Silver Uses || Properties of Silver || Role in Living Organisms

Silver (Argentum), a kind of transition metal. Chemical symbol Ag. Silver is one of the metals known and used in ancient times, and it is an important precious metal. Silver exists in nature as a simple substance, but most of it exists in silver ore in the form of a compound. 

Silver element

The physical and chemical properties of silver are relatively stable, with good thermal and electrical properties, softness and rich ductility. Its reflectivity is extremely high, reaching over 99%. There are many important uses.

The production of silver as a main raw material 12 species: 

  • NATURAL silver (Ag), 
  • Ag – Au (AgAu), 
  • Argentite (Ag2S), 
  • Magenta silver (Ag 3 the SbS . 3 ), 
  • Pink silver (Ag3AsS3 ), 
  • Angular silver ore (AgCl), 
  • Brittle silver ore (Ag2SbS3), 
  • Antimony silver ore (Ag3Sb), 
  • Selenium silver ore (Ag3Se), 
  • Tellurium silver ore (Ag2Te),
  • Zinc antimony fanghui silver (5Ag2Sb2S3), 
  • Sulfur antimony copper-silver ore (8 [AgCu] SSb2S3).

Name Origin

The chemical symbol Ag for silver, derived from the Latin name Argentum for silver, means “light and bright“.

Silver characters belong to the Gen word family. In the Gen character family, Gen characters are all vowels and synonyms. The Chinese characters of the Gen character family are all related to the meanings of “boundary” and “limit”. The original meaning of silver is “metal (value) close to gold.” 

Physical properties

Silver is a white shiny metal, and its atomic structure is a face-centered cubic structure

Melting point 961.93 ℃
Boiling point 2212 ℃
Heat of vaporization 250.58 kJ / mol
Heat of fusion 11.3 kJ / mol
Speed ​​of sound 2600 m / s (293.15K)
Resistivity 1.586 × 10⁻⁸ Ω · m (20 ℃)
Electronegativity 1.93 ( Bowling scale )
Specific heat capacity 232 J / (kg · K)
Conductivity 63 × 10⁶ / (meter ohm)
Thermal conductivity 429 W / (m · K)

Chemical properties

Chemical properties of silver

It was dissolved in silver nitrate to produce silver nitrate .

Ag + 2HNO3 (concentrated) = AgNO3 + H2O + NO2 ↑

3Ag + 4HNO3 (lean) = 3AgNO3 + 2H2O + NO ↑

Silver is not easy to react with sulfuric acid, so sulfuric acid can be used to clean copper oxide fire marks left after silver welding and annealing in jewelry manufacturing. Silver easily reacts with sulfur and hydrogen sulfide to produce black silver sulfide, which is common on tarnished silver coins or other items.

Silver can react with oxygen at high temperatures to produce brown-black silver oxide (it can also react at normal temperature, but the speed is very slow). 

In the presence of potassium bromide (KBr), metallic silver can be attacked by strong oxidants such as potassium permanganate or potassium dichromate, these compounds are used in photography to bleach visible images and convert them to silver halide, which can be used both The sodium thiosulfate is removed and re-developed to enhance the original image.

Reacts with hydrogen sulfide and oxygen

4Ag + 2H2 S + O2 ==== 2Ag2 S + 2H2O (Principle of silver deterioration and blackening at room temperature)

React with concentrated sulfuric acid

2Ag + 2H2SO4 (concentrated) ==== Ag2SO4 + SO2 ↑ + 2H2O

Reacts with sulfur

2Ag + S ==== Ag2S (mix and react)

React with oxygen

4Ag + O2 ==== 2Ag2O (heated to 1000 degrees Celsius in pure oxygen and reacts obviously, the reaction is very slow in air at room temperature)

React with halogen acid

1. Does not react with hydrofluoric acid

2. reaction with concentrated hydrochloric acid:

2Ag + 4HCl (conc.) = 2 [AgCl2] + H2 ↑, heating conditions, a high concentration of silver chloride can be generated dichloride complex of silver ion complexions (AgCl2 ) However, because the coordination ions are not stable enough and the driving force for the reaction is not great, it is very difficult to carry out the reaction.

