Which of the following best describes the effect of adding a nonvolatile solute to a solvent on the boiling point of the solution?

• A. The boiling point of the solution decreases compared to the pure solvent.
• B. The boiling point of the solution becomes equal to the freezing point.
• C. The boiling point of the solution remains unchanged.
• D. The boiling point of the solution increases compared to the pure solvent.

Answer: (D)

Verified step by step guidance

1. Understand that adding a nonvolatile solute to a solvent causes a colligative property change, specifically boiling point elevation.
2. Recall that a nonvolatile solute does not evaporate easily, so it lowers the solvent's vapor pressure when dissolved.
3. Use the concept that boiling point is the temperature at which the vapor pressure of the liquid equals the external pressure; lowering vapor pressure means a higher temperature is needed to boil.
4. Apply the boiling point elevation formula: \(\Delta T_b = i K_b m\), where \(\Delta T_b\) is the boiling point increase, \(i\) is the van't Hoff factor, \(K_b\) is the ebullioscopic constant of the solvent, and \(m\) is the molality of the solution.
5. Conclude that because the vapor pressure is lowered by the solute, the boiling point of the solution increases compared to the pure solvent.