Experiment 5 Synthesis and Analysis of a Really Weird and Curiously Green Iron Compound Part 1: Synthesis CH 204 Fall 2006 Dr. Brian AndersonLast Week Acid/Base titration Standardizing a solution moles H + = moles OH - Calculating moles by and Molarity x Volume grams MWThree-week experimental adventure quest! This week: Synthesis of a potassium oxalatoferrate salt. K x [Fe y (C 2 O 4 ) x ]•zH 2 O Starting material → → → → Product Next two weeks: Qualitative identification of the compound through quantitative analysis of oxalate and iron. Series of reactions “Precursors”, “Intermediate products”Coordinate Covalent Bonds Coordinate covalent bond: two shared electrons in a bond, but both electrons come from the same atom. Our compound will have coordinate covalent bonds between the central iron ion and the oxygen atoms in oxalate.What is potassium oxalatoferrate? K x [Fe y (C 2 O 4 ) x ]•zH 2 O Cation: K + Anion: Fe y (C 2 O 4 ) x x Waters of hydration An ionic crystal with a big, covalently-bound anion. Oxa-who? Oxalic acid Oxalate i onProcedure Overview • Dissolve an Fe 2+ salt in water and add oxalate to precipitate the iron as Iron (II) Oxalate solid. • Oxidize the iron to Fe 3+ in the presence of excess oxalate. The precipitate will dissolve as the complex ion forms in solution. • Precipitate the iron complex ion as the potassium salt by adding ethanol to the mix.A sneak peek at redox half-reactions Oxidation half reaction: Fe 2+ Fe 3+ + e – Reduction half reaction: H 2 O 2 + 2 H + + 2 e – 2 H 2 O Add the two halves: 2 Fe 2+ + H 2 O 2 + 2 H + Fe 3+ + 2 H 2 OGrading this lab • No real data to speak of, so not the usual lab report • Discussion questions count for more • Record your observations during the experiment – precipitation, color changes, evolution of gases, dissolving of precipitates.W A R N I N G ! Follow lab directions carefully or there will be no green crystalline delight for you! (And this will make you cry.) Do NOT overheat solutions in the lab today! Potassium oxalate = Oxalic acid! If crystals don’t form in the end, add another 10 ml of ice-cold ethanol.What’s going to be on the quiz next week? Look at the post-lab problems. Be able to calculate: Limiting reagent Theoretical yield Percent
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