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Standardization of Potassium Permanganate

General Aim of standardization of potassium permanganate

To determine the strength of potassium permanganate with a standard oxalic acid solution.

 

Method of standardization of potassium permanganate

Potassium permanganate titration - Determination of Potassium permanganate by redox titration.

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