Objective: To find out the molarity of the KMnO4 solution
Chemical principle: Potassium permanganate is a strong oxidizing agent. It dissolves in water to give intense purple solutions. It reacts with reducing agents and gives colourless Mn2+ ions. So the solution itself acts as the indicator for the titration, the end point is noted when the first permanent pink colour appears. The sulphuric acid is used as a catalyst for the reaction. The oxalic acid is heated before titration because if the temperature is too low, the interaction between the acid and the potassium permanganate will move too slowly.
250cm3 conical flasks X2 250.0cm3 volumetric flask 250cm3 beaker 100cm3 beaker
Burette White tile
Wash bottle Glass rod
Burette clamp and stand Pipette
Funnel Thermometer (10-110oC)
0.2M KMnO4 solution
Standard 0.1M iron (II) ammonium sulphate
Standard 0.05M oxalic acid dihydrate
2M of sulphuric acid
A. Standardization of KMnO4 solution with standard iron(II) salt solution 1. 25.0cm3 of the given KMnO4 solution was diluted to exactly 250cm3 in a volumetric flask. 2. 25.0cm3 of the standard iron (II) salt solution was added into a conical flask with the pipette. 3. 15cm3 of 2M sulphuric acid was added to the flask.
4. The solution was titrated with diluted KMnO4 solution until the first persistent pink colour obtained. 5. The titration was repeated to obtain 3 consistent results.
B. Standardization of KMnO4 solution with standard oxalic acid solution 1. 25.0cm3 of the standard 0.05M oxalic acid solution was added into a 250cm3 conical flask with the pipette. 2. 15cm3 of 2M sulphuric acid was added to the flask.
3. The mixture was heated to 70oc with the use of Bunsen burner. 4. The solution was titrated with diluted KMnO4 solution until a permanent pink colour obtained. 5. The titration was repeated to obtain 3 consistent results.
Results and observations:
| Trial| 2nd| 3rd| 4th|
Final burette reading (cm3)| 38.00| 35.10| 36.00| 36.60| Initial burette reading (cm3)| 13.90| 11.60| 12.70| 13.40| Volume of KMnO4 used| 24.10| 23.50| 23.30| 23.20|
| Trial| 2nd| 3rd| 4th|
Final burette reading (cm3)| 38.30| 32.10| 36.40| 27.10| Initial burette reading (cm3)| 14.60| 9.10| 12.80| 3.40| Volume of KMnO4 used| 23.70| 23.00| 23.60| 23.70|
The concentration of KMnO4 calculated in A is 0.219M and the concentration calculated in B is 0.211M. The result in A is slightly greater than that in B. The difference may due to experimental errors. During heating the iron (II) ammonium sulphate and the oxalic acid, some of the solution may evaporate and their volume may decrease slightly. Also, while transferring the KMnO4 solution to the volumetric flask, the pipette used should be rinsed thoroughly. Otherwise the concentration of the KMnO4 solution may be lowered. These may lead to errors in the calculation. Other than that, errors may occur when observing the readings of the burette and noticing the end point of the titration.
The concentration of the KMnO4 solution is about 0.200M.