Facts about silver
Silver is the shiny white, lustrous transition metal of Group 11 or IB in the periodic table with atomic number 47 and symbol Ag. It is used from the ancient age to jewelry and coinage due to its decorative beauty. The name silver comes from Assyrian serpu or Gothic silbur meaning white and from Latin name, Argentum means shiny white (Greek latter Argos). It forms an FCC crystal lattice with characteristic silvery-white colour.
Properties of silver
Chemically, silver metal is a quite unreactive element with a good conductor of electricity. In learning chemistry, it dissolved in water to the extent of 0.07 mg liter-1 in presence of dissolved oxygen. It is attacked by atmospheric sulfur compounds, mainly hydrogen sulfide (H2S). Some properties of the element are maintained below the table.
|Properties of Silver|
|Electronic Configuration||[Kr] 4d10 5S1|
|Melting point||961.8 °C or 1763.2 °F|
|Boiling point||2162 °C or 3924 °F|
|Ionization energy||1st – 731.0 kJ/mol
2nd – 2070 kJ/mol
3rd – 3361 kJ/mol
|Electrical resistivity||15.87 nΩ·m|
Silver in periodic table
It is placed on group 11 in the periodic table with d-block elements. The atomic states of copper, silver, and gold or noble metal contain ns1 (n-1)d10 outer electron configuration or filled d-subshell. They considered transition metals because, in +2 or +3 oxidation number or state, they possess incompletely filled d-orbital.
Where is silver found?
The relative occurrence of metal in earth crust 0.08 ppm while that of gold 0.004 ppm. It is widely distributed in nature as sulfide ore like silver glance or argentite (Ag2S). Horn silver (AgCl) is found in some minerals in Chile and New South Wales formed by the action of salt water. It is now largely discovered as a byproduct in the extraction of copper and lead. Siver is produced mainly by countries like United States, Canada, Peru, Mexico, Bolivia, and New South Wales. In India, it is obtained from Kolar gold mines produces from the smelting of Zawar lead ores.
Production of silver
Mostly silver was obtained as a byproduct for the production of copper, lead, and zinc by collecting anode slime or mud. The anode slime or mud is heated with dilute sulfuric acid in a stream of air to dissolve some metals. The remaining anode slug was heated with lime and silica to remove most of the base metal as a slug. Finally, Ag-containing materials are dissolved in dilute nitric acid. Electrolysis of AgNO3 solution gives a pure form of silver metal at the cathode.
Extraction of silver from ore
It is extracted from its important ores by leaching the finely powdered of ore with dilute (0.4 percent) sodium cyanide solution. The sludge is ignited well with air. The Na2S oxidized by aeration, otherwise, it would tend to reverse reaction. The sludge is removed by filtration and the filtrate silver is precipitated by zinc or aluminum. The precipitate is washed and melted with a flux of nitrate to remove the excess of zinc.
The physical and chemical properties of silver are similar to the two vertical neighbors copper and gold of the periodic table. The higher effective nuclear charge or ionic potential and large shielding electron suggest that the covalent bonding of Ag and Au compounds are stable in +1 and +2 states. The +1 state is the most common oxidation state of silver which offering oxides, sulfide, halides, and a number of oxoacids salts. The salts are primarily ionic and quite soluble in water but Ag2SO4 and CH3COOAg are sparingly soluble in water. The halide (except AgF) is formed by covalent chemical bonding.
Oxidation state of silver
The +1 oxidation state of silver is most common and stable. The first ionization energy is lowest for Ag, the sum of the first and second ionization is lowest for Cu, and the sum of first, second, and third ionization energy is lowest for Au atoms. The fact reflects that Ag chemistry predominant in the +1 oxidation state but copper and gold chemistry predominates in the +2 and +3 oxidation state.
The facts also describe by hydration energy. The hydration energy of the copper (II) ion is much higher than the copper (I) ion which overcomes the second ionization of Cu in an aqueous medium. Due to higher ionic radii of Ag, the hydration energy cannot stabilize Ag (II) ion over Ag (I). For gold atoms, atomization, ionization, and hydration energy favor the formation of Au (III) in an aqueous medium.
The dark brown silver oxide (formula Ag2O) is obtained by adding alkali to an aqueous Ag+ ion. It is more soluble in alkali than pure water owing to the formation of Ag(OH)2–. Ag2O dissolve in ammonia to produce [Ag(NH3)2]OH. When the solution exposure to air, it deposits the black explosive silver nitride (Ag3N). It is called fulminating silver. Moist Ag2O is used as a mild oxidizing agent for organic compounds. A black oxide like AgO is formed by oxidation of Ag2O ozone molecule or by electrolysis 2M AgNO3 solution.
Silver (II) compounds
Ag(II) compounds are obtained by direct oxidation or disproportionate of chemical element which is extremely unfavorable due to low heat of hydration of Ag+2 ion. AgF2 is the only known silver halide obtained by the action of fluorine on AgF or Ag at 250 °C temperature uses as a fluorinating agent.
Silver (III) compounds
Compounds of Ag(III) are very few, Ag2O3, Ag(OH)4–, KAgF4 or Cs2KAgF6 are the common examples of the +3 oxidation state of silver. The formal oxidation number +1/2 is present in the yellow green solid Ag2F.
Uses of Silver
- Silver and its compounds are widely used in photography, in silvering mirrors or plates, in silverware, jewelry, dentistry, and coins. It is also used in high-capacity electrical cells (Ag-Zn, Ag-Cd). Copper serves to increases the hardness of alloy to improve the wearing qualities.
- The photographic light sensitivity plate consists of an emulsion of fine-grain silver halides like bromide, chloride, or iodide (diameter <1 μm) on a transparent medium like glass or celluloid.
- The halide, usually AgBr with some amount of AgCl and organic dyes but AgI is used in very fast films. Organic dyes act as a photosensitizer to help light absorption over the entire visible band.
- Silver plating in chemistry is done at the cathode of the electrolytic cell. A piece of pure Ag element acts as anode with the electrolytic solution sodium dicyanoargentate, Na[Ag(CN)2].
Detection of silver ion
Silver salts in an aqueous solution produce a curdy white precipitate of AgCl with chlorine ion. The precipitate is insoluble in nitric acid but readily dissolved in aqueous ammonia. Ag+ also forms a red precipice (Ag2CrO4) with potassium dichromate solution which is insoluble in acetic acid. All the silver compounds produce a lustrous white malleable bed on heating with sodium carbonate on charcoal. The bead may be dissolved in nitric acid and tested with hydrogen chloride (HCl).
In learning chemistry or chemical science, silver may be estimated gravimetrically as chloride or by electrodeposition (coulometer), volumetrically. In Mohrs’s method, a known volume of standard sodium chloride solution triturated with AgNO3 solution using potassium chromate as an indicator. In Volhard’s method, the silver nitrate (AgNO3) is triturated by standard potassium or ammonium thiocyanate using ferric alum as an indicator. The Ag+ ion forms a white precipitate of AgSCN but when the concentration falls below the solubility, the blood-red color of thiocyanate ions produce with ferric ion.