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Preparation of Chromium(II) and Copper(II) Acetate

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Synthesis of Chromium(II) Acetate Hydrate1

All work must be done in a fume hood.

Place 45 g of Na(CH3CO2)·3H2O in 40 mL of deoxygenated water in the 250 mL Erlenmeyer flask. Bubble nitrogen through the mixture for a few minutes, then cover the flask with parafilm.

Place 6 g of zinc mesh, 7.5 g of CrCl3·6H2O and 25 mL of deoxygenated water in the filter flask. Bubble nitrogen over the mixture and carefully attach the stopper containing the dropping funnel and side tube. Add 12.5 mL of concentrated HCl to the dropping funnel after making sure the stopcock is closed. Carefully open the stopcock and add enough of the HCl to the mixture slowly, drop by drop until the solution in the flask has a clear blue color. The hydrogen evolved is allowed to escape through the rubber tubing into the beaker containing water. While hydrogen is still being rapidly evolved, tightly clamp off the rubber tubing so as to force the chromium(II) solution over into the sodium acetate solution. A red precipitate of chromous acetate forms. Immediately stopper the flask and cool by swirling in running water.

Note: Do not add the chromium solution to the acetate unless the solution is a pure blue. A muddy blue or greenish-blue color indicates the presence of chromium(III) which will cause the formation of chromic hydroxide.

Filter the chromous acetate on a Buchner funnel using 2 pieces of filter paper and no vacuum. Add some nitrogen gas to the funnel and keep it covered with parafilm as much as possible. Wash the precipitate with four 25 mL portions of ice cold deoxygenated water. Add the wash carefully so as not to disturb the precipitate. Wash with three portions of 15 ml of 95% alcohol and then with five portions of 15 mL of ether. Transfer the product and filter paper into a 400 mL beaker and let dry under a stream of nitrogen in the fume hood. Your product should be brick red in colour, if it turns gray-green, the Cr(II) has been oxidized to Cr(III) and the product can be discarded.

Transfer the product, when dry, to a vial, flush the vial with N2 and seal the screwcap with parafilm.

Synthesis of Copper(II) Acetate Hydrate2

In a 400 mL beaker equipped with a magnetic stirring bar, dissolve 6.25 g (0.025 mol) of copper(II) sulfate pentahydrate in 125 mL of water. Stir the mixture and warm it to 40-50°C to aid the dissolution. Add a total of ~15 mL of 50% ammonia to the warm, stirred, light blue solution until the intense blue color of the copper ammonium complex is evident. During this addition a precipitate of copper hydroxide may form initially, but it should dissolve on further addition of the ammonia solution.

Add 2.0 g (0.050 mol) of sodium hydroxide pellets to the deep blue solution and stir the mixture for ~30 min. at 55-65°C. Be careful not to burn the compound. A light blue solid, copper(II) hydroxide precipitates during this time. Allow the mixture to cool to room temperature and collect the precipitate by suction filtration using a Buchner funnel. Wash the blue solid with three 50 mL portions of warm water.

Transfer the solid Cu(OH)2 to a 250 mL beaker and dissolve it in 10-20 mL of 10% acetic acid or until you get a clear dark blue solution. Warming with stirring aids the dissolution process. Concentrate the solution nearly to dryness by warming it. Dry the product on filter paper.


  1. W.L. Jolly, The Synthesis and Characterization of Inorganic Compounds, Ch. 32, Prentice-Hall, N. J. (1970)
  2. J. Catterick and P. Thornton, Adv. Inorg. Chem. Radiochem. 20, 291 (1977)