Charles Montesquieu years of life. Chapter VI
Potassium was discovered in the fall of 1807 by the English chemist Davy during the electrolysis of solid caustic potassium. Having moistened caustic potassium, the scientist isolated the metal, which he gave the name potassius, hinting at production potash(a necessary ingredient for making detergents) from ash. The metal received its usual name two years later, in 1809, the initiator of the renaming of the substance was L.V. Gilbert, who suggested the name potassium(from Arabic al-kali- potash).
Potassium (lat. Kalium) is a soft alkali metal, an element of the main subgroup of group I, period IV of the periodic table of chemical elements D.I. Mendeleev, has atomic number 19 and the designation - TO.
Being in nature
Potassium does not occur in a free state in nature; it is part of all cells. A fairly common metal, it ranks 7th in terms of content in the earth’s crust (calorizator). The main suppliers of potassium are Canada, Belarus and Russia, which have large deposits of this substance.
Physical and chemical properties
Potassium is a low-melting silver-white metal. It has the property of turning an open fire a bright purple-pink color.
Potassium has high chemical activity and is a strong reducing agent. When reacting with water, an explosion occurs; when exposed to air for a long time, it completely collapses. Therefore, potassium requires certain conditions for storage - it is filled with a layer of kerosene, silicone or gasoline to prevent contact with water and the atmosphere that is harmful to the metal.
The main food sources of potassium are dried nut butters, citrus fruits, and all green leafy vegetables. There is quite a lot of potassium in fish and... In general, potassium is included in almost all plants. and - champions in potassium content.
Daily potassium requirement
The daily need of the human body for potassium depends on age, physical condition and even place of residence. Healthy adults need 2.5 g of potassium, pregnant women - 3.5 g, athletes - up to 5 grams of potassium daily. The amount of potassium required for adolescents is calculated by weight - 20 mg of potassium per 1 kg of body weight.
Beneficial properties of potassium and its effect on the body
Potassium is involved in the process of conducting nerve impulses and transmitting them to innervated organs. Promotes better brain activity by improving its supply. Has a positive effect on many allergic conditions. Potassium is necessary for skeletal muscle contractions. Potassium regulates the content of salts, alkalis and acids in the body, which helps reduce swelling.
Potassium is found in all intracellular fluids; it is necessary for the normal functioning of soft tissues (muscles, blood vessels and capillaries, endocrine glands, etc.)
Potassium absorption
Potassium is absorbed into the body from the intestines, where it enters with food, and is excreted in the urine, usually in the same amount. Excess potassium is eliminated from the body in the same way and is not retained or accumulated. Excessive consumption of coffee, sugar, and alcohol can interfere with the normal absorption of potassium.
Interaction with others
Potassium works closely with sodium and magnesium; with an increase in potassium concentration, sodium is rapidly removed from the body, and a decrease in the amount of magnesium can interfere with the absorption of potassium.
Signs of potassium deficiency
A lack of potassium in the body is characterized by muscle weakness, fatigue, decreased immunity, disruptions in myocardial function, abnormal blood pressure, rapid and difficult breathing. The skin may peel, damage does not heal well, and hair becomes very dry and brittle. Malfunctions in the gastrointestinal tract occur - nausea, vomiting, indigestion, even gastritis and ulcers.
Signs of excess potassium
An excess of potassium occurs with an overdose of drugs containing potassium and is characterized by neuromuscular disorders, increased sweating, excitability, irritability and tearfulness. A person constantly experiences a feeling of thirst, which leads to frequent urination. The gastrointestinal tract reacts with intestinal colic, alternating constipation and diarrhea.
Uses of potassium in life
Potassium in the form of basic compounds is widely used in medicine, agriculture and industry. Potassium fertilizers are necessary for normal growth and ripening of plants, and everyone knows potassium permanganate, this is nothing more than potassium permanganate, a time-tested antiseptic.
The content of the article
POTASSIUM(Kalium) K, chemical element 1 (Ia) of group of the Periodic table, belongs to the alkaline elements. 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%, but 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 may has a certain influence on their development.
