Final answer:
Titration with KMnO4 solution determines oxalic acid concentration inaccurately in the presence of HCl because HCl itself is oxidized, altering the KMnO4 and not reflecting the true amount of oxalic acid.
Step-by-step explanation:
The amount of oxalic acid present in a solution can be determined by titration with KMnO4 solution in the presence of H2SO4. The titration gives unsatisfactory results when carried out in the presence of HCl because HCl reduces the oxidation state of Mn in KMnO4.
In a redox reaction involving KMnO4 and oxalic acid, KMnO4 acts as an oxidizing agent, getting reduced in the process. If HCl is present during the titration, it would interfere by itself being oxidized by KMnO4, thus reducing the KMnO4 before it can react with the oxalic acid. This leads to misleading titration results because the amount of KMnO4 needed to reach the endpoint does not accurately reflect the concentration of oxalic acid. Therefore, a non-reducing acid such as sulfuric acid is used instead to provide the acidic environment without participating in the redox reaction.