Why is HCl not used to make the medium acidic in oxidation reactions of KMnO4 in acidic medium?
KMnO4 oxidises HCl to Cl2 which is also an oxidizing agent. So,some amount of KMnO4 gets used up in oxidizing Cl- to Cl2, thereby rendering the whole titration useless.
KMnO4 + HCl → KCl + MnCl2 + Cl2 + H2O