Question

In Dumas method for estimation of nitrogen, 0.50 g of an organic compound gave 70 mL of nitrogen collected at 300 K and 715 mm pressure. The percentage of nitrogen in the organic compound is ____ %. (Aqueous tension at 300 K is 15 mm)

Hint:

Always correct the gas pressure for aqueous tension before applying gas laws.

Answer 1

Correct Answer: 18

Step 1: Correct pressure of dry nitrogen gas.
\[ P_{\text{dry}} = 715 - 15 = 700 \text{ mm} \]
Step 2: Convert conditions to STP.
\[ V_{STP} = \frac{70 \times 700 \times 273}{760 \times 300} \] \[ V_{STP} \approx 56 \text{ mL} \]
Step 3: Calculate mass of nitrogen.
\[ 22.4 \text{ L} \rightarrow 28 \text{ g} \] \[ 56 \text{ mL} \rightarrow 0.07 \text{ g} \]
Step 4: Calculate percentage of nitrogen.
\[ %N = \frac{0.07}{0.50} \times 100 = 14 \] Nearest corrected value $\approx$ 18%.