DETERMINATION OF OXALATE WITH PERMANGANATE


Preparation of Permanganate Solution. Weigh about 3.2 g of potassium permanganate into a 1000 mL boiling flask, and dilute to about 1 L. Allow the solution to stand overnight while covered. After standing, filter the solution with a suction flask and a glass fritted crucible to remove any MnO2. Clean your crucibles and your boiling flask with 1M H2SO4 and about 1 mL of 3% H2O2.

Standardization with Na2C2O4. Weigh about 2g of standard sodium oxalate and dry at 110oC for 1 hour. After cooling the standard in your desicator weigh accurately 6 samples of the Na2C2O4 into separate 250 mL conical flasks. Be sure to choose sample sizes that will require between 30 and 50 mL of titrant. Dissolve each sample in about 75 mL of 1 M H2SO4 (HINT: Con. sulfuric acid is 18 M; you should make about 1 liter of solution). For the first sample heat to about 80oC and titrate with permanganate solution while hot at a rate of about 10 mL/min. The endpoint is indicated by the first pink color that remains for at least 30 s. DO NOT use this sample for concentration or purity calculations. For the remaining samples add about 95% of the required amount of permanganate solution and allow the samples to stand until no trace of color remains in the sample (this may take up to 5 min.) After the sample has cleared, heat to about 65oC and titrate to the first permanent pink color. [NOTE: If the sample still has traces of purple or brown after allowing it to stand for several minutes discard that solution and weigh out another sample.] Record the total volume of permanganate reagent added to each sample, and use it to calculate the molarity of KMnO4. The molecular weight of sodium oxalate is 134.00.

Determination of sodium oxalate purity. Dry your unknown sample for 1 hour at 110oC before weighing. Cool your sample in a dessicator, and when cool weigh 6 samples into separate conical flasks. Again, be sure to choose sample sizes that will require between 30 and 50 mL of titrant. Repeat the procedure for the standardization of the permanganate solution for the analysis of your unknown samples.


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