Determination of concentration of KMnO₄ solution

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 A. To determine of the strength of the given KMnO4 solution using standard oxalic acid solution

Materials Required

Real Lab Procedure

Preparation of standard solution of oxalic acid [250 ml M/10 (0.1 M) solution]

•  Using an electronic balance, first weigh exactly 3.15g of oxalic acid crystals in a weighing bottle.
• Transfer these into a 250ml beaker.
• Then wash the weighing bottle 2 or 3 times with distilled water and transfer all the washings into the beaker.
• Dissolve the oxalic acid crystals in the beaker by gentle stirring with a clean glass rod.
• When the oxalic acid crystals in the beaker are completely dissolved, transfer the entire solution from the beaker into a 250ml standard flask through a funnel and a glass rod.
•  Wash the beaker 2 to 3 times with distilled water and transfer all the washings into the standard flask.
• Finally wash the funnel thoroughly with distilled water to transfer the drops of the solution on the sides of the funnel into the standard flask.
•  Add enough distilled water to the standard flask so that the level is just below the calibration mark on it.
• Add the last few drops of distilled water with a pipette until the lower level of the meniscus just touches the mark on the standard flask.
•  Stopper the measuring flask and shake gently to make the solution uniform throughout.

Determination of strength of given KMnO4

• Take a burette and wash it with distilled water.
• Rinse and fill the burette with the given KMnO4 solution and set the initial burette reading as zero.
• Clamp it vertically to the burette stand.
• Rinse the pipette with water and then with the given oxalic acid solution.
• Then pipette out 20ml of the given oxalic acid solution into a conical flask and add one test tube (~20ml) full of dil.H2SO4 into it.
• Heat the contents of the conical flask to 60-70°C.
• Titrate it against the KMnO4 solution taken in the burette till the colour of the solution in the conical flask changes from colourless to light pink.
• Note down the final burette reading.
• Repeat the titration until concordant values are obtained.

Observation

The readings are recorded in a tabular form as shown and the molarity of the given KMnO4 solution can be calculated using the molarity equation given in the theory.

SI. No	Initial burette reading	Final burette reading	Volume of KMnO4 (in ml)

The Result

The strength of the given KMnO4 solution = ............g/litre

B. To determine the strength of the given KMnO4 solution using standard solution of Mohr’s salt

Materials Required

Real Lab Procedure

Preparation of standard solution of Mohr’s salt (Ferrous Ammonium Sulphate).[250 ml M/20 (0.05 M) solution]

•  Using an electronic balance weigh exactly 4.9g of Mohr’s salt crystals in a weighing bottle.
• Transfer these into a 250ml beaker.
• Add 5ml conc.H2SO4 into the beaker.
• Wash the weighing bottle well with distilled water and transfer all the washings into the beaker.
• Dissolve Mohr’s salt crystals in the beaker by gentle stirring with a clean glass rod.
• When the crystals in the beaker are completely dissolved, transfer the entire solution from the beaker into a 250ml standard flask through a funnel and a glass rod.
• Wash the beaker thoroughly with distilled water and transfer all the washings into the standard flask.
• Finally, wash the glass rod and the funnel thoroughly with distilled water to transfer the solution on the sides of the funnel into the standard flask.
• Add enough distilled water to the standard flask so that the level is just below the calibration mark on it.
• Add the last few drops of distilled water with a pipette until the lower level of the meniscus just touches the mark on the standard flask.
• Stopper the measuring flask and shake gently to make the solution uniform throughout.

Determination of strength of KMnO4

• Take a burette and wash it with distilled water.
•  Rinse and fill the burette with the given KMnO4 solution and set the initial burette reading as zero.
• Clamp it vertically to the burette stand.
• Rinse the pipette with water and then with the given Mohr’s salt solution.
• Pipette out 20ml of the given Mohr’s salt solution into a conical flask and add one test tube (~20ml) full of dil.H2SO4 into it.
• Titrate it against the KMnO4 solution taken in the burette till the colour of the solution in the conical flask changes from colourless to light pink.
• Note down the final burette reading.
• Repeat the titration until concordant values are obtained.

Observation

The readings are recorded in a tabular form as shown and the molarity of the given KMnO4 solution can be calculated using the molarity equation given in the theory.

SI. No	Initial burette reading	Final burette reading	Volume of KMnO4 (in ml)

The Result

The strength of the given KMnO4 solution = .............g/litre