Discovery history. Potassium: the history of the discovery of the element Chemical properties of the most important compounds of potassium
POTASSIUM(lat. Kalium), K (read "potassium"), a chemical element with atomic number 19, atomic mass 39.0983.
Potassium occurs in nature in the form of two stable nuclides: 39 K (93.10% by mass) and 41 K (6.88%), as well as one radioactive 40 K (0.02%). The half-life of potassium-40 T 1/2 is approximately 3 times less than T 1/2 of uranium-238 and is 1.28 billion years. At b the decay of potassium-40 produces stable calcium-40, and the decay by the type of electron capture produces an inert gas argon-40.
2K + 2H 2 O = 2KOH + H 2
8K + 4H 2 SO 4 \u003d K 2 S + 3K 2 SO 4 + 4H 2 O.
When heated to 200-300°C, potassium reacts with hydrogen (H) to form a salt-like hydride KH:
Receipt: Potassium is currently produced by reacting with liquid sodium (Na) molten KOH (at 380-450°C) or KCl (at 760-890°C):
Na + KOH = NaOH + K
Potassium is also obtained by electrolysis of a KCl melt mixed with K 2 CO 3 at temperatures close to 700 ° C:
2KCl \u003d 2K + Cl 2
Potassium is purified from impurities by vacuum distillation.
Application: metallic potassium material for electrodes in chemical current sources. An alloy of potassium with another alkali metal, sodium (Na), is used as a coolant in nuclear reactors.
On a much larger scale than metallic potassium, its compounds are used. Potassium important component mineral nutrition of plants (this takes about 90% of the extracted potassium salts), they need it in significant quantities for normal development, therefore potash fertilizers are widely used: potassium chloride KCl, potassium nitrate, or potassium nitrate, KNO 3, potash K 2 CO 3 and other potassium salts. Potash is also used in the manufacture of special optical glasses, as an absorber of hydrogen sulfide in the purification of gases, as a dehydrating agent and in tanning leather.
Potassium iodide KI is used as a drug. Potassium iodide is also used in photography and as a microfertilizer. A solution of potassium permanganate KMnO 4 ("potassium permanganate") is used as an antiseptic.
Biological role: Potassium is one of the most important biogenic elements, constantly present in all cells of all organisms. Potassium ions K + are involved in the operation of ion channels and the regulation of the permeability of biological membranes, in the generation and conduction of a nerve impulse, in the regulation of the activity of the heart and other muscles, in various processes metabolism. The content of potassium in the tissues of animals and humans is regulated by steroid hormones of the adrenal glands. On average, the human body (body weight 70 kg) contains about 140 g of potassium. Therefore, for normal life with food, the body should receive 2-3 g of potassium per day. Potassium-rich foods such as raisins, dried apricots, peas and others.
Potassium (English Potassium, French Potassium, German Kalium) was discovered in 1807 by Davy, who produced the electrolysis of solid, slightly moistened caustic potash. Davy called the new metal Potassium, but the name did not stick. The godfather of the metal turned out to be Hilbert, the well-known publisher of the journal "Annalen deg Physik", who suggested the name "potassium"; it was adopted in Germany and Russia. Both names are derived from terms used long before the discovery of potassium metal. The word potasium is derived from the word potash, which probably appeared in the 16th century. It is found at Van Helmont and in the second half of the 17th century. is widely used as the name of a commercial product - potash - in Russia, England and Holland. Translated into Russian, the word potashe means "pot ash or ash boiled in a pot"; in the XVI - XVII centuries. potash was obtained in large quantities from wood ash, which was boiled in large boilers. From potash, mainly litreed (purified) saltpeter was prepared, which was used to make gunpowder. Especially a lot of potash was produced in Russia, in the forests near Arzamas and Ardatov in mobile factories (Maidans) that belonged to a relative of Tsar Alexei Mikhailovich, a close boyar B.I. Morozov. As for the word potassium, it comes from the Arabic term alkali (alkaline substances). In the Middle Ages, alkalis, or, as they said then, alkali salts, almost did not differ from each other and called them names that had the same meaning: natron, borax, varek, etc. The word kali (qila) occurs around 850 in Arab writers, then the word Qali (al-Qali) begins to be used, which denoted a product obtained from the ashes of certain plants, the Arabic qiljin or qaljan (ash) and qalaj (burn) are associated with these words. In the era of iatrochemistry, alkalis began to be subdivided into "fixed" and "volatile". In the 17th century there are names alkali fixum minerale (mineral fixed alkali or caustic soda), alkali fixum. vegetabile (vegetable fixed alkali or potash and caustic potash), as well as alkali volatile (volatile alkali or NH 3). Black distinguished between caustic and soft or carbonic alkalis. Alkalis do not appear in the Table of Simple Bodies, but in a footnote to the table, Lavoisier indicates that fixed alkalis (potash and soda) are probably complex substances, although the nature of their constituents has not yet been studied. In Russian chemical literature of the first quarter of the 19th century. potassium was called potassium (Soloviev, 1824), potash (Insurance, 1825), potash (Shcheglov, 1830); in the "Dvigubsky Shop" already in 1828. along with the name potash (potash sulphate) there is the name kali (caustic potash, potassium hydroxide, etc.). The name potassium became generally accepted after the publication of Hess's textbook.
