Silver is quite heavy (ρ = 10.5 g/cm3), shiny (light reflection coefficient is close to 100%), silvery-white metal, malleable and ductile (1 g of silver can stretch the thinnest wire almost 2 km long!), It is the best conductor of heat among metals (that’s why a silver spoon in a glass of hot tea heats up quickly) and electricity. Melting point 962°C.
Application
Silver has been known since ancient times. This is due to the fact that at one time silver, as well as gold, was found in its native form - it did not have to be smelted from ores.
In the old days, coins, vases, jewelry were made from it, and clothes were decorated with the finest silver threads. Now the use of silver is not limited jewelry making– it is used in the production of highly reflective mirrors (inexpensive mirrors are coated with aluminum), electrical contacts, batteries, used in dentistry, used in gas mask filters, as a disinfectant for water disinfection. Some time ago, solutions of colloidal silver - protargol and collargol - were used to treat colds.
Silver iodide (AgI) is used for climate control (“cloud clearing”). The crystal lattice of silver iodide is very similar in structure to the lattice of ice, so the introduction is not large quantity iodide causes the formation of condensation centers in the clouds, thereby causing precipitation.
Silver is registered as a food additive E-174.
Silver is used to make electrodes for powerful zinc-silver batteries. Thus, the batteries of the sunken American submarine Thrasher contained three tons of silver. The high thermal conductivity and chemical inertness of silver are used in electrical engineering: electrical contacts are made from silver and its alloys, and wires in critical devices are coated with silver. Dentures are made from silver-palladium alloy (75% Ag).
Huge amounts of silver used to be used to make coins. Nowadays, mainly commemorative and commemorative coins are made from silver. A lot of silver is spent to make jewelry and cutlery. On such products, as a rule, they put a test indicating the mass of pure silver in grams per 1000 g of alloy (modern test), or the number of spools in one pound of alloy (pre-revolutionary test). 1 pound contains 96 spools, therefore, for example, the old standard 84 corresponds to the modern one [(84/96) 1000] = 875. Soviet rubles and fifty dollars had a standard 900. Modern silver products can have a standard 960, 925, 916, 875, 800 and 750.
Silver compounds are often unstable to heat and light. The discovery of the photosensitivity of silver salts led to the advent of photography and a rapid increase in the demand for silver. Back in the mid-20s, about 10,000 tons of silver were mined annually around the world, and much more was spent (the deficit was covered by old reserves). The displacement of black and white photographs and films by color has significantly reduced silver consumption.
“Silver does not oxidize in air,” wrote D.I. Mendeleev in his textbook “Fundamentals of Chemistry,” “and therefore is classified as a so-called noble metal.” But although silver does not react directly with oxygen, it can dissolve significant amounts of this gas. Even solid silver at a temperature of 450° C can absorb five times the volume of oxygen. Significantly more oxygen (up to 20 volumes per 1 volume of silver) dissolves in the liquid metal.
This property of silver leads to the beautiful (and dangerous) phenomenon of silver spattering, which has been known since ancient times. If molten silver has absorbed significant amounts of oxygen, then the solidification of the metal is accompanied by the release of large amounts of gas. The pressure of the released oxygen breaks the crust on the surface of the solidifying silver, often with great force. The result is a sudden explosive spattering of metal.
At 170° C, silver in air is covered with a thin film of Ag 2 O oxide, and under the influence of ozone, higher oxides are formed (for example, Ag 2 O 3). But silver is especially “afraid” of iodine (iodine tincture) and hydrogen sulfide. Over time, silver items often become tarnished and may even turn black. The reason is the action of hydrogen sulfide. Its source can be not only rotten eggs, but also rubber, some polymers and even food. In the presence of moisture, silver easily reacts with hydrogen sulfide to form a thin film of Ag 2 S sulfide on the surface; due to surface irregularities and the play of light, such a film sometimes appears iridescent. Gradually the film thickens, darkens, turns brown, and then black.
