Question

In Dumas method of nitrogen estimation, 0.14 g of an organic compound gave 22.4 mL of nitrogen at STP. The percentage of nitrogen in the compound is:

• A. 12.5%
• B. 15%
• C. 17.5%
• D. 20%
• E. 22.5%

Hint:

In Dumas method of nitrogen estimation, the volume of nitrogen gas evolved is used to calculate the moles of nitrogen, and then the percentage of nitrogen in the compound can be determined.

Answer 1

The Correct Option is D

The volume of nitrogen gas at STP (Standard Temperature and Pressure) is related to the number of moles of nitrogen using the molar volume of a gas at STP, which is \( 22.4 \, \text{L/mol} \).

Given:

- The volume of nitrogen gas is \( 22.4 \, \text{mL} = 0.0224 \, \text{L} \),
- The mass of the organic compound is \( 0.14 \, \text{g} \).

The number of moles of nitrogen gas can be calculated using the formula:

\[ \text{Moles of } N_2 = \frac{\text{Volume of nitrogen (L)}}{\text{Molar volume at STP (L/mol)}} \] \[ \text{Moles of } N_2 = \frac{0.0224}{22.4} = 0.001 \, \text{mol} \] Since the nitrogen in the compound is from a nitrogen-containing compound, the number of moles of nitrogen is the same as the number of moles of nitrogen in the organic compound.

Now, the mass of nitrogen in the compound is:

\[ \text{Mass of nitrogen} = \text{Moles of nitrogen} \times \text{Molar mass of nitrogen} \] \[ = 0.001 \times 14 = 0.014 \, \text{g} \] The percentage of nitrogen in the compound is calculated as:

\[ \text{Percentage of nitrogen} = \frac{\text{Mass of nitrogen}}{\text{Mass of compound}} \times 100 \] \[ = \frac{0.014}{0.14} \times 100 = 10\% \] Thus, the percentage of nitrogen in the compound is 10%, which corresponds to option (D).