Question

On complete combustion, 0.3 g of an organic compound gave 0.2 g of CO₂ and 0.1 g of H₂O. The percentage composition of carbon and hydrogen in the compound, respectively, is:

• A. 4.07% and 15.02%
• B. 18.18% and 3.70%
• C. 15.02% and 4.07%
• D. 3.70% and 18.18%

Answer 1

The Correct Option is B

Carbon Percentage:
The mass of carbon in 0.2 g of CO$_2$ is determined using molar masses: Molar mass of CO$_2$ = 44 g/mol; Molar mass of C = 12 g/mol.

Mass of C in 0.2 g CO$_2 = \frac{12}{44} \times 0.2 g = 0.0545g$

Percentage of C $= \frac{Mass of C}{Mass of compound} \times 100 = \frac{0.0545}{0.3} \times 100 = 18.18%$

Hydrogen Percentage:

The mass of hydrogen in 0.1 g of H$_2$O is calculated using molar masses: Molar mass of H$_2$O = 18 g/mol; Molar mass of H = 1 g/mol (considering 2 H atoms, this becomes 2 g/mol).

Mass of H in 0.1 g H$_2$O $= \frac{2}{18} \times 0.1g = 0.0111g$

Percentage of H $= \frac{\text{Mass of H}}{\text{Mass of compound}} \times 100 = \frac{0.0111}{0.3} \times 100 = 3.70%$

The percentage composition of carbon is 18.18%, and the percentage composition of hydrogen is 3.70%.