The 40 K isotope is used to determine the age of rocks using 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.
Oxidation state +1.
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 prepared by electrolysis of molten potassium hydroxide (KOH) in 1807 by the English chemist and physicist Humphry Davy. The name "potassium" chosen by Davy reflects the element's origins in potash. The Latin name of the element is derived from the Arabic name for potash - “al-kali”. The word “potassium” was introduced into Russian chemical nomenclature in 1831 by a 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 were 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. Potash was mined from them on an industrial scale from 1861 to 1972.
Ocean water contains about 0.06% potassium chloride. In some inland bodies of water, such as Salt Lake or the Dead Sea, its concentration can reach 1.5%, which makes the extraction of the element economically feasible. 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, the ocean contains about 30 times less potassium than sodium. 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 firmly bound in complex silicates and aluminosilicates in the soil due to ion exchange in clays. In addition, potassium that is leached from rocks is absorbed to a greater extent by plants. It is estimated that of the thousand potassium atoms released by chemical weathering, only two reach marine 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 potassium availability. With a lack of potassium, plants grow more slowly, their leaves, especially old ones, turn yellow and brown at the edges, the stem becomes thin and fragile, and the seeds lose their viability. The fruits of such a plant - this is especially noticeable in fruits - will be less sweet than those of plants that received a normal dose of potassium. The lack of potassium is compensated with fertilizers.
Potash fertilizers are the main type of potassium-containing products (95%). KCl is the most used, accounting for more than 90% of the potassium used as fertilizer.
World production of potash fertilizers in 2003 was estimated at 27.8 million tons (in terms of K 2 O, the potassium content in potash fertilizers is usually converted to K 2 O). Of these, 33% were produced in Canada. The Uralkali and Belaruskali production associations account for 13% of the global production of potash fertilizers.
Characteristics of simple substances 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 associated with 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 reacts with explosion and ignition. Sulfuric acid is reduced to hydrogen sulfide, sulfur and sulfur dioxide, and nitric acid is reduced to nitrogen oxides and N 2.
When heated to 200–350° C, potassium reacts with hydrogen to form the hydride KH. Potassium metal ignites in a fluorine atmosphere, reacts weakly with liquid chlorine, but explodes on contact with bromine and trituration with iodine. Potassium reacts with chalcogens and phosphorus. With graphite at 250–500° C it forms layered compounds of the composition C 8 K–C 60 K.
Potassium dissolves in liquid ammonia (35.9 g per 100 ml at –70 ° C) to form bright blue metastable solutions with unusual properties. This phenomenon was apparently first observed by Sir Humphry Davy in 1808. Solutions of potassium 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 melting points of about 35 ° C. With mercury it forms an amalgam containing two mercurides KHg 2 and KHg with melting points 270 and 180° C, respectively.
Potassium reacts vigorously with many oxides, reducing them to simple substances. With alcohols it forms alcoholates.
Unlike sodium, potassium cannot be obtained by electrolysis of molten chloride, 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 potassium metal explosively, so the method of industrial production of potassium metal is to reduce molten potassium chloride with sodium metal 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 equilibrium is established:
Na(g) + K + (l) Na + (l) + K(g)
Since potassium is more volatile, it evaporates earlier, which shifts the equilibrium and promotes the reaction. Fractional distillation in a packed column can produce potassium of 99.5% purity, but usually a mixture of potassium and sodium is 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 the most important areas of application is the production of superoxide KO 2 by direct combustion of 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 crumbs get into your eyes, loss of vision can occur. The ignited potassium is poured with mineral oil or covered with a mixture of talc and sodium chloride.
Store potassium in hermetically sealed boxes under a layer of dehydrated kerosene or mineral oil. Potassium waste is disposed of by treating it 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. The 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 prepared by heating potassium with potassium hydroxide, peroxide, nitrate or 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 K2O2 from simple substances, since it is easily oxidized to superoxide KО2, so 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 salt of the dibasic acid 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 by 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, sesquioxide “K 2 O 3” is formed in the form of a dark paramagnetic powder. It can also be obtained by oxidation of the metal dissolved in liquid ammonia, or by controlled oxidation of peroxide. It is assumed to be a dinad peroxide 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 air regeneration in closed systems.