3. Reaction with concentrated hydroiodic acid: Because the solubility of the generated silver iodide is extremely small, the electrode potential of silver decreases, so the reaction can proceed spontaneously. If HI is excessive, a more stable [AgI2-] complexion will be formed, which is more conducive to the spontaneous reaction.

Chemical equation: 2Ag + 2HCI (concentrated) = 2AgCl + H2 ↑

2Ag + 4HCI (concentrated) = 2H [AgCI2] + H2 ↑

The principle of silver needle test

In ancient times, arsenic was often used as a poison, and due to technical limitations, arsenic was mixed with a large amount of sulfur or sulfide. Silver will react with sulfur to form a black silver sulfide precipitate, which will test the poison.  It  can be seen that the silver needle test only detected sulfur in arsenic, and for today’s countless kinds of poisons, the silver needle test is powerless.

Chemical properties of silver compounds

Adding chloride ions to the silver nitrate solution will precipitate silver chloride (AgCl). Silver chloride is insoluble in water and does not dissolve in dilute nitric acid, so silver nitrate solutions are often used to check for the presence of chloride ions. Similarly, the addition of bromine or iodide can precipitate other silver halides used in the manufacture of photosensitive emulsions. 

Silver chloride is used to make glass electrodes for detecting pH and measuring potential, as well as transparent cement for glass. The silver iodide (AgI) can be thrown into the clouds artificial rainfall. Silver halide is highly insoluble in water (except silver fluoride) and is often used for gravimetric analysis.

A base was added to the silver nitrate solution and precipitated to obtain silver oxide . Silver oxide is used as the positive electrode of a coin cell. Sodium carbonate (Na2CO3) was added to the silver nitrate solution, and silver carbonate (Ag2CO3) was precipitated.

Reaction ion equation with alkaline solution:

2AgNO3 + 2OH = of Ag2O + H2O + 2NO3

Reaction equation with sodium carbonate:

2AgNO3 + Na2 FCO3 = Ag2CO3 ↓ + 2NaNO3

Silver arsenate is a strong, collision-sensitive explosive that is obtained by reacting silver with nitric acid in the presence of ethanol and is used in detonators.

 Other dangerous and explosive silver compounds include silver azide, obtained by reacting silver nitrate with sodium azide, and silver acetylene, obtained by reacting silver nitrate or silver ammonia solution with acetylene.

The latent image formed after the silver halide crystals are exposed to a developing agent, such as hydroquinone, metol or ascorbic acid, is subjected to a development treatment, and the exposed silver halide is reduced to metallic silver. 

The alkaline solution of silver nitrate (silver ammonia solution) can be reduced to metallic silver by reducing sugars such as glucose. This reaction is used to make silver mirrors and the inner surface of glass Christmas ornaments. 

Silver halide is soluble in sodium thiosulfate solution, so sodium thiosulfate can be used as a fixer to remove excess silver halide on the photosensitive emulsion after development.

An excess of cyanide ion (the CN) in the presence of silver cyanide (AgCN) may form a water-soluble silver cyanide. A silver cyanide complex solution is used for silver plating.

Metal activity sequence

Silver is less mobile than hydrogen, so in general it cannot react with dilute acids to displace hydrogen.

However, it can be replaced with hydrochloric acid when energized.

2Ag + 2HCl == Power on == 2AgCl + H2 ↑

Its mobility is weaker than copper (Cu) and mercury (Hg), and stronger than platinum (Pt) and gold (Au).

Silver Isotope

The silver in nature is silver 107 and silver 109, of which silver 107 is the most abundant (51.839%). The abundance of two isotopes of silver is almost the same, which is very rare in the periodic table. There are 28 isotopes of silver (from silver 93 to silver 130). The half-lives of most isotopes are less than three minutes.

Application range

Sterling silver application

Sterling silver is a beautiful silver-white metal, it has good ductility, and its electrical and thermal conductivity.

It is the highest of all metals. Silver is often used to make highly sensitive physical instrument components, various automation devices, rockets, submarines, computers, nuclear devices, and communication systems. A large number of contact points in all these devices are made of silver.