Potassium
POTASSIUM-I; m.[Arab. kali] Chemical element (K), silvery metal white color extracted from carbon-potassium salt (potash).
◁ Potassium, th, th. K-th deposits. K salts. Potash, th, th. K-th industry. K fertilizers.
potassium(lat. Kalium), a chemical element of group I of the periodic system, belongs to the alkali metals. The name is from the Arabic al-kali - potash (a long-known potassium compound extracted from wood ash). Silver-white metal, soft, fusible; density 0.8629 g / cm 3, t pl 63.51ºC. It oxidizes rapidly in air, reacts explosively with water. In terms of prevalence in the earth's crust, it occupies the 7th place (minerals: sylvin, kainite, carnallite, etc.; see Potassium salts). It is part of the tissues of plant and animal organisms. About 90% of the extracted salts are used as fertilizers. Potassium metal is used in chemical current sources, as a getter in electron tubes, to obtain superperoxide KO 2 ; alloys K with Na - coolants in nuclear reactors.
POTASSIUMPOTASSIUM (lat. Kalium), K (read "potassium"), a chemical element with atomic number 19, atomic mass 39.0983.
Potassium occurs naturally as two stable nuclides (cm. NUCLIDE): 39 K (93.10% by mass) and 41 K (6.88%), as well as one radioactive 40 K (0.02%). The half-life of potassium-40 T 1/2 is approximately 3 times less than T 1/2 of uranium-238 and is 1.28 billion years. During the b-decay of potassium-40, stable calcium-40 is formed, and during the decay by the type of electron capture (cm. ELECTRONIC CAPTURE) the inert gas argon-40 is formed.
Potassium is one of the alkali metals (cm. ALKALI METALS). In the periodic system of Mendeleev, potassium occupies a place in the fourth period in the subgroup IA. Outer electron layer configuration 4 s 1, so potassium always exhibits an oxidation state of +1 (valency I).
The atomic radius of potassium is 0.227 nm, the radius of the ion is K + 0.133 nm. The energies of successive ionization of the potassium atom are 4.34 and 31.8 eV. Electronegativity (cm. ELECTRIC NEGATIVITY) potassium according to Pauling 0.82, which indicates its pronounced metallic properties.
IN free form- soft, light, silvery metal.
Discovery history
Compounds of potassium, as well as its closest chemical analogue - sodium (cm. SODIUM), have been known since antiquity and have been used in various fields of human activity. However, these metals themselves were first isolated in a free state only in 1807 during the experiments of the English scientist G. Davy (cm. DEVI Humphrey). Davy, using galvanic cells as a source of electric current, carried out the electrolysis of potash melts (cm. POTASH) and caustic soda (cm. CAUSTIC SODA) and thus isolated metallic potassium and sodium, which he called "potassium" (hence the name of potassium preserved in English-speaking countries and France) and "sodium". In 1809, the English chemist L. V. Gilbert proposed the name "potassium" (from the Arabic al-kali - potash).
Being in nature
The content of potassium in the earth's crust is 2.41% by mass, potassium is among the top ten most common elements in the earth's crust. The main minerals containing potassium: sylvin (cm. SILVIN) KCl (52.44% K), sylvinite (Na, K) Cl (this mineral is a densely compressed mechanical mixture of crystals of potassium chloride KCl and sodium chloride NaCl), carnallite (cm. CARNALLITE) KCl MgCl 2 6H 2 O (35.8% K), various aluminosilicates (cm. ALUMOSILICATES) containing potassium, kainite (cm. Cainite) KCl MgSO 4 3H 2 O, polyhalite (cm. POLYHALITH) K 2 SO 4 MgSO 4 2CaSO 4 2H 2 O, alunite (cm. ALUNITE) KAl 3 (SO 4) 2 (OH) 6. Sea water contains about 0.04% potassium.
Receipt
Currently, potassium is obtained by reacting with liquid sodium molten KOH (at 380-450°C) or KCl (at 760-890°C):
Na + KOH = NaOH + K
Potassium is also obtained by electrolysis of a KCl melt mixed with K 2 CO 3 at temperatures close to 700 ° C:
2KCl \u003d 2K + Cl 2
Potassium is purified from impurities by vacuum distillation.
Physical and chemical properties
Potassium metal is soft, easily cut with a knife, and amenable to pressing and rolling. It has a cubic body-centered cubic lattice, the parameter A= 0.5344 nm. The density of potassium is less than the density of water and is equal to 0.8629 g/cm 3 . Like all alkali metals, potassium easily melts (melting point 63.51°C) and begins to evaporate even at relatively low heat (potassium boiling point 761°C).
Potassium, like other alkali metals, is chemically very active. Easily interacts with atmospheric oxygen to form a mixture, mainly consisting of K 2 O 2 peroxide and KO 2 superoxide (K 2 O 4):
2K + O 2 \u003d K 2 O 2, K + O 2 \u003d KO 2.
When heated in air, potassium burns with a violet-red flame. With water and dilute acids, potassium interacts with an explosion (the resulting hydrogen ignites):
2K + 2H 2 O = 2KOH + H 2
Oxygen-containing acids can be reduced in this interaction. For example, the sulfur atom of sulfuric acid is reduced to S, SO 2 or S 2–:
8K + 4H 2 SO 4 \u003d K 2 S + 3K 2 SO 4 + 4H 2 O.
