When performing a standard volumetric titration of an acidified solution against a hot oxalic acid ( — d and f Block Elements Chemistry Question
Question
When performing a standard volumetric titration of an acidified $KMnO_4$ solution against a hot oxalic acid ($H_2C_2O_4$) solution, it is observed that the initial decolourisation of the purple permanganate is noticeably slow, but the rate of decolourisation dramatically increases after some time. What is the primary chemical reason for this kinetic behaviour?
💡 Solution & Explanation
The oxidation of oxalic acid by permanganate in an acidic medium produces $Mn^{2+}$ ions as a primary reduction product. These newly formed $Mn^{2+}$ ions effectively act as an auto-catalyst for the reaction. Therefore, the reaction starts slowly but its rate increases significantly as soon as a sufficient concentration of the $Mn^{2+}$ catalyst accumulates in the reacting mixture.