potassium

[jiǎ]

chemical element

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Kalium, the element symbol K, plays an important role in preventing chronic diseases such as hypertension.^[4] The atomic number is 19, located in the fourth periodic IA family of the periodic table, belonging to Alkali metal element 。 The simple substance is a silvery white soft metal, waxy, which can be cut with a knife, has low melting and boiling point, less density than water, and extremely active chemical properties (more active than sodium). Potassium does not exist in the form of a single substance in nature. Potassium is widely distributed in land and sea in the form of salt, and it is also one of the important components in human muscle tissue and nerve tissue.

Chinese name: potassium
Foreign name: Potassium
Kalium
CAS login number: 7440-09-7
EINECS login number: 231-119-8
Melting point: 63.65 ℃
Boiling point: 759 ℃
Density: 0.862 g/cm³
Appearance: Silver white soft metal
Element symbol: K
Atomic weight: thirty-nine point zero nine eight three

Control type: Explosive chemicals
Discoverer: humphry davy
Element Type: Alkali metal element
Atomic number: nineteen
Cycle: Fourth cycle
family: I A
Electronic layout: [Ar]4s one
area: S area
Common oxidation state: +1,0
Electronegativity: zero point eight two
Common isotopes: K-39，K-40，K-41

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Research History

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Sylvite

Potassium salt and saltpeter（ potassium nitrate ，KNO three ）, Alum（ Potassium aluminum sulfate dodecahydrate ，KAl(SO four ) two ·12H two O）， And grass ash（ Potassium carbonate ，K two CO three ）Its form has been recognized for centuries. They are used in the manufacture of gunpowder, fuel and soap.^[1] The reduction of potassium containing substances to elements defeated early chemists, and potassium was Lavoisier It is classified as "soil". Due to the strong activity of potassium, it is difficult to use common reducing agents (such as carbon) to reduce metal potassium from potassium compounds. Then in 1807, humphry davy It is found that a metal ball is formed when electrolyzing molten potassium hydroxide. This is potassium. He noticed that when potassium was thrown into the water, it would swim on the water and burn out a beautiful purple flame. The name of potassium comes from the Latin Kalium, which means "alkali". Latin name from arabic Qali borrowed it. When Chinese scientists named this element, because its activity ranked first among the known metals at that time, the word "potassium" was created by adding the word "A" next to the word "gold" to indicate the first place.

physical property

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Potassium is a silver white cubic metal with physical and chemical properties very similar to sodium. The potassium is soft and light, and can be cut with a knife. The new section has silvery white luster.

Potassium density 0.862g/cm three (293K), melting point 336K (63 ℃), boiling point 1032K (759 ℃).

Potassium is a good conductor of heat and electricity and has good magnetic conductivity. The potassium sodium alloy formed by 77.2% potassium and 22.8% sodium has a melting point of only 12 ℃ and is a heat conductor for nuclear reactors. Potassium also has good ductility and low hardness. It can dissolve in mercury and liquid ammonia, and form blue solution in liquid ammonia.

There are 28 kinds of potassium isotopes found, including thirty-two K to fifty-five K， Among them, only thirty-nine K、 forty K and forty-one K， Other isotopes are manufactured artificially. forty K is radioactive, which is in rock and soil Natural radioactive background One of the important sources of.^[1]

Potassium ion Can make the flame purple, available Flame reaction and Flame photometer testing.

chemical property

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Potassic chemical property More active than sodium cesium 、 rubidium Weak activity. Exposed to air, the surface is quickly covered Potassium oxide and Potassium carbonate , make it lose Metallic luster (The surface appears blue and purple), so the metal potassium should be stored in Liquid paraffin or argon To prevent oxidation. Potassium will burn when heated in air. It is limited oxygen Medium heating, generation Potassium oxide ； Heating in excess oxygen, generating Potassium peroxide and Potassium superoxide A mixture of. Potassium metal is soluble in liquid ammonia It generates a dark blue liquid, which can conduct electricity. Experiments show that the liquid ammonia solution containing potassium will decompose into hydrogen and potassium amino if it is left for a long time or under the catalysis of iron. The liquid ammonia solution of potassium reacts with oxygen to form Potassium superoxide ， ozone Function to generate orange Potassium ozonate 。

Potassium reacts violently with water and can ignite even on ice Potassium hydroxide With hydrogen, the heat released during reaction can melt the metal potassium and cause combustion of potassium and hydrogen.

Potassium can react with fluorine, chlorine, bromine and iodine to form corresponding halides. Potassium does not react with nitrogen. It reacts with ammonia to generate potassium amino and release hydrogen. Potassium and mercury form potassium amalgam (chemical formula: K+Hg=K [Hg]), which is a reducing agent and does not react violently with water. Strong exothermic reaction will occur when potassium and mercury interact. The oxidation state of potassium is+1, and only compounds with+1 valence are formed^[2] 。

In high school chemistry, it is believed that potash is soluble in water, but in fact Potassium perchlorate 、 Potassium hydrogen tartrate 、 Potassium hexachloroplatinate The solubility of cobalt, sodium potassium nitrite and potassium tetraphenylborate is low.^[1]

chemical compound

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Potassium oxide

Potassium oxide, chemical formula K two O， Molecular weight 94.2, density 2.32g/cm three 。 Easily deliquescent and soluble in water. It is a white powder, dissolved in water to generate potassium hydroxide, and gives off a lot of heat. Heating in the air flow can be oxidized into potassium peroxide or potassium superoxide, which can easily absorb carbon dioxide in the air to become potassium carbonate.

