A common task in chemistry is the determination of a substance present in a product. If the product contains a substance that can be oxidized, then it is possible to determine the number of moles of that substance by titrating the sample with a solution of a strong oxidizing agent. In this lab, a solution of KMnO4, an oxidizing agent, will be standardized by titration with a solution containing a known concentration of iron (II) ions, (Fe+). The concentration of oxalic acid solution will be determined by titration with the MnO4- solution that had been standardized first. The purpose of this lab is to standardize a solution of potassium permanganate by redox titration with a standard solution of iron (II) ions. A solution of oxalic acid is then titrated with the permanganate solution to determine the exact concentration of oxalic acid. Purpose:
The purpose of the experiment was to use the permanganate ion, a strong oxidizing agent, in a titration in order to determine the concentration of a FeSO4 solution. Purple MnO4- ion from a standardized potassium permanganate solution was titrated thrice to give clear Mn2+ with an analyte of acidified FeSO4 until all the Fe2+ in the solution was oxidized to Fe3+. The color of the MnO4-/Mn2+ was used as the indicator for the titration. A balanced oxidation-reduction, the molarity/normality of the standards potassium permanganate, and the volume of potassium permanganate used allowed the determination of the concentration of the FeSO4. Equipment and Chemicals:
* Iron (II) ammonium sulfate solution, Fe(NH4)2∙6H2O, 0.100 M, 50 mL * Manganese sulfate solution, MnSO4∙ H2O, 1.0 M, 50 mL
* Oxalic acid solution, H2C2O4, 0.25 M, 60 mL
* Potassium permanganate solution, KMnO4, approx. 0.02 M, 100 mL * Sulfuric acid solution, H2SO4, 6 M, 50 mL
* Buret, 50-mL
* Erlenmeyer flasks, 250-mL, 3
* Hot plate
* Volumetric pipet, 10-mL
* Volumetric pipet, 25-mL
* Beakers, 100-mL, 3
* Graduated cylinder, 10-mL
* Wash bottle
* Water, distilled or deionized
1. Obtain approximately 80 mL of the potassium permanganate solution in a 100-mL beaker. Obtain 50 mL of the 0.100 M Fez+ solution in another 100-mL beaker. Label both beakers. 2. Set up a clean, 50-mL buret in the ring stand and buret clamp. 3. Rinse the buret with approximately 10 mL of distilled or deionized water and then with two 5 mL portions of the MnO4- solution. 4. Close the stopcock and fill the buret to above the zero mark with M n 0 4 solution. 5. Open the stopcock to allow any air bubbles to escape from the tip. Close the stopcock when the liquid level is between the 0- and 10-mL marks. 6. Record the precise level of the solution in the buret in the Part 1 Data Table 1. This is the initial volume of the MnO4- solution. 7. With the volumetric pipet, transfer 10 mL of the 0.100 M Fe2+ solution to a clean 250-mL Erlenmeyer flask. Record this volume in the Part 1 Data Table. 8. Measure out 10 mL of the 6 M H2SO4 into a clean 10-mL graduated cylinder and add this to the Erlenmeyer flask. Swirl to mix. 9. Position the flask under the buret so that the tip of the buret is within the flask but at least 2 cm above the liquid surface. 10. Titrate the Fe2+ solution with the MnO4- solution until the first trace of pink color persists for 30 seconds. Remember to swirl the flask and to rinse the walls of the flask with distilled water before the endpoint is reached. 11. Record final buret reading as the final volume of the MnO4- solution in the Part 1 Data Table. 12. Repeat the standardization titration two more times.
Part 2. Determination of Concentration of an Oxalic Acid Solution 1. Obtain approximately 60 mL of the oxalic acid solution in a clean 100-mL beaker. 2. With a 25-mL volumetric pipet, transfer 25 mL samples of the oxalic acid solution to each of two 250-mL Erlenmeyer flasks. Record the volume in the Part 2 Data...