Chemistry - Solutions (31 of 53) Colligative Properties- Vapor Pressure & Volatile Solute: Case

Summary

This video explains an ideal solution case where two similar substances, benzene and toluene, are mixed. The molecular structures, intermolecular forces, and enthalpy of solution are similar, resulting in no significant energy change when combined. The vapor pressures of the two substances depend on their molar fractions, with the total vapor pressure being the sum of their individual contributions. The video also touches on fractional distillation as a method to separate the two substances based on their different boiling points, highlighting how ideal solutions behave in such scenarios.

Takeaways

• 😀 Mixing benzene and toluene results in an ideal solution due to their similar molecular structure and intermolecular forces.
• 😀 The enthalpy of solution for the benzene-toluene mixture is zero, meaning no energy advantage is gained by mixing them.
• 😀 It's difficult to determine which compound is the solute and which is the solvent in a mixture of benzene and toluene.
• 😀 The vapor pressure of a solution depends on the mole fraction of its components (benzene and toluene).
• 😀 If the solution is 100% benzene, the vapor pressure is equal to the vapor pressure of benzene, which is 760 mmHg at 80°C.
• 😀 If the solution is 100% toluene, the vapor pressure is equal to the vapor pressure of toluene at 80°C, which is lower than benzene's vapor pressure.
• 😀 At 80°C, benzene reaches its boiling point at 80.1°C due to its vapor pressure reaching one atmosphere (760 mmHg).
• 😀 In an ideal case, the total vapor pressure of the solution is the sum of the vapor pressures of benzene and toluene.
• 😀 For a 50/50 mixture of benzene and toluene, the total vapor pressure is the sum of the individual contributions of each compound.
• 😀 Fractional distillation can be used to separate benzene and toluene in a mixture by increasing the temperature above 80°C, causing benzene to boil off first due to its higher vapor pressure.

Q & A

What is the main idea behind mixing benzene and toluene in this case?

The main idea is to explore how mixing two similar substances, benzene and toluene, results in an ideal solution where the properties of both solute and solvent are nearly identical, making it hard to distinguish between them.

What makes benzene and toluene ideal for this experiment?

Benzene and toluene are ideal for this experiment because their molecular structures, properties, and intermolecular forces are very similar. Both have benzene rings, with toluene only differing by the addition of a methyl group.

What happens to the enthalpy of solution when benzene and toluene are mixed?

When benzene and toluene are mixed, the enthalpy of solution (ΔH) is equal to zero, meaning there is no significant energy change when the two are combined.

How is the vapor pressure of a solution involving benzene and toluene determined?

The vapor pressure of the solution depends on the molar fraction of each component. Each component, benzene and toluene, contributes to the total vapor pressure in proportion to its molar fraction in the solution.

What does the dashed line on the vapor pressure chart represent?

The dashed line on the vapor pressure chart represents the vapor pressure contributed by benzene at different molar fractions, ranging from 100% benzene to 100% toluene.

Why is the temperature in the chart set at 80°C?

The temperature is set at 80°C because it corresponds to the boiling point of benzene, which is 80.1°C. This makes it a relevant reference point for observing how the vapor pressure behaves as the solution changes.

How does the molar fraction of benzene affect the vapor pressure of the solution?

The molar fraction of benzene directly influences the total vapor pressure of the solution. If the solution consists entirely of benzene, it contributes 100% of the vapor pressure. As the fraction of benzene decreases, its contribution to the vapor pressure also decreases.

How can fractional distillation be used to separate benzene and toluene?

Fractional distillation can be used to separate benzene and toluene by exploiting the difference in their vapor pressures. As the temperature exceeds the boiling point of benzene (80.1°C), benzene will evaporate more readily, allowing it to be separated from the toluene.

What does the chart show about a 50/50 solution of benzene and toluene?

In a 50/50 solution of benzene and toluene, the chart shows that the vapor pressures of each substance contribute equally to the total vapor pressure of the solution, with each substance contributing 50%.

What is the significance of the vapor pressure reaching atmospheric pressure in terms of boiling?

When the vapor pressure of a solution reaches the atmospheric pressure (760 mmHg), the solution will boil. In the case of benzene, this occurs at 80.1°C, which is its boiling point.