Solubility silver-copper example

Other two-component systems may exhibit either limited solubility or complete insolubility in the solid state. An example with limited solubUity is the silver-copper system, of which the reduced-phase diagram is shown in Figure 13.5. Region L represents a liquid phase, with F = 2, and S and 5s represent solid-solution phases rich in Ag and Cu, respectively, so they are properly called one-phase areas. S2 is a two-phase region, with F= 1, and the curves AB and DF represent the compositions of the two solid-solution phases that are in equilibrium at any... 

In aquatic environments, more research is needed on the chemical speciation of silver to evaluate risk to the organism and its consumers. Most silver criteria formulated for the protection of aquatic life are now expressed as total recoverable silver per liter. But total silver measurements do not provide an accurate assessment of potential hazard. Silver ion (Ag+), for example, is probably the most toxic of all silver chemical species and must be accurately measured in the assessment of silver risks in aquatic environments, perhaps as acid-soluble silver. Little is known of the biocidal properties of Ag + andAg + that are the active ingredients in disinfectants and used increasingly in water purification systems of drinking water and swimming pools. The effects of these silver species on organism health clearly must be researched. Silver interactions with other metals and compounds in solution are not well defined. For example, mixtures of salts of silver and copper markedly increased the survival of oyster embryos, but only when... 

These are practically insoluble in water, are not hydrolysed and so may be prepared by addition of a sufficient concentration of sulphide ion to exceed the solubility product of the particular sulphide. Some sulphides, for example those of lead(II), copper(II) and silver(I), have low solubility products and are precipitated by the small concentration of sulphide ions produced by passing hydrogen sulphide through an acid solution of the metal salts others for example those of zincfll), iron(II), nickel(II) and cobalt(II) are only precipitated when sulphide ions are available in reasonable concentrations, as they are when hydrogen sulphide is passed into an alkaline solution. 

Ammonia forms a great variety of addition or coordination compounds (qv), also called ammoniates, ia analogy with hydrates. Thus CaCl2 bNH and CuSO TNH are comparable to CaCl2 6H20 and CuSO 4H20, respectively, and, when regarded as coordination compounds, are called ammines and written as complexes, eg, [Cu(NH2)4]S04. The solubiHty ia water of such compounds is often quite different from the solubiHty of the parent salts. For example, silver chloride, AgQ., is almost iasoluble ia water, whereas [Ag(NH2)2]Cl is readily soluble. Thus silver chloride dissolves ia aqueous ammonia. Similar reactions take place with other water iasoluble silver and copper salts. Many ammines can be obtained ia a crystalline form, particularly those of cobalt, chromium, and platinum. 

The reaction is a sensitive one, but is subject to a number of interferences. The solution must be free from large amounts of lead, thallium (I), copper, tin, arsenic, antimony, gold, silver, platinum, and palladium, and from elements in sufficient quantity to colour the solution, e.g. nickel. Metals giving insoluble iodides must be absent, or present in amounts not yielding a precipitate. Substances which liberate iodine from potassium iodide interfere, for example iron(III) the latter should be reduced with sulphurous acid and the excess of gas boiled off, or by a 30 per cent solution of hypophosphorous acid. Chloride ion reduces the intensity of the bismuth colour. Separation of bismuth from copper can be effected by extraction of the bismuth as dithizonate by treatment in ammoniacal potassium cyanide solution with a 0.1 per cent solution of dithizone in chloroform if lead is present, shaking of the chloroform solution of lead and bismuth dithizonates with a buffer solution of pH 3.4 results in the lead alone passing into the aqueous phase. The bismuth complex is soluble in a pentan-l-ol-ethyl acetate mixture, and this fact can be utilised for the determination in the presence of coloured ions, such as nickel, cobalt, chromium, and uranium. 

