The boiling point of a compound is the temperature at which the transition from the liquid into the gas phase occurs. This occurs when the vapor pressure of the solution is equal to the atmospheric pressure.
Vapor pressure is the force of the gaseous phase on the liquid phase of a compound in a closed system at equilibrium.
The type and strength of the intermolecular forces determine the amount of energy required to break those attractive forces. As such, compounds that can hydrogen bond have higher boiling points than compounds that only interact through London dispersion forces.
Volatility is the tendency of a compound to vaporize spontaneously. The more volatile a substance, the lower its boiling point.
An inverted capillary is inserted into a test tube of the liquid of interest. When heated, the air in the capillary expands, and the vapor pressure of the liquid increases. As the air expands, it exits the capillary as a stream of bubbles. When the heat is removed, the vapor pressure decreases. When the vapor pressure equals the atmospheric pressure, liquid enters the capillary. The temperature at which this occurs is the boiling point.
Source: Lara Al Hariri at the University of Massachusetts Amherst, MA, USA
Here, we show the laboratory preparation for 10 students working in pairs, with some excess. Please adjust quantities as needed.
| 1 Lab stand |
| 1 Hotplate |
| 1 Lab jack |
| 1 Rubber band |
| 1 Medium 3-prong clamp |
| 3-4 Glass capillary tubes |
| 1 Pipette bulb |
| 2 1-mL volumetric pipettes |
| 2 Glass test tubes |
| 1 250-mL beaker |
| 1 25-mL beaker |
| 1 Digital thermometer |