When heated to 200-300 °C, potassium reacts with hydrogen to form salt-like hydride KN:
2K + H 2 = 2KH
With halogens (cm. HALOGENS) potassium interacts with the explosion. It is interesting to note that potassium does not interact with nitrogen.
Like other alkali metals, potassium readily dissolves in liquid ammonia to form blue solutions. In this state, potassium is used to carry out certain reactions. During storage, potassium slowly reacts with ammonia to form the amide KNH 2:
2K + 2NH 3 fl. \u003d 2KNH 2 + H 2
The most important potassium compounds are K 2 O oxide, K 2 O 2 peroxide, K 2 O 4 superoxide, KOH hydroxide, KI iodide, K 2 CO 3 carbonate and KCl chloride.
Potassium oxide K 2 O, as a rule, is obtained indirectly due to the reaction of peroxide and metallic potassium:
2K + K 2 O 2 \u003d 2K 2 O
This oxide exhibits pronounced basic properties, easily reacts with water to form potassium hydroxide KOH:
K 2 O + H 2 O \u003d 2KOH
Potassium hydroxide, or caustic potash, is highly soluble in water (up to 49.10% by weight at 20°C). The resulting solution is a very strong base related to alkalis ( cm. ALKALI). KOH reacts with acidic and amphoteric oxides:
SO 2 + 2KOH \u003d K 2 SO 3 + H 2 O,
Al 2 O 3 + 2KOH + 3H 2 O \u003d 2K (so the reaction proceeds in solution) and
Al 2 O 3 + 2KOH \u003d 2KAlO 2 + H 2 O (this is how the reaction proceeds when the reagents are fused).
In industry, potassium hydroxide KOH is obtained by electrolysis of aqueous solutions of KCl or K 2 CO 3 using ion-exchange membranes and diaphragms:
2KCl + 2H 2 O \u003d 2KOH + Cl 2 + H 2,
or due to exchange reactions of solutions of K 2 CO 3 or K 2 SO 4 with Ca (OH) 2 or Ba (OH) 2:
K 2 CO 3 + Ba(OH) 2 = 2KOH + BaCO 3
Contact with solid potassium hydroxide or drops of its solutions on the skin and eyes causes severe burns of the skin and mucous membranes, so you should only work with these caustic substances with goggles and gloves. Aqueous solutions of potassium hydroxide during storage destroy glass, melts - porcelain.
Potassium carbonate K 2 CO 3 (commonly called potash) is obtained by neutralizing a solution of potassium hydroxide with carbon dioxide:
2KOH + CO 2 \u003d K 2 CO 3 + H 2 O.
Significant amounts of potash are found in the ashes of some plants.
Application
Potassium metal is a material for electrodes in chemical current sources. An alloy of potassium with another alkali metal - sodium is used as a coolant (cm. COOLANT) in nuclear reactors.
On a much larger scale than metallic potassium, its compounds are used. Potassium is an important component of the mineral nutrition of plants, they need it in significant quantities for normal development, therefore potash fertilizers are widely used. (cm. POTASH FERTILIZERS): potassium chloride KCl, potassium nitrate, or potassium nitrate, KNO 3, potash K 2 CO 3 and other potassium salts. Potash is also used in the production of special optical glasses, as an absorber of hydrogen sulfide in the purification of gases, as a dehydrating agent and in tanning leather.
Potassium iodide KI is used as a drug. Potassium iodide is also used in photography and as a microfertilizer. A solution of potassium permanganate KMnO 4 ("potassium permanganate") is used as an antiseptic.
By content in rocks ah radioactive 40 K determine their age.
potassium in the body
Potassium is one of the most important biogenic elements (cm. BIOGENIC ELEMENTS) present in all cells of all organisms. Potassium ions K + are involved in the operation of ion channels (cm. ION CHANNELS) and regulation of the permeability of biological membranes (cm. BIOLOGICAL MEMBRANES), in the generation and conduction of a nerve impulse, in the regulation of the activity of the heart and other muscles, in various metabolic processes. The content of potassium in the tissues of animals and humans is regulated by steroid hormones of the adrenal glands. On average, the human body (body weight 70 kg) contains about 140 g of potassium. Therefore, for normal life with food, the body should receive 2-3 g of potassium per day. Potassium-rich foods such as raisins, dried apricots, peas and others.
Features of handling metallic potassium
Potassium metal can cause very severe skin burns, if the smallest particles of potassium get into the eyes, severe injuries occur with loss of vision, so you can work with potassium metal only with protective gloves and goggles. Ignite potash is poured with mineral oil or covered with a mixture of talc and NaCl. Potassium is stored in hermetically sealed iron containers under a layer of dehydrated kerosene or mineral oil.
encyclopedic Dictionary. 2009 .
