You were instructed to rinse the filter pipettes with methanol and with hexane. obviously the reason for this is to remove any contaminants that may be present on the glass or cotton. using what you learned about the physical properties of organic compounds in 40a, why were the solvents methanol and hexane chosen?

See explanation below.

Explanation:

The compounds can be polar or nonpolar. The dipolar moment for a nonpolar molecule must be 0. Because of this difference, the compounds have different properties, and the solubility is one of the most affected, polar molecules dissolve polar molecules, and nonpolar molecules dissolve nonpolar molecules.

Hexane is a hydrocarbon, and all the hydrocarbons are nonpolar, so it is a good solvent for nonpolar compounds. Methanol is alcohol, which has the hydroxyl group (OH) so it's a polar molecule and a good solvent for polar compounds.

That's why the both are chosen: hexane removes the nonpolar contaminants, and methanol the polar contaminants.