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Difficulty: EasyPure and Impure Substances and Criteria of Purity

The presence of a soluble non-volatile impurity in a liquid sample lowers its boiling point below that of the pure liquid.

Answer: Answer

Answer

The statement is False. Soluble non-volatile impurities elevate the boiling point of a pure liquid rather than lowering it.
A soluble non-volatile solute reduces the vapor pressure of a liquid solvent. As a result, extra thermal energy (a higher temperature) is required for the vapor pressure to equal atmospheric pressure, causing boiling point elevation.

Step-by-Step Solution

1
Identify the physical effect of a dissolved non-volatile impurity on liquid vapor pressure.
Dissolved non-volatile solute particles occupy surface area and reduce the vapor pressure of the solvent liquid at a given temperature.
Fewer solvent molecules can escape into the gas phase due to solute-solvent interactions and physical surface blockage.
2
Determine the impact of lower vapor pressure on the boiling point.
The liquid must be heated to a higher temperature for its vapor pressure to equal external atmospheric pressure.
Boiling occurs when vapor pressure equals atmospheric pressure, leading to boiling point elevation.

Key Concept

Effect of Impurities on Boiling Point
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Topics

Pure and Impure Substances and Criteria of Purity