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: 73

To determine the percentage of oxygen in compound A, we first need to calculate the amounts of carbon and hydrogen from the given data.
Step 1: Calculate the mass of hydrogen
The increase in mass of the CaCl₂ tube indicates the mass of water (H₂O) produced: 0.15 g.
The molar mass of H₂O is 18 g/mol, of which 2 g/mol is hydrogen.
Therefore, the mass of hydrogen is calculated as follows: (2/18) × 0.15 g = 0.0167 g.
Step 2: Calculate the mass of carbon
The increase in mass of the potash tube indicates the mass of CO₂ produced: 0.1837 g.
The molar mass of CO₂ is 44 g/mol, of which 12 g/mol is carbon.
Therefore, the mass of carbon is calculated as follows: (12/44) × 0.1837 g ≈ 0.0501 g.
Step 3: Calculate the mass of oxygen
The total mass of the compound A is 0.25 g.
The mass of oxygen is obtained by subtracting the masses of carbon and hydrogen from the total:
Mass of oxygen = 0.25 g - (0.0167 g + 0.0501 g) = 0.1832 g.
Step 4: Calculate the percentage of oxygen
The percentage of oxygen is computed using:
[(Mass of oxygen)/(Total mass of compound A)] × 100 = (0.1832/0.25) × 100 = 73.28%
Rounding to the nearest integer, the percentage of oxygen in compound A is 73%.