Amines behave as bases due to the lone pair of electrons on the nitrogen atom. When they react with strong acids like HCl, they accept a proton (H⁺) to form ammonium salts. The primary amine (propylamine) forms a primary ammonium salt, while the tertiary amine (triethylamine) forms a tertiary ammonium salt. These are acid-base neutralization reactions where the amine is the base and HCl is the acid.