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In Dumas’ method for nitrogen estimation, 0.25 g of an organic substance yields 40 mL of nitrogen gas collected at 300 K and 725 mm pressure. If the vapour pressure of water at 300 K is 25 mm, the nitrogen percentage in the compound is:

1. 18.20
2. 16.76
3. 15.76
4. 17.36

Correct answer: 16.76

Solution

The correct option is derived by first adjusting the pressure of the nitrogen gas to account for the vapor pressure of water, then using the ideal gas law to calculate the number of moles of nitrogen produced. Finally, the percentage of nitrogen in the original compound is calculated based on the mass of the organic substance and the moles of nitrogen obtained.

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