High School

The vapor pressure of pure methanol (\( \text{CH}_3\text{OH} \)) at \( 40^\circ\text{C} \) is 97.7 torr. What is the vapor pressure (in torr) of a solution containing 39.2 g of nonvolatile, nonelectrolyte glycerol (\( \text{C}_3\text{H}_8\text{O}_3 \)) in 94.3 g of methanol at \( 40^\circ\text{C} \)?

Answer :

The vapor pressure of the solution is 85.4 torr.

To answer this question, we'll first need to calculate the mole fraction of methanol and glycerol in the solution and use it to calculate the vapor pressure of the solution using Raoult's law. Raoult's law is a law of thermodynamics which states that the vapor pressure of a solution is directly proportional to the mole fraction of the solvent present in the solution, where the mole fraction is the ratio of the number of moles of a substance to the total number of moles of all the substances present in the solution. Now, let's calculate the mole fraction of methanol and glycerol in the solution.

Number of moles of methanol = 94.3 g / 32.04 g/mol = 2.944

Number of moles of glycerol = 39.2 g / 92.1 g/mol = 0.425

Mole fraction of methanol = 2.944 / (2.944 + 0.425) = 0.874

Mole fraction of glycerol = 0.425 / (2.944 + 0.425) = 0.126

Now, we can use Raoult's law to calculate the vapor pressure of the solution:

P = (mole fraction of methanol) x (vapor pressure of pure methanol)

= (0.874) x (97.7 torr)

= 85.4 torr

Therefore, the vapor pressure of the solution is 85.4 torr.

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