Amount of oxalic acid present in a solution can be determined by its titration with KMnO4  solution in the presence of H2SO4 . The titration gives unsatisfactory result when carried out in the presence of HCl, because HCl

KMnO4 is a very good oxidation agent in acidic medium.Reducing agent like Fe+2 ,Sn+2 ,C2O4-2,SO3-2 can all be estimated using KMnO4 in acidic medium.But while selecting the acidic medium always select an oxidizing acid like H2SO4 but not  HCl, HBr, HI. This is because KMnO4 oxidizes the acid HX  to X2 and itself gets reduced to Mn+2