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Question
The vapour pressure of pure liquid X and pure liquid Y at 25°C are 120 mm Hg and 160 mm Hg respectively. If equal moles of X and Y are mixed to form an ideal solution, calculate the vapour pressure of the solution.
Solution
At 25°C, Pure vapour pressure of liquid X and Y are
P0X = 120 mm Hg and P0Y = 160 mm Hg
Let the number of moles of liquid X and Y be ‘n’
XX = `n/(n + n)`
then, XX = XY = `1/2` = 0.5
Total vapour pressure of solution will be,
PT = P0X XX + P0Y XY
= 120 × 0.5 + 160 × 0.5
= 60 + 80
= 140 mm of Hg
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