Place the thermometer in the solution making sure the

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Place the thermometer in the solution, making sure the bulb of the thermometer is completely above the stir bar. Carefully heat the solution to 40ºC. Obtain 20 mL of 3% H 2 O 2 (hydrogen peroxide) in a 25 mL graduated cylinder. Add the 20 mL of H 2 O 2 very slowly (a few drops at a time) stirring continuously and keeping the temperature near 40ºC. A small amount of a slimy red precipitate [iron(III) hydroxide, Fe(OH) 3 ] might appear briefly. After adding all the hydrogen peroxide, heat to boiling. To the boiling solution, add 8 mL of 1 M H 2 C 2 O 4 —the first 5 mL all at once and the last 3 mL very slowly—keeping the solution boiling. Set up a funnel with filter paper on a ring-stand and gravity filter the boiling solution into a clean plastic specimen cup (not a beaker as shown in Figure 2). Figure 2 Gravity filtration apparatus
Synthesis of Potassium Tris(oxalato)Ferrate(III) Trihydrate 2090 – Fall 2017 4 Allow the solution to cool to room temperature, and then add 10 mL of ethanol to the plastic cup. Cover the plastic cup with its lid, and place it in your laboratory desk until the next laboratory period. The reason that the plastic cup should be placed in your desk is that the product, potassium tris(oxalato)ferrate(III) trihydrate [K 3 Fe(C 2 O 4 ) 3 ·3H 2 O], decomposes in the presence of light. The products of the decomposition are carbon dioxide (from the oxidation of C 2 O 4 2– ) and a complex of Fe 2+ (from the reduction of Fe 3+ ). The beaker is covered to prevent complete evaporation of the water. Complete evaporation of the water would make it impossible to separate the pure K 3 Fe(C 2 O 4 ) 3 ·3H 2 O crystals from the other salts, which will otherwise remain dissolved in solution. Also, slower solvent evaporation encourages the development of larger, purer crystals. Week 2 Determine and record the mass of a piece of filter paper. Assemble a Büchner funnel using a second filter paper. Using a stirring-rod equipped with a rubber policeman, transfer the crystals of K 3 Fe(C 2 O 4 ) 3 ·3H 2 O from the plastic cup to the filter paper in the funnel. When the crystals are free of solution, pull air through the sample for 10 to 15 minutes in order to air-dry the crystals. Remove the filter paper and carefully transfer the crystals (using your rubber policeman) to the previously massed, dry filter paper resting atop a watch-glass; spread the crystals out on the filter paper to assess dryness & purity. Obtain the combined mass of the filter paper and crystals. Determine the mass of K 3 Fe(C 2 O 4 ) 3 ·3H 2 O by difference. Show your crystals to your instructor. Finally, take a 0.5 g portion of your sample (massed to the nearest mg by difference in your smallest beaker) and place it in a drying oven for roughly an hour at 115°C. (Note: your beaker need not be clean, but it must be dry prior to use.) Dry the sample to constant mass and determine the number of moles of water per mole of salt. Waste Disposal: All excess solutions can go down the sink.

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