mass percentage of H = $\frac{10}{249.5} \times 100 = 4.01 \%$