During use, each contact point must work millions of times, must be wear-resistant and reliable, can withstand strict working requirements, and silver can fully meet various requirements. If rare earth elements are added to silver, the performance is even better. The contact points made with this rare earth- added silver can extend their life several times.

The most important compound of silver is silver nitrate. In medicine, an aqueous solution of silver nitrate is commonly used as eye drops.

Electronic and electrical materials

Electronic appliances are the industries that use the largest amount of silver, and their use is divided into electrical contact materials, composite materials and welding materials. 

Silver and silver-based electrical contact materials can be divided into: pure silver, silver alloy, silver-oxide, and sintered alloy. The annual output of silver and silver-based electrical contact materials around the world is about 2900-3000 tons.

Composite materials are materials prepared using composite technology and are divided into silver alloy composite materials and silver-based composite materials. From the point of view of silver-saving technology, silver composite materials are a promising new material. Silver soldering materials such as pure silver solder, silver-copper solder, and the like.

Photosensitive material

The silver halide photosensitive material is one of the fields with the largest amount of silver. The most sensitive materials produced and sold are photographic film, photo paper, X-ray film, fluorescent information recording film, electron microscope photographic film, and printing film. In the 1990s, the world’s photographic industry used about 6,000 to 6,500 tons of silver.

Due to the development of electronic imaging and digital imaging technology, the amount of silver halide photosensitive material has been reduced, but the application of silver halide photosensitive material is still irreplaceable in some aspects, and there is still a large market space.

Chemical materials

Silver has two main applications in this regard. One is as a catalyst, such as widely used in redox reactions and polymerization reactions , and used to treat industrial waste gases containing sulfides. The second is the preparation of electronic plating industry, such as silver paste , silver potassium cyanide and so on.

Craft jewelry

Silver has an attractive white luster, high chemical stability and collectible ornamental value. It is deeply favored by people, so it has the reputation of “woman’s metal” and is widely used as jewelry, ornaments, silverware, tableware, and congratulation Gifts, medals and coins. 

Silver jewelry has a vast market in developing countries, and silver meals are popular with families. Silver commemorative coins are exquisitely designed, have a small circulation, and have the function of preserving and increasing value.

They are popular among coin collectors and coin investors. In the 1990s, only coinage silver remained at around 1000-1500t per year, accounting for about 5% of silver consumption.

Role in organisms

Silver ions and compounds are toxic to certain bacteria, viruses, algae and fungi, but are almost completely harmless to the human body.

This bactericidal effect allows it to kill organisms in vitro. However, the testing and standardization of silver products is difficult.

Hippocrates once described the utility of silver in the treatment and prevention of disease. The Phoenicians used silver bottles to hold water, wine, and vinegar to prevent these liquids from spoiling. In the early 20th century, people also put silver coins in milk to extend the shelf life of milk. 

The bactericidal mechanism of silver has been debated for a long time, but there is no firm conclusion so far. One good example is the microdynamic effect, which successfully explained the effect of silver ions on microorganisms, but could not explain its effect on viruses.

A large amount of silver is added to gels and bandages. The antibacterial properties of silver are derived from silver ions. Because silver ions can form strong binding bonds with some microorganisms’ substances used for breathing (such as some molecules containing oxygen, sulfur, and nitrogen elements), these substances cannot be used by microorganisms, which can cause them to suffocate and die.

Prior to the invention of antibiotics, silver-related compounds were used to prevent infection during World War I.

New applications of silver as a broadly effective antibacterial agent are underway. One aspect is to dissolve silver nitrate in alginate to prevent wound infections, especially burn wound infections. In 2007, a company designed a silver-coated glass that claims to have good antibacterial properties. 

In addition, the American Food and Drug Administration ( FDA ) has also approved the application of an inner silver-plated airway, because research shows that this airway can effectively reduce airway pneumonia.

Silver is not toxic to the human body, but long-term exposure to silver metals and non-toxic silver compounds can also cause silver deposits. Due to changes in body pigments, the skin surface appears grayish blue. Although not toxic, it still affects appearance.

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