If Unknown 31B were to be an amine, it would likely be soluble in HCl but not soluble in water or NaOH. The acidity from the HCl allowed the amine group to be protonated allowing Unknown 31B to be soluble. Water and NaOH are not acidic and therefore could not protonate the amine group and therefore not being soluble with an amine. It can also be that Unknown 31B contained five or more carbons making it less soluble in water due to longer chains; the longer the chain, the less the functional group has polar influence, decreasing its water
