Why we add hcl in liquid liquid extraction?

Answer 1

HCl is an acid and is capable of protonating basic functional groups such as amines. When this happens, the functional group will often take on a formal charge which increases its polarity. It can then be moved into the aqueous phase which would separate it from the organic phase. Thus, the compound can be efficiently separated from other compounds (assuming the other compounds were not also sensitive to the acid).