Determination of Iron by Reaction with Permanganate

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Determination of Iron by Reaction With Permanganate [Document Subtitle] Brianna A., Mary, Maabo, & Zarel Purpose: The purpose of this lab was to determine the mass percent of iron in an unknown compound. Procedure: 1. Weigh out 1g of the unknown with a scale and pour into a clean Erlenmeyer flask. 2. Clean the burette. Get 50 mL of .05 M KMnO4 and rinse the burette with a couple mL. 3. Add 50 mL of 1 M H2SO4 to the sample in the Erlenmeyer flask. 4. Titrate the solution with the KMnO4 solution. If a light yellow color develops, add 3mL of 85% H3PO4. Continue titrating until you get the first pink color that lasts for longer than 15 to 30 seconds. 5. Repeat 2x more. Background: Oxidation is the loss of an electron while reduction is gaining an electron. An oxidizing agent accepts electrons from another reactant while a reducing agent gives up electrons in order to reduce the oxidation state of one of its atoms. Results: a. Data | Sample 1 | Sample 2 | Sample 3 | Mass of iron compound | .94g | .96g | .97g | Initial burette reading | 0 mL | 0 mL | 0 mL | Final burette reading | 17 mL | 15 mL | 14.5 mL | Volume KMnO4 required | 17 mL | 15 mL | 14.5 mL | b. Calculations 1. MnO4- + 5Fe2+ +8H+ ⟶ 4H2O +Mn2+ + 5Fe3 2. | Sample 1 | Sample 2 | Sample 3 | Moles KMnO4 required | 8.5 x 10-4 mol | 7.5 x 10-4 mol | 7.25 x 10-4 mol | Moles of Fe2+ in sample | 4.25 x 10-3 mol | 3.75 x 10-3 mol | 3.63x 10-3 mol | Mass of Fe in sample | .237 g | .209g | .202g | Mass of sample | .94g | .96g | .97g | % of Fe in sample | 25.2% | 21.8% | 20.8% | Sample 1: .017 L x .050 mol KMnO41L = .00085 mol MnO4 .00085 mol MnO4 x 5Fe2+1MnO4 = 4.25 x 10 -3 mol Fe2+ 4.25 x 10 -3 mol Fe2+ x 55.8g1 mol = .237g %= .237g.94 g x100= 25.2% Sample 2: .015 L x .050 mol KMnO41L = .00075 mol MnO4

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