Oxidation-Reduction Titrations Lab5 June 2012

PurposeTo understand how oxidation-reduction reactions work in the case of titration; to use

oxidation-reduction titrations to determine experimentally the number of moles and molarity of a given substance that may be oxidized or reduced.

Discussion of TheoryOxidation-reduction titrations were performed in order to determine experimentally the

concentrations of ions present in given mixtures.

ProcedurePart I:80mL of potassium permanganate solution were obtained and placed in a 100mL beaker which was labeled. 50mL of iron (II) ammonium sulfate solution was obtained in another 100mL beaker which was also labeled. A buret was then attached to a ring stand using a buret clamp, and the buret was rinsed with approximately 10mL of deionized water, and then with two 5mL portions of the MnO4

- solution. The buret was then closed and filled to the 0mL mark with MnO4-

solution. Then, 10mL of the Fe2+ solution was transferred to a clean 250mL Erlenmeyer flask and the volume was recorded. Next, 10mL of 6M H2SO4 was measured out into a clean 10mL graduated cylinder and added to the flask containing the Fe2+ solution. This flask was placed under the buret and the Fe2+ solution was titrated until the first trace of pink color persisted for 30 seconds. The final volume of MnO4

- was recorded, and the titration was repeated once more.Part II:60mL of oxalic acid solution was obtained and placed in a 100mL beaker. Next, using a 25mL volumetric pipet, 25.0mL samples of oxalic acid were transferred to each of two Erlenmeyer flasks, and the volumes contained in each flask were recorded. 5 drops of 1.0M MnSO4, 10mL samples of 6M H2SO4, and 20mL of deionized water were added to each Erlenmeyer flask, and the flasks were swirled to mix the reagents. Then, the first flask was warmed to 85oC using a hot plate, and the solution in this heated beaker was immediately titrated using the standardized MnO4

- solution from part 1. Then, this process was repeated with the second flask.

ConclusionThe molarity of the H2C2O4 solution was 0.0260 mol/L

Experimental Sources of ErrorThe buret and ring stand used to perform titrations can often have inaccurate results due

to overshooting of the titration endpoint. It’s incredibly difficult to be precise with the burets, and using more precise instrumentation would lead to a more conclusively accurate molarity.