One of the important areas of use of silver was medicine. The ancient Egyptians, for example, applied a silver plate to wounds to achieve fast healing. The Persian king Cyrus transported water only in silver vessels during his military campaigns. The famous medieval physician Paracelsus treated some diseases with AgNO 3 - silver nitrate (lapis). This remedy is still used in medicine today.
Relatively recently, studies of body cells for silver content led to the conclusion that it is elevated in brain cells.
The bactericidal effect of small concentrations of silver on drinking water is well known. At a content of 0.05 mg/l, water can be drunk without harm to health. Its taste does not change. (For cosmonauts to drink, the concentration of Ag + is allowed up to 0.1 - 0.2 mg/l.).
To disinfect water in swimming pools, it was proposed to saturate it with silver bromide. A saturated AgBr solution contains 0.08 mg/l, which is harmless to human health, but harmful to microorganisms and algae.
However, as often happens, what is beneficial in small doses is harmful in large ones. Ag is no exception.
Silver, when excessively introduced into the body, causes a decrease in immunity, changes in the tissues of the brain and spinal cord, and leads to diseases of the liver, kidneys, and thyroid gland. Cases of severe mental disorders in people caused by poisoning with silver preparations have been described. Fortunately, after 1-2 weeks only 0.02 - 0.1% of the injected silver remains in our body, the rest is excreted from the body.
After many years of working with silver and its salts, when they enter the body for a long time, But small doses, an unusual disease may develop - argyria. Silver entering the body can be slowly deposited as metal in the connective tissue and capillary walls of various organs, including the kidneys, bone marrow, and spleen. Accumulating in the skin and mucous membranes, silver gives them a gray-green or bluish color, especially strong on open areas of the body exposed to light. Occasionally, the coloring can be so intense that the skin resembles the skin of blacks.
Argyria develops very slowly, its first signs appear after 2–4 years continuous operation with silver, and strong darkening of the skin is observed only after decades. The lips, temples and conjunctiva of the eyes darken first, then the eyelids. The mucous membranes of the mouth and gums, as well as the sockets of the nails, can be severely stained. Sometimes argyria appears as small blue-black spots. Once it appears, argyria does not disappear, and the skin cannot be returned to its previous color. Apart from purely cosmetic inconveniences, a patient with argyria may not experience any pain or discomfort (if the cornea and lens of the eye are not affected); in this regard, argyria can be called a disease only conditionally. This disease also has its own “spoon of honey” - it does not happen with argyria infectious diseases: a person is so “impregnated” with silver that it kills all pathogenic bacteria that enter the body.
Silver in nature
This beautiful metal has been known to people since ancient times. Silver products found in Western Asia are more than 6 thousand years old. The world's first coins were made from an alloy of gold and silver (electrum). And for several millennia, silver was one of the main coin metals.
The Ore Mountains, the Harz, and the mountains of Bohemia and Saxony located in Central Europe were especially rich in silver. Millions of coins were minted from silver mined near the city of Joachimsthal (now Jáchymov in the Czech Republic). At first they were called “Joachimsthalers”; then the name was shortened to “thaler” (in Russia, the first part of the word is “efimka”). These coins were in circulation throughout Europe, becoming the most common silver coin in history. The name of the dollar comes from the thaler.
After the discovery of America, many silver nuggets were found in the territory of modern Peru, Chile, Mexico, and Bolivia. Thus, a nugget in the form of a plate weighing 1420 kg was discovered in Chile. Many elements have “geographical” names, but Argentina is the only country named after an already known element. The last of the largest silver nuggets were found already in the 20th century in Canada (Ontario). One of them, called the “silver pavement,” was 30 m long and went 18 m deep into the earth. When pure silver was smelted from it, it turned out to be 20 tons!
Native silver is rarely found; The bulk of silver in nature is concentrated in minerals, the main one being argentite Ag 2 S. Even more silver is scattered among various rocks.
