Principle: Oxalic acid is primary standard substance and reducing agent / reductant. Potassium permanganate is secondary standard substance and oxidizing agent / oxidant. So the strength of KMnO4 can be found out by the standard C2O4H2 solution. Since KMnO4 Change the color of its own. So we need not add extra indicator. In Red-Ox reaction Oxalate ion gives electron and permanganate ion receive electron in acid medium. The reaction are happened such way
2KMnO4 + 5C2O4H2 + 3H2SO4 = K2SO4 + 2MnSO4 + 10CO2 + 8H2O
C2O4 2- - 2e- = 2CO2 (Oxidation)
5C2O4 2- - 10e- = 10CO2 (Oxidation)
2MnO4- + 10e- =2 Mn2+ (reduction)
Since KMnO4 solution has to standard by the standard Oxalic acid solution. Firstly have to prepare Oxalic acid solution.
Apparatus: Digital balance, Measuring flask, Wash bottle, conical flask, pipette, Burette, Stand, and Cramps.
Chemical: Oxalic acid, Sulphuric Acid, Potassium Permanganate.
Preparation of Oxalic Acid solution:
Molecular weight of C2O4H2. 2H2O = 12 X 2 + 16 X 4 + 1 X 2 + 18 X 2
= 126
Equivalent weight = 126 / 2
= 63
1000 ml 1N solution C2O4H2 present = 63 g
100 ml 0.1N solution C2O4H2 present = 63 x 100 x 0.1 / 1000
= 0.63 g
Concentration of Oxalic acid solution = 0.63 /0.63 X 0.1 N
= 0.1 N
Procedure:
1. By taking weight 0.63g C2O4H2 and transfer to 100 ml measuring flask. Dissolve it in distilled water and made up to the mark. Shake well and mixed thoroughly.
2. We took clean burette rinsed and then filled it with KMnO4 solution. Then the burette was stood by stand and cramps.
3. We took a pipette of 10 ml which was cleaned and washed with distilled water and then ringed with C2O4H2 solution.
4. Took 10ml solution of C2O4H2 in a conical flask from the measuring flask (Beaker if the solution pours in the beaker) with the help of an appropriate pipette.
5. Added 20ml H2SO4 & diluted with a little of water.
6. Heat the solution up to 60-70 o C .
7. This experiment there was no needed to add extra indicator because KMnO4 itself acts as an indicator.
8. Place the burette such way that its tip 1 inch up from the mouth of the conical flask. But do not touch it.
9. Noted the burette reading.
10. Slowly run the KMnO4 solution in to the C2O4H2 solution and continuously rotated the conical flask. But not touch with the tip of the burette.
11. Add slowly until the solution comes colorless to light pink colors. This is the end point of the titration.
12. Noted the burette reading in the data table.
13. The difference between the initial and final burette reading gives the volume of the KMnO4 solution required to completely neutralize 10 ml of C2O4H2 solution.
14. The procedure is repeated three or four times.
Table: Determination volume of KMnO4
Calculation: Here,
V1S1 = V2S2
S2 = V1S1 / V2 V1 = Volume of C2O4H2 solution = 10 ml
S1 = Concentration of C2O4H2 solution = 0.1 N
V2 = volume of KMnO4 solution = Burette
S2 = Concentration of KMnO4 solution =?
Result : Concentration of KMnO4 …….. N .