Question

Why are KMnO4 filtered before they are standardized?

Answer 1

When making a solution of KMnO4 to be standardized, there are impurities, chiefly MnO2, that are left in the final solution because MnO2 is not soluble in water. Since the presence of MnO2 increases the speed with which KMnO4 deteriorates, it is filtered to remove the MnO2 and any other solids that may have been in the original crystals of KMnO4. Generally one standardizes the KMnO4 solution to be used as the titrant immediately before using it in the titration. It must be re-standardized every day or so.