Question

In this experiment you will use an oxidation - reduction titration to determine the percent of oxalate ion, CO2 in an unknown sample containing oxalate ion. Potassium permanganate (KMnO.) will be titrated against the oxalic acid (C2H:08) as shown by the following oxidation-reduction reaction: +3 +7 5C,044 2MnO4 + 16H* → 10CO, 8H0 + 2Mn2 +4 + + Mno. Mn? is the reduction process C2042 → CO2 is the oxidation process The underlying principle behind a titration is that an equivalence point can be reached at which the number of moles of one reactant is equal to the number of moles of the other reactant. Since this is a redox reaction, the number of electrons must be equivalent. Hence, at the equivalence point, sufficient electrons will have been added to permanganate to completely reduce all of the Mnto Mn, and those electrons would have been produced by oxidizing carbon from +3 in oxalate to +4 in carbon dioxide. Using the balanced redox equation above, we can calculate the molar ratio of permanganate to oxalate. The reagents react in a molar ratio of 5:2 5 mole C2042 = 2 mole MnO41 This equation tells you that if you want to convert moles of MnO4 into moles of C20/2 you must multiply by 5/2 This will allow us to determine the number of moles of oxalate in the unknown. Materials: Ring stand/ring Thermometer Buret/buret clamp 3 250ml Erlenmeyer flasks Unknown oxalate compound Hot plate .01 M KMnO4 soln. distilled water 600 ml beaker Procedure: 1. You will be working in the lab fume hood 2. Fill the 600ml beaker with 300ml of water and set on the hot plate to heat 3. Into 3 separate, clean, dry 250 mL Erlenmeyer flasks, weigh out approximately 0.10 g of unknown oxalate compound. Use caution: oxalate salts are toxic and must be cleaned up immediately 4. To each Erlenmeyer flask add approximately 125 mL of 1.0 M H2SO4. 5. Fill your buret with .02M KMnO4 (the KMnO4 was previously standardized) solution and note the initial volume. Read the volumes from the top of the meniscus each time, and read to 0.01 mL. 6. Put the Erlenmeyer flask in the 600ml beaker and heat and stir until the solution reaches 70°C, then turn the heat down, the unknown will dissolve. Once the mixture is warm, begin titrating, stirring frequently. 7. The end point will be reached when an extremely faint pale pink/lavendar color persists in the solution for 15 seconds. The presence of a deep purple color indicates you have overshot the end point. Note: this purple color is not permanent; if a pink color remains after 15 seconds, use this as the end point. 8. Repeat for each Erlenmeyer flask 9. Calculate the % oxalate ion for each unknown sample.