Titration of oxalic acid with potassium permanganate is a classic example of redox titration, where a reduction and oxidation reaction takes place between two chemical substances. In this experiment, potassium permanganate (KMnO4) acts as a strong oxidizing agent, while oxalic acid (H2C2O4) serves as the reducing agent. The main goal of this titration is to determine the concentration or strength of the potassium permanganate solution using a known concentration or strength of oxalic acid. This reaction is commonly performed in chemistry labs to understand redox behaviour and practice accurate measurement skills.

Principles of Titration

In this titration, a redox reaction takes place where electrons are transferred between oxalic acid and potassium permanganate.Potassium permanganate (KMO4) gets reduced from Mn7+ to Mn2+, while oxalic acid gets oxidised to carbon dioxide (Co2). This reaction only happens in an acidic medium, and that’s where sulfuric acid (H2SO4) comes in- it provides the necessary acidic environment for the reaction to proceed smoothly. The overall equation for the reaction is:

Chemistry Notes Free PDFs

2 \mathrm{KMnO}_4+5 \mathrm{H}_2 \mathrm{C}_2 \mathrm{O}_4+3 \mathrm{H}_2 \mathrm{SO}_4 \rightarrow 2 \mathrm{MnSO}_4+10 \mathrm{CO}_2+\mathrm{K}_2 \mathrm{SO}_4+8 \mathrm{H}_2 \mathrm{O}

This reaction is temperature-sensitive and needs to be carried out in warm conditions to ensure the oxalic acid reacts properly with KMnO4.

For the titration of oxalic acid with potassium permanganate, you will need the following chemical and apparatus:

Chemicals:

• Oxalic acid (H2C2O4) (solid form or in a known concentration solution)
• Potassium permanganate (KMnO4) (a strong purple solution, used as the titrant)
• Sulfuric acid (H2SO4) (concentrated, to provide an acidic medium)
• Distilled Water (for rinsing and dilution purpose)

Apparatus:

• Burette (to hold the KMnO4 solution for accurate dispensing)
• Conical flask (for the oxalic acid solution and the reaction to take place)
• Pipette (to measure the exact volume of oxalic acid solution)
• White tile or paper (to clearly observe the color change during titration)
• Beaker (to prepare and dilute solutions)
• Glass rod (to stir the solution if needed)
• Thermometer ( to monitor and maintain the temperature)
• Funnel ( to safely fill the burette with KMnO4 solution)

Apparatus Setup:

• In the burette – KMnO4 solution
• In the conical flask – 10ml of oxalic acid + sulphuric acid
• Indicator – Self indicator (KMnO4)
• End Point – Appearance of permanent pale pink colour.

Procedure:

(a) Preparation of 0.1M standard solution of oxalic acid:

To begin the experiment, we will first calculate the amount required for 0.1 M of oxalic acid. The molecular mass of oxalic acid is 126 g. To prepare a M/10 oxalic acid solution, we need to dissolve 12.6 g of oxalic acid per litre of solution. Alternatively, we can dissolve 3.15 g of oxalic acid crystals in water and make the solution exactly 250 ml.

For the preparation of 1 litre of M/10 oxalic acid solution, the amount of oxalic acid required is 3.15g.

• Weigh an empty watch glass using a chemical balance.
• Weigh 3.15g of oxalic acid accurately in the watch glass.
• With the help of a funnel, transfer the oxalic acid into the measuring flask.
• Now wash the funnel with distilled water without removing the funnel from the flask.
• Make the solution up to the marked point with distilled water and make sure the oxalic acid is fully dissolved.
• This solution is a 0.1M standard solution of oxalic acid.

(b) Titration of potassium permanganate solution against standard oxalic acid solution:

• Rinse the burette with the potassium permanganate solution and fill the burette with potassium permanganate solution.
• Fix the burette in the burette stand and place the white tile below the burette to accurately find the end point.
• Pipette out 10ml of 0.1N standard oxalic acid solution into a conical flask.
• Add a test tube full of sulphuric acid in order to prevent oxidation of manganese to form manganese dioxide.
• Heat the mixture up to 60oC before titrating with potassium permanganate.
• Note down the initial reading in the burette before starting the titration.
• The hot solution is titrated against potassium permanganate solution while gently swirling the solution in the flask.
• Initially, the purple colour of KMnO4 is discharged with oxalic acid. The appearance of a permanent pink colour signals the end point.
• Repeat the titration until concordant values are obtained.
• Note down the upper meniscus on the burette readings. Record the reading in the observation table given below to calculate the molarity of KMnO4.

Observation:

To find the strength (molarity) of the potassium permanganate (KMnO4) solution, we use the following formula based on the reaction between oxalic acid and KMnO4:

a1M1V1 = a2M2V2

To find the strength (molarity) of the potassium permanganate (KMnO4) solution, we use the following formula based on the reaction between oxalic acid and KMnO4:

Where 

• a1 and a2 are the coefficient of oxalic acid and KMnO4 in the balanced chemical equation.

• M1 and M2 are the molarities (concentrations) of the oxalic acid and KMnO4 solutions used.
• V1 and V2 are the volumes of the oxalic acid and KMnO4 solutions used in the titration.

From the balanced equation, we know that the ratio of oxalic acid to KMnO₄ is 5:2, so we rearrange the formula to calculate the molarity of KMnO₄ (M₂):

 M_2=\left(2 \times M_1 \times V_1\right) /\left(5 \times V_2\right)

From the balanced equation, we know that the ratio of oxalic acid to KMnO4 is 5:2, so we rearrange the formula to calculate the molarity of KMnO4 (M2):

Once we find the molarity of KMnO4, we can calculate its strength (in terms of molarity) by multiplying the molarity by the molar mass of KMnO4:

\text { Strength }=\text { Molarity } \times \text { Molar Mass }

This gives us the concentration of KMnO4 Solution, which is the goal of the titration.

Results and Discussion:

• The molarity of KMnO4 is 0.0253 M
• The Strength of KMnO4 is 4.00 g/L

Precautions:

• Before starting the experiment, clean all the apparatus with distilled water and then rinse with the solution to be taken in them.
• Rinse the pipette and burette before use.
• Potassium permanganate is dark in colour, so always read the upper meniscus.
• Use dilute sulfuric acid for acidifying the potassium permanganate.
• Take accurate readings once it reaches the end point and don’t go with average readings.
• Use an anti-parallex card or auto-parallex card while taking the burette readings.
• Do not use a rubber cork burette as it can be attacked by KMnO4.
• The strength of the unknown solution should be taken up to two decimal places only.

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