The melting point of a compound is measured as a range of temperatures from where the solid phase transitions into the liquid phase. The upper limit of the range is the temperature where the first liquid drops are observed, and the lower limit of the range is the temperature where the solid phase has fully turned into liquid.
The melting point is a physical property that is unique to a compound. In organic chemistry, the melting point can help identify the compound in the sample being tested.
The three major types of intermolecular forces are hydrogen bonding, which occurs in compounds containing oxygen and hydrogen, dipole-dipole interactions, and London dispersion forces, which occur in all molecules.
The strength of the intermolecular forces affect the amount of energy required to break apart the ordered structure found in the solid phase. Hydrogen bonds are the strongest type of intermolecular forces, followed by dipole-dipole interactions, and lastly, London dispersion forces. Compounds with hydrogen bonds have higher melting points than nonpolar compounds with only London dispersion forces.
Impurities cause the melting point of a mixture to be lower than the melting point of the pure compound. This occurs due to the disordered nature of the structure in the solid phase of the mixture, which requires less energy to transition into the liquid phase.
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 Stir bar |
| 1 Stirring hotplate |
| 1 Lab stand |
| 1 Thermometer clamp |
| 1 Digital thermometer (pre-calibrated, 60 – 150°C) |
| 4 Melting point capillary tubes |
| 3 Metal spatulas |
| 3 Watch glasses |
| 1 Rubber band |
