The following phase diagram shows part of the liquid–vapor phase-transition boundaries for two solutions of equal con- centration, one containing a nonvolatile solute and the other containing a volatile solute whose vapor pressure at a given temperature is approximately half that of the pure solvent.
(d) Based on your drawing, what is the approximate normal boiling point of the pure solvent?

Verified step by step guidance

1. Identify the curve that represents the pure solvent. This is typically the curve that is not affected by the presence of solutes.
2. Locate the point on the pure solvent curve where the pressure is equal to 1 atm (normal atmospheric pressure).
3. Determine the temperature at this point, as this temperature represents the normal boiling point of the pure solvent.
4. Compare this temperature with the temperatures of the solutions containing nonvolatile and volatile solutes to understand the effect of solutes on boiling points.
5. Note that the normal boiling point is the temperature at which the vapor pressure of the liquid equals the external pressure (1 atm).

Key Concepts

Phase Diagram

A phase diagram is a graphical representation that shows the phases of a substance as a function of temperature and pressure. It illustrates the boundaries between different phases, such as solid, liquid, and gas, and indicates the conditions under which these phases coexist. In the context of solutions, phase diagrams can also depict the effects of solutes on the boiling and freezing points of solvents.

Boiling Point and Vapor Pressure

The boiling point of a liquid is the temperature at which its vapor pressure equals the external pressure surrounding the liquid. When a solute is added to a solvent, it typically lowers the vapor pressure of the solution compared to the pure solvent, which in turn raises the boiling point. This phenomenon is known as boiling point elevation and is crucial for understanding how solutes affect the boiling point of a solvent.

Volatile vs. Nonvolatile Solutes

Volatile solutes have significant vapor pressures and can evaporate easily, while nonvolatile solutes have negligible vapor pressures and do not contribute to the vapor phase. In a solution, the presence of a nonvolatile solute will lower the vapor pressure more than a volatile solute at the same concentration, affecting the phase behavior and boiling point of the solution. Understanding these differences is essential for interpreting phase diagrams.