Argentum, a type of transition metal. Chemical symbol Ag. Silver is one of the metals known and used in ancient times and is an important precious metal. Silver Uses
Silver has a simple substance in nature, but most of it exists in the form of a chemical form in silver ore.
The physical and chemical properties of silver are relatively stable, with good thermal conductivity and electrical conductivity, soft texture and rich ductility. Its reflectivity is extremely high, reaching more than 99%. There are many important uses.
The silver chemical symbol Ag, derived from the Latin name of the silver, Argentum, means “light, bright.”
Silver is a white shiny metal, and the atomic structure is a face-centered cubic structure.
|Melting point||961.93 ° C|
|Boiling point||2212 ° C|
|Relative density (water = 1)||10.49|
|Heat of vaporization||250.58 kJ/mol|
|Heat of fusion||11.3 kJ/mol|
|Vapor Pressure||0.34 Pa (1234K)|
|Sound speed||2600 m/s (293.15K)|
|Resistivity||1.586×10−8 Ω·m (20°C)|
|Electronegativity||1.93 ( Pauling scale )|
|Specific heat capacity||232 J/(kg·K)|
|Thermal conductivity||429 W/(m·K)|
Chemical properties of silver
It was dissolved in silver nitrate to produce silver nitrate.
Ag+2HNO 3 (concentrated) = AgNO 3 + H 2 O + NO 2 ↑
3Ag+4HNO 3 (lean) = 3AgNO 3 +2H 2 O+NO↑
Silver is not easily reacted with sulfuric acid, so sulfuric acid can be used in jewelry manufacturing to clean silver oxide and copper oxide fire marks left after annealing.
Silver easily reacts with sulfur and hydrogen sulfide to form black silver sulfide, which is common on tarnished silver coins or other items. Silver reacts with oxygen at high temperatures to form brown-black silver oxide (which can react at room temperature but at a very slow rate).
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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 into silver halide, which can be the sodium thiosulfate is removed and redeveloped to enhance the original image.
Reacts with hydrogen sulfide and oxygen
4Ag +2H2S+O2 ==== 2Ag2S + 2H2O
(the principle of blackening and blackening at normal temperature)
Reaction with concentrated sulfuric acid
2Ag + 2H2SO4 (concentrated) ==== Ag2SO4 + SO2 ↑ + 2H2O
Reaction with sulfur
2Ag + S ==== Ag2S (mixed to react)
React with oxygen
4Ag + O2 ==== 2Ag2O
(increased reaction in pure oxygen to 1000 ° C, a very slow reaction in the air at normal temperature)
Reacting with Hydrohalic acid
- Does not react with hydrofluoric acid
- Reaction with concentrated hydrochloric acid: 2Ag + 4HCl (concentrated) = 2 [AgCl 2] + H 2↑, under the condition of heating, silver can be complexed with a high concentration of chloride ions to form silver dichloride complex ions AgCl 2 –However, since the counterion is not stable enough, the reaction driving force is not so large, so the reaction is very difficult.
- Reaction with concentrated hydriodic acid: Since the generated silver iodide has a very small solubility and the electrode potential of silver is lowered, the reaction can proceed spontaneously. If the HI is excessive, a relatively stable [AgI2-] complex ion is formed, which is more favorable for the reaction to proceed spontaneously.
2Ag+2HCI (concentration) = 2AgCl+H 2 ↑
2Ag+4HCI (concentrated) = 2H[AgCI 2 ]+H 2 ↑
The principle of silver needle test
In ancient times, arsenic was often used as a poison, and due to technical limitations, a large amount of sulfur or sulfide was mixed in the arsenic. The silver reacts with sulfur to form a black silver sulfide precipitate, which is tested for toxicity.
It can be seen that the silver needle test only detects the sulfur in the arsenic, and for the numerous poisons of today, the silver needle can’t do anything to test the poison.
Chemical properties of silver compounds
The addition of chloride ions to the silver nitrate solution precipitates silver chloride (AgCl), which is insoluble in water and insoluble in dilute nitric acid. Therefore, the presence of chloride ions is often checked using a silver nitrate solution.