As examples of some water-soluble salts, mention may be made of potassium chloride, copper sulfate, and sodium vanadate. As examples of some water-insoluble salts, mention may be made of some typical ones such as lead chloride, silver chloride, lead sulfate, and calcium sulfate. The solubilities of most salts increases with increasing temperature. Some salts possess solubilities that vary very little with temperature or even decline. An interesting example is provided by ferrous sulfate, the water solubility of which increases as temperature is raised from room temperature, remains fairly constant between 57 and 67 °C, and decreases at higher temperatures to below 12 g l-1 at 120 °C. Table 5.2 presents the different types of dissolution reactions in aqueous solutions, and Table 5.3 in an indicative way presents the wide and varied types of raw materials that different leaching systems treat. It will be relevant to have a look at Table 5.4 which captures some of the essential and desirable features for a successful leaching system. 

Diammino-silver nitrate forms glistening rhombic or prismatic crystals which blacken on exposure to light. It is fairly stable, and may be heated to 100° C. without loss of ammonia. Further heating causes it to decompose, and finally to melt with evolution of nitrogen and ammonia, leaving a residue of metallic silver and ammonium nitrate. It is soluble in water, but partial dissociation takes place so that the solution is alkaline in reaction, and it therefore yields a precipitate of silver chloride and soluble chlorides. Certain of the metals—for example, zinc, cadmium, and copper—quickly reduce the ammine in solution to metallic silver. 

Silver chloride is a common source and intermediate product in many extractive metallurgical processes, for example it occurs in the anode slimes from copper refineries, the residues of leaching processes for base metals, as a product of the chlorination of impure gold—silver bullion, and in photographic waste. A novel process for the leaching and purification of silver chloride, which was devised by Parker et a/.,26 is based on the observation that silver chloride is very soluble in some dipolar aprotic solvents containing chloride ion but is much less soluble when water is present. The very different behaviour of the equilibrium... 

The formation of mixed crystals results from limited solubility or insolubility of one solid metal in the other. Lead and tin and lead and antimony are examples of pairs of metals that form alloys consisting of intimate mixtures of tiny pure crystals of each metal. The formation of solid solutions results when the liquid metals are miscible in all proportions and are capable of solidification to compositions that are essentially the same as those of the melts. Many of the most common and useful alloys consist of homogeneous solid solutions of one metal in the other (e.g., alloys of copper and zinc, gold and silver, nickel and... 

The mutual solubilities of metals are not reciprocal. A metal of low valency is more likely to dissolve one of higher valency than vice versa. For example, in the solid solutions of copper and silicon, a silicon atom may replace four copper atoms in the copper lattice, but a copper atom, with only a single valency electron, cannot replace a silicon atom which is linked tetrahedrally with four other silicon atoms. Hence the solubility of silicon in copper is 14 per cent but that of copper in silicon only 2 per cent. In a similar way tin dissolves only I per cent of silver whereas silver can dissolve up to I2 2 per cent of tin. 

As a result of increasingly stringent environmental regulations, much attention has been devoted in recent years to the possibility that gold and silver can be leached by ligands other than cyanide. Other considerations, for example the presence of excessive quantities of soluble copper in the ore or the occurrence of gold in refractory (to cyanidation) minerals such as arsenopyrite or stibnite, have also prompted the search for alternatives to cyanide. Of the various possibilities, the one most studied and applied is the use of thiourea in acidic solutions with iron(III) as the oxidant. The principal leaching reaction is... 

The low acidity of 1-alkynes means that strong bases must be used to form the alkynide ions and that water is not a suitable solvent aqueous solutions have a very low concentration of alkynide ions. Some transition metal alkynides can be prepared by precipitation from aqueous solution because their solubilities are very low. Suitable solvents for the preparation of alkynide ions must be less acidic than the alkyne, and preferably allow the alkyne and the alkynide ion to remain in solution. Liquid ammonia, te-trahydrofuran, ether and hydrocarbons have all been used, particularly the first, the alkynide anion being readily formed by metal amides. Alkynides of many types have been prepared from various metals. Besides Groups I and III, copper(I), silver, gold(I), zinc, mercury and, more recently, aluminum alkynides have been synthesized. The alkynides of Groups I and II have been principally used as nucleophiles in alkylation reactions, but there are now many examples of other metal alkynides in this role. Palladium-catalyzed reactions, as remarked above, have become increasingly important for the reactions of alkynides of metals other than Groups I and II, but these have not usually involved alkylation. 

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