Question

0.4 g of an organic compound in Dumas method gives 22.4 mL of nitrogen collected at S.T.P. What is the percentage of nitrogen in the compound?

• A. 13.67%
• B. 7.0%
• C. 8.5%
• D. 10.0%

Hint:

In Dumas method, the percentage of nitrogen can be determined using the volume of nitrogen gas collected at S.T.P. and the molar volume of the gas.

Answer 1

The Correct Option is B

Step 1: Using the ideal gas law.
At S.T.P., 1 mole of gas occupies 22.4 L. The volume of nitrogen gas is given as 22.4 mL (which is 0.0224 L). The number of moles of nitrogen can be calculated as: \[ n = \frac{V}{22.4} = \frac{0.0224}{22.4} = 1 \text{ mole of N$_2$} \] Step 2: Calculating the mass of nitrogen.
The molecular weight of nitrogen (N) is 14 g/mol, and the total nitrogen mass in the sample is: \[ \text{Mass of N} = 1 \times 14 = 14 \text{ g} \] Step 3: Calculating percentage of nitrogen.
The percentage of nitrogen in the sample is: \[ \frac{14}{0.4} \times 100 = 7.0% \] Step 4: Conclusion.
The correct answer is (B) 7.0%, as it represents the percentage of nitrogen in the compound.