To determine the Molarity of KMnO4  solution by titrating it against a standard solution of Mohr’s salt. (M/20 Mohr’s salt solution).

Experiment – 3

Class – XII

Subject – Chemistry

Aim:-

To determine the Molarity of KMnO₄  solution by titrating it against a standard solution of Mohr’s salt. (M/20 Mohr’s salt solution).

Theory:-

The reaction between oxalic acid and KMnO₄ in acidic medium is a redox reaction as Mohr’s salt in acidic medium is a good reducing agent and KMnO₄ in acidic medium is a good oxidizing agent.

The reactions can be written as:

Molecular reactions:-

Apparatus Required:-

Burette, Burette Stand, Pipette, Titration flask, Test tube, Funnel, Beaker, Burette, Burner etc.

Chemical Required:-

Mohr’s salt crystals, distilled water, Sulphuric acid etc.

Calculation of the amount of Mohr’s salt required to prepare 250cc of M/20 solution.

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Procedure:-

        i.            4.9 g of mohr’s salt crystal was weighted on the analytical balance.

      ii.            250 ml of M/20 Mohr’s salt solution was prepared by dissolving 4.9 of Mohr’s salt in water and 20 ml of it was pipetted out in a clean titration flask.

    iii.            The burette was filled and rinsed with the given KMnO₄ solution.

   iv.            One test tube full of dil. H₂So₄ was added to the solution in titration flask.

     v.            The initial reading of burette was noted.

   vi.            KMnO₄ solution was added from the burette till a permanent light Pink color was imparted to the solution in the titration flask on addition of last single drop of KMnO₄ solution.

 vii.            The final reading of the burette was noted.

viii.            The above steps were repeated till two continuous. Concordant volume of KMnO₄ were recorded.

Observation:-

Weight of watch glass = …………….. gms

            Weight of watch glass + Mohr’s salt = ……………… gms

            Weight of Mohr’s salt = 0.63 gms

            Volume of solution prepared = 250 ml

            Molarity of solution = M/20

            Volume of solution taken for each titration = 20 ml

S.No.	Initial Reading of burette (R1)	Final reading of burette (R2)	Volume of KMnO4  Solution used (R1 +R2)
1.	0	9.7 ml	9.7 ml
2.	0	9.2 ml	9.2 ml
3.	0	9.2 ml	9.2 ml
Final Reading			9.2 ml

 

Calculation:-                      

A.  

       Determination of strength of KMnO₄  solution:

 

Strength = Molarity X molecular mass of KMnO₄

0.021 x 158 = 3.318 g/l

Result:-

The molarity and strength of given KMnO₄   solution is.

Precaution:-

1.     Transfer the oxalic acid crystals from the watch glass to the beaker carefully, so the not even a single crystal is lost.

2.     Read upper meniscus in the burette as KMnO₄  solution is highly coloured solution.

3.     Do not rinse titration flask with oxalic acid solution.

4.     Oxalic acid solution should not be heated beyond 70’C.

5.     Oxalic acid solution should keep warm during titration.

 

S. No.	Name of Experiment	Link
1.	To prepare 250 ml of M/20 of oxalic acid solution.	Click Here
2.	To determine the molarity and Strength of KMnO4 solution by treating with standard solution oxalic acid	Click Here
3.	To determine the molarity and strength of KMnO4 solution by treating with standard solution of Mohr’s Salt.	Click Here
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