Question

In the titration of KMnO₄ and oxalic acid in acidic medium, the change in oxidation number of carbon at the end point is _____.

Answer 1

Correct Answer: 1

In the titration of potassium permanganate (KMnO₄) and oxalic acid (H₂C₂O₄) in acidic medium, we examine the change in oxidation number of carbon in oxalic acid. Initially, carbon in oxalic acid is in the +3 oxidation state because each carbon is bonded to one hydrogen (+1, oxidation number of hydrogen) and two oxygens (-2 each, oxidation number of oxygen) in a manner that maintains the molecule's overall neutrality (2 × (+3) + 2 × (-2) + 2 × (+1) = 0).

During the reaction, oxalic acid gets oxidized to carbon dioxide (CO₂). In CO₂, the carbon is in the +4 oxidation state (C=+4 with each O=-2 to maintain neutrality: +4 + 2×(-2) = 0). Thus, the change in oxidation number for carbon is from +3 to +4, which is an increment of 1 unit per carbon atom.

Since both carbon atoms undergo this change simultaneously, the increment remains consistent. Therefore, the total change in oxidation number per molecule of oxalic acid is also 1 unit for carbon considered collectively. This value is within the specified range of 1 to 1.