Potassium hydroxide KOH is a strong base and belongs to alkalis. Its traditional name “caustic potassium” reflects the corrosive effect of this substance on living tissue.
In industry, potassium hydroxide is produced 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 reaction of potassium carbonate with calcium hydroxide or potassium sulfate with barium hydroxide.
Potassium hydroxide is used to produce 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 reacting 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 occurs naturally. The raw materials for its isolation are sylvin, sylvinite, and carnallite.
Potassium chloride is obtained from sylvinite using the methods of halurgy and flotation. Galurgy (translated from Greek as “salt work”) 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 them. The halurgical separation method is based on the different solubilities of KCl and NaCl in water at elevated temperatures. At normal temperatures, the solubility of potassium and sodium chlorides is almost the same. With increasing temperature, the solubility of sodium chloride remains almost unchanged, but the solubility of potassium chloride increases sharply. A saturated solution of both salts is prepared in the cold, 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 of it. The crystals are separated in centrifuges and dried, and the mother liquor is used to process a new portion of sylvinite. To isolate 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. Apart from its use as a fertilizer, it is mainly used to produce 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 reactions of 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 for recording IR spectra of solids.
Potassium iodide KI forms colorless crystals, which in the light become yellowish due to oxidation by atmospheric oxygen and the release of iodine. Therefore, potassium iodide is stored in dark glass bottles.
Potassium iodide is obtained by reacting iodine with potassium hydroxide in the presence of formic acid or hydrogen peroxide, as well as by 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 it gives K and K, respectively.
Potassium iodide is used as a medicine in human and veterinary medicine. It is a reagent in iodometry. Potassium iodide is an anti-foiling agent in photography, an electrolyte component in electrochemical converters, an additive for increasing 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 easily oxidizes in air and burns when ignited. It is obtained by reacting potassium or potassium carbonate with sulfur without access to air, as well as by reducing potassium sulfate with carbon.
Potassium sulfide is a component of photosensitive emulsions in photography. It is used as an analytical reagent for the separation of metal sulfides and as a component of compositions for the treatment of hides.
When an aqueous solution is saturated with hydrogen sulfide, potassium hydrosulfide KHS is formed, which can be isolated in the form of 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 sulfide with sulfur. When potassium carbonate is sintered with excess sulfur in air, the so-called sulfur liver is formed - KS mixture n and K 2 S 2 O 3 .
Polysulfides are used for sulfidation of steel and cast iron. Liver sulfur is used as a medicine to treat skin diseases and as a pesticide.
Potassium sulfate K 2 SO 4 occurs naturally in deposits of potassium salts 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 is not hygroscopic and does not caking; unlike potassium chloride, potassium sulfate can be used on any soil, including saline soils.
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 called potassium nitrate. In nature, it is formed during the decomposition of organic substances as a result of the activity of nitrifying bacteria.
Potassium nitrate is obtained by the 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 the high cost of 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 canning 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 during the processing of nepheline into alumina.
A significant amount of potassium carbonate is contained in plant ash. The most potassium is in sunflower ash – 36.3%. There is significantly less potassium oxide in the ash of firewood - from 3.2% (spruce firewood) to 13.8% (birch firewood). There is even less potassium in peat ash.
Potassium carbonate is used primarily 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, whitening 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 when heated. Potassium hydride is the strongest reducing agent. It ignites in moist air and in fluorine or chlorine environments. Potassium hydride can be oxidized even by weak oxidizing agents such as water and carbon dioxide:
KH + H 2 O = KOH + H 2
KH + CO 2 = K(HCOO) (potassium formate)
Potassium hydride also reacts with acids and alcohols, which may cause fire. It reduces hydrogen sulfide, hydrogen chloride and other substances containing hydrogen (I):
2KH + H 2 S = K 2 S + 2H 2
KH + HCl = KCl + H2
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, unusual reactions can occur, for example, copper reacts with water, releasing hydrogen from it and forming potassium dicyanocuprate(I):
In similar conditions, interaction occurs in the case of gold. True, this less active metal is not able to be oxidized by water, but in the presence of oxygen it goes into solution in the form of a cyano complex - potassium dicyanoaurate(I):
4Au + 8KCN + 2H 2 O + O 2 = 4K + 4NaOH
Potassium cyanide is prepared by reacting hydrogen cyanide with excess potassium hydroxide. It is a reagent for the extraction of silver and gold from low-grade 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 very toxic. The lethal dose for humans is 120 mg.
