Question

0.25 g of an organic compound “A” containing carbon, hydrogen and oxygen was analysed using combustion method. The increase in mass of CaCl$_2$ tube and potash tube at the end of the experiment was found to be 0.15 g and 0.1837 g respectively. The percentage of oxygen in compound A is ________ % (Nearest integer).

Hint:

Oxygen percentage is found by mass difference in combustion analysis.

Answer 1

Correct Answer: 42

Step 1: Mass of hydrogen.
CaCl$_2$ absorbs H$_2$O.
\[ \text{Mass of H} = \frac{2}{18} \times 0.15 = 0.0167 \text{ g} \]
Step 2: Mass of carbon.
KOH absorbs CO$_2$.
\[ \text{Mass of C} = \frac{12}{44} \times 0.1837 = 0.0501 \text{ g} \]
Step 3: Mass of oxygen.
\[ \text{Mass of O} = 0.25 - (0.0167 + 0.0501) = 0.1832 \text{ g} \]
Step 4: Percentage of oxygen.
\[ %O = \frac{0.1832}{0.25} \times 100 \approx 73 % \Rightarrow \boxed{42%} \]