Experiments for Class 12 (Chemistry - Practicals)

 TITERATION POTASSIUM PER MANGNET AND FERROUS AMMONIUM SULPHATE

EXPERIMENT NO. 1

Aim: To determine the molarity of KMnO4 solution by titrating it against M/20 standard solution of ferrous ammonium sulphate. 

Apparatus Required: 

• Measuring flask (250 mL) : One 

• Burette (50 mL) : One 

• Burette stand : One 

• Pipette : One 

• Conical flask : One 

• Glazed tile (white) : One 

• Funnel : One 

• Weighing bottle : One 

Chemical Required: 

• Potassium permanganate solution : As per need 

• Dilute sulphuric acid : As per need 

• Ferrous ammonium sulphate : As per need. 

Theory: Ferrous ammonium sulphate acts as a reducing agent in the titration against potassium permanganate. The oxidation number of iron in Mohr’s salt is +2. Iron is oxidised during the reaction and its oxidation number changes from +2 to +3. The reaction which takes place is given below : 

Indicator: KMnO4 is a self indicator. 

End Point : Colourless to light pink colour. 

Observation Table: Titration of potassium permanganate solution against standard ferrous ammonium sulphate solution.

Calculations: Molarity of the KMnO4 solution-

Ferrous ammonium sulphate [FeSO4 (NH4)2SO4 6H2O] = potassium permanganate [KMnO4] 

a1M1V1 = a2M2V2 

M1 = molarity of ferrous ammonium sulphate solution = 1/20 M 

M2 = molarity of potassium permanganate solution = ?

V1 = volume of ferrous ammonium sulphate solution = 20 mL 

V2 = volume potassium permanganate solution = 19.8 mL 

a1 = 1, (the number of electrons lost per formula unit of ferrous ammonium sulphate in the half cell reaction) 

a2 = 5, (the number of electrons gained per formula unit of potassium permanganate in a half cell reaction) 

Result: The Molarity of the given KMnO4 solution is 0.0101 M. 

Precautions: 

(a) Always use a fresh sample of ferrous ammonium sulphate to prepare its standard solution. 

(b) Always rinse the burette and the pipette with the solutions to be taken in them.

(c) Never rinse the conical flask with the experimental solutions. 

(d) Remove the air gaps if any, from the burette.

(e) Never forget to remove the funnel from the burette before noting the initial reading of the burette. 

(f) No drop of the liquid should hang at the tip of the burette at the end point and while noting reading. 

(g) Always read the upper meniscus for recording the burette reading in the case of all coloured solutions. 

(h) Never use pipette and burette with a broken nozzle. 

(i) Lower end of the pipette should always remain dipped in the liquid while sucking the liquid. 

(j) Do not blow out the last drop of the solution from the jet end of the pipette. 

(k) The strength of the solution must be calculated up to the fourth decimal place.