Potassium peroxide

Potassium peroxide, chemical formula K two O two , yellow amorphous block, easy to deliquescence. When heated and decomposed, oxygen is released when encountering water, hydrogen peroxide is generated when encountering acid, and potassium peroxide can absorb carbon dioxide and release oxygen. yes Strong oxidant 。 It can be composed of potassium hydroxide and hydrogen peroxide Reaction.

Potassium superoxide

Potassium superoxide, chemical formula KO two , is a primary oxidant, similar to Group I metals in many aspects peroxide 。 It may cause combustion or even explosion when encountering combustibles, organics, reducing agents, etc. When encountering water or steam, a large amount of heat will be generated, which may also cause explosion. Hygroscopicity Extremely strong, it reacts violently with water to generate oxygen and alkaline peroxide solution that can be further decomposed.

Potassium hydroxide

Potassium hydroxide, chemical formula KOH, white powder or flake solid. It is strongly alkaline, corrosive and moderately toxic. It is easy to absorb moisture in the air Deliquescence , absorbing carbon dioxide to form potassium carbonate. Soluble in water, soluble in ethanol and glycerin. When dissolved in water, alcohol or treated with acid, a lot of heat is generated.

Content distribution

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Crust

Potassium compounds have long been used by humans. Because of its extremely active chemical properties, potassium only exists in the form of compounds in nature. It was known in ancient times that potassium oxaline (i.e Potassium carbonate ）, can be used as detergent. Potassium nitrate is also used as Black powder One of the ingredients of. The content of potassium in the crust is 2.47%, accounting for the seventh place. The minerals that can be used to extract potash are Potash mine （ KCl ）、 Carnallite （KCl·MgCl two ·6H two O）、 Polyhalite （2CaSO four ·K two SO four ·2H two O）。 Nature with extremely wide distribution silicate Minerals also contain potassium, such as Potash feldspar K[AlSi three O eight ]。 It is rich in potassium in mica, potassium feldspar and other silicates.^[1]

ocean

It exists in the form of potassium ion in sea water, and the content is about 0.38g/kg.^[3] The reason why the content of potassium in seawater is less than that of sodium ion is that it is absorbed more by soil and plants. Potassium is also found in animals and plants. In addition to oxygen, hydrogen, chlorine, sodium, magnesium, sulfur and calcium, potassium has the highest content in seawater.

human body

The normal human body contains about 175 grams of potassium, 98% of which is stored in the form of potassium ions Cytosol Internal; The serum contains 3.5-5.5mmol/L potassium. Potassium is the most important cation one of.

Main purpose

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human body

Potassium can regulate the appropriate osmotic pressure in cells and the acid-base balance of body fluids, and participate in the metabolism of sugar and protein in cells. It helps maintain neural health and normal heartbeat, can prevent stroke, and helps muscles contract normally. When high sodium intake leads to hypertension, potassium has the effect of lowering blood pressure.

(1) It is involved in sugar, protein and energy metabolism: when glycogen is synthesized, potassium is required to enter the cell with it, and when glycogen is decomposed, potassium is released from the cell. When protein is synthesized, about 3mmol of potassium is needed per gram of nitrogen. When protein is decomposed, potassium is released. Potassium is also required for ATP formation.

(2) It is involved in maintaining the osmotic pressure and acid-base balance of intracellular and extracellular fluid: potassium is the main cation in the cell, so it can maintain the osmotic pressure of intracellular fluid. In acidosis, blood potassium tends to increase at the same time due to the reduction of potassium excretion by the kidney and the outward migration of potassium from the cell. In alkalosis, the opposite is true.

(3) Maintain neuromuscular excitability.

(4) Maintenance of myocardial function: one of the main driving forces for the potential change of myocardial cell membrane is the intracellular and extracellular transfer of potassium ions.

Human potassium deficiency can cause irregular and accelerated heartbeat, abnormal ECG, muscle weakness and irritability, and finally lead to cardiac arrest. Generally speaking, healthy people will automatically discharge excess potassium out of the body. However, nephrotic patients should pay special attention to avoid excessive potassium intake.

It is rich in potassium in dairy products, fruits, vegetables, lean meat, viscera, bananas and raisins

The main symptoms of potassium deficiency in human body are: tachycardia and irregular heart rate, muscle weakness, numbness, irritability, nausea, vomiting, diarrhea, hypotension, insanity, and apathy.

Botany

Potassium can promote healthy plant stems, improve fruit quality, enhance plant cold resistance, and increase sugar and vitamin C content in fruits. Like nitrogen and phosphorus, potassium deficiency symptoms first appear in old leaves. When potassium supply is insufficient, carbohydrate metabolism is disturbed, photosynthesis is inhibited, and respiration is strengthened. Therefore, in case of potassium deficiency, the plant's resistance to stress is weakened, and it is vulnerable to disease, fruit quality is reduced, and coloring is poor. The demand for potash fertilizer for melons, fruits and tomatoes is mainly in the period of rapid fruit expansion.

Potassium fertilizer is generally applied during base fertilizer, flushing, topdressing, spraying and soilless nutrition cultivation, and 0.5% potassium dihydrogen phosphate, potassium nitrate, potassium sulfate and potassium chloride solution is flushed, topdressing or sprayed on the leaf surface at the early stage of fruit expansion. Potassium chloride cannot be used for melons and tobacco leaves.

When potassium is insufficient, the plant stems are weak and prone to lodging, and the cold resistance and drought resistance are poor; The leaves turn yellow and gradually become necrotic. Since potassium can move to tender leaves, potassium deficiency starts in the older leaves, and then develops to the base of the plant. There are also withered and scorched leaf margins, curled or shrunken leaves.

(1) Promote enzyme activation. There are more than 60 enzymes in organisms that need potassium ion as an activator.

(2) Promote the use of light energy and enhance photosynthesis. First K