Synonyms:See what "potassium" is in other dictionaries:
Potassium 40 ... Wikipedia
Novolatinsk. kalium, from Arabic. kali, alkali. The soft and light metal that makes up the base of Kali. Discovered by Devi in 1807. Explanation 25000 foreign words that came into use in the Russian language, with the meaning of their roots. Michelson A.D., 1865. ... ... Dictionary of foreign words of the Russian language
- (Kalium), K, a chemical element of group I of the periodic system, atomic number 19, atomic mass 39.0983; refers to alkali metals; mp 63.51shC. In living organisms, potassium is the main intracellular cation involved in the generation of bioelectric ... ... Modern Encyclopedia
POTASSIUM- (Kalium, s. Potassium), chem. element, char. K, serial number 19, silvery white, lustrous metal, having the density of wax at ordinary ta; discovered by Devi in 1807. Oud. V. at 20° 0.8621, atomic weight 39.1, monovalent; melting point … Big Medical Encyclopedia
Potassium- (Kalium), K, a chemical element of group I of the periodic system, atomic number 19, atomic mass 39.0983; refers to alkali metals; mp 63.51°C. In living organisms, potassium is the main intracellular cation involved in the generation of bioelectric ... ... Illustrated encyclopedic Dictionary
- (symbol K), a common chemical element related to alkali metals. It was first isolated by Sir Humphry Davy in 1807. Its main ores are sylvin (potassium chloride), carnallite and polyhalite. Potassium is a coolant in atomic ... Scientific and technical encyclopedic dictionary
Husband. potasium, a metal that makes up the base of potassium, very similar to sodium (sodium). Kali cf., neskl., vegetable alkali or alkaline salt; potassium carbonate, pure potash. Potassium, pertaining to potassium. Calistic, containing potassium. Explanatory ... ... Dahl's explanatory dictionary - POTASSIUM, potassium, pl. no, masculine, and kali, indistinct, cf. (arab. potash) (chem.). The chemical element is a silver-white alkali metal, extracted from carbon-potassium salt. Explanatory Dictionary of Ushakov. D.N. Ushakov. 1935 1940 ... Explanatory Dictionary of Ushakov
Potassium is an element of the main subgroup of the first group, the fourth period of the periodic system of chemical elements, with atomic number 19. It is denoted by the symbol K (lat. Kalium). The simple substance potassium (CAS number: 7440-09-7) is a soft, silvery-white alkali metal.
In nature, potassium is found only in compounds with other elements, for example, in sea water, as well as in many minerals. It oxidizes very quickly in air and very easily enters into chemical reactions, especially with water, forming an alkali. In many respects, the chemical properties of potassium are very similar to sodium, but in terms of biological function and their use by the cells of living organisms, they are still different.
History and origin of the name
Potassium (more precisely, its compounds) has been used since ancient times. Thus, the production of potash (which was used as detergent) already existed in the 11th century. The ash formed during the combustion of straw or wood was treated with water, and the resulting solution (lye) was evaporated after filtering. The dry residue, in addition to potassium carbonate, contained potassium sulfate K 2 SO 4 , soda and potassium chloride KCl.
In 1807, the English chemist Davy isolated potassium by electrolysis of a melt of caustic potash (KOH) and named it "potassium" (lat. potassium; this name is still in common use in English, French, Spanish, Portuguese and Polish). In 1809, L.V. Gilbert proposed the name "potassium" (lat. kalium, from Arabic al-kali - potash). This name is included in German, from there to most of the languages of Northern and Eastern Europe (including Russian) and "won" when choosing a symbol for this element - K.
Receipt
Potassium, like other alkali metals, is obtained by electrolysis of molten chlorides or alkalis. Since chlorides have more high temperature melting (600-650 ° C), then more often electrolysis of straightened alkalis is carried out with the addition of soda or potash (up to 12%). During the electrolysis of molten chlorides, molten potassium is released at the cathode, and chlorine is released at the anode:
K + + e - → K
2Cl - - 2e - → Cl 2
During the electrolysis of alkalis, molten potassium is also released at the cathode, and oxygen at the anode:
4OH - - 4e - → 2H 2 O + O 2
The water from the melt quickly evaporates. To prevent potassium from interacting with chlorine or oxygen, the cathode is made of copper and a copper cylinder is placed above it. The formed potassium in molten form is collected in the cylinder. The anode is also made in the form of a cylinder of nickel (in the electrolysis of alkalis) or graphite (in the electrolysis of chlorides).
Physical properties
Potassium is a silvery substance with a characteristic sheen on a freshly formed surface. Very lightweight and lightweight. Relatively well soluble in mercury, forming amalgams. Being introduced into the flame of the burner, potassium (as well as its compounds) colors the flame in a characteristic pink-violet color.
Chemical properties
Elemental potassium, like other alkali metals, exhibits typical metallic properties and is very reactive, being a strong reducing agent. In air, a fresh cut quickly tarnishes due to the formation of films of compounds (oxides and carbonates). With prolonged contact with the atmosphere, it can completely collapse. Reacts explosively with water. It must be stored under a layer of gasoline, kerosene or silicone in order to prevent contact of air and water with its surface. With Na, Tl, Sn, Pb, Bi, potassium forms intermetallic compounds.
The content of the article
POTASSIUM(Kalium) K, a chemical element of Group 1 (Ia) of the Periodic Table, is an alkaline element. Atomic number 19, atomic mass 39.0983. It consists of two stable isotopes 39 K (93.259%) and 41 K (6.729%), as well as a radioactive isotope 40 K with a half-life of ~10 9 years. This isotope plays a special role in nature. Its share in the mixture of isotopes is only 0.01%, however, it is the source of almost all argon 40 Ar contained in the earth's atmosphere, which is formed during the radioactive decay of 40 K. In addition, 40 K is present in all living organisms, which, perhaps, has some influence on their development.
The 40 K isotope is used to determine the age of rocks by the potassium-argon method. The artificial isotope 42 K with a half-life of 15.52 years is used as a radioactive tracer in medicine and biology.
