Prepare a standard solution M/50 of oxalic acid. Using this solution, determine the molarity of the given solution of KMnO₄

Prepare a standard solution M/50 of oxalic acid. Using this solution, determine the molarity of the given solution of KMnO₄

Requirements:

Burette, pipette, burner, watch glass, funnel, test tube glass rod.

Chemical Required:

Oxalic acid, distilled water, KMnO₄ solution, dilute H₂SO₄.

Theory:

KMnO₄ oxidizes oxalic acid into carbon dioxide in an acidic medium at 60°c and is itself reduced. The reactions involved are:

2KMnO₄ + 3H₂SO₄   →  K₂SO₄ + 2MnSO₄ + 3H₂O + 5[O] 

[ (COOH)₂    + [O]  (at 60°C)  → 2CO₂ + H₂O] × 5

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2KMnO₄, + 3H₂SO₄, +5(COOH)₂ → K₂SO₄ +2MnSO₄ +10CO₂ + 8H₂O

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Ionic Equation:

 2MnO4–  + 16H+ + 5C₂H42- → 2Mn2+ + 10CO₂ + 8H₂O

Indicator: KMnO₄ is a self-indicator.

End Point: Colourless to light pink.

Procedure: For preparing M/50 Oxalic acid solution :

1. Take a clean and dry watch glass.

2. Weight it. Now put crystalline oxalic acid on the watch glass and weigh till the difference between the two is 0.63 grams.

3. Transfer the weighed acid from the watch glass to a 250 ml beaker. Dissolve the acid in water. 

4. Transfer the solution into a 250 ml measuring flask. Add sufficient distilled water to make the volume exactly 250 ml.

5. Shake the solution to make it a uniform solution. Label the solution as M/50 oxalic acid solution.

For Titration: 

1. Rinse the burette with KMnO₄ solution. Full it with the given  KMnO₄ solution. 

2. Pipette out 20 ml of oxalic acid solution (M/50) in a titration flask and then add half a test tube of dilute  H₂SO₄.

3. Heat the flask to about 60°C.

4. Note the initial reading of the burette and allow KMnO₄, the solution to run into the flask dropwise with constant stirring till a permanent light pink color is obtained. This is the endpoint.

5. Take 3 concordant readings.

Observations:- 

Molarity of oxalic acid = M/50,                             The volume of oxalic acid taken =20 ml.

 

 
 

S.No.	Initial Reading	Final Reading	Vol of KMnO₄ used
1.
2.
3.
4.

                                Concordant reading =____ ml. 

Calculations:-

According to Molarity Equation,

M1V1 /a1                                   =                     M2V2/a2

(KMnO₄, )                                              (Oxalic Acid)

where a1 and a2 are the number of moles

               2M1V1= 5M2V2

                M1 = 5M2V2 /2 V1      

                 = 4/25x   M.

Precautions:-

(i) Read the upper meniscus in the burette reading.

(ii) Oxalic acid shouldn't be heated beyond 70°C. 

(iii)Oxalic acid should stay warm during titration.

(iv) Weighing should be done very carefully.

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