Cupric ammonia complex hydroxide

If copper is present in the boiler FW (normally as the cupric ammonia complex ion), boiler surfaces are directly attacked by electrolytic reduction. In strongly alkaline conditions the ferrous ion is present as ferrous hydroxide [Fe(OH)2] ... 

An ion which contains several atoms, such as the sulfate ion, SO4 is called a complex ion. Familiar examples of complex ions other than those of the oxygen acids are the deep blue cupric ammonia complex ion, Cu(NH3)4++, which is formed by adding ammonium hydroxide... 

The solution of the precipitate cannot be attributed to increase in hydroxide-ion concentration, because sodium hydroxide does not cause it, nor to ammonium ion, because ammonium salts do not cause it. There remains undissociated NH OH or NHg, which might combine with the cupric ion. It has in fact been found that the new deep blue ion species formed by addition of an excess of ammonium hydroxide is the cupric ammonia complex Cu(NH3)4+, similar to the hydrated cupric ion except thar the four water molecules have been replaced by ammonia molecules. This complex is sometimes called the cupric tetrammlne complex the word ammine meaning an attached ammonia molecule. 

The reason that the precipitate of cupric hydroxide dissolves in an excess of ammonium hydroxide can be given in the following way. A precipitate of cupric hydroxide is formed because the concentration of cupric ion and the concentration of hydroxide ion are greater than the alues corresponding to the solubility product of cupric hydroxide. If there were some way for copper to be present in the solution without exceeding the solubility product of cupric hydroxide then precipitation would not occur. In the presence of ammonia, copper exists in the solution not as the cupric ion (that is, the hydrated cupric ion), but principally as the cupric ammonia complex Cu(NHg)4++. This complex is far more stable than the hydrated cupric ion. The reaction of formation of the cupric ammonia complex is... 

An inorganic molecule that contains several atoms, including one or more metal atoms, is called an inorganic complex or coordination compound. An example is nickel tetracarbonyl, Ni(CO)4. An inorganic complex with an electric charge is called a complex ion. Familiar examples of complex ions are the ferrocyanide ion, Fe(CN)e - the ferricyanide ion, Fe(CN)e the hydrated aluminum ion, A1(H20)6, and the deep blue cupric ammonia complex ion, Cu(NH3)4 +, which is formed by adding ammonium hydroxide to a solution of cupric salt. Complex ions are important in the methods of separation used in qualitative and quantitative chemical analysis and in various industrial processes. 

We see from the equation for the reaction that the addition of ammonia to the solution causes the equilibrium to shift to the right, more of the cupric ion being converted into cupric ammonia complex as more and more ammonia is added to the solution. When sufficient ammonia is present a large amount of copper may exist in the solution as cupric ammonia complex, at the same time that the cupric ion concentration is less than that required to cause precipitation of cupric hydroxide. When ammonia is added to a solution in contact with the precipitate of cupric hydroxide, the cupric ion in the solution is converted to cupric ammonia... 

To explain this phenomenon we might postulate the formation of a complex ion, remembering the solubility of cupric hydroxide and nickel hydroxide in ammonium hydroxide with formation of ammonia complexes. This is indeed the explanation the complex ion which is formed is the rincate ion, Zn(OH)4, by the reaction... 

All coppei -nickel catalysts were prepared from the magnetically pure copper which was itself completely inactive in the hydrogenation of benzene under the conditions described below. Cupric hydroxide was precipitated from a nitrate solution by dilute ammonium hydroxide solution so that the supernatant liquid was faintly colored by the copper-ammonia complex. The precipitate was filtered and washed. Nickel nitrate in water solution was now added in the proportion desired, and the mixture was stirred to a paste of even consistency. It was dried at 95°, ignited at 180° for 36 hours, and finally at 400° for 20 hours. The oxide mixture was reduced in purified hydrogen at 150° for 20 hours. Most finished catalysts contained 1.0 per cent of nickel. 

Aqueous ammonia also acts as a base precipitating metallic hydroxides from solutions of their salts, and in forming complex ions in the presence of excess ammonia. For example, using copper sulfate solution, cupric hydroxide, which is at first precipitated, redissolves in excess ammonia because of the formation of the complex tetramminecopper(TT) ion. 

Forms cupric hydroxide, Cu(OH)2 with CUSO4 the precipitate, however, dissolves in excess ammonia, forming a tetrammine copper (II) complex ion. 

Hence, to prepare a cone. soln. of ammonium monosulphide, a current of washed hydrogen sulphide is passed into cone, aqua ammonia cooled to 0° until the neutral point is reached. Attempts to obtain crystals by cooling the soln. to —40° were not successful. W. P. Bloxam believes that the soln. so obtained is not really the monosulphide at all, but rather a soln. of a mol. of the complex (NH4)2S.2NH4SH in two mols. of ammonium hydroxide, NH4OH because of (i) its action on cupric sulphate (ii) its failure to yield crystals by cooling, attributed to the solvent action of free ammonia and (iii) because it exhibits no tendency to dissolve sulphur. 

In presence of oxygen the metal is rapidly dissolved by solutions containing free ammonia, with formation of complex cupric ammonium derivatives, the ammonia being oxidized to nitrite (p. 256). At 568° C. sodium hydroxide begins to attack copper.9 The action of alkali-metal persulphates on copper and its alloys has been investigated by Groschuff.10... 

The cupric ion displays a characteristic power of forming complex derivatives with ammonia2 and substituted ammonias, an example being the cupric ammonium hydroxides mentioned on p. 254. A great number of other complex derivatives are derived from cuprous or cupric ions. In certain of these compounds both kinds of copper ions are present simultaneously, examples being the complex cupric-cuprous... 

Black crystalline CuO is obtained by pyrolysis of the nitrate or other oxo salts above 800°C it decomposes to Cu20. The hydroxide is obtained as a blue bulky precipitate on addition of alkali hydroxide to cupric solutions warming an aqueous slurry dehydrates this to the oxide. The hydroxide is readily soluble in strong acids and also in concentrated alkali hydroxides, to give deep blue anions, for example, [Cu(OH)4]2" and [Cu(OH)6]4". In aqueous ammonia deep blue ammine complexes are formed, as described later. 

Catalysis by Cu(NH3)4S04 has been examined by Nikolev (98) who found a maximum rate at pH 8.5 to 9.0. The reaction is strictly first order in peroxide up to 0.25 M peroxide but decreases to zero order at 0.5 M. Addition of ammonium hydroxide at first increases the rate but ultimately depresses it, an effect also noted by Bobtelsky and Kirson (99). Unfortunately the experiments are not very extensive, and it is impossible to separate the effect of ammonia in complexing from the effect of the accompanying pH increase. Information on the relative activities of the complexes with various amounts of coordinated ammonia would be interesting. The only indication from this work is that the depressing effect of high ammonia concentrations supports the authors view that the hexammine probably formed in these conditions is less active than the tetrammine. One other point of interest is that it seems probable that radicals are formed in the reaction, possibly in conjunction with a cupric ammine-cuprous ammine redox system, since organic substances can be oxidized by the cuprammonium-peroxide mixtures. 

As has been noted in numerous cases already, ammonium hydroxide often differs from sodium hydroxide in its action upon salts, particularly when present in excess. In the case of cupric salts the ammonia present in the solution forms a complex ion of the formula Cu(NH3)4++. 

When ammonia is added to a solution of a cupric salt, a light-blue precipitate of cupric hydroxide is first formed which dissolves in excess of ammonia to form a deep purplish-blue solution. The color is due to the complex ion Cu(NH8)4. The sulfate of... 

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