+1 oxidation state.
Potassium compounds have been known since ancient times. Potash - potassium carbonate K 2 CO 3 - has long been isolated from wood ash.
Potassium metal was obtained by electrolysis of molten caustic potash (KOH) in 1807 by the English chemist and physicist Humphry Davy. The name "potassium", chosen by Davy, reflects the origin of this element from potash. The Latin name of the element is derived from the Arabic name for potash - "al-kali". The word "potassium" was introduced into the Russian chemical nomenclature in 1831 by the St. Petersburg academician Hermann Hess (1802–1850).
Distribution of potassium in nature and its industrial extraction.
Large deposits of potassium salts in relatively pure form formed as a result of the evaporation of ancient seas. The most important potassium minerals for the chemical industry are sylvin (KCl) and sylvinite (a mixed salt of NaCl and KCl). Potassium is also found in the form of double chloride KCl MgCl 2 6H 2 O (carnallite) and sulfate K 2 Mg 2 (SO 4) 3 (langbeinite). Massive layers of potassium salts were first discovered in Stassfurt (Germany) in 1856. From them, from 1861 to 1972, potash was mined on an industrial scale.
Ocean water contains about 0.06% potassium chloride. In some inland waters, such as the Salt Lake or the Dead Sea, its concentration can be as high as 1.5%, making it economically viable to extract the element. A huge plant has been built in Jordan, capable of extracting millions of tons of potassium salts from the Dead Sea.
Although sodium and potassium are almost equally abundant in rocks, there is about 30 times less potassium than sodium in the ocean. This is due, in particular, to the fact that potassium salts containing a larger cation are less soluble than sodium salts, and potassium is more strongly bound in complex silicates and aluminosilicates in soil due to ion exchange in clays. In addition, potassium, which is leached from rocks, is more absorbed by plants. It is estimated that out of a thousand potassium atoms released during chemical weathering, only two reach the sea basins, and 998 remain in the soil. “The soil absorbs potassium, and this is its miraculous power,” wrote Academician Alexander Evgenievich Fersman (1883–1945).
Potassium is an essential element of plant life, and the development of wild plants is often limited by the availability of potassium. With a lack of potassium, plants grow more slowly, their leaves, especially old ones, turn yellow and turn brown at the edges, the stem becomes thin and fragile, and the seeds lose their germination capacity. The fruits of such a plant - this is especially noticeable on fruits - will be less sweet than those of plants that have received a normal dose of potassium. The lack of potassium is compensated by fertilizers.
Potash fertilizers are the main type of potassium-containing products (95%). KCl is the most used, accounting for over 90% of the potassium used as fertilizer.
The world production of potash fertilizers in 2003 was estimated at 27.8 million tons (in terms of K 2 O, the content of potassium in potash fertilizers is usually converted to K 2 O). Of these, 33% were made in Canada. 13% of the world production of potash fertilizers is accounted for by the production associations Uralkali and Belaruskali.
Characterization of a simple substance and industrial production of potassium metal.
Potassium is a soft, silvery-white metal with a melting point of 63.51°C and a boiling point of 761°C. It gives the flame a characteristic red-violet color, which is due to the ease of excitation of its outer electrons.
It is chemically very active, easily interacts with oxygen, and ignites when heated in air. The main product of this reaction is potassium superoxide KO 2 .
With water and dilute acids, potassium interacts with explosion and ignition. sulfuric acid reduces to hydrogen sulfide, sulfur and sulfur dioxide, and nitrogen - to nitrogen oxides and N 2.
When heated to 200–350°C, potassium reacts with hydrogen to form KH hydride. Potassium metal ignites in an atmosphere of fluorine, weakly interacts with liquid chlorine, but explodes on contact with bromine and rubbing with iodine. Potassium reacts with chalcogens and phosphorus. With graphite at 250–500°C, it forms layered compounds with the composition C 8 K–C 60 K.
Potassium dissolves in liquid ammonia (35.9 g in 100 ml at -70°C) to form bright blue metastable solutions with unusual properties. This phenomenon was apparently observed for the first time by Sir Humphrey Davy in 1808. Potassium solutions in liquid ammonia have been widely studied since they were obtained by T. Weil in 1863.
Potassium does not dissolve in liquid lithium, magnesium, cadmium, zinc, aluminum and gallium and does not react with them. With sodium, it forms an intermetallic compound KNa 2, which melts with decomposition at 7 ° C. With rubidium and cesium, potassium gives solid solutions with minimum temperatures melting at about 35 ° C. With mercury, it forms an amalgam containing two mercurides KHg 2 and KHg with melting points of 270 and 180 ° C, respectively.
Potassium interacts vigorously with many oxides, reducing them to simple substances. With alcohols, it forms alcoholates.
Unlike sodium, potassium cannot be obtained by electrolysis of a chloride melt, since potassium dissolves very well in molten chloride and does not float to the surface. An additional difficulty is created by the formation of superoxide, which reacts with metallic potassium with an explosion, therefore, the method of industrial production of metallic potassium consists in the reduction of molten potassium chloride with metallic sodium at 850 ° C.
