0.25 g of an organic compound "A" containing carbon, hydrogen and oxygen was analysed using the combustion method. There was an increase in mass of CaCl₂ tube and potash tube at the end of the experiment. The amount was found to be 0.15 g and 0.1837 g, respectively. The percentage of oxygen in compound A is ____ %. (Nearest integer) (Given: molar mass in g mol⁻¹ H : 1, C : 12, O : 16)

0.25 g of an organic compound A containing carbon hydrogen and oxygen was analysed using the combustion method

Q. 0.25 g of an organic compound "A" containing carbon, hydrogen and oxygen was analysed using the combustion method. There was an increase in mass of CaCl₂ tube and potash tube at the end of the experiment. The amount was found to be 0.15 g and 0.1837 g, respectively. The percentage of oxygen in compound A is ____ %. (Nearest integer)

(Given: molar mass in g mol⁻¹ H : 1, C : 12, O : 16)

Correct Answer: 73

Explanation

Increase in mass of CaCl₂ tube corresponds to mass of water formed.

Mass of H₂O = 0.15 g

Moles of H₂O:

0.15 / 18 = 0.00833 mol

Moles of hydrogen atoms:

= 2 × 0.00833 = 0.01666 mol

Mass of hydrogen:

= 0.01666 × 1 = 0.01666 g

Increase in mass of potash tube corresponds to mass of CO₂.

Mass of CO₂ = 0.1837 g

Moles of CO₂:

0.1837 / 44 = 0.004175 mol

Moles of carbon atoms:

= 0.004175 mol

Mass of carbon:

= 0.004175 × 12 = 0.0501 g

Total mass of compound = 0.25 g

Mass of oxygen in compound:

= 0.25 − (0.0501 + 0.01666)

= 0.18324 g

Percentage of oxygen:

(0.18324 / 0.25) × 100 ≈ 73.3%

Nearest integer value:

= 73%

Hence, the percentage of oxygen in compound A is 73%.

Explanation

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