Determine the Percentage Composition of a Mixture of Sodium Oxalate and Oxalic Acid Provided N/20 Potassium Permanganate

Determine the Percentage Composition of a Mixture of Sodium Oxalate
  and Oxalic Acid . Provided N/20 KMnO₄ 

Chemistry Lab ManualNCERT Solutions Class 12 Chemistry Sample Papers

Chemical Equations

Theory
Both oxalic acid and sodium oxalate can be titrated against N/20 KMnO₄ since both of them are reducing agents.
So normality (N₂) of the solution will be due to both of them. From the combined normality (N₂), the composition of each can be calculated.

Indicator
KMn04 is a self-indicator.

End Point
Colourless to permanent pink (KMnO₄ in burette).

Procedure

1. Rinse and fill the burette with the N/20 KMnO₄, solution.
2. Weigh exactly 1.0 g of the given mixture of oxalic acid and sodium oxalate and dissolve in water to prepare exactly 250 ml of solution using a 250 ml measuring flask. Rinse the pipette with the prepared oxalate solution and pipette out 20.0 ml of it in a washed titration flask.
3. Add one test-tube (~ 20 ml) full of dilute sulphuric acid (~ 4 N) to the solution in titration flask.
4. Note the initial reading of the burette.
5. Heat the solution of titration flask to 60-70°C and run down KMnO₄ solution from the burette till a permanent light pink colour is just imparted to the solution in the titration flask.
6. Note the final reading of the burette.
7. Repeat the above steps 4-5 times to get three concordant readings.

Observations
Normality of KMnO₄ solution = 1/20
Volume of oxalate solution taken for each titration = 20.0 ml.

Calculations
x ml of N/20 KMnO₄ solution are equivalent to 20 ml of the given oxalate solution.
Applying normality equation,