When describing any element, it is customary to indicate its discoverer and the circumstances of its discovery. Humanity does not have such data about element No. 47. People began to use silver even when there were no scientists.
The Latin name for silver Argentum comes from the Greek “argos” - white, shiny. Russian word“silver,” according to scientists, comes from the word “sickle” (sickle of the moon). The shine of silver was reminiscent of the moonlight and alchemists, who used the sign of the moon as a symbol of the element.
Silver and glass. These two substances are found not only in the production of mirrors. Silver is needed to make signal glasses and light filters. A small addition (0.15 - 0.20%) of silver nitrate (or silver nitrate) gives the glass an intense golden-yellow color. And orange glass is obtained by introducing gold and silver into the glass melt at the same time.
Silver resists the action of alkalis better than many other metals. That is why the walls of pipelines, autoclaves, reactors and other apparatus in the chemical industry are coated with silver as a protective metal.
And in terms of sonority, silver stands out noticeably among other metals. It is not for nothing that silver bells appear in many fairy tales. Bellmakers have long added silver to bronze “for a crimson ringing.” Nowadays, the strings of some musical instruments are made from an alloy that contains 90% silver.
If the silver has turned black...
During long-term storage, silver items become dull and become covered with a thin layer of silver sulfide Ag 2 S. To restore the item to its former shine, it is necessary to remove the sulfide film. This can be done in several ways.
1) Mix water, ammonia and tooth powder in the form of gruel. Apply this product to soft cloth and clean the products until the darkening is removed.
2) Boil silver product(about 20 minutes) in water with added baking soda and pieces of aluminum foil or wire (or in an aluminum container).
3) Regular tooth powder or toothpaste are still not inferior to any of the newest means. By rubbing the product with a former toothbrush, you will restore its original shine.
No matter what product you choose to clean your products, be sure to rinse them thoroughly after the procedure and wipe them dry with a cloth.
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IODINE MOLECULAR.
a) on the chloride ion - the effect of a solution of silver nitrate → a white cheesy precipitate of silver chloride is formed:
Cl - + Ag + = AgCl↓
silver diammine chloride
b) for Bromide ion:
Br - + Ag + = AgBr↓
The reaction is pharmacopoeial.
2) with chlorine water
Cl 2 + 2 NaBr = 2 NaCl + Br 2
The reaction is pharmacopoeial.
c) for iodide ion:
KI + AgNO 3 = AgI↓ + KNO 3
I - + Ag + = AgI↓
The reaction is pharmacopoeial.
Cl 2 + 2 NaI = 2 NaCl + I 2
The reaction is pharmacopoeial.
Conclusions: a) on the chloride ion - the effect of a solution of silver nitrate → a white cheesy precipitate of silver chloride is formed:
NaCl + AgNO 3 = AgCl↓ + NaNO 3
Cl - + Ag + = AgCl↓
The precipitate is insoluble in nitric acid, but is easily soluble in ammonia to form a complex compound:
AgCl + 2 NH 3 = Cl
or AlCl + 2 NH 4 OH = Cl + 2 H 2 O
silver diammine chloride
When concentrated sulfuric acid is added to a solution of silver diammine chloride, a precipitate is released again:
Cl + 2 HNO 3 = AgCl↓ + 2 NH 4 NO 3
The reaction is pharmacopoeial.
AgCl – also soluble in sodium thiosulfate.
T.V.: add 2 drops of AgNO 3 solution to 2 drops of NaCl solution.
A concentrated ammonia solution is added to the solution containing the precipitate until the precipitate is completely dissolved. The resulting solution is acidified with concentrated nitric acid and the formation of a precipitate is observed.
b) for Bromide ion:
1) action of silver nitrate → yellowish-white precipitate of silver bromide:
NaBr + AgNO 3 = AgBr↓ + NaNO 3
Br - + Ag + = AgBr↓
The precipitate is insoluble in HNO3, poorly soluble in ammonia, unlike silver chloride, and readily soluble in sodium thiosulfate solution.
