after looking into it some more, pKa is measure of acid's strength; lower number, stronger acid.
don't know much about degree of protonation but
we want nicotene to be in organic phase so we should deprotonate it; the H ions give it a + charge & deprotonating it will remove the H ions
we want pKa at least 6.5 b/c the solvent is probably really acidic like pH 1 or 2 & the greater distance b/t pKa & pH means we've isolated more nicotene
but why 6.5 specifically?
also chloroform is trichloromethane, not dichloromethane, not sure if that changes much though