Cupric hydroxide complexes

Paulsen, A.3., 1978. Potentiometric studies of cupric hydroxide complexation. Thesis. Graduate School of Oceanography, Univ. of Rhode Island USA. 

Discussion When soluble cupric compounds are reduced in alkaline solution, cuprous oxide is precipitated. Since ordinary cupric salts can not exist in an alkaline solution, because of the precipitation of cupric hydroxide, complex compounds must be used. Such a compound is formed by adding a solution containing sodium potassium tartrate and sodium hydroxide to one of cupric sulphate. When this mixture, known as Fehling s solution, is boiled with a reducing agent, such as glucose, cuprous oxide is precipitated. 

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. 

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] ... 

The following relative second-order rate constants have been obtained for hydroxide ion-catalysed hydrolysis glycine ethyl ester, 1 protonated glycine ethyl ester, 41 and the cupric ion complex of glycine ethyl ester, F3 x 10 (Conley and Martin, 1965). The large effect of the cupric ion cannot be due entirely to electrostatic effects, but rather to catalysis by direct co-ordination with the ester function. 

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

Cupric hydroxide is nearly insoluble in NaOH solution alone, but it dissolves when a soluble tartrate is added, the copper going into a complex negative ion similar in color to the ammonio-cupric ion. 

Adsorption of cupric hydroxide from ammonium hydroxide by starch causes the sorption of Cu(NH3)2(OH)2. The sorption of this copper species is more effective than the sorption of Ba(OH)2 however, the process is complex and cannot be expressed by a simple formula.481 On the other hand, fractionation of potato starch by means of Al(OH)3 has been reported.482 The complex of Cu(OH)2, ammonium hydroxide, and starch has been patented as a germicide and algicide composition.483... 

The results with Cu - and Cu -TSMs (27) are also shown in Table III. Cu -TSM was obtained similarly to Cu -TSM using the Cu(I) ammine complex salt in the ion-exchange reaction. Cu -TSM, copper supported on TSM, was prepared by calcination and subsequent hydrogen reduction of an oligomeric cupric hydroxide intercalate, which had been obtained by precipitating the hydroxide into the interlayer spaces of TSM after the titration method developed by Yamanaka and Brindley (8). The catalytic activity of Cu -TSM is so poor as to be less than one-tenth of that of Cu -TSM, although the molar content of Cu is about twice as high. Because a weak sig-... 

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... 

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... 

Cupric hydroxide, Cu(OH)o, forms as a pale blue gelatinous precipitate when an alkali hydroxide or ammonium hydroxide is added to a cupric solution. It dissolves very readily in excess ammonium hydroxide, forming the deep-blue complex Cu(NH3) ++ (Chap. 23). Cupric hydroxide is slightly amphoteric, and dissolves to a small extent in very concentrated alkali, forming Cu(OH) —. 

In one such method (details of which are found on the Evolve site that accompanies this book), using Benedict s reagent (cupric ion complexed to citrate in alkaline solution), reducing substances convert cupric to cuprous ions, forming yellow cuprous hydroxide or red cuprous oxide. 

Copper (Cu, at. mass 63.54) occurs in its compounds in the n, and less often in the I, oxidation state. The properties of copper(I) are similar to those of Ag, Au(I), and T1(I). Copper(I) forms sparingly soluble compounds with the halogens. In solution, copper(I) exists only in complexes, e.g., Cu(CN)2", CuCb", and Cu(NH3)2. Cupric hydroxide, Cu(OH)2, begins to precipitate at pH 5 and shows no amphoteric properties. Copper(II) forms ammine, chloride, tartrate, and EDTA complexes. As a result of oxidizing properties of Cu(ll), its cyanide complex is converted into copper(I) cyanide complex, and sparingly-soluble CuSCN is precipitated from Cu(II) thiocyanate. 

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... 

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. 

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... 

A second process for producing regenerated cellulose fibre was introduced in 1897 in Germany. In this method, cellulose is treated with an ammoniacal solution of cupric hydroxide (Cu(NH3)4(OH)2) to form a soluble complex. The solution is then spun into dilute sulphuric acid to regenerate the cellulose. This process is relatively expensive because of the need to recover copper. However, the product, called cuprammonium rayon, is still made on a limited scale because of its pleasing appearance and feel. 

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