The reduction of potassium chloride with sodium, at first glance, contradicts the usual order of reactivity (potassium is more reactive than sodium). However, at 850–880 ° C, an equilibrium is established:
Na(g) + K + (g) Na + (g) + K(g)
Since potassium is more volatile, it evaporates earlier, which shifts the equilibrium and promotes the reaction. Potassium can be obtained by fractional distillation in a packed column in 99.5% purity, but a mixture of potassium and sodium is usually used for transportation. Alloys containing 15–55% sodium are (at room temperature) liquid, so they are easier to transport.
Sometimes potassium is reduced from chloride by other elements that form stable oxides:
6KCl + 2Al + 4CaO = 3CaCl 2 + CaO Al 2 O 3 + 6K
Potassium metal, which is more difficult and expensive to produce than sodium, is produced in much smaller quantities (world production is about 500 tons per year). One of critical areas applications - obtaining superoxide KO 2 by direct combustion of the metal.
Potassium metal is used as a catalyst in the production of certain types of synthetic rubber, as well as in laboratory practice. An alloy of potassium and sodium serves as a coolant in nuclear reactors. It is also a reducing agent in the production of titanium.
Potassium causes severe skin burns. If even the smallest of its crumbs get into the eyes, loss of vision is possible. Ignite potash is poured with mineral oil or covered with a mixture of talc and sodium chloride.
Potassium is stored in hermetically sealed boxes under a layer of dehydrated kerosene or mineral oil. Potassium wastes are disposed of by treating them with dry ethanol or propanol, followed by decomposition of the resulting alcoholates with water.
Potassium compounds.
Potassium forms numerous binary compounds and salts. Almost all potassium salts are highly soluble. Exceptions are:
KHC 4 H 4 O 6 - potassium hydrogen tartrate
KClO 4 - potassium perchlorate
K 2 Na 6H 2 O - sodium dipotassium hexanitrocobaltate (III) hydrate
K 2 - potassium hexachloroplatinate (IV)
potassium oxide K 2 O forms yellowish crystals. It is obtained by heating potassium with hydroxide, peroxide, nitrate or potassium nitrite:
2KNO 2 + 6K = 4K 2 O + N 2
Heating of a mixture of potassium azide KN 3 and potassium nitrite or oxidation of potassium dissolved in liquid ammonia with a calculated amount of oxygen is also used.
Potassium oxide is an activator of sponge iron, which is used as a catalyst in the synthesis of ammonia.
Potassium peroxide It is difficult to obtain K 2 O 2 from simple substances, since it is easily oxidized to superoxide KO 2, therefore metal oxidation with NO is used. However, the best method for its preparation is the quantitative oxidation of the metal dissolved in liquid ammonia.
Potassium peroxide can be considered as a dibasic acid salt H 2 O 2 . Therefore, when it interacts with acids or water in the cold, hydrogen peroxide is quantitatively formed.
Potassium superoxide KO 2 (orange) is formed during the normal combustion of metal in air. This compound is used as a backup source of oxygen in breathing masks in mines, submarines and spacecraft.
With careful thermal decomposition of KO 2, the sesquioxide “K 2 O 3 ” is formed in the form of a dark paramagnetic powder. It can also be obtained by oxidation of a metal dissolved in liquid ammonia, or by controlled oxidation of peroxide. It is assumed that it is dinaperoxide-peroxide [(K +) 4 (O 2 2–)(O 2 –) 2].
Potassium ozonide KO 3 can be obtained by the action of ozone on anhydrous potassium hydroxide powder at low temperature, followed by extraction of the product (red) with liquid ammonia. It is used as a component of compositions for regeneration of air in closed systems.
Potassium hydroxide KOH is a strong base and belongs to alkalis. Its traditional name "caustic potash" reflects the corrosive effect of this substance on living tissues.
In industry, potassium hydroxide is obtained by electrolysis of aqueous solutions of potassium chloride or carbonate with an iron or mercury cathode (world production is about 0.7 million tons per year). Potassium hydroxide can be isolated from the filtrate after separating the precipitates formed by the interaction of potassium carbonate with calcium hydroxide or potassium sulfate with barium hydroxide.
Potassium hydroxide is used to make liquid soap and various potassium compounds. In addition, it serves as an electrolyte in alkaline batteries.
Potassium fluoride KF forms the rare mineral carobbiite. Potassium fluoride is obtained by the interaction of aqueous solutions of hydrogen fluoride or ammonium fluoride with potassium hydroxide or its salts.
Potassium fluoride is used for the synthesis of various fluorine-containing potassium compounds, as a fluorinating agent in organic synthesis, and also as a component of acid-resistant putties and special glasses.
potassium chloride KCl is found in nature. The raw materials for its isolation are sylvin, sylvinite, carnallite.
Potassium chloride is obtained from sylvinite by the methods of galurgy and flotation. Galurgy (translated from Greek - "salt business") includes the study of the composition and properties of natural salt raw materials and the development of methods for the industrial production of mineral salts from it. The halurgical separation method is based on the different solubility of KCl and NaCl in water at elevated temperatures. At normal temperature, the solubility of potassium and sodium chlorides is almost the same. With increasing temperature, the solubility of sodium chloride almost does not change, and the solubility of potassium chloride increases sharply. In the cold, a saturated solution of both salts is prepared, then it is heated and sylvinite is treated with it. In this case, the solution is additionally saturated with potassium chloride, and part of the sodium chloride is displaced from the solution, precipitates and is separated by filtration. The solution is cooled and excess potassium chloride crystallizes out. The crystals are separated in centrifuges and dried, and the mother liquor is used to process a new portion of sylvinite. For the isolation of potassium chloride, this method is used more widely than the flotation method, which is based on different wettability of substances.
