1.0 g of a sample containing KMnO4 and some inert impurity was dissolved in dilute solution of KOH and volume was made up to 100 mL. To this solution, some ammonia gas was passed where the following redox reaction occured:
Volume of N2 measured at N.T.P. was 28 mL. The solution was filtered off to remove MnO2(s) and a 10 mL portion of the filtrate required 22.5 mL of a 0.01 M oxalate solution to reach the end point. The mass percentage of KMnO4 in the original sample is .