| Aim | The aim of this experiment is to determine the concentration or molarity of a KMnO4 solution by titrating it against a standard solution of oxalic acid and ferrous ammonium sulphate that will be prepared by the student themselves. |
| Apparatus Required | KMnO4 solution Oxalic acid and Ferrous Ammonium Sulphate crystals Weighing balance Volumetric flask (100 mL) Burette (50 mL) Pipette (25 mL) Conical flask (250 mL) Distilled water Indicator (phenolphthalein) |
| Theory | This experiment involves titrating the unknown concentration of KMnO4 solution against a standard solution of either oxalic acid or ferrous ammonium sulphate, which are both reducing agents. The balanced chemical equation for the reaction between KMnO4 and oxalic acid is: 5(C2O4H2) + 2MnO4- + 6H+ → 10CO2 + 2Mn2+ + 8H2O The balanced chemical equation for the reaction between KMnO4 and ferrous ammonium sulphate is: 5Fe(NH4)2(SO4)2•6H2O + 8H2SO4 + KMnO4 → 5Fe2(SO4)3 + MnSO4 + K2SO4 + 24H2O + N2 In both reactions, KMnO4 acts as the oxidizing agent, while oxalic acid and ferrous ammonium sulphate act as reducing agents. The end point of the titration is determined by the disappearance of the pink color of the KMnO4 solution, indicating that all of the reducing agent has been oxidized. |
| Procedure | Preparation of Standard Solutions: a. Oxalic Acid Solution: Weigh accurately about 1.575 g of oxalic acid crystals and dissolve it in distilled water in a 100 mL volumetric flask. Dilute the solution to the mark with distilled water and mix it well. b. Ferrous Ammonium Sulphate Solution: Weigh accurately about 3.15 g of ferrous ammonium sulphate crystals and dissolve it in distilled water in a 100 mL volumetric flask. Dilute the solution to the mark with distilled water and mix it well. Determination of KMnO4 Concentration: a. Take 25 mL of KMnO4 solution in a clean conical flask. b. Add a few drops of phenolphthalein indicator to the solution. c. Fill the burette with the standard solution (either oxalic acid or ferrous ammonium sulphate) and note its initial burette reading. d. Titrate the KMnO4 solution with the standard solution until the pink color of KMnO4 disappears, indicating the end point of the titration. Stir the solution continuously while adding the standard solution. e. Note the final burette reading and calculate the volume of the standard solution used in the titration. f. Repeat the titration at least two more times to obtain accurate results. Calculation of KMnO4 Concentration: a. Calculate the molarity of the standard solution by dividing the number of moles of the solute by the volume of the solution used. b. Using the balanced chemical equation, calculate the number of moles of KMnO4 that reacted with the known number of moles of oxalic acid or ferrous ammonium sulphate. c. Calculate the molarity of the KMnO4 solution by dividing the number of moles of KMnO4 by the volume of the KMnO4 solution used in the titration. Note: Always wash the burette, pipette, and conical flask with distilled water before using them. Be careful while measuring the mass of the solutes and transferring them to the volumetric flask. Use a funnel to avoid spillage. Perform the titration carefully and slowly to avoid overshooting the end point. |
| Observation and Result | Observation: Weigh a known mass of oxalic acid or ferrous ammonium sulphate and dissolve it in distilled water to prepare a standard solution of known concentration. Fill the burette with the standard solution and titrate it against the KMnO4 solution. Add a few drops of phenolphthalein indicator to the KMnO4 solution. Slowly add the standard solution from the burette to the KMnO4 solution with continuous stirring until the pink color of the KMnO4 solution disappears. Record the volume of the standard solution used to reach the end point. Result: Calculate the molarity of the standard solution by dividing the number of moles of the solute by the volume of the solution used. Using the balanced chemical equation, calculate the number of moles of KMnO4 that reacted with the known number of moles of oxalic acid or ferrous ammonium sulphate. Calculate the molarity of the KMnO4 solution by dividing the number of moles of KMnO4 by the volume of the KMnO4 solution used in the titration. By performing the above steps, the concentration or molarity of the KMnO4 solution can be determined accurately. |