Approximate Redox Titration Between KMnO4 and KI in an Acidic Medium

Redox titration is a common analytical method used to determine the concentrations of redox couples in solution. One such titration involves the reaction between potassium permanganate (KMnO4) and potassium iodide (KI) in an acidic medium. This article will explore the detailed process of this titration, including the relevant chemical reactions, stoichiometry, and identification methods.

Chemical Reactions Involved in Redox Titration

The redox titration between potassium permanganate and potassium iodide in an acidic medium involves the oxidation of iodide ions (I-) to iodine (I2) by permanganate ions (MnO4-). The reaction can be broken down into two half-responses:

Oxidation Half-Response

2 I- rarr; I2 2 e-

Reduction Half-Response

MnO4- 8 H 5 e- rarr; Mn2 4 H2O

Overall Reaction

2 MnO4- 10 I- 16 H rarr; 2 Mn2 5 I2 8 H2O

The overall reaction shows that 2 moles of MnO4- reacts with 10 moles of I- to produce 5 moles of I2. For this reaction to occur, the medium must be acidic, typically with the addition of sulfuric acid (H2SO4), to ensure the proper reduction of MnO4- to Mn2 .

Stoichiometry of the Reaction

The stoichiometry of the reaction is as follows:

Reactants Products 2 MnO4- 10 I- 16 H 2 Mn2 5 I2 8 H2O

The balanced equation demonstrates the precise amounts of reactants and products involved in the titration.

Central Issues in the Titration

Marker

The permanganate ion (MnO4-) acts as its own indicator since it is purple in solution and decolorizes as its concentration decreases, signaling the reduction to Mn2 .

End Point

The titration is considered to be at its end point when the solution turns colorless, indicating that all the iodide ions have been oxidized to iodine and the permanganate ions are fully reduced.

Viable Perceptions

The iodine formed in the reaction can be identified as a brown color or as a blue-black complex if starch is added as an external indicator.

In practical terms, three moles of the oxidation half-reaction are added to one mole of the reduction half-reaction to remove the electrons, resulting in:

MnO4- 4 H 3 I- rarr; 1/2 I2 3 e-

MnO4- 4 H 3 I- rarr; 1/2 I2 3 e-

MnO4- 4 H 3 I- rarr; 3/2 I2 MnO2 2 H2O

KMnO4 4 HI rarr; 1/2 I2 MnO2 KI 2 H2O

This method ensures that the appropriate amount of iodine and permanganate ions are present for accurate titration readings.