The reaction is pharmacopoeial.
T.V.: To 4 drops of NaBr solution add 4 drops of AgNO 3 solution. The solution with the precipitate is divided into two parts. A sodium thiosulfate solution is added to one part, and a concentrated ammonia solution is added to the other, and the dissolution of the AgBr precipitate in these reagents is compared.
2) with chlorine water
Chlorine water added to a bromide solution releases free bromine, which dissolves in carbon disulfide or chloroform, turning the solvent layer orange:
Cl 2 + 2 NaBr = 2 NaCl + Br 2
With a large excess of chlorine water, the color disappears due to the formation of BrCl, which has a lighter color.
The reaction is pharmacopoeial.
T.V. To 5 drops of NaBr solution add 1 ml of chloroform, 1-2 drops of diluted H2SO4 and then drop by drop, with vigorous shaking, 2-3 drops of chlorine water. Coloration of the chloroform layer is observed.
c) for iodide ion:
1) silver nitrate releases a light yellow cheesy precipitate of silver from iodides:
KI + AgNO 3 = AgI↓ + KNO 3
I - + Ag + = AgI↓
The precipitate is insoluble in nitric acid and ammonia solution and is poorly soluble in sodium thiosulfate solution.
The reaction is pharmacopoeial.
T.V.: A little AgNO3 solution is added to the KI solution. Check the dissolution of the precipitate in a sodium thiosulfate solution.
2) Chlorine water releases free iodine from iodide solutions, which colors carbon disulfide or chloroform reddish-violet and the starch solution blue.
Cl 2 + 2 NaI = 2 NaCl + I 2
T.V.: To 5 drops of NI (KI) solution add 1 ml of chloroform, 2-3 drops of diluted H2SO 4 and then drop by drop, with vigorous shaking, 2-3 drops of chlorine water. The chloroform layer is observed to turn reddish-violet. 1 drop of KI solution, 1 drop of chlorine water and 2 drops of starch solution are poured into another test tube. Observe the color change.
3) Iron (III) chloride, conc. H 2 SO 4 and some other oxidizing agents oxidize the I ion to free iodine; For example:
2 FeCl 3 + 2 KI = 2 FeCl 2 + 2 KCl + I 2
The reaction is pharmacopoeial.
T.V.: Solutions of KI, HCl, FeCl 3 are applied sequentially, 1 drop at a time, onto the filter paper in one place. Observe the appearance of a brown spot, turning blue from a drop of starch.
d) On molecular iodine → effect of starch → blue color.
Qualitative reactions:
a) on the chloride ion - the effect of a solution of silver nitrate → a white cheesy precipitate of silver chloride is formed; the precipitate is insoluble in nitric acid, but is easily soluble in ammonia to form the complex compound silver diammine chloride.
When concentrated sulfuric acid is added to a solution of silver diammine chloride, a precipitate is released again:
b) for Bromide ion:
1) action of silver nitrate → yellowish-white precipitate of silver bromide; the precipitate is insoluble in HNO3, poorly soluble in ammonia, unlike silver chloride, and soluble in sodium thiosulfate solution.
The reaction is pharmacopoeial.
2) with chlorine water
Chlorine water added to a bromide solution releases free bromine, which dissolves in carbon disulfide or chloroform, turning the solvent layer orange.
The reaction is pharmacopoeial.
c) for iodide ion:
1) silver nitrate releases a light yellow cheesy precipitate of silver from iodides.
The precipitate is insoluble in nitric acid and ammonia solution and is poorly soluble in sodium thiosulfate solution.
The reaction is pharmacopoeial.
2) Chlorine water releases free iodine from iodide solutions, which colors carbon disulfide or chloroform reddish-violet and the starch solution blue.
3) Iron (III) chloride oxidizes the I ion to free iodine;
The reaction is pharmacopoeial.
d) On molecular iodine → effect of starch → blue color.
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