Final answer:
Oxalic acid (H2C2O4) is the common standard used to titrate an unknown concentration of potassium permanganate (KMnO4), due to its known reaction stoichiometry and clear end-point in the titration process. option c.
Step-by-step explanation:
The common standard to titrate an unknown concentration of potassium permanganate (KMnO4) is oxalic acid (H2C2O4). This is because oxalic acid reacts in a 1:2 stoichiometry with KMnO4 under acidic conditions, providing a clear end-point when all of the oxalic acid is oxidized and the purple color of KMnO4 persists.
Titration involving KMnO4 and oxalic acid is commonly conducted in an acidic medium, often adding sulfuric acid to the solution to ensure that the medium is adequately acidic for the reaction to proceed.
The reaction between KMnO4 and oxalic acid is as follows:
5 H2C2O4 (aq) + 2 KMnO4 (aq) + 6 H2SO4 (aq) → K2SO4 (aq) + 2 MnSO4 (aq) + 10 CO2 (g) + 14 H2O (l)\
So option c.