Final answer:
The boiling point of a potassium nitrate solution is higher than pure water due to boiling point elevation, a process where dissolved solute particles cause a decrease in vapor pressure requiring a higher temperature to reach boiling.
Step-by-step explanation:
The boiling point of the potassium nitrate solution is higher than that of pure water because of a phenomenon known as boiling point elevation. This occurs because the dissolved solute particles, such as potassium and nitrate ions from potassium nitrate, decrease the vapor pressure of the water. As a result, a higher temperature is required for the vapor pressure to reach atmospheric pressure, which is the point at which water begins to boil. The presence of a nonvolatile solute means that the solution has a lower rate of evaporation at any given temperature compared to the pure solvent, requiring additional heat to reach boiling.
The relationship between the amount of solute and the increase in boiling point is quantified by the equation ΔT = Kb × m, where ΔT is the boiling point elevation, Kb is the molal boiling-point elevation constant, and m is the molality of the solution. For water, the value of Kb is 0.512°C/m. Moreover, ionic compounds like potassium nitrate split into individual ions when they dissolve, effectively producing more particles and a greater elevation in boiling point than molecular compounds that stay as complete molecules when dissolved.