Difference between revisions of "Silver"
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==Properties== | ==Properties== | ||
===Chemical=== | ===Chemical=== | ||
| − | Silver is resistant to many acids, such as halogen acids and cold [[sulfuric acid]], but will slowly dissolve in nitric acid forming [[silver nitrate]], reaction sped up by heating | + | Silver is resistant to many acids, such as organic acids, halogen acids and cold [[sulfuric acid]], but will slowly dissolve in conc. [[nitric acid]] forming [[silver nitrate]], reaction sped up by heating. |
| − | [[ | + | : 3 Ag + 4 HNO<sub>3</sub> (cold and diluted) → 3 AgNO<sub>3</sub> + 2 H<sub>2</sub>O + [[nitric oxide|NO]] |
| + | : Ag + 2 HNO<sub>3</sub> (hot and concentrated) → AgNO<sub>3</sub> + H<sub>2</sub>O + NO<sub>2</sub> | ||
| − | Silver halides, such as silver chloride, are photosensitive and are known for their ability to record a latent image, that can later be developed chemically, process that made photography possible. | + | [[Perchloric acid]] will also react with silver metal, more so when hot<ref>Gmelins Handbuch der anorganischen Chemie, Silber Teil B1, 8th edition 1971, p. 508ff</ref>, as does hot sulfuric acid. |
| + | |||
| + | : 2 Ag + 3 HClO<sub>4</sub> → 2 AgClO<sub>4</sub> + HClO<sub>3</sub> + H<sub>2</sub>O | ||
| + | : 2 Ag + 2 H<sub>2</sub>SO<sub>4</sub> → Ag<sub>2</sub>SO<sub>4</sub> + SO<sub>2</sub> + 2 H<sub>2</sub>O | ||
| + | |||
| + | It's stable in pure air and water, but tarnishes when it is exposed to air or water containing [[ozone]] or [[hydrogen sulfide]], in case of the latter it forms a black layer of [[silver sulfide]] which can be cleaned off with dilute [[hydrogen peroxide]] or [[hydrochloric acid]]. This phenomenon can be used as an indicator of air quality. Silver can be attacked by strong oxidizers, such as [[potassium dichromate]] or [[potassium permanganate]], in the presence of [[potassium bromide]]. | ||
| + | |||
| + | In the presence of air, or even hydrogen peroxide, silver dissolves readily in aqueous solutions of cyanide.<ref>Chemistry of the Elements 2nd Edition, by N. N. Greenwood (Author), A. Earnshaw (Author), 1997</ref> | ||
| + | |||
| + | [[Silver fulminate]] (AgCNO) is a powerful touch sensitive explosive obtained from silver metal, that has little value in chemistry because it's extremely sensitive to shock, heat, static electricity. It is however used in bang snaps. | ||
| + | |||
| + | Silver halides, such as [[silver chloride]], are photosensitive and are known for their ability to record a latent image, that can later be developed chemically, process that made photography possible. | ||
===Physical=== | ===Physical=== | ||
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Silver can be obtained from certain coins and jewelries, as an alloy, so purification might be required. US quarters and dimes made before 1964 were made of a 90% silver and 10% copper alloy. Nickels made between 1942-1945 ("War nickels") contain 35% silver, the rest being copper and manganese.<ref>https://www.youtube.com/watch?v=lLNf-vRKTmU</ref> However it may be illegal to destroy local money in order to obtain the metal from them, depending where you live. | Silver can be obtained from certain coins and jewelries, as an alloy, so purification might be required. US quarters and dimes made before 1964 were made of a 90% silver and 10% copper alloy. Nickels made between 1942-1945 ("War nickels") contain 35% silver, the rest being copper and manganese.<ref>https://www.youtube.com/watch?v=lLNf-vRKTmU</ref> However it may be illegal to destroy local money in order to obtain the metal from them, depending where you live. | ||
| − | Silver is also found in many contacts from various electronic devices, such as switches, circuit breakers, relays, as a sintered alloy, usually with [[nickel]], [[copper]] and [[tungsten]] or [[tungsten carbide]]. There is no standard mixture, sometimes other elements are also present such as [[cadmium]], which makes extraction difficult due to its toxicity. The specific gravity varies among the contacts, some can be as low as 6 g/cm<sup>3</sup>, while other may reach 10 g/cm<sup>3</sup>. Determining the exact percentage of silver presents challenges. | + | Silver is also found in many contacts from various electronic devices, such as switches, circuit breakers, relays, as a sintered alloy, usually with [[nickel]], [[copper]] and [[tungsten]] or [[tungsten carbide]]. There is no standard mixture, sometimes other elements are also present such as [[cadmium]], which makes extraction difficult due to its toxicity. The specific gravity varies among the contacts, some can be as low as 6 g/cm<sup>3</sup>, while other may reach 10 g/cm<sup>3</sup>. Determining the exact percentage of silver from electrical contacts presents challenges. |
