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Lecture 07 Handout - Experiment 7 Synthesis and Analysis...

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1 Experiment 7 Synthesis and Analysis uff those Same Green Crystals vat ve made two veeks ago Part 3: Spectrophotometric Determination of Iron Content CH 204 Fall 2008 Dr. Brian Anderson Last week Redox Chemistry Oxidation – loss of electrons Reduction – gain of electrons Balancing redox reactions Titration with KMnO 4 Experiment 7 in a nutshell Convert our green crystals into an orange solution , Fe(phen) 3 2+ , then use a spectrophotometer to measure how much light this solution absorbs at 510 nm. Then compare the absorbance of our sample to the absorbances of some solutions that we know the concentration of to determine how much Fe(phen) 3 2+ is in our solution.
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2 The Plan for Today It’s a long experiment, but has lots of repetition. You can finish faster by doing the procedure out of order: Part 1 (free up Fe 2+ from sample)... until the hot solution has to cool Part 2 (make up standard solution)... until the solution has to sit for 20 minutes Finish Part 1, start Part 4 (make up sample solution)... until the solution has to sit for 20 minutes Do Part 3 (measure absorbance of standards) Finish Part 4 (measure absorbance of sample) Lab Procedure, Part 1 1. Weigh out 0.15 g of green crystals and dissolve in deionized H 2 O. Transfer the dissolved sample to a 25 mL volumetric flask. Dissolve it right there in the weighing boat! 2. Add 8 mL of 6 M H 2 SO 4 , and fill to the line with deionized water using a disposable pipette. Your sample is now dissolved in 25 mL of solution. Part 1, continued... 3-4. Pipet 5 mL into a 30 mL beaker, add about 10 mL deionized water, start heating. 5. Add KMnO 4 dropwise until the solution turns light pink. This might take about 50-60 drops.
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