Potassium chloride is the most common potash fertilizer. In addition to its use as a fertilizer, it is mainly used for the production of potassium hydroxide by electrolysis. Other potassium compounds are also obtained from it.
Potassium bromide KBr is obtained by reacting bromine with potassium hydroxide in the presence of ammonia, as well as by reacting bromine or bromides with potassium salts.
Potassium bromide is widely used in photography. It often serves as a source of bromine in organic synthesis. Previously, potassium bromide was used as a sedative in medicine ("bromine"). Potassium bromide single crystals are used in the manufacture of prisms for IR spectrometers, and also as a matrix when taking IR spectra of solids.
potassium iodide KI forms colorless crystals, which become yellowish in light due to oxidation with atmospheric oxygen and release of iodine. Therefore, potassium iodide is stored in dark glass bottles.
Potassium iodide is obtained by the interaction of iodine with potassium hydroxide in the presence of formic acid or hydrogen peroxide, as well as by the exchange reactions of iodides with potassium salts. It is oxidized with nitric acid to potassium iodate KIO 3 . Potassium iodide reacts with iodine to form a water-soluble complex K, and with chlorine and bromine gives K and K, respectively.
Potassium iodide is used as a drug in medicine and veterinary medicine. It is a reagent in iodometry. Potassium iodide is an anti-fogging agent in photography, an electrolyte component in electrochemical converters, an additive to increase the solubility of iodine in water and polar solvents, a microfertilizer.
potassium sulfide K 2 S is highly soluble in water. During hydrolysis, it creates an alkaline environment in the solution:
K 2 S = 2K + + S 2– ; S 2– + H 2 O HS – + OH –
Potassium sulfide is easily oxidized in air and burns when ignited. It is obtained by the interaction of potassium or potassium carbonate with sulfur without access to air, as well as the reduction of potassium sulfate with carbon.
Potassium sulfide is a component of photosensitive emulsions in photography. It is used as an analytical reagent for separating metal sulfides and as a component of hide treatment formulations.
When an aqueous solution is saturated with hydrogen sulfide, potassium hydrosulfide KHS is formed, which can be isolated as colorless crystals. It is used in analytical chemistry for the separation of heavy metals.
By heating potassium sulfide with sulfur, yellow or red potassium polysulfides KS are obtained. n (n= 2–6). Aqueous solutions of potassium polysulfides can be obtained by boiling solutions of potassium hydroxide or potassium sulfide with sulfur. When potassium carbonate is sintered with excess sulfur in air, the so-called sulfur liver is formed - a mixture of KS n and K 2 S 2 O 3 .
Polysulfides are used for sulfiding steel and cast iron. Sulfuric liver is used as medicine for the treatment of skin diseases and as a pesticide.
potassium sulfate K 2 SO 4 occurs naturally in potassium salt deposits and in the waters of salt lakes. It can be obtained by an exchange reaction between potassium chloride and sulfuric acid or sulfates of other elements.
Potassium sulfate is used as a fertilizer. This substance is more expensive than potassium chloride, but not hygroscopic and non-caking, unlike potassium chloride, potassium sulfate can be used on any soil, including saline.
Alum and other potassium compounds are obtained from potassium sulfate. It is part of the charge in glass production.
potassium nitrate KNO 3 is a strong oxidizing agent. It is often referred to as potassium nitrate. In nature, it is formed during the decomposition of organic substances as a result of the vital activity of nitrifying bacteria.
Potassium nitrate is obtained by an exchange reaction between potassium chloride and sodium nitrate, as well as by the action of nitric acid or nitrous gases on potassium carbonate or chloride.
Potassium nitrate is an excellent fertilizer containing both potassium and nitrogen, but is used less than potassium chloride due to high cost production. Potassium nitrate is also used for the manufacture of black powder and pyrotechnic compositions, in the production of matches and glass. In addition, it is used in the preservation of meat products.
Potassium carbonate K 2 CO 3 is also called potash. Obtained by the action of carbon dioxide on solutions of potassium hydroxide or suspensions of magnesium carbonate in the presence of potassium chloride. It is a by-product in the processing of nepheline into alumina.
A significant amount of potassium carbonate is found in plant ash. Most of all potassium is in sunflower ash - 36.3%. In the ashes of firewood, potassium oxide is much less - from 3.2% (spruce firewood) to 13.8% (birch firewood). There is even less potassium in peat ash.
Potassium carbonate is mainly used to produce high quality glass used in optical lenses, color television tubes and fluorescent lamps. It is also used in the production of porcelain, dyes and pigments.
Potassium permanganate KMnO 4 forms dark purple crystals. Solutions of this substance have a red-violet color. Potassium permanganate is obtained by anodic oxidation of manganese or ferromanganese in a strongly alkaline medium.
Potassium permanganate is a strong oxidizing agent. It is used as a bleaching, bleaching and cleansing agent. It is also used in organic synthesis, for example, in the production of saccharin.
