Silver metallic

Yttrium has a silver-metallic luster and is relatively stable in air. Turnings of the metal, however, ignite in air if their temperature exceeds 400oC. Finely divided yttrium is very unstable in air. 

These salts are corrosive and are to be considered toxic because of the presence of Ag+ ions. The American Conference of Government Industrial Hygienists (ACGIH) (1992—1993) has adopted TWA values of 0.01 mg/m for silver metal and 0.01 mg/m for soluble silver salts. TWA for fluorides as F ions is 2.5 mg/m. The MSDS should be consulted prior to use. Skin contact and inhalation should be avoided. 

Miscellaneous. Electron beams can be used to decompose a gas such as silver chloride and simultaneously deposit silver metal. An older technique is the thermal decomposition of volatile and extremely toxic gases such as nickel carbonyl [13463-39-3] Ni(CO)4, to form dense deposits or dendritic coatings by modification of coating parameters. 

Fig. 13. Single-sheet diffusion transfer plate (a) stmcture (b) upon exposure to light (c) development and (d) washing off and finish. In (a) the plate is first coated with a receiver layer of small (<5 nm) catalytic sites. The photographic layer is a spectrally sensitized silver haUde emulsion. In (c) the exposed areas develop as silver metal. Unexposed areas diffuse down to the receiver layer and form the printing image. In (d) the emulsion is washed off, revealing...

Silver, a white, lustrous metal, slightly less malleable and ductile than gold (see Gold and gold compounds), has high thermal and electrical conductivity (see SiLVERAND SILVER alloys). Most silver compounds are made from silver nitrate [7761-88-8], AgNO, which is prepared from silver metal. 

In the absence of organic matter, silver nitrate is not photosensitive. It is easily reduced to silver metal by glucose, tartaric acid, formaldehyde, hydrazine, and sodium borohydride. 

Silver sulfate decomposes above 1085°C into silver, sulfur dioxide, and oxygen. This property is utilized ia the separation of silver from sulfide ores by direct oxidation. Silver sulfate is reduced to silver metal by hydrogen, carbon, carbon monoxide, zinc, and copper. 

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). 

Because of increasing environmental concerns, the disposal of all batteries is being reviewed (70—76). Traditionally silver batteries were reclaimed for the silver metal and all other alkaline batteries were disposed of in landfills or incinerators. Some aircraft and industrial nickel —cadmium batteries are rebuilt to utilize the valuable components. 

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. 

Thin films of photochromic silver complex oxides were prepared by anodic oxidation of silver metal films (15). Complex oxides, such as Ag2V04, Ag SiO, and Ag2P04, darkened by exposure to visible light, but required heating to 150—250°C for thermal bleaching. 

Fig. 9. Corrosion model of silver development. As the haUde ion, X, is removed into solution at the etch pit, the silver ion,, travels interstitiaHy, Ag/ to the site of the latent image where it is converted to silver metal by reaction with the color developer, Dev. Dev represents oxidized developer.

Silver nitrate is astringent and a protein precipitant, which is not medically desirable. Other forms of silver have been used to avoid this problem, including coUoidal silver, silver-protein preparations, and finely divided silver metal called Katadyn silver. 

A copper strip with a mass of 2.00 g is dipped into a solution of AgN03. After some time has elapsed, the copper strip is coated with silver. The strip is removed from the solution, dried, and weighed. The coated strip has a mass of 4.18 g. What are the masses of copper and silver metals in tile strip (Hint Remember that the copper metal is being used up as silver metal forms.)... 

Listing the Zn-Zn+2 half-reaction first tells us that it releases electrons more readily than does the Cu-Cu+2 half-reaction. But if this is true, then the Zn-Zn+2 half-reaction must also release electrons more readily than does the Ag-Ag+ half-reaction. Our list leads us to expect that zinc metal will release electrons to silver ion, reacting to produce zinc ion and silver metal. 

The Cu+2 ion drifts away into the solution but the electrons remain in the copper rod. They move up through the copper anode, through the wire, and enter the silver cathode. At the surface of this rod, the electrons encounter Ag ions in the solution. The electrons react with Ag+ ions to give neutral silver atoms which remain on the rod as silver metal ... 

Our conclusions are again in agreement with experiment. The cell operates so as to dissolve zinc metal and precipitate silver metal. The voltage is indeed about 1.5 volts. Finally, experiment shows that one mole of zinc does react with two moles of silver ion, as required by the balance of electrons. 

This will not always be the case, however. Consider the question Will silver metal dissolve in 1 M H+ According to Table 12-11,... 

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. 

How many grams of silver metal will react with 2.0 liters of 6.0 M HNO3 The reaction is... 

---