Know the Process of Titration of Oxalic Acid with KMnO4

Titration of Oxalic acid with potassium permanganate is an example of a redox reaction. Redox reactions are also known as reduction and oxidation reactions, Redox reaction is the transfer of electrons from one species to another simultaneously in an aqueous solution. 

During oxidation reaction, electrons are transferred from the species; in the reduction reaction, species gain electrons, and Redox reactions may occur simultaneously. 

The titrations used to study redox reaction is called Redox Titrations, as similar to that of acid-base titration indicators are used, indicators are sensitive to change in oxidation potential. The ideal indicators have oxidation potential between the values for the titrated solution and the titrant; indicators produce sharp detectable colour change at the endpoint of the redox reaction. 

Let’s learn more about the Titration of Oxalic acid with KMnO4.

Aim

To determine the concentration/molarity of KMnO4 solution by titrating it against a 0.1M standard solution of Oxalic acid.

Theory

In this experiment, Potassium Permanganate acts as a powerful oxidising agent. In an alkaline medium, KMnO4 acts as an oxidising agent; for quantitative analysis, the mostly acidic medium is used. The following equation can represent the oxidising action of KMnO4 in the acidic medium:

MnO4– 8H  5e–→ Mn2  4H2O

Dilute Sulphuric acid is used in this titration. Nitric acid (HN O3) is not used as an oxidising agent because hydrochloric acid is usually reacted with KMnO4 according to the equation given below to produce chlorine. In an aqueous solution, chlorine is an oxidising agent.

2KMnO4 16 HCl→ 2KCl 2 MnCl2 5Cl2 8 H2O

Since oxalic acid acts as a reducing agent; it can be titrated against potassium permanganate in the acidic medium according to the following equation:

Reactions of Oxalic Acid

1. Chemical Equation

Reduction half reaction: 2KMnO4 + 3H2SO4 → K2 SO4 + 2MnSO4 + 3H2O 5 [O] 

Oxidation half reaction: H2C2O4 [O] —-60°C–→ 2CO2 +  H2O] × 5______________    

2KMnO4 + 3H2 SO4 + 5H2C2O4→ K2 SO4 + 2MnSO4 + 8H2O + 10 CO2

1. Ionic Equation 

Reduction half reaction: MnO4– + 5e– + 8H → Mn2 + 4H2O] × 2 

Oxidation half reaction:C2O4–→ 2CO2 + 2e– ] × 5____________________________

 2 MnO4‑ + 5C2O42– + 16H   → 2Mn2  + 10CO2 + 8H2O 

As per these equations, MnO4– is reduced to Mn2, and C2O4–is oxidised to CO2. The oxidation number of carbon in C2O42–increased from 3 to 4. In this titration, Potassium Permanganate acts as a self-indicator. 

• Potassium Permanganate’s colour is initially discharged due to its reduction by Oxalic acid. 
• After complete consumption of oxalate ions, the light pink colour appears. It indicates the endpoint of reaction: little excess unreacted Potassium Permanganate ions produces the colour.

Higher temperature is required for Oxalic acid versus Potassium Permanganate to complete titration reaction; since heating of Oxalic acid solution (50°–60°C) with dilute H2SO4 is required.

In this reaction, Manganous Sulphate is formed initially, which acts as a catalyst for the Potassium Permanganateby Oxalic acid; the rate of initial reaction is slow as the reaction forwards, the rate of the reaction increases.

Material Required

• Measuring flask 
• Burette and burette stand 
• Pipette and dropper
• Conical flask 
• Funnel 
• Weighing bottle
• Burner
• Wire gauze
• Chemical balance

Reagents  

• Oxalic acid
• Potassium permanganate solution and 1.0 M Sulphuric acid

Procedure 

1. Preparation of 0.1 M Oxalic acid standard solution. Take 1.26 g of Oxalic Acid in a volumetric flask and add less amount of distilled water. Shake the flask to dissolve the solute completely. Mark up to 100mL mark by adding water.
2. Titration of Oxalic acid solution versus potassium Permanganate solution 
3. Take a clean burette and rinse with Potassium Permanganate solution. In case of air bubbles present in the burette, open the nozzle to remove. Use a glass stop cock burette rather than a rubber stop cock since it attracts permanganate ions.
4. In a clean conical flask, take 10 mL of 0.1 M Oxalic acid solution and add approximately 5 mL of 1.0 M H2 SO4.  Sulphuric acid is added to stop the formation of any manganese dioxide precipitates at the time of titration. 
5. Heat the conical flask having Oxalic acid solution, heat up to temperature around 50°– 60°C, for better visibility of colour change at the endpoint using white glazed tile in the background.
6. Slowly continue adding Permanganate solution to the heated conical flask while swirling it gently. 
7. Note down the initial and final readings in the burette. Repeat the titration till three concordant readings are obtained; consider the upper meniscus of burette readings because of the dark colour of KMnO4.
8. Write down the readings as shown in the recording table and calculate the KMnO4solutionin moles/litre strength.

Recording Table for Titration of KMnO4solutionagainst standard Oxalic acid solution

Calculations 

• The following equation can calculate the strength of the unknown solution molarity.

a1M1 V1 = a 2 M2 V2 (Equation 1) 

For oxalic acid vs potassium permanganate titration: 

a1 =2, (total number of electrons lost per formula unit of Oxalic acid in a balanced equation of half cell reaction) 

a2 = 5, (total number of electrons added per formula unit of Potassium Permanganate in the equation of half cell reaction) 

M1 and M2 are the Oxalic acid and Potassium Permanganate solutions molarities, respectively. 

V1 and V2 are the Oxalic acid and Potassium permanganate solutions volumes, respectively.

On putting the value of a1 and a2 in equation (Equation 1), we get-

Oxalic acid KMnO4 

2M1V1= 5M2V2

        2M1V1

M2=———  ——(Equation 2)

         5 V2

The molarity of the Potassium Permanganate solution can be calculated by using Equation 2. 

The following equation gives the strength of the solution: 

Strength = Molarity × Molar mass 

Result

1. KMnO4 solution Molarity is found to be  _______.
2. KMnO4 solution Strength is found to be  _______.

Precautions:

1. Always use proper personal protective equipment while doing experiments
2. Always use the clean, undamaged and dead glassware 
3. Burette and the pipette shall be rinsed thoroughly with the solutions to be taken in them.
4. Remove the funnel from the burette after the addition of KMNO4.
5. Carefully add solvent from a burette, ensure that no drop of the liquid is hanging at the tip of the burette when the endpoint arrives.
6. Always make sure the tip of the pipette is dipped in the liquid while drawing the liquid.
7. Very carefully add the last drop of the solution from the pipette, don’t blow out.
8. Remember to heat the mixture of Oxalic acid and H2SO4solutions between 50°–60° C before titrating it against Potassium Permanganate.
9. The strength of the solution must be calculated up to the fourth decimal place.

Conclusion:

This redox titrimetric analysis analyses the strength /molarity of KMnO4 solution by titrating it with a 0.1M Oxalic acid standard solution. Therefore, a careful reading of this article can help you understand the concept of the Titration of Oxalic acid with KMnO4.

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