Redox titration of ferricyanide to ferrocyanide with ascorbic acid: Illustrating the Nernst equation and beer-Lambert law

Redox titration of ferricyanide ion is incorporated to ferrocyanide ion to show how the reduction potential of a redox couple is affected by the concentrations of the redox species. Also, the experiment can show how students can use the Nernst equation to calculate the standard reduction potential of a half-reaction. The students started by immersing platinum working electrode and the Ag/AgCl reference electrode in potassium hexacyanoferrate solution. The solution is stirred constantly via magnetic stirring. Once the electrodes are set up properly and a stable voltage reading is obtained, a portion of the bright yellow solution is removed to measure the absorbance of the ferricyanide. The measured absorbance is used to calculate the initial concentration of ferricyanide. Meanwhile, to start the titration, ascorbic acid is added to the beaker with the electrodes using the micropipets. After adding the ascorbic acid, the solution is allowed to equilibrate for two minutes. The readings should decrease over the course of the titration. Another aliquot of titrant is added and the entire process is repeated until the solution appears to the colorless.