Question

In a laboratory, a student makes a solution by completely dissolving 80.0 grams of KNO₃(s) in 100.0 grams of hot water. The resulting solution has a temperature of 60.0°C. The room temperature in the laboratory is 22°C. Compare the boiling point of the solution at standard pressure to the boiling point of water at standard pressure.

a) The boiling point of the solution is higher than that of water.
b) The boiling point of the solution is lower than that of water.
c) The boiling point of the solution is the same as that of water.
d) The boiling point of the solution cannot be determined from the given information.

Answer 1

The presence of KNO₃ in water raises the boiling point of the solution compared to pure water due to boiling point elevation. Thus, the solution will have a higher boiling point than the standard boiling point of water at 100°C.

Step-by-step explanation:

When a solute is added to a solvent, it causes a phenomenon known as boiling point elevation. This occurs because the dissolved solute particles disrupt the solvent's ability to easily enter the gas phase, hence more energy (higher temperature) is needed for the solvent to boil. In the provided scenario, 80.0 grams of KNO₃ are completely dissolved in hot water. The presence of KNO₃ in water will result in a higher boiling point than that of pure water.

For water, the boiling point elevation is about 0.51°C for every mole of solute particles per kilogram of water. The key concept here is that the boiling point of the solution, which now contains KNO₃, is higher because KNO₃ is a nonvolatile solute that decreases the vapor pressure of water. Therefore, the boiling point of the solution at standard pressure will be higher than the standard boiling point of pure water at 100°C. Hence, the correct answer is: a) The boiling point of the solution is higher than that of water.