The vapour pressure of a substance of low volatility can be measured by passing an unreactive gas over a sample of the substance and analysing the composition of the resulting gas mixture. When nitrog

Question

The vapour pressure of a substance of low volatility can be measured by passing an unreactive gas over a sample of the substance and analysing the composition of the resulting gas mixture. When nitrogen was passed over mercury at 23°C, the mixture analysed to 0.8 mg of Hg, 50.4 g of nitrogen, at a total pressure of 720 torr. The vapour pressure of mercury at this temperature is (Hg = 200)

Prashant Kotian · Accepted Answer

Correct answer: B. n_Hg = 0.8 × 10⁻³/200 = 4 × 10⁻⁶ mol. n_N₂ = 50.4/28 = 1.8 mol. P_Hg = (n_Hg/n_N₂) × P_total = (4 × 10⁻⁶/1.8) × 720 = 1.6 × 10⁻³ torr.

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