Tin-silver-copper solders also contain small amounts of silver in their composition. | Tin-silver-copper solders also contain small amounts of silver in their composition. | ||
Various other electronics that contain appreciable amounts of silver: | Various other electronics that contain appreciable amounts of silver: | ||
| − | *Mylar sheets from old keyboards contain silver. You can get | + | *Mylar sheets from old keyboards contain silver. You can get between 1-4 g of silver from around 25 mylars, depending on when the keyboard was made. |
| − | *Coin and button batteries (found on motherboards and in small electronics) often use silver oxide and zinc to generate power electrochemically. When these batteries are fully spent, the silver oxide inside has been reduced to silver metal, which can be carefully collected and purified. Another option is simply to dissolve the contents of the battery in [[nitric acid]] and precipitate the silver by adding [[copper]], comparatively a much more reactive metal, to a solution of silver nitrate or another | + | *Coin and button batteries (found on motherboards and in small electronics) often use silver oxide and zinc to generate power electrochemically. When these batteries are fully spent, the silver oxide inside has been reduced to silver metal, which can be carefully collected and purified. Another option is simply to dissolve the contents of the battery in [[nitric acid]] and precipitate the silver by adding [[copper]], comparatively a much more reactive metal, to a solution of silver nitrate or another reducing agent. |
| − | *Certain monolithic capacitors may contain silver instead of palladium | + | *Certain monolithic capacitors may contain silver instead of [[palladium]]. Some may not even have palladium. |
*Varistor disks tend to be coated with a small amount of silver | *Varistor disks tend to be coated with a small amount of silver | ||
| − | Note that extracting silver (and other precious metals) from electronics may or may not be legal depending on your jurisdiction. Consult your lawyer before you start doing | + | Note that extracting silver (and other precious metals) from electronics may or may not be legal depending on your jurisdiction. Consult the law or your lawyer before you start doing any precious metal refining. |
| − | Lastly, silver can also be bought as ingots and bars, thought | + | Lastly, silver can also be bought as ingots and bars, thought its price will vary depending on the market. |
| + | |||
| + | Silver can be found in nature in native form, as nuggets, often as a natural alloy. It requires a lot of work to obtain any significant amounts of Ag metal this way, and silver extraction may not be legal, depending on the country. Many former silver mines tend to still be property of the previous company, so it's illegal to mine other private properties. | ||
==Isolation== | ==Isolation== | ||
| − | Silver can be obtained by reducing its salt with a reducing agent, such as ascorbic acid. | + | Silver can be obtained by reducing its salt with a reducing agent, such as ascorbic acid. Silver metal precipitates as a very fine powder, which is then filtered, dried and melted if desired to keep the silver in bulk. |
It can also be obtained by chemical purification of silver alloys used to make jewelry and coins. This is a process done in several steps. | It can also be obtained by chemical purification of silver alloys used to make jewelry and coins. This is a process done in several steps. | ||
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==Projects== | ==Projects== | ||
| − | *[[ | + | *Make [[silver nitrate]] |
| − | *[[ | + | *Make [[silver fulminate]] |
| − | *[[ | + | *Make [[silver acetylide]] |
| − | *[[ | + | *Make [[silver azide]] |
*Electrolytic silver cell | *Electrolytic silver cell | ||
*Silver crystal growing, caused by insertion of a well-cleaned [[copper]] object such as wire into [[silver nitrate]] solution. The end product is a plant-like growth of silver crystals in a blue solution ([[copper(II) nitrate]]). | *Silver crystal growing, caused by insertion of a well-cleaned [[copper]] object such as wire into [[silver nitrate]] solution. The end product is a plant-like growth of silver crystals in a blue solution ([[copper(II) nitrate]]). | ||
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===Storage=== | ===Storage=== | ||
| − | Silver does not require special disposal, though if stored in sulfide polluted air, it will form a dark layer. The layer can be removed with hydrogen peroxide. | + | Silver does not require special disposal, though if stored in sulfide polluted air, it will form a dark layer. The layer can be removed by washing the silver metal with hydrogen peroxide. To limit this, you can keep the silver in a closed bottle or bag. |
