Why n sulphuric acid is added in the assay of hyrgogen peroxide?
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The used analytical reaction of purple permanganate to colourless Mn2+MnX2+occurs under acidic conditions:
MnO4−+8H++5e−↽−−⇀Mn2++4H2OMnOX4X−+8HX++5eX−↽−−⇀MnX2++4HX2O
Under neutral conditions, permanganate would be reduced to dark brown manganese(IV) oxide:
MnO4−+4H++3e−↽−−⇀MnO2+2H2OMnOX4X−+4HX++3eX−↽−−⇀MnOX2+2HX2O
Therefore, sulfuric acid is added to make the solution acidic. Actually, excess acid is required since H+HX+ is consumed during the reaction (8 mol H+HX+ per 1 mol MnO4−MnOX4X−).
Sulfuric acid is used because it is stable towards oxidation; whereas, for example, hydrochloric acid would be oxidized to chlorine by permanganate.
MnO4−+8H++5e−↽−−⇀Mn2++4H2OMnOX4X−+8HX++5eX−↽−−⇀MnX2++4HX2O
Under neutral conditions, permanganate would be reduced to dark brown manganese(IV) oxide:
MnO4−+4H++3e−↽−−⇀MnO2+2H2OMnOX4X−+4HX++3eX−↽−−⇀MnOX2+2HX2O
Therefore, sulfuric acid is added to make the solution acidic. Actually, excess acid is required since H+HX+ is consumed during the reaction (8 mol H+HX+ per 1 mol MnO4−MnOX4X−).
Sulfuric acid is used because it is stable towards oxidation; whereas, for example, hydrochloric acid would be oxidized to chlorine by permanganate.
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