Potassium aquo ferricyanide

Potassium aquo ferricyanide, K2Fe(CN)5.H20, is obtained by the prolonged action of chlorine upon potassium ferrocyanide solution. At first potassium ferricyanide is formed, which undergoes further decomposition, the chlorine abstracting one (CN) group, water taking its place. Thus —1... 

Potassium sulphito ferrocyanide, K5Fe(CN)5.S03, is obtained by reduction of potassium aquo ferricyanide, K2Fe(CN)5.H20, with excess of potassium sulphite in potassium hydroxide.1 It crystallises from aqueous alcohol in small yellow prisms. 

Potassium aquo ferrocyanide, K3Fe(CN)5.H20, is obtained by reducing potassium aquo penta-ferricyanide, K2Fe(CN)6.H20, with alkaline hydroxylamine chloride, with alkali sulphide, or with formaldehyde and acetone in the presence of alkali.1... 

The double compound, [Cr(NH3)6H20][Cr(CN)8], is precipitated from the aquo-pentammino-chloride on addition of potassium chromi-cyanide it separates as a sparingly soluble yellow crystalline powder, and on heating with concentrated hydrochloric acid decomposes with formation of ehloro-pentammino-chloride. The ferricyanide, [Cr(NH3)B H20][Fe(CN)6], is precipitated from a dilute solution of the aquo-pentammino-ehloride on addition of potassium ferricyanide, and crystallises in vellowish-brown prisms. The cobalti-cyanide, [Cr(NH3)5H20] [Co(CN)6], obtained, by the addition of potassium cobalti-cyanide, in yellowish-brown crystals, is isomeric with the chromi-eyanide of aquo-pentammino-cobalt, [Co(NH3)sH20][Cr(CN)6]. 

Aquo - pentammino - iridium Ferricyanide, [Ir(NH8)6H20] [Fe(CN)e], is precipitated as a reddish-brown crystalline powder on the addition of potassium ferricyanide to the aquo-pentammino-salts. All the aquo-salts yield violet-coloured solutions with chlorine, due probably to the formation of iridic compounds. 

Owing to the high charge of the anions, the effect of ionic strength is also large (E° = 0.46 V for 0.1 M solutions of both potassium ferrocyanide and ferricyanide), and the potential shift is in a direction opposite that observed for the aquo Fe(III)-Fe(II) couple because the more highly charged species is the reductant rather than the oxidant. 

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