Complex connections. Potassium forms the most stable complex compounds with polydentate ligands (molecules or ions that can be connected to an atom by several bonds), for example, with macrocyclic polyethers (crown ethers).
Crown ethers (from the English crown - crown) contain over 11 atoms in the ring, at least four of which are oxygen atoms. In the trivial names of crown ethers, the total number of atoms in the ring and the number of oxygen atoms are designated by numbers, which are placed, respectively, before and after the word “crown”. Such names are much shorter than systematic ones. For example, 12-crown-4 (Fig. 1) according to the international nomenclature is called 1,4,7,10,13-tetraoxocyclododecane.
Rice. 1. GRAPHIC FORMULA 12-crown-4 compounds.
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 the ion-dipole interaction with oxygen atoms. The most stable complexes are those with cations whose geometric parameters correspond to the cavity of the crown ether. With the potassium cation, the most stable complexes are formed by crown ethers containing 6 oxygen atoms, for example, 18-crown-6 (Fig. 2).
Rice. 2. GRAPHIC FORMULA complex kalias 18-crown-6 .
Biological role of potassium(and sodium). Potassium together with sodium regulate metabolic processes in living organisms. In the human body, inside the cells there is 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 emergence 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 trigger mechanisms. 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 released through the kidneys is controlled by certain hormones. Thus, mineralocorticoids increase the release of potassium ions and reduce 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 suitable ligands according to their chemical activity. The role of such ligands is played by macrocyclic compounds, the model analogues of which are crown ethers. Some antibiotics (like valinomycin) transport potassium ions into the mitochondria.
It has been established that the operation of (Na + –K +)-ATPase (adenosine triphosphatase), a membrane enzyme that catalyzes the hydrolysis of ATP, requires both sodium and potassium ions. ATP transportase 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. In this case, structural changes in the enzyme lead to the fact that sodium and potassium cations are accepted on one side of the membrane and released on the other. Thus, simultaneously with the hydrolysis of ATP, the selective movement of cations of alkaline elements occurs (the work of the so-called Na–K pump).
The daily potassium requirement for a child is 12–13 mg per 1 kg of weight, and for an adult – 2–3 mg, i.e. 4–6 times less. A person gets most of the potassium he needs from foods of plant origin.
Elena Savinkina
Atomic number | |
Appearance of a simple substance |
Silver-white soft metal |
Properties of the atom | |
Atomic mass (molar mass) |
39.0983 a. e.m. (g/mol) |
Atomic radius | |
Ionization energy (first electron) |
418.5 (4.34) kJ/mol (eV) |
Electronic configuration | |
Chemical properties | |
Covalent radius | |
Ion radius | |
Electronegativity (according to Pauling) |
|
Electrode potential | |
Oxidation states | |
Thermodynamic properties of a simple substance | |
Density | |
Molar heat capacity |
29.6 J/(K mol) |
Thermal conductivity |
79.0 W/(m K) |
Melting temperature | |
Heat of Melting |
102.5 kJ/mol |
Boiling temperature | |
Heat of vaporization |
2.33 kJ/mol |
Molar volume |
45.3 cm³/mol |
Crystal lattice of a simple substance | |
Lattice structure |
cubic body-centered |
Lattice parameters | |
c/a ratio | — |
Debye temperature |
K | 19 |
39,0983 | |
4s 1 | |
- an element of the main subgroup of the first group, the fourth period of the periodic system of chemical elements of D.I. Mendeleev, with atomic number 19. Denoted by the symbol K (lat. Kalium). The simple substance potassium (CAS number: 7440-09-7) is a soft alkali metal with a silvery-white color. In nature, potassium is found only in combination 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 use by the cells of living organisms, they are still different. History and origin of the name potassium
Potassium (more precisely, its compounds) has been used since ancient times. Thus, the production of potash (which was used as a detergent) existed already in the 11th century. The ash formed when burning 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 K2SO4, soda and potassium chloride KCl.
