In flushing and cleaning columns used in liquid chromatography to remove adsorbed contaminants, a series of solvents is used. Hexane \(\left(\mathrm{C}_{6} \mathrm{H}_{14}\right),\) chloroform \(\left(\mathrm{CHCl}_{3}\right),\) methanol $\left(\mathrm{CH}_{3} \mathrm{OH}\right),$ and water are passed through the column in that order. Rationalize the order in terms of intermolecular forces and the mutual solubility (miscibility) of the solvents.

To contextualize the order in which the solvents are used, we must understand the types of intermolecular forces present in each solvent: 1. Hexane \(\left(\mathrm{C}_{6} \mathrm{H}_{14}\right)\): London dispersion forces 2. Chloroform \(\left(\mathrm{CHCl}_{3}\right)\): London dispersion forces and dipole-dipole interactions 3. Methanol \(\left(\mathrm{CH}_{3} \mathrm{OH}\right)\): London dispersion forces, dipole-dipole interactions, and hydrogen bonding 4. Water: London dispersion forces, dipole-dipole interactions, and hydrogen bonding We can see that the strength of intermolecular forces increases as we go down the list.

Another important factor is the mutual solubility (miscibility) of the solvents. Certain solvents are miscible with one another, which allows for efficient removal of contaminants from the column. The rule of thumb is "like dissolves like," meaning that substances with similar types of intermolecular forces will be more likely to dissolve each other. The miscibility of our solvents are as follows: 1. Hexane and chloroform: Miscible (both have London dispersion forces and dipole-dipole interactions) 2. Chloroform and methanol: Miscible (both have dipole-dipole interactions) 3. Methanol and water: Miscible (both have hydrogen bonding)

Now that we understand intermolecular forces and miscibility, let's explain the order in which the solvents are used to clean the column: - Hexane is used first because it has the weakest intermolecular forces (London dispersion forces) among the solvents. This means it will be effective at removing contaminants that might not be attracted to the other solvents or even be insoluble in the other solvents. - Chloroform is used next as it has stronger intermolecular forces (London dispersion forces and dipole-dipole interactions) compared to hexane which will help to remove contaminants that may not have been removed effectively by hexane. The transition from hexane to chloroform is also facilitated by their miscibility. - Methanol, with even stronger intermolecular forces (including hydrogen bonding), will remove more polar contaminants that might not have been removed by hexane or chloroform. Since it is miscible with chloroform, the transition will be smooth during column cleaning. - Water is used as the final solvent due to its polar nature and the highest intermolecular forces among the solvents (hydrogen bonding). This final cleaning stage will remove any polar contaminant remaining on the column. The miscibility of methanol with water ensures that the transition between solvents is smooth as well.