The titration reaction between potassium permanganate, the acid in the reaction, and sodium oxalate, the base, is conducted slowly so that the equivalence point of the neutralization reaction can be accurately determined. When the sodium oxalate is added to potassium permanganate, excess acid remains in the bottom flask until the equivalence point is reached. At the equivalence point, the acid-base indicator changes color and the acid is effectively neutralized.
As the reaction proceeds, the titrant, sodium oxalate, is slowly added to the potassium permanganate drop-by-drop through a burette. An acid-base indicator changes color to reflect when an acidic solution becomes basic or vice versa. A popularly used indicator is phenolphthalein, which is bright purple when basic and colorless when acidic.
When phenolphthalein is added to the acid during the titration, the point where the solution turns from colorless to purple indicates the end point of the reaction. If the titration is conducted slowly, then it’s more likely that the end point of the titration reaction matches its equivalence point. This method is popularly used to determine the concentration of an acid by reacting it with another compound of known concentration. This reaction is also called an neutralization reaction.