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Ch.13 - Solutions
Chapter 13, Problem 76

A solution of methanol and water has a mole fraction of water of 0.312 and a total vapor pressure of 211 torr at 39.9 °C. The vapor pressures of pure methanol and pure water at this temperature are 256 torr and 55.3 torr, respectively. Is the solution ideal? If not, what can be inferred about the relative strengths of the solute–solvent interactions compared to the solute–solute and solvent–solvent interactions?

Verified step by step guidance
1
Identify the components of the solution: methanol and water.
Use Raoult's Law to calculate the expected vapor pressure of the solution if it were ideal. Raoult's Law states that the partial vapor pressure of each component in an ideal solution is equal to the vapor pressure of the pure component multiplied by its mole fraction in the solution.
Calculate the partial vapor pressure of methanol: \( P_{\text{methanol}} = X_{\text{methanol}} \times P^0_{\text{methanol}} \), where \( X_{\text{methanol}} = 1 - X_{\text{water}} \).
Calculate the partial vapor pressure of water: \( P_{\text{water}} = X_{\text{water}} \times P^0_{\text{water}} \).
Add the partial pressures of methanol and water to find the total vapor pressure of the ideal solution and compare it to the given total vapor pressure to determine if the solution is ideal. If the calculated total vapor pressure is different from the given total vapor pressure, the solution is not ideal, indicating that the solute-solvent interactions differ in strength from the solute-solute and solvent-solvent interactions.
Related Practice
Textbook Question

A solution contains 50.0 g of heptane (C7H16) and 50.0 g of octane (C8H18) at 25 °C. The vapor pressures of pure heptane and pure octane at 25 °C are 45.8 torr and 10.9 torr, respectively. Assuming ideal behavior, answer the following: d. Why is the composition of the vapor different from the composition of the solution?

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Textbook Question

A solution contains a mixture of pentane and hexane at room temperature. The solution has a vapor pressure of 258 torr. Pure pentane and hexane have vapor pressures of 425 torr and 151 torr, respectively, at room temperature. What is the mole fraction composition of the mixture? (Assume ideal behavior.)

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Open Question
A solution contains 4.08 g of chloroform (CHCl3) and 9.29 g of acetone (CH3COCH3). The vapor pressures at 35 °C of pure chloroform and pure acetone are 295 torr and 332 torr, respectively. Assuming ideal behavior, calculate the vapor pressures of each of the components and the total vapor pressure above the solution. The experimentally measured total vapor pressure of the solution at 35 °C is 312 torr. Is the solution ideal? If not, what can you say about the relative strength of chloroform–acetone interactions compared to the acetone–acetone and chloroform–chloroform interactions?
Textbook Question

A glucose solution contains 55.8 g of glucose (C6H12O6) in 455 g of water. Determine the freezing point and boiling point of the solution.

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Open Question
An ethylene glycol solution contains 21.2 g of ethylene glycol (C2H6O2) in 85.4 mL of water. Determine the freezing point and boiling point of the solution. (Assume a density of 1.00 g/mL for water.)
Open Question
Calculate the freezing point and boiling point of a solution containing 10.0 g of naphthalene (C10H8) in 100.0 mL of benzene. Benzene has a density of 0.877 g/cm³.