Question

A solution was prepared by dissolving 2moles of methanol in 5moles of water at 25°c. If the vapour pressure of pure water is 23.8mmHg calculate the partial pressure of water over the solution and depression of vapour pressure of pure water.

Answer 1

Answer on Question #80376 - Chemistry - Physical Chemistry

Question:

A solution was prepared by dissolving 2moles of methanol in 5moles of water at $25^{\circ}\mathrm{C}$. If the vapour pressure of pure water is $23.8\mathrm{mmHg}$ calculate the partial pressure of water over the solution and depression of vapour pressure of pure water.

Solution:

$$\mathrm{Pi} = \mathrm{P0} \cdot \mathrm{xi}$$ $$\mathrm{Xi} = \frac{5}{5 + 2} = \frac{5}{7} = 0.7143 = 71.43\%;$$ $$\mathrm{Pi} = 23.8 \cdot 0.7143 = 17 \mathrm{mmHg}.$$

Answer: 17 mmHg.