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A gas X is present in a sealed container along with saturated water vapour at a total pressure of 1.5 atm. The vapour pressure of water at this temperature is 0.5 atm. Using Henry's law constant KH = 10⁻⁴ (in mole fraction per atm), find the number of moles of gas X dissolved in 10 moles of water, expressed as x * 10⁻³. What is x?
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Correct answer: 1
Solution
By Dalton's law, P_X = 1.5 - 0.5 = 1.0 atm. Henry's law gives mole fraction of X in water = KH * P_X = 10⁻⁴ * 1 = 10⁻⁴. With 10 moles water and dilute solution, moles of X dissolved = 10⁻⁴ * 10 = 10⁻³, so x = 1.
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