When determining the identity of a pure liquid, why is the boiling point critical?

The boiling point of a pure liquid is critical in determining its identity because it remains consistently the same under defined conditions, specifically at a given atmospheric pressure. This characteristic allows for reliable identification, as pure substances will boil at a specific temperature that is well-documented and can be measured accurately.

In contrast, if a liquid is impure or if it contains a mixture, its boiling point can vary. For example, impurities can elevate or depress the boiling point depending on their nature and concentration. The uniformity of the boiling point for pure substances makes it a vital measurement in laboratory settings, particularly for distinguishing one compound from another.

The boiling point is particularly useful for quality control and in various applications because precise boiling points serve as key identifiers in chemical databases, enabling chemists to ascertain the purity or potential identity of unknown liquids through comparison with established data.