Silver metallic state

Elemental sulfur in either its ore or its refined state can generaUy be recognized by its characteristic yeUow color or by the generation of sulfur dioxide when it is burned in air. Its presence in an elemental state or in a compound can be detected by heating the material with sodium carbonate and mbbing the fused product on a wet piece of silver metal. A black discoloration of the silver indicates the presence of sulfur. The test is quite sensitive. Several other methods for detecting smaU amounts of elemental sulfur have also been developed (34). 

The capability of zinc to reduce the ions of many metals to theh metallic state is the basis of important appHcations. However, metals are removed from zinc solutions by displacement with finely divided zinc before winning by electrolysis. Gold and silver are displaced from cyanide leach solutions with zinc and the following metals are similarly recovered from various solutions platinum group, cadmium, indium, thallium, and sometimes copper. 

The darkening reaction involves the formation of silver metal within the silver haUde particles containing traces of cuprous haUde. With the formation of metallic silver, cuprous ions are oxidized to cupric ions (1,4). The thermal or photochemical (optical bleaching) reversion to the colorless or bleached state corresponds to the reoxidation of silver to silver ion and the reduction of cupric ion to reform cuprous ion. 

The higher ionisation energy and smaller ionic radius of copper contribute to its forming oxides much less polar, less stable, and less basic than those of the alkah metals (13). Because of the relative instabiUty of its oxides, copper joins silver in occurring in nature in the metallic state. 

Chemical reduction is used extensively nowadays for the deposition of nickel or copper as the first stage in the electroplating of plastics. The most widely used plastic as a basis for electroplating is acrylonitrile-butadiene-styrene co-polymer (ABS). Immersion of the plastic in a chromic acid-sulphuric acid mixture causes the butadiene particles to be attacked and oxidised, whilst making the material hydrophilic at the same time. The activation process which follows is necessary to enable the subsequent electroless nickel or copper to be deposited, since this will only take place in the presence of certain catalytic metals (especially silver and palladium), which are adsorbed on to the surface of the plastic. The adsorbed metallic film is produced by a prior immersion in a stannous chloride solution, which reduces the palladium or silver ions to the metallic state. The solutions mostly employed are acid palladium chloride or ammoniacal silver nitrate. The etched plastic can also be immersed first in acidified palladium chloride and then in an alkylamine borane, which likewise form metallic palladium catalytic nuclei. Colloidal copper catalysts are of some interest, as they are cheaper and are also claimed to promote better coverage of electroless copper. 

The negative voltage shows that the state of equilibrium favors the reactants more than the products for the reaction as written. For standard conditions, the reaction will not tend to occur spontaneously. However, if we place Ag(s) in 1 M H+, the Ag+ concentration is not 1 M— it is zero. By Le Chatelier s Principle, this increases the tendency to form products, in opposition to our prediction of no reaction. Some silver will dissolve, though only a minute amount because silver metal releases electrons so reluctantly compared with H2. It is such a small amount, in fact, that no silver chloride precipitate forms, even though silver chloride has a very low solubility. 

That some silver does dissolve to form Ag+ can be verified experimentally by adding a little KI to the solution. Silver iodide has an even lower solubility than does silver chloride. The experiment shows that the amount of silver that dissolves is sufficient to cause a visible precipitate of Agl but not of AgCl. This places the Ag+ ion concentration below 10-10 M but above 10-17 M. Either of these concentrations is so small that we can consider our prediction for the standard state to be applicable here too—silver metal does not dissolve appreciably in 1 M HC1. In general, the question of whether a prediction based upon the standard state will apply to other conditions depends upon how large is the magnitude of °. If ° for the overall reaction is only one- or two-tenths volt (either positive or negative), then deviations from standard conditions may invalidate predictions that do not take into account these deviations. 

Ag(I) and Cu(II) are readily used in neutral solution, although oxidations by Ag(I) are often affected by the deposition of silver metal. Theoretically Cu(II) can behave either as a two- or a one-equivalent reagent, but it usually functions as the latter. The tendency of Cu(I) to disproportionate is normally suppressed by working with solvents such as pyridine which form stable complexes with this oxidation state. 

Many carbonyl and carbonyl metallate complexes of the second and third row, in low oxidation states, are basic in nature and, for this reason, adequate intermediates for the formation of metal— metal bonds of a donor-acceptor nature. Furthermore, the structural similarity and isolobal relationship between the proton and group 11 cations has lead to the synthesis of a high number of cluster complexes with silver—metal bonds.1534"1535 Thus, silver(I) binds to ruthenium,15 1556 osmium,1557-1560 rhodium,1561,1562 iron,1563-1572 cobalt,1573 chromium, molybdenum, or tungsten,1574-1576 rhe-nium, niobium or tantalum, or nickel. Some examples are shown in Figure 17. 

Atomic hydrogen is a powerful reducing agent, even at room temperature. For example, it reacts with the oxides and chlorides of many metals, including silver, copper, lead, bismuth, and mercury, to produce the free metals. It reduces some salts, such as nitrates, nitrites, and cyanides of sodium and potassium, to the metallic state. It reacts with a number of elements, both metals and nonmetals, to yield hydrides such as NH3, NaH, KH, and PH3. Sulfur forms a number of hydrides the simplest is H2S. Combining with oxygen, atomic... 

Fig. 3-4. Energy for formation of gaseous silver ions in the standard state from siirface silver atoms of solid silver metal = unitary...

Sodium is a soft, wax-like silver metal that oxidizes in air. Its density is 0.9674 g/cm, and therefore it floats on water as it reacts with the water releasing hydrogen. It has a rather low melting point (97.6°C) and a boiling point of 883°C. Sodium is an excellent conductor of heat and electricity. It looks much like aluminum but is much softer and can be cut with a knife like butter. Its oxidation state is +1. 

Indium is a rather rare metal. It is the 69th most abundant element, which is about as abundant as silver at 0.05 ppm. Although it is widely spread over the Earths crust, it is found in very small concentrations and always combined with other metal ores. It is never found in its natural metallic state. 

MxtraeMon,—1. The silver minerals are roasted with sodio obloride, by which the metal is converted into chloride the mass is then mixed with water, scrap iron, and mercnry, ond ajptated for some hours. The iron reduces the argentic chloride to the metallic state, and the silver is then dissolved by the mercuiy. 

Fig. 2.9 Current pathways in a solid state cell the electrode consists of granular silver metal and solid electrolyte...

Macrocyclic tetraaza ligand complexes of silver have been found for oxidation states +1, +2 and +3. In the presence of water, the silver(I) complexes generally disproportionate to silver(II) depositing silver metal. Some of the silver(II) species obtained have been oxidized, both chemically (N0C104-H20 in acetonitrile) and electrochemically, to silver(III) complexes of substantial stability.496... 

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