| + | |||
| + | Silver jewelry should be kept in a safe. | ||
===Disposal=== | ===Disposal=== | ||
| − | Due to its high price, it's best to try to recycle the silver. | + | Due to its high price and scarcity, it's best to try to recycle all the silver. |
==References== | ==References== | ||
Latest revision as of 16:36, 4 April 2023
 One troy ounce of fine silver | |||||
| General properties | |||||
|---|---|---|---|---|---|
| Name, symbol | Silver, Ag | ||||
| Appearance | Lustrous silvery metal | ||||
| Silver in the periodic table | |||||
| |||||
| Atomic number | 47 | ||||
| Standard atomic weight (Ar) | 107.8682(2) | ||||
| Group, block | 11; d-block | ||||
| Period | period 5 | ||||
| Electron configuration | [Kr] 4d10 5s1 | ||||
per shell | 2, 8, 18, 18, 1 | ||||
| Physical properties | |||||
| Silvery white | |||||
| Phase | Solid | ||||
| Melting point | 1234.93 K (961.78 °C, 1763.2 °F) | ||||
| Boiling point | 2435 K (2162 °C, 3924 °F) | ||||
| Density near r.t. | 10.49 g/cm3 | ||||
| when liquid, at | 9.320 g/cm3 | ||||
| Heat of fusion | 11.28 kJ/mol | ||||
| Heat of | 254 kJ/mol | ||||
| Molar heat capacity | 25.350 J/(mol·K) | ||||
| pressure | |||||
| Atomic properties | |||||
| Oxidation states | −2, −1, 1, 2, 3, 4 | ||||
| Electronegativity | Pauling scale: 1.93 | ||||
| energies |
1st: 731.0 kJ/mol 2nd: 2070 kJ/mol 3rd: 3361 kJ/mol | ||||
| Atomic radius | empirical: 144 pm | ||||
| Covalent radius | 145±5 pm | ||||
| Van der Waals radius | 172 pm | ||||
| Miscellanea | |||||
| Crystal structure | face-centered cubic (fcc) | ||||
| Speed of sound thin rod | 2680 m/s (at ) | ||||
| Thermal expansion | 18.9 µm/(m·K) (at 25 °C) | ||||
| Thermal conductivity | 429 W/(m·K) | ||||
| Thermal diffusivity | 174 mm2/s (at 300 K) | ||||
| Electrical resistivity | 15.87 Ω·m (at 20 °C) | ||||
| Magnetic ordering | Diamagnetic | ||||
| Young's modulus | 83 GPa | ||||
| Shear modulus | 30 GPa | ||||
| Bulk modulus | 100 GPa | ||||
| Poisson ratio | 0.37 | ||||
| Mohs hardness | 2.5 | ||||
| Vickers hardness | 251 MPa | ||||
| CAS Registry Number | 206–250 | ||||
| History | |||||
| Discovery | before 5000 BC | ||||
 |
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Silver is a chemical element and transitional metal, with the symbol Ag and atomic number 47. Silver has the highest electrical and thermal conductivity of any metal and is the most reflective metal.
Contents
Properties
Chemical
Silver is resistant to many acids, such as organic acids, halogen acids and cold sulfuric acid, but will slowly dissolve in conc. nitric acid forming silver nitrate, reaction sped up by heating.
- 3 Ag + 4 HNO3 (cold and diluted) → 3 AgNO3 + 2 H2O + NO
- Ag + 2 HNO3 (hot and concentrated) → AgNO3 + H2O + NO2
Perchloric acid will also react with silver metal, more so when hot[1], as does hot sulfuric acid.
- 2 Ag + 3 HClO4 → 2 AgClO4 + HClO3 + H2O
- 2 Ag + 2 H2SO4 → Ag2SO4 + SO2 + 2 H2O
It's stable in pure air and water, but tarnishes when it is exposed to air or water containing ozone or hydrogen sulfide, in case of the latter it forms a black layer of silver sulfide which can be cleaned off with dilute hydrogen peroxide or hydrochloric acid. This phenomenon can be used as an indicator of air quality. Silver can be attacked by strong oxidizers, such as potassium dichromate or potassium permanganate, in the presence of potassium bromide.
In the presence of air, or even hydrogen peroxide, silver dissolves readily in aqueous solutions of cyanide.[2]
Silver fulminate (AgCNO) is a powerful touch sensitive explosive obtained from silver metal, that has little value in chemistry because it's extremely sensitive to shock, heat, static electricity. It is however used in bang snaps.
Silver halides, such as silver chloride, are photosensitive and are known for their ability to record a latent image, that can later be developed chemically, process that made photography possible.
Physical
Silver is soft, white metal. It has the highest electrical conductivity of any known metal and compound (except superconductors) and highest thermal conductivity of all known metals. It melts at 961.78 °C and boils at 2162 °C. It is a dense metal (10.49 g/cm3), though slightly less dense than lead.
Availability
Silver can be obtained from certain coins and jewelries, as an alloy, so purification might be required. US quarters and dimes made before 1964 were made of a 90% silver and 10% copper alloy. Nickels made between 1942-1945 ("War nickels") contain 35% silver, the rest being copper and manganese.[3] However it may be illegal to destroy local money in order to obtain the metal from them, depending where you live.
Silver is also found in many contacts from various electronic devices, such as switches, circuit breakers, relays, as a sintered alloy, usually with nickel, copper and tungsten or tungsten carbide. There is no standard mixture, sometimes other elements are also present such as cadmium, which makes extraction difficult due to its toxicity. The specific gravity varies among the contacts, some can be as low as 6 g/cm3, while other may reach 10 g/cm3. Determining the exact percentage of silver from electrical contacts presents challenges.
Tin-silver-copper solders also contain small amounts of silver in their composition.
Various other electronics that contain appreciable amounts of silver:
- Mylar sheets from old keyboards contain silver. You can get between 1-4 g of silver from around 25 mylars, depending on when the keyboard was made.
- Coin and button batteries (found on motherboards and in small electronics) often use silver oxide and zinc to generate power electrochemically. When these batteries are fully spent, the silver oxide inside has been reduced to silver metal, which can be carefully collected and purified. Another option is simply to dissolve the contents of the battery in nitric acid and precipitate the silver by adding copper, comparatively a much more reactive metal, to a solution of silver nitrate or another reducing agent.
- Certain monolithic capacitors may contain silver instead of palladium. Some may not even have palladium.
- Varistor disks tend to be coated with a small amount of silver
Note that extracting silver (and other precious metals) from electronics may or may not be legal depending on your jurisdiction. Consult the law or your lawyer before you start doing any precious metal refining.
Lastly, silver can also be bought as ingots and bars, thought its price will vary depending on the market.
Silver can be found in nature in native form, as nuggets, often as a natural alloy. It requires a lot of work to obtain any significant amounts of Ag metal this way, and silver extraction may not be legal, depending on the country. Many former silver mines tend to still be property of the previous company, so it's illegal to mine other private properties.
Isolation
Silver can be obtained by reducing its salt with a reducing agent, such as ascorbic acid. Silver metal precipitates as a very fine powder, which is then filtered, dried and melted if desired to keep the silver in bulk.
It can also be obtained by chemical purification of silver alloys used to make jewelry and coins. This is a process done in several steps.
- The coin, ring or another object made of a silver alloy is dissolved in nitric acid. The reaction should be done under a fume hood or outdoors, because of nitrogen dioxide.
- The solution at the end of the reaction is of a bluish-green color, because it contains a mixture of copper, silver and other metal nitrates.
- Sodium hydroxide is added into the solution. All dissolved metals precipitate in the form of hydroxides.
- The precipitate is removed from the solution and dried.
- The dried precipitate is heated to the temperature of 280-300 degrees Celsius. This temperature is enough to decompose the silver (I) oxide, but not enough to decompose the oxides of copper, nickel or whatever other metals are there. After heating, the precipitate turns into a mixture of powdered elemental silver and various oxides.
- The calcinated powder is treated with hydrochloric acid, which dissolves all oxides but does not attack elemental silver. It is the only substance left in the powder.
- The powdered pure silver is washed with water to remove the remnants of acid.
If you are sure that copper is the only contaminant, a simpler process can be used. Do not add the hydroxide, evaporate the solution and crystallize the nitrate mixture and heat it to the temperature of 280 degrees. Copper nitrate will decompose, and silver nitrate won't, and it will be available for extraction with water, recrystallization and decomposition under 500 degrees to produce elemental silver. Filtering the silver powder from the reaction product is not easy, as due to its density it tends to compact, which prevents the removal of water, while also retaining copper nitrate/oxide.
Projects
- Make silver nitrate
- Make silver fulminate
- Make silver acetylide
- Make silver azide
- Electrolytic silver cell
- Silver crystal growing, caused by insertion of a well-cleaned copper object such as wire into silver nitrate solution. The end product is a plant-like growth of silver crystals in a blue solution (copper(II) nitrate).
- Anti-bacterial surfaces
Handling
Safety
Silver metal has antiseptic properties and does not react with the organism. Silver compounds are harmful, and in large doses, silver compounds or colloids will deposit in various body tissues, leading to argyria, which results in a blue-grayish pigmentation of the skin.
Storage
Silver does not require special disposal, though if stored in sulfide polluted air, it will form a dark layer. The layer can be removed by washing the silver metal with hydrogen peroxide. To limit this, you can keep the silver in a closed bottle or bag.
Silver jewelry should be kept in a safe.
Disposal
Due to its high price and scarcity, it's best to try to recycle all the silver.
References
- ↑ Gmelins Handbuch der anorganischen Chemie, Silber Teil B1, 8th edition 1971, p. 508ff
- ↑ Chemistry of the Elements 2nd Edition, by N. N. Greenwood (Author), A. Earnshaw (Author), 1997
- ↑ https://www.youtube.com/watch?v=lLNf-vRKTmU
