Potassium Hexacyanocobaltate III

Submitted bt John H. Bigelow Checked bt John C. Bailar, Ja-t 

Grube gives a method whereby potassium hexacyano-cobaltate(III) can be prepared from potassium cyanide and cobalt carbonate, with subsequent oxidation of cyano-cobaltate(II) to cyanocobaltate(III), and purified by repeated crystallization from water. The following method was first described by Zwenger and later by Benedetti-Pichler. It has the advantage over Grube s method that cobalt(II) cyanide is first precipitated and washed free 

Cobalt cyanide is precipitated from a vigorously-stirred boiling solution of 48 g. of cobalt chloride 6-hydrate in 500 ml. of water by dropwise addition of a solution of 30 g. of potassium cyanide in about 200 ml. of water. The reddish-brown precipitate of cobalt cyanide is removed by filtration, with suction, washed with cold water, and, while still moist, transferred to a beaker containing 60 g. of potassium cyanide dissolved in 150 to 200 ml. of water the mixture is stirred imtil the precipitate is completely dissolved. The deep-red solution of potassium hexacyanocobaltate(II), K4Co(CN)6, is heated to boiling and kept at the boiling point for 10 or 15 minutes. The solution acquires the yellow color of potassium hexacyanocobaltate(III). It is filtered while still hot while the solution cools, yellow crystals of the salt are formed. These are filtered and washed with a little cold water. The mother liquor can be concentrated on a steam bath, filtered and cooled, and the resulting crystals filtered and washed. The process may be repeated two or three times. 

For purification, the crude crystals may be recrystallized from water two recrystaUizations are sufficient to give a pure product. A quick test for purity is to boil some of the salt solution for a short time after acidifying with acetic acid. The pure salt will give little or no turbidity. Yields of better than 90 per cent of the theoretical are possible. 

Nitrogen is determined by the Dumas method. Cobalt and potassium are determined in the same sample. The 

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The potassium hexacyanocobaltate(III) (or cobalticyanide) test paper is prepared by soaking drop-reaction paper or quantitative filter paper in a solution containing 4 g potassium hexacyanocobaltate(III) and 1 g potassium chlorate in 100 ml water, and drying at room temperature or at 100°C. The paper is yellow and keeps well. 

Potassium hexacyanocobaltate(HI) reagent (4%). Dissolve 4g potassium hexacyanocobaltate(III) (potassium cobalticyanide) K3[Co(CN)6] and 1 g potassium chlorate, KC103, in water and dilute to 100 ml. 

Neither isomer reacts with ammonia at low temperature. Both react with potassium cyanide giving potassium hexacyanocobaltate(III) and potassium glycinate. The red isomer reacts readily with potassium nitrite to give a solution yielding ruby red crystals, whereas the violet isomer undergoes this reaction only with difficulty. 

Place a few drops of the neutral (litmus) test solution upon potassium hexacyanocobaltate(III) (or cobalticyanide, Rinmann s green) test paper. Dry the paper over a flame and ignite in a small crucible. Observe the colour of the ash against a white background part of it will be green. 

Potassium hexacyanocobaltate(III) crystals have a faint yellow color and belong to the monoclinic system. Their specific gravity is 1.906. The compound is not appreciably hydrolyzed iii solution, but concentrated mineral acids decompose it. On heating to moderately high temperatures it melts, with decomposition, to an olive-green mass. The crystals are very soluble in water at room temperature, only very slightly soluble in liquid ammonia at —33°, and insoluble in alcohol. The preparation of potassium hexacyanocobaltate(III) is sometimes used in qualitative analysis in the separation of cobalt and nickel. 

Potassium hexacyanocobaltate (3-) Potassium hexacyanocobaltate (III) Tripotassium hexacyanocobaltate... 

Potassium guanylate Potassium 5 -guanylate. See Dipotassium 5 -guanylate Potassium hexacyanocobaltate (3-) Potassium hexacyanocobaltate (III). See Cobalt potassium cyanide... 

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