Inorganic Chemistry: Silver Report

Outline

Since the ancient world Silver has been known to be used and has a lot of benefits. Research in Asian countries recommends that several people were extracting silver from lead as long ago as several 3000 B.C.E before. Similar to gold, it is a very precious metal and has several uses, mostly liked for its beauty and usefulness.

Silver’s atomic number is 47, and it mostly exists on the Earth as the mineral native silver. In Latin word is called Argentum and the chemical symbol is Ag. Silver has a white color when untarnished, with a bright and metallic luster. Silver can react with several other compounds and exist on Earth in form of a compound (combined with several different elements to form a variety of minerals and ores). It also exists in minute amounts in traces in ores of gold, copper, and lead.

“As a mineral, silver crystallizes in the cubic (isometric) system. In rare cases, it forms crystals. Usually, it is found in thin sheets or as long wires and bundles of wires. Silver is rather soft at 2 to 3 on Mohs’ hardness scale. Like gold, it is malleable which means it can be hammered into thin sheets. It is also ductile, meaning it can be drawn into wire.” (Draggon, 2008).

Hydrolysis products (hydroxide complexes)

Ag exists in hydroxide state AgoH. IN acidic media cation and anions exchange ions and shift the coefficient. In different PH and alkaline concentrations, Ag is a strong ion exchanger, as in lower pH the coefficient distribution increases if the pH is also increased with the slope of +1. When further pH is increased the distribution coefficient decreases. It also decreases with a lower concentration of Ag.

What binary oxides and halides are known to exist for Silver and which of these are likely to be found in Nature?

Complexes like AgHL²⁺ and AgH₂L₂³⁺ are formed. In solution which is alkaline, the AgL⁺, Ag₂L₂²⁺, and AgL₂⁺ complexes and their relative amounts of the complexes in the solution depending on the concentrations of the metal and ligand (L). It also depends on the ratio of these concentrations. The AgOH and Ag(OH)L complexes are the main products at the highest pH tested. In some other solutions tested the formation of the AgHL₂²⁺, Ag₂HL₂³⁺, and Ag₂L²⁺ complexes are formed, and their formation and concentration at which they are formed are uncertain. The formation complexes concentration varies depending upon the constants of the solution. At different pH range tested, the AgHL²⁺, AgH₂L₂³⁺, AgL⁺, and Ag₂L₂²⁺ complexes are most abundant and predominant in all the systems (Ohtaki and Cho, 2007).

Silver oxide can combine with silver nitrate and alkali hydroxide.

2 AgOH → Ag₂O + H₂O (pK = 2.875^[3])

However, this reaction does not produce considerable amounts of silver hydroxide Ag₂O is a binary oxide and a three-dimensional polymer. It has a covalent metal-oxygen bonding hence it is (Ag₂O) insoluble in all solvents. However, there is one except for this and it is soluble by the reaction. One more property of silver is that it gets slightly soluble in an aqueous solution because it forms ions, Ag(OH)₂^– and some other related hydrolysis products. Ag hydrolyzes in water only slightly (1 part per 40,000) and gets dissolved in AH(OH) solution [ammonium hydroxide] to form soluble derivatives.

Binary oxides of Silver Ag₂O when exposed to acid solution it is immediately attacked by acids

Ag₂O + 2 HX → 2 AgX + H₂O

HX = HF, HCl, HBr, or HI, HO₂CCF₃.

Solution of binary oxide also reacts with alkaline chloride solution to form a precipitate of silver chloride (NaCl), separating a solution of the by-products formed alkali hydroxide. Binary oxide decomposes at high temperatures and is also photosensitive.

What are the common minerals of Silver in Nature?

Silver’s largest reserves are in the USA, Canada, Peru, Mexico, and CIS. It is mostly mined in approximately 56 countries. Due to its high conductivity its uses are in chemistry, photography, and electronics. It is a precious metal and is used in making jewelry and alloy. It is used in mining equipment, vats, chemical reaction vessels, and water distillation. Used as currency.

“Ag(CN)₂^– is reduced at a low rate by radiolytically generated hydroxymethyl radicals. The reduction occurs on tiny nuclei in the solution formed by hydrolysis. When colloidal silver seed particles are present in the solution, the reduction of Ag(CN)₂^– is much faster, and larger silver particles with a narrow size distribution are produced. A mechanism is proposed, in which the ^•CH₂OH radicals transfer electrons to the seed particles, and the stored electrons finally reduce Ag(CN)₂^– directly on the surface of the seeds. The limitations of this kind of radiolytic particle enlargement are discussed. In the presence of colloidal platinum, Ag(CN)₂^–is also rapidly reduced by the organic radicals. Bimetallic particles of the Pt_coreAg_shell type with a rather nonsymmetric shape of the shell are formed; despite this irregular structure, the optical spectra agree fairly well with literature spectra calculated for symmetric bimetallic particles.” (Henglein, 2001)

References

1. Hitoshi Ohtaki and Kenji Cho. (2007) Complex Formation of Silver(I) Ion with Some Aliphatic Diamines
2. Henglein, A. (2001) Reduction of Ag(CN)₂^– on Silver and Platinum Colloidal Nanoparticles. Langmuir, 2001, 17 (8), pp 2329–2333. Web.
3. Draggon, S (2008). Silver. The Encyclopedia of Earth.