In a laboratory estimation using Dumas' method, exactly of an organic compound yielded of gas collec — Qualitative and Quantitative Analysis Chemistry Question
Question
In a laboratory estimation using Dumas' method, exactly $0.35 \text{ g}$ of an organic compound yielded $55 \text{ mL}$ of $N_2$ gas collected over an aqueous KOH solution at $300 \text{ K}$ and $715 \text{ mm Hg}$ total pressure. If the aqueous tension at $300 \text{ K}$ is $15 \text{ mm Hg}$, the percentage of nitrogen in the compound is closest to:
Answer: C
💡 Solution & Explanation
Dry pressure $P_{dry} = 715 - 15 = 700 \text{ mm Hg}$. Using $P_1V_1/T_1 = P_2V_2/T_2$, volume at STP ($V_{STP}$) = $(273 \times 700 \times 55) / (300 \times 760) = 46.098 \text{ mL}$. Mass of $N_2 = (28 / 22400) \times 46.098 = 0.0576 \text{ g}$. Percentage = $(0.0576 / 0.35) \times 100 \approx 16.45\%$.
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