In 1807, the English chemist Davy isolated potassium by electrolysis of solid potassium hydroxide (KOH) and named it "potassian"(lat. potassium; this name is still used 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 entered the German language, from there into most languages of Northern and Eastern Europe (including Russian) and “won” when choosing a symbol for this element - K.
Presence of potassium in nature
Not found in a free state. Potassium is part of sylvinite KCl NaCl, carnallite KCl MgCl 2 6H 2 O, kainite KCl MgSO 4 6H 2 O, and is also present in the ash of some plants in the form of carbonate K 2 CO 3 (potash). Potassium is found in all cells (see section below Biological role).
Potassium - getting potassium
Potassium, like other alkali metals, is obtained by electrolysis of molten chlorides or alkalis. Since chlorides have a higher melting point (600-650 °C), electrolysis of straightened alkalis is more often 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 is released at the anode:
4OH − − 4e − → 2H 2 O + O 2
The water from the melt evaporates quickly. To prevent potassium from interacting with chlorine or oxygen, the cathode is made of copper and a copper cylinder is placed above it. The resulting potassium is collected in molten form in a cylinder. The anode is also made in the form of a cylinder of nickel (for the electrolysis of alkalis) or of graphite (for the electrolysis of chlorides).
Physical properties of potassium
Potassium is a silvery substance with a characteristic shine on a freshly formed surface. Very light and fusible. It dissolves relatively well in mercury, forming amalgams. When potassium (as well as its compounds) is added to the burner flame, it colors the flame in a characteristic pink-violet color.
Chemical properties of potassium
Potassium, like other alkali metals, exhibits typical metallic properties and is very chemically active, easily donating electrons.
Is a strong reducing agent. It combines so actively with oxygen that not an oxide is formed, but potassium superoxide KO 2 (or K 2 O 4). When heated in a hydrogen atmosphere, potassium hydride KH is formed. It interacts well with all non-metals, forming halides, sulfides, nitrides, phosphides, etc., as well as with complex substances such as water (the reaction occurs explosively), various oxides and salts. In this case, they reduce other metals to a free state.
Potassium is stored under a layer of kerosene.
Potassium oxides and potassium peroxides
When potassium reacts with atmospheric oxygen, it forms not an oxide, but a peroxide and superoxide:
Potassium oxide can be obtained by heating the metal to a temperature not exceeding 180 °C in an environment containing very little oxygen, or by heating a mixture of potassium superoxide with potassium metal:
Potassium oxides have pronounced basic properties and react violently with water, acids and acid oxides. They have no practical significance. Peroxides are yellowish-white powders that, soluble in water, form alkalis and hydrogen peroxide:
The ability to exchange carbon dioxide for oxygen is used in insulating gas masks and on submarines. An equimolar mixture of potassium superoxide and sodium peroxide is used as an absorber. If the mixture is not equimolar, then in the case of an excess of sodium peroxide, more gas will be absorbed than released (when absorbing two volumes of CO 2, one volume of O 2 is released), and the pressure in a confined space will drop, and in the case of an excess of potassium superoxide (when absorbing two volumes of CO 2 three volumes of O are released 2) more gas is released than absorbed, and the pressure will increase.
In the case of an equimolar mixture (Na 2 O 2:K 2 O 4 = 1:1), the volumes of absorbed and released gases will be equal (when four volumes of CO 2 are absorbed, four volumes of O 2 are released).
Peroxides are strong oxidizing agents, so they are used to bleach fabrics in the textile industry.
Peroxides are obtained by calcining metals in air freed from carbon dioxide.
