Калий

Описание

Potassium has atomic number 19 and the chemical symbol K, which is derived from its Latin name kalium . Potassium was first isolated from potash, which is potassium carbonate (K₂CO₃). Potassium occurs in nature only in the form of its ion (K⁺) either dissolved in the ocean or coordinated in minerals because elemental potassium reacts violently with water . Potassium ions are essential for the human body and are also present in plants. The major use of K⁺ can be found in fertilisers, which contains a variety of potassium salts such as potassium chloride (KCl), potassium sulfate (K₂SO₄) and potassium nitrate (KNO₃).

Химические свойства

Potassium is a soft silvery metal, tarnishing upon exposure to air.

Физические свойства

Elemental potassium is a soft, butter-like silvery metal whose cut surface oxidizes in dryair to form a dark gray potassium superoxide (KO₂) coating. KO₂ is an unusual compound,in that it reacts with both water and carbon dioxide to produce oxygen gas. It appears morelike a hard wax than a metal. Its density (specific gravity) is 0.862 g/cm³, its melting point is63.25°C, and its boiling point is 760°C. It has an oxidation state of +1 and reacts explosivelywith room temperature air or water to form potassium hydroxide as follows: 2K + 2 H₂O→? 2KOH + H₂. This is an endothermic reaction, which means the heat generated is greatenough to ignite the liberated hydrogen gas. Potassium metal must be stored in a non-oxygen,non-aqueous environment such as kerosene or naphtha.

Изотопы

A total of 18 isotopes of potassium have been discovered so far. Just two ofthem are stable: K-39 makes up 93.2581% of potassium found in the Earth’s crust, andK-41 makes up 6.7301% of the remainder of potassium found on Earth. All the other16 potassium isotopes are unstable and radioactive with relatively short half-lives, and asthey decay, they produce beta particles. The exception is K-40, which has a half-life of1.25×10⁹ years.

Происхождение имени

Its symbol “K” is derived from the Latin word for alkali, kalium, but it is commonly called “potash” in English.

Вхождение

Potassium is the eighth most abundant element in the Earth’s crust, which contains about2.6% potassium, but not in natural elemental form. Potassium is slightly less abundant thansodium. It is found in almost all solids on Earth, in soil, and in seawater, which contains 380ppm of potassium in solution. Some of the potassium ores are sylvite, carnallite, and polyhalite. Ore deposits are found in New Mexico, California, Salt Lake in Utah, Germany, Russia,and Israel. Potassium metal is produced commercially by two processes. One is thermochemical distillation, which uses hot vapors of gaseous NaCl (sodium chloride) and KCl (potassiumchloride); the potassium is cooled and drained off as molten potassium, and the sodium chloride is discharged as a slag. The other procedure is an electrolytic process similar to that used toproduce lithium and sodium, with the exception that molten potassium chloride (which meltsat about 770°C) is used to produce potassium metal at the cathode.

Характеристики

Because its outer valence electrons are at a greater distance from its nuclei, potassium ismore reactive than sodium or lithium. Even so, potassium and sodium are very similar in theirchemical reactions. Due to potassium’s high reactivity, it combines with many elements, particularly nonmetals. Like the other alkali metals in group 1, potassium is highly alkaline (caustic) with a relatively high pH value. When given the flame test, it produces a violet color.

Использование

In synthesis of inorganic potassium Compounds; in organic syntheses involving condensation, dehalogenation, reduction, and polymerization reactions. As heat transfer medium together with sodium: Chem. Eng. News 33, 648 (1955). Radioactive decay of 40K to 40Ar used as tool for geological dating.

Подготовка

Potassium metal is not produced commercially by a fused salt electrolysis of the chloride —as is sodium—for several reasons: the metal is too soluble in the molten chloride to separate and float on top of the bath; potassium metal vapors may also issue from the molten bath, thus creating hazardous conditions; and potassium superoxide may form in the cell and react explosively with potassium metal. Consequently, the established method of preparing potassium metal commercially? involves the reduction of molten potassium chloride by metallic sodium at elevated temperatures (850°C). Molten potassium chloride is fed into the midpoint of a steel vessel provided with a fractionating tower packed with stainless steel rings. Sodium is vaporized at the bottom and rises countercurrent to the molten potassium chloride with which it reacts according to the equilibrium expression.
Although the left-hand side of the equation is favored thermodynamically, the escape of the potassium vapors causes the reaction to proceed very efficiently to the right. The potassium vapors are condensed and the product normally contains sodium metal as the only major impurity up to about 1 % by weight. This product is sometimes purified by fractionating it in a 38 ft high 316 stainless steel tower equipped with a reflux return reservoir. The condensate is potassium metal of 99.99 % purity.

Методы производства

Potassium superoxide (KO2) can create oxygen from water vapor (H2O) and carbon dioxide (CO2) and is used in respiratory equipment and is produced by burning potassium metal in dry air.

