Multiple choice

Calculate the vapour pressure of a 65 percent (W/W) solution of ordinary cane sugar (C22O11H22, MW = 342 g mol−1) in water. The vapour pressure of pure water at the same temperature is 26.0 torr.

  1. 16.9 torr

  2. 26.0 torr

  3. 23.7 torr

  4. 34.2 torr

  5. 52.0 torr
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C Correct answer
Explanation

Correct answer. 100 g of solution contains 65/342 = 0.19 mol of sugar and 36/18 = 2 mol of water  The mole fraction of water in the solution = 2 / (0.19 + 2) = 0.91 So, its vapour pressure will be 0.91 × 26.0 torr = 23.7 torr

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