Potassium hydroxides
Potassium hydroxide (or caustic potassium) are hard white opaque, very hygroscopic crystals that melt at a temperature of 360 °C. Potassium hydroxide is an alkali. It dissolves well in water and releases a large amount of heat. The solubility of potassium hydroxide at 20 °C in 100 g of water is 112 g.
Potassium uses
- An alloy of potassium and sodium, liquid at room temperature, is used as a coolant in closed systems, for example, in fast neutron nuclear power plants. In addition, its liquid alloys with rubidium and cesium are widely used. The alloy of composition sodium 12%, potassium 47%, cesium 41% has a record low melting point of −78 °C.
- Potassium compounds are the most important biogenic element and are therefore used as fertilizers.
- Potassium salts are widely used in electroplating because, despite their relatively high cost, they are often more soluble than the corresponding sodium salts, and therefore provide intensive operation of electrolytes at increased current densities.
Important Connections
Purple color of potassium ions flame in burner flame
- Potassium bromide is used in medicine and as a sedative for the nervous system.
- Potassium hydroxide (caustic potash) - used in alkaline batteries and when drying gases.
- Potassium carbonate (potash) - used as fertilizer in glass making.
- Potassium chloride (sylvin, "potassium salt") - used as a fertilizer.
- Potassium nitrate (potassium nitrate) is a fertilizer, a component of black powder.
- Potassium perchlorate and chlorate (Bertholet salt) are used in the production of matches, rocket powders, lighting charges, explosives, and in electroplating.
- Potassium dichromate (chrompic) is a strong oxidizing agent, used to prepare a “chromium mixture” for washing chemical dishes and in leather processing (tanning). It is also used to purify acetylene in acetylene plants from ammonia, hydrogen sulfide and phosphine.
- Potassium permanganate is a strong oxidizing agent, used as an antiseptic in medicine and for the laboratory production of oxygen.
- Sodium potassium tartrate (Rochelle salt) as a piezoelectric.
- Potassium dihydrogen phosphate and dideuterophosphate in the form of single crystals in laser technology.
- Potassium peroxide and potassium superoxide are used for air regeneration in submarines and in insulating gas masks (absorbs carbon dioxide to release oxygen).
- Potassium fluoroborate is an important flux for soldering steels and non-ferrous metals.
- Potassium cyanide is used in electroplating (silvering, gilding), gold mining and nitrocarburizing of steel.
- Potassium, together with potassium peroxide, is used in the thermochemical decomposition of water into hydrogen and oxygen (potassium cycle "Gaz de France", France).
Biological role
Potassium is the most important biogenic element, especially in the plant world. If there is a lack of potassium in the soil, plants develop very poorly, the yield decreases, therefore about 90% of the extracted potassium salts are used as fertilizers.
Potassium in the human body
Potassium is found mostly in cells, up to 40 times more than in the intercellular space. As cells function, excess potassium leaves the cytoplasm, so to maintain concentration it must be pumped back through the sodium-potassium pump.
Potassium and sodium are functionally related to each other and perform the following functions:
- Creating conditions for the occurrence of membrane potential and muscle contractions.
- Maintaining blood osmotic concentration.
- Maintaining acid-base balance.
- Normalization of water balance.
- Ensuring membrane transport.
- Activation of various enzymes.
- Normalization of heart rhythm.
The recommended daily dose of potassium is from 600 to 1700 milligrams for children, and from 1800 to 5000 milligrams for adults. The need for potassium depends on total body weight, physical activity, physiological state, and climate of the place of residence. Vomiting, prolonged diarrhea, profuse sweating, and the use of diuretics increase the body's need for potassium.
The main food sources are dried apricots, melon, beans, kiwi, potatoes, avocados, bananas, broccoli, liver, milk, nut butters, citrus fruits, grapes. There is a lot of potassium in fish and dairy products.
Absorption occurs in the small intestine. The absorption of potassium is facilitated by vitamin B6, and complicated by alcohol.
With a lack of potassium, hypokalemia develops. There are disturbances in the functioning of the cardiac and skeletal muscles. Long-term potassium deficiency can cause acute neuralgia.