Определение

potassium: Symbol K. A soft silverymetallic element belonging to group1 (formerly IA) of the periodic table(see alkali metals); a.n. 19; r.a.m.39.098; r.d. 0.86; m.p. 63.7°C; b.p.774°C. The element occurs in seawaterand in a number of minerals,such as sylvite (KCl), carnallite(KCl·MgCl2·6H2O), and kainite(MgSO4·KCl·3H2O). It is obtained byelectrolysis. The metal has few usesbut potassium salts are used for awide range of applications. Potassiumis an essential element for livingorganisms. The potassium ion,K+, is the most abundant cation inplant tissues, being absorbed throughthe roots and being used in suchprocesses as protein synthesis. In animalsthe passage of potassium andsodium ions across the nerve-cellmembrane is responsible for thechanges of electrical potential thataccompany the transmission of impulses.Chemically, it is highly reactive,resembling sodium in itsbehaviour and compounds. It alsoforms an orange-coloured superoxide,KO₂, which contains the O2^- ion.Potassium was discovered by SirHumphry Davy in 1807.

Общее описание

Potassium is potassium mixed with some other metal, usually sodium. Potassium is a liquid under normal conditions. Potassium reacts vigorously with water to form potassium hydroxide, a corrosive material and hydrogen, a flammable gas. The heat from this reaction may be sufficient to ignite the hydrogen. Potassium alloy may ignite spontaneously in contact with air. Once ignited, potassium burns quite violently. Potassium is used as a heat exchange fluid.

Реакции воздуха и воды

Reacts vigorously with oxygen. Reacts vigorously with water even at less than 100°C [Merck, 11th ed., 1989]. Water (caustic solution, H2) The oxidation of potassium in air is so rapid that the heat generated by the reaction melts and ignites the metal. This is particularly the case when pressure is applied at ordinary temperatures [Sidgwick 1. 1950]. Potassium burns in moist air at room temperature [Mellor 2:468. 1946-47]. The higher oxides of potassium, formed in air, react explosively with pure potassium, sodium, sodium-potassium alloys, and organic matter [Mellor 2, Supp. 3:1559. 1963].

Угроза здоровью

Potassium reacts with the moisture on skin and other tissues to form highly corrosive potassium hydroxide. Contact of metallic potassium with the skin, eyes, or mucous membranes causes severe burns; thermal burns may also occur due to ignition of the metal and liberated hydrogen.

Воспламеняемость и взрывоопасность

Potassium metal may ignite spontaneously on contact with air at room temperature. Potassium reacts explosively with water to form potassium hydroxide; the heat liberated generally ignites the hydrogen formed and can initiate the combustion of potassium metal itself. Potassium fires must be extinguished with a class D dry chemical extinguisher or by the use of sand, ground limestone, dry clay or graphite, or "Met-L-X?" type solids. Water or CO2, extinguishers must never be used on potassium fires.

Возможный контакт

Used as a reagent and in sodiumpotassium alloys which are used as high-temperature heat transfer media.

Экологическая судьба

Potassium metal in the environment will react with air, oxidizing the exposed surfaces, and reacts violently with water, yielding potassium hydroxide and hydrogen gas, which reacts with oxygen in air, producing flame.

хранилище

Safety glasses, impermeable gloves, and a fire-retardant laboratory coat should be worn at all times when working with potassium, and the metal should be handled under the surface of an inert liquid such as mineral oil, xylene, or toluene. Potassium should be used only in areas free of ignition sources and should be stored under mineral oil in tightly sealed metal containers under an inert gas such as argon. Potassium metal that has formed a yellow oxide coating should be disposed of immediately; do not attempt to cut such samples with a knife since the oxide coating may be explosive.

Перевозки

UN2257Potassium, Hazard Class: 4.3; Labels: 4.3-Dangerous when wet material. UN1420 Potassium, metal alloys and metal alloys, liquid, Hazard Class: 4.3; Labels: 4.3-Dangerous when wet material. UN3089 Metal powder, flammable, n.o.s. Hazard Class: 4.2; Labels: 4.2-Spontaneously combustible material.

Несовместимости

Air contact causes spontaneous ignition. Violent reaction with water, forming heat, spattering, corrosive potassium hydroxide and explosive hydrogen. The heat from the reaction can ignite the hydrogen that is generated. A powerful reducing agent. Violent reaction with oxidizers, organic materials; carbon dioxide; heavy metal compounds; carbon tetrachloride; halogenated hydrocarbons; easily oxidized materials; and many other substances. Store under nitrogen, mineral oil, or kerosene. Oxidizes and forms unstable peroxides under storage conditions. Potassium metal containing an oxide coating is an extremely dangerous explosion hazard and should be removed by an expert and destroyed.

Утилизация отходов

Excess potassium and waste material containing this substance should be placed in an appropriate container under an inert atmosphere, clearly labeled, and handled according to your institution's waste disposal guidelines. Experienced personnel can destroy small scraps of potassium by carefully adding t-butanol or nbutanol to a beaker containing the metal scraps covered in an inert solvent such as xylene or toluene.