The boiling point of a compound is the temperature where the liquid-gas phase change occurs. In more technical terms, it is when a liquid's vapor pressure equals its applied pressure (typically the atmospheric pressure). Boiling points are very sensitive to changes in applied pressure, so all boiling points should be reported along with the measured pressure. A compound's "normal boiling point" refers to its boiling point at a pressure of 760 mmHg. A compound's boiling point is a physical constant just like melting point, and so can be used to support the identification of a compound.
- 6.2A: Overview of Boiling Point
- A compound's boiling point is a physical constant just like melting point, and so can be used to support the identification of a compound. Unlike melting points however, boiling points are not generally used as a gauge of purity. Impure liquids do boil over a range of temperatures (similar to how melting points have breadth), but the temperature span does not correlate well to purity. Thus, measurement of a compound's boiling point is mainly used to support its identification.
- 6.2B: Step-by-Step Procedures for Boiling Point Determination
- There are a variety of methods by which a sample's boiling point can be determined, including distillation, reflux, and by using a Thiele tube. The most straightforward method uses a Thiele tube, and has the advantage of using less than