Standardization of Potassium Permanganate

Theoretical Background / Context

• Quantitative analysis deals with the determination of the quantity of the substance to be analyzed. 

Methods of quantitative analysis may be classified into:

1. Gravimetric analysis: It depends on isolating and weighing the final product with known pure, stable, and definite form.
2. Instrumental analysis: It depends on measuring some physical properties which change quantitatively with changing the concentration of the sample.
3. Volumetric analysis (Titration): It depends on measuring the volume of standard solution (titrant) used for complete reaction with the sample, such as in KMnO4 titration procedures.

• Titration is the capacity of the sample to combine with the suitable standard quantitatively through quantitative reaction. 

A quantitative reaction:

Is the reaction that proceeds forward to produce stable product(s) such as weakly ionizable compounds, e.g. H2O, weak acids & base, sparingly soluble salts (precipitate), complex ion, etc. 

The types of quantitative Reactions can be:

1. Neutralization Reactions.

a.    H2O formation.     

b.    Displacement: Formation of a weak acid or a weak base.

2. Complexometric reactions.
3. Redox reactions (Electron transfer) 
4. Preciptimetric reactions.

Any sample is a solution of unknown concentration and a Standard is a solution of exactly known concentration. 

The requirements of titrimetric reactions are:

• The reaction must be simple and expressed by a chemical equation.
• A single reaction must occur between the sample and titrant.
• The reaction must be instantaneous (rapid).
• Suitable standard solutions must be available.
• The endpoint should be easily detected

Oxidation is the loss of electrons and increases in valency number, the gain of oxygen, or the loss of hydrogen.

      Fe2+ →Fe3+ + e-1

Reduction is the gain of electrons and reduction in valency number, loss of oxygen, or gain of hydrogen.

     Fe3+ + e-1→Fe2+ , Fe2+ + 2e-1 → Fe0

Oxidizing agent or oxidant is the substance that gains electrons.

     Ex: KMnO4, K2Cr2O7, Ce(SO4)2

Reducing agent or reductant is the substance that donates (lose) electrons.

    FeSO4, Na2S2O3, H2C2O4

Principle of Work

• The KMnO4 standardization experiment is a redox titration procedure for standardization of potassium permanganate where potassium permanganate (KMnO4) is the titrant and oxalic acid is the analyte. 
• Also, KMnO4 is the oxidizing agent and oxalic acid is the reducing agent. 
• The reaction between KMnO4 and oxalic acid is carried out in an acidic medium because the permanganate ion in the acidic medium is a very strong oxidizing agent.
• Acidity is introduced by adding dil. H2SO4. 
• No indicators are used to determine the endpoint because KMnO4 is a self-indicator. In standardization of potassium permanganate process KMnO4 self indicator is used.
• Permanganate (MnO4-) ion has a dark purple color. In an acidic medium, MnO4- is reduced to colorless manganous (Mn2+) ions. 
• On reaching the endpoint, the addition of the last single drop of permanganate imparts a light purple color to the solution.

2MnO4- + 5 C2O4- -  + 16H +  = 10CO2 + 2Mn + + + 8H2O