Silver is a noble metal since it is a rare and precious metal. In addition, it does not react or get oxidized easily. It can be found in very minute amounts that does not exceed 0.05 parts per million in the earth. For example, 20 million shovels of dirt should be collected to obtain only one shovel full of silver. Long ago, silver was more valuable than gold owing to the facile location and refining of gold at that time. However, nowadays, silver is ten times more abundant and consequently cheaper than gold.
Abundance of Silver in Nature: Silver occurs naturally in a pure as well as combined forms in ores. Some of the important silver ores include Argentite (Ag2S), Copper silver glance, Horn silver, and Ruby silver. Silver ores can be found accompanied with gold ores. Argentite ores are considered as the most abundant ones.
Extraction of Silver from Argentite Ores: Silver is extracted from Argentite (Ag2S) via cyanide extraction process using sodium cyanide solution. The ore is obtained and crushed then treated with sodium cyanide solution. Reaction of the ore and cyanide solution results in formation of sodium argento cyanide as shown in the following equation:
Ag2S + 4NaCN ⇌ 2 Na [Ag (CN)2] + Na2S
Afterwards, sodium argento cyanide solution reacts with zinc forming sodium tetra cyanozicate and precipitated silver.
Zn + 2Na[Ag(CN)2] → Na2[Zn(CN)4] + 2Ag↓
The obtained silver is purified by its fusion with potassium nitrate, then the silver is extra purified again through some electrolytic processes.
Properties and Uses of Silver: Mixed silver and mercury are used in some preparations in dental applications owing to antibacterial activity. Since, silver is a good conductor, it can be used in electroplating as well as manufacturing of batteries and catalysts.
Pure silver is too soft to manufacture jewelry and utensils. Therefore, it is usually alloyed with at least one more metal. For instance, sterling silver consists of about 93% silver and 7% other metals.
Silver Salts: Silver nitrate is one of the most commonly available and used silver salts. Silver nitrate is an inorganic compound with a chemical formula of AgNO3. Silver nitrate was once called lunar caustic since silver was called luna by the ancient alchemists who believed that silver was associated with the moon. Silver nitrate was first discovered and prepared by Albertus Magnus.
Preparation of Silver Salts: Silver nitrate is prepared by adding dilute or concentrated nitric acid to silver as they react together resulting in formation of silver nitrate, water and nitrogen oxides as shown in the following reaction. The reaction should be carried out in a fume hood to keep away the toxic nitrogen oxides gases.
3 Ag + 4 HNO3(dil) → 3 AgNO3 + 2 H2O + NO
Ag + 2 HNO3(conc) → AgNO3 + 2 H2O + NO
Properties and Uses of Silver Nitrate:
- Silver nitrate is a white crystalline salt that is freely soluble in hot water forming colorless aqueous solutions.
- Silver nitrate has antiseptic and antimicrobial activities therefore it is used in some medical applications such as dental preparations, healing ulcers and microbial disinfectants.
- Silver nitrate solutions can stain some biological specimens, so it is used to investigate reticular fibers, proteins and nucleic acids.
- Silver nitrate has been used long ago in photography, then recently has been used in radiography.