Similarly, the addition of a bromide or iodide salt can precipitate other silver halides used in the manufacture of 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 halides are highly insoluble in aqueous solutions (except silver fluoride) and are therefore commonly used for gravimetric analysis.
A base is added to the silver nitrate solution to precipitate silver oxide. Silver oxide is used as the positive electrode of the button battery. Sodium carbonate (Na2CO3) was added to the silver nitrate solution to precipitate silver carbonate (Ag2CO3).
Reaction ion equation with the alkaline solution:
2AgNO3 + 2OH– = Ag2O + H2O + 2NO3–
Reaction equation with sodium carbonate:
2AgNO3 + Na2CO3 = Ag2CO3 ↓ + 2NaNO3
Silver sulfate is a strong, collision-sensitive explosive that is obtained by reacting silver with nitric acid in the presence of ethanol for use in detonators.
Other dangerous and explosive silver compounds include silver azide, which is obtained by reacting silver nitrate with sodium azide, and silver acetylide, which is obtained by reacting silver nitrate or silver ammonia solution with acetylene.
After the latent image formed by exposure of the silver halide crystal is developed by a reducing agent such as an alkaline solution of hydroquinone, meter or ascorbic acid, the exposed silver halide is reduced to metallic silver. Silver Uses
The alkaline solution of silver nitrate (silver ammonia solution) can be reduced to metallic silver by reducing sugars such as glucose, which is used to make silver mirrors, as well as the inner surface of glass Christmas ornaments.
The silver halide is soluble in the sodium thiosulfate solution, so sodium thiosulfate can be used as a fixer to remove excess silver halide on the developed emulsion.
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An excess of cyanide ion (CN) in the presence of silver cyanide (AgCN) may form water-soluble silver cyanide. A silver cyanide complex solution is used to electroplate silver.
Metal activity sequence
Silver is weaker than hydrogen, so in general, it cannot react with dilute acid to replace hydrogen.
However, it can be replaced with hydrochloric acid when it is energized.
Its activity is weaker than copper (Cu) and mercury (Hg), and stronger than platinum (Pt) and gold (Au).
Silver in nature is silver 107 and silver 109, with silver 107 having the most abundance (51.839%). The abundance of the two isotopes of silver is almost the same, which is very rare in the periodic table. There are 28 isotopes in silver (from silver 93 to silver 130). Most of the isotopes have a half-life of fewer than three minutes.
Application range (Silver Uses)
Sterling silver application
Sterling silver is a beautiful silver-white metal with good ductility, electrical conductivity, and thermal conductivity.
It is the highest of all metals. Silver is commonly used to make highly sensitive physical instrument components, automation devices, rockets, submarines, computers, nuclear devices, and communication systems, all of which have a large number of contact points made of silver.
During use, each contact point must work millions of times, must be wear-resistant and reliable, can withstand strict work requirements, and silver can fully meet various requirements. Silver Uses
If rare earth elements are added to silver, the performance is even better. With this kind of contact point made of silver with rare earth elements, the life can be extended several times.
The most important compound of silver is silver nitrate. In medical treatment, an aqueous solution of silver nitrate is commonly used as an eye drop.
Electronic and electrical materials
Electronic appliances are the industries with 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 classified into pure silver, silver alloys, silver-oxides, and sintered alloys.
The annual production of silver and silver-based electrical contact materials in the world is about 2,900 to 3,000 tons.
Composite materials are materials prepared by composite technology and are classified into silver alloy composites and silver-based composite materials.
From the perspective of silver-saving technology, silver composite materials are a new class of materials with great development prospects. Silver soldering materials such as pure silver solder, silver-copper solder, and the like.
Silver halide photographic materials are one of the areas with the largest amount of silver.
The most sensitive materials currently produced and sold are photographic film, photographic paper, X-ray film, fluorescent information recording film, electron microscope photographic film, and printed film.
In the 1990s, the amount of silver used in the world’s photographic industry was about 6,000 to 6,500 tons. 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 and chemical materials
Silver has two main applications in this regard. One is used as a catalyst, such as a wide range of redox reactions and polymerizations, for treating industrial waste gas containing sulfides. Silver Uses
The second is the electronic plating industrial preparations, such as silver paste, silver potassium cyanide and the like.
