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Determining the boiling point of a liquid is one of the most fundamental experimental techniques in physical chemistry and organic chemistry laboratories. The boiling point is defined as the temperature at which the vapor pressure of a liquid equals the external atmospheric pressure, and the liquid begins to change into vapor.
The primary reason chemists determine boiling points is to check the purity and identity of a liquid:
Purity Check:
A pure liquid has a sharp, constant boiling point at a given pressure. For example, pure ethanol boils at 78°C.
If a liquid contains impurities, its boiling point will either increase or decrease and may not remain constant throughout heating. This is similar to how the presence of salt raises the boiling point of water.
A broad boiling point range usually indicates contamination or mixture of substances.
Identification of Nature:
Since different liquids have characteristic boiling points, the value can help identify an unknown liquid.
For instance, acetone boils at 56°C, benzene at 80°C, and chloroform at 61°C. If an unknown sample boils at 56°C, it can be compared with reference data to suggest that it may be acetone.
Practical Importance:
In distillation processes, boiling points are used to separate mixtures of liquids.
In quality control, industries often verify the boiling point to ensure the authenticity of solvents, fuels, and chemicals.
In pharmaceuticals, boiling point data help in solvent recovery and purification.
Thus, determining boiling point provides valuable information about the purity, identity, and chemical nature of a liquid. It is not used to measure acidity or basicity, nor is it simply a way to check temperature.
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