H2O2 solution of 0.2 N is prepared and after 5 hours it is titrated with KMnO4 solution. If the volume of the H2O2 solution taken is half of the volume of KMnO4 used (in acidic medium), find the molarity of KMnO4 solution?
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Correct option is B)
5 hours corresponds to half life period for hydrogen peroxide in which its strength will reduce to half. In 5 hours, the normality of hydrogen peroxide solution will decrease from 0.2 N to 0.1 N. 0.1 N hydrogen peroxide corresponds to 0.05 M hydrogen peroxide as its normality is twice its molarity. 2MnO4−+6H++5H2O2→2Mn2++8H2O+5O2. Thus 2 moles of potassium permanganate reacts with 5 moles of hydrogen peroxide. Hence, the number of moles of potassium permanganate that will react with 1 L of 0.05 M hydrogen peroxide solution are 0.05×52=0.02 moles. Since double volume of potassium permanganate is take, the molarity of potassium permanganate solution is 20.02mol/L=0.01 M.