Silver has attractive white luster, high chemical stability, and collectible ornamental value, and is very popular among people. Therefore, it has the reputation of “woman’s metal” and is widely used as jewelry, decorations, silverware, tableware, and congratulations.
Gifts, medals and commemorative coins. Silver jewelry has a broad market in developing countries, and silver meals are popular with families.
The silver commemorative coins are beautifully designed, with a small circulation, and have the function of maintaining and increasing value. They are well received by coin collectors and coin investors. In the 1990s, only silver for coinage was kept at around 1000-1500 tons per year, accounting for about 5% of silver consumption.
Role in living organisms
Silver ions and compounds show toxicity to certain bacteria, viruses, algae, and fungi, but silvery are almost completely harmless to humans.
This bactericidal effect allows it to kill organisms in vitro. However, the testing and standardization of silver products are very difficult.
Hippocrates once described the role of silver in the treatment and prevention of disease. Phoenicians used silver bottles to hold water, wine, and vinegar to prevent the liquid from spoiling. Silver Uses
In the early 20th century, silver coins were also placed in milk to extend the shelf life of milk. The sterilization mechanism of silver has been debated for a long time, but there is no conclusive conclusion yet.
A good example of this is the micro-dynamic effect, which successfully explains the effect of silver ions on microorganisms, but does not explain its effect on the virus.
A large amount of silver is added to the gel and the bandage. The antibacterial properties of silver are derived from silver ions. Because silver ions can form strong bonds with some microorganisms for breathing (such as some molecules containing oxygen, sulfur, nitrogen) so that these substances cannot be used by microorganisms so that the microorganisms suffocate.
Prior to the invention of antibiotics, silver related compounds were used to prevent infection during World War I.
Silver is being used as a new utility for a wide range of antimicrobial agents. One of them is to dissolve silver nitrate in alginate to prevent infection of wounds, especially burn wounds. In 2007, a company designed a glass-coated glass that was known to have good antibacterial properties. In addition, the US Food and Drug Administration ( FDA ) has approved the use of an inner layer of silver-plated airways, as studies have shown that such airways can effectively reduce airway pneumonia.
Silver does not cause toxicity to the human body, but long-term exposure to silver metal and non-toxic silver compounds can also cause silver stagnation. Because the body pigment changes, the skin surface will appear grayish-blue. Although not toxic, it still affects the appearance.
Treatment (Silver Uses)
Skin contact: Immediately remove contaminated clothing and rinse with plenty of running water for 20 to 30 minutes. Seek medical attention if you feel uncomfortable. Silver Uses
Eye contact: Immediately lift eyelids and rinse thoroughly with plenty of running water or saline for 10 to 15 minutes. Seek medical attention if you feel uncomfortable.
Inhalation: Remove quickly from the scene to fresh air. Keep the airway open. If breathing is difficult, give oxygen. Breathing, heartbeat stops, cardiopulmonary resuscitation immediately, seek medical advice.
Ingestion: Drinking water, no vomiting. Seek medical attention if you feel uncomfortable.
Hazardous combustion products: silver/silver oxide
Extinguishing methods: Use water spray, alcohol-resistant foam, dry powder or carbon dioxide to extinguish the fire.
Fire-fighting precautions and measures: Wear self-contained breathing apparatus for firefighting if necessary.
Leakage emergency measures
Emergency treatment: prevent the formation of dust. Prevent the inhalation of steam, aerosols or gases.
Operation and storage
Handling precautions: Provide suitable exhaust equipment in places where dust is generated. General fire protection measures. Silver Uses
Storage Precautions: Store in a cool place. Keep container tightly closed and store in a dry, well-ventilated place. Sensitive to the air.
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Respiratory protection: no need to protect your breathing.
Eye protection: Wear chemical safety glasses.
Hand protection: Wear rubber gloves.
Other protection: Operate according to industrial hygiene and safe use rules. Wash your hands before the break and at the end of the work.
Common rumors: Silver cannot react with ferric ions because silver ions are more oxidizing than ferric ions.
Refuting: At high concentrations, silver can also react with ferric ions because the standard electrode potential of ferric ions is very different from the standard electrode potential of silver, and the change in reaction temperature and the increase in iron ion concentration the electrode potential of the silver is lowered to allow the reaction to proceed.