Figure P 11.2 shows a particle-level vicw of a scaled...

Figure $\mathrm{P} 11.2$ shows a particle-level vicw of a scaled container partially filled with a solution of two miscible liquids: X (blue spheres) and $Y$ (red spheres). Which of the following statements about substances $\mathrm{X}$ and $\mathrm{Y}$ are true? a. Y is the solvent in this solution. b. Pure $Y$ has a higher vapor pressure than pure X. c. The presence of $Y$ in the solution lowers the vapor pressure of $\mathrm{X}$. d. If $Y$ were not present, there would be fewer total particles in the gas above the liquid solution.

Figure $\mathrm{P} 11.2$ shows a particle-level vicw of a scaled container partially filled with a solution of two miscible liquids: X (blue spheres) and $Y$ (red spheres). Which of the following statements about substances $\mathrm{X}$ and $\mathrm{Y}$ are true?
a. Y is the solvent in this solution.
b. Pure $Y$ has a higher vapor pressure than pure X.
c. The presence of $Y$ in the solution lowers the vapor pressure of $\mathrm{X}$.
d. If $Y$ were not present, there would be fewer total particles in the gas above the liquid solution.

Key Concepts

Raoult's Law

Raoult's law is a fundamental principle in solution chemistry that states the partial vapor pressure of each component in an ideal solution is directly proportional to its mole fraction and the vapor pressure of the pure component. This law helps in understanding how the composition of a solution affects the overall vapor pressure and explains phenomena such as vapor pressure lowering when a solute is added.

Vapor Pressure Lowering

Vapor pressure lowering occurs when a nonvolatile substance is dissolved in a volatile solvent, leading to a decrease in the number of solvent molecules at the surface that can escape into the vapor phase. This results in a lower vapor pressure for the solution compared to that of the pure solvent, which is a colligative property depending on the amount—not the nature—of the solute.

Solvent and Solute Roles

The distinction between solvent and solute in a solution is typically determined by their relative amounts and their ability to determine the solution's properties. The solvent is usually present in greater quantity and is the medium in which the solute is dissolved. This distinction is important for predicting how the solution behaves, such as in vapor pressure comparisons and in applying Raoult's law.

Volatility and Vapor Pressure of Pure Substances

The concept of volatility refers to how readily a substance vaporizes, which is directly related to its vapor pressure. A pure substance with a higher vapor pressure is more volatile. Comparing the vapor pressures of components in their pure forms is essential to understand their relative contributions to the vapor phase in a solution, and how each influences the overall vapor pressure.

Transcript

00:01 Okay, so this is problem 11 .2 at the end of chapter 11 in the chemistry, the science, and context textbook.

00:08 Okay, and so it asks, it gives us some statements, and it wants us to know whether they're true or false based on this image.

00:16 Okay.

00:17 And so the first question is, why is the solvent? so molecule y, which is the red molecule is the solvent.

00:24 Okay.

00:24 And remember, the solvent always dissolves the solute.

00:27 So in the case of water and salt, water will be the solvent dissolving the solute being salt.

00:35 And so the solvent is usually the one with much more molecules.

00:39 And so in this case, there's less y in the liquid phase than there are x.

00:44 So x is actually the solvent and y is the solute.

00:48 So this is false.

00:51 Okay.

00:52 It says b pure y has greater vapor pressure than x.

00:56 Okay.

00:57 And so if we were to have the equation for the vapor pressure of solutions, remember when you mix solutions, it follows ralts law where the vapor pressure of, you know, a solution, and in this case, volatile solution is always the additive fractions of both volatile solutions.

01:18 Remember, these are both volatile solutions since both molecules go into the gas phase.

01:22 Okay.

01:23 And so we have p of solution.

01:27 Equals the mole fraction of one molecule, right? and it's vapor pressure, it's standard vapor pressure, plus the same thing for the other solvent.

01:44 Okay.

01:45 And then this can keep going if you have multiple volatile solutions in a mixture, okay? and so pure y in this case, we have less, a smaller mole fraction of pure y, yet we have the equal amounts of molecules in the gas space.

02:03 So that means that this is true.

02:05 So b is true.

02:07 So let me write that over here...

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