Potassium hydride KH is a white solid that decomposes into simple substances. Potassium hydride is the strongest reducing agent. It ignites in humid air and in fluorine or chlorine environments. Potassium hydride can be oxidized even with weak oxidizing agents such as water and carbon dioxide:
KH + H 2 O \u003d KOH + H 2
KH + CO 2 \u003d K (HCOO) (potassium formate)
Potassium hydride also reacts with acids and alcohols and may ignite. It reduces hydrogen sulfide, hydrogen chloride and other substances containing hydrogen (I):
2KH + H 2 S = K 2 S + 2H 2
KH + HCl \u003d KCl + H 2
Potassium hydride is used as a reducing agent in inorganic and organic syntheses.
Potassium cyanide KCN, known as potassium cyanide, forms colorless crystals that are highly soluble in water and some non-aqueous solvents. In an aqueous solution, it gradually hydrolyzes with the release of hydrogen cyanide HCN, and when aqueous solutions are boiled, it decomposes into potassium formate and ammonia.
In the presence of potassium cyanide, not quite ordinary reactions can take place, for example, copper reacts with water, releasing hydrogen from it and forming potassium dicyanocuprate (I):
Under similar conditions, interaction takes place in the case of gold. True, this less active metal is not capable of being oxidized by water, however, in the presence of oxygen, it passes into solution in the form of a cyano complex - potassium dicyanoaurate(I):
4Au + 8KCN + 2H 2 O + O 2 \u003d 4K + 4NaOH
Potassium cyanide is prepared by reacting hydrogen cyanide with an excess of potassium hydroxide. It is a reagent for the extraction of silver and gold from poor ores, a component of electrolytes for the purification of platinum from silver and for electroplating gilding and silvering. Potassium cyanide is used as a reagent in chemical analysis for the determination of silver, nickel and mercury.
Potassium cyanide is highly toxic. The lethal dose for humans is 120 mg.
Complex compounds. Potassium forms the most stable complex compounds with polydentate ligands (molecules or ions that can combine with an atom by several bonds), for example, with macrocyclic polyesters (crown ethers).
Crown ethers (from the English crown - crown) contain more than 11 atoms in the cycle, of which at least four are oxygen atoms. In the trivial names of crown ethers, the total number of atoms in the cycle and the number of oxygen atoms are denoted by numbers, which are placed before and after the word "crown", respectively. Such names are much shorter than systematic ones. For example, 12-crown-4 (Fig. 1) is called 1,4,7,10,13-tetraoxocyclododecane according to the international nomenclature.
Rice. 1. GRAPHIC FORMULA compounds 12-crown-4.
Crown ethers form stable complexes with metal cations. In this case, the cation is included in the intramolecular cavity of the crown ether and is retained there due to ion-dipole interaction with oxygen atoms. The most stable complexes are those with cations whose geometrical parameters correspond to the crown ether cavity. The most stable complexes with the potassium cation form crown ethers containing 6 oxygen atoms, for example, 18-crown-6 (Fig. 2).
Rice. 2. GRAPHIC FORMULA potassium complex 18-crown-6 .
The biological role of potassium(and sodium). Potassium together with sodium regulate metabolic processes in living organisms. In the human body, cells contain a large amount of potassium ions (0.12–0.16 mol/l), but relatively few sodium ions (0.01 mol/l). The content of sodium ions is much higher in the extracellular fluid (about 0.12 mol / l), therefore, potassium ions control intracellular activity, and sodium ions control intercellular activity. These ions cannot replace each other.
The existence of a sodium-potassium gradient from the inner and outer sides of the cell membrane leads to the appearance of a potential difference on opposite sides of the membrane. Nerve fibers are able to transmit impulses, and muscles are able to contract precisely due to the existence of an internal negative charge in relation to the outer surface of the membrane. Thus, in the body, sodium and potassium ions exercise physiological control and triggers. They contribute to the transmission of nerve impulses. The human psyche depends on the balance of sodium and potassium ions in the body. The concentration of sodium and potassium ions retained and excreted through the kidneys is controlled by certain hormones. Thus, mineralocorticoids contribute to an increase in the release of potassium ions and a decrease in the release of sodium ions.
Potassium ions are part of enzymes that catalyze the transfer (transport) of ions through biomembranes, redox and hydrolytic processes. They also serve to maintain the structure of cell walls and control their condition. The sodium ion activates several enzymes that potassium cannot activate, just as the sodium ion cannot act on potassium-dependent enzymes. When these ions enter the cell, they are bound by the appropriate ligands according to their chemical activity. The role of such ligands is played by macrocyclic compounds, the model analogs of which are crown ethers. Some antibiotics (like valinomycin) transport potassium ions into the mitochondria.
It has been established that for the operation of (Na + –K +)-ATPase (adenosine triphosphatase), a membrane enzyme that catalyzes the hydrolysis of ATP, sodium and potassium ions are needed simultaneously. The transport ATPase binds and releases sodium and potassium ions at certain stages of the enzymatic reaction, since the affinity of the active sites of the enzyme for sodium and potassium ions changes as the reaction proceeds. At the same time, structural changes in the enzyme lead to the fact that sodium and potassium cations are accepted on one side of the membrane, and are released on the other. Thus, simultaneously with the hydrolysis of ATP, there is also a selective movement of cations of alkaline elements (the operation of the so-called Na–K pump).
The daily requirement for potassium in a child is 12-13 mg per 1 kg of weight, and in an adult - 2-3 mg, i.e. 4-6 times less. A person receives most of the potassium he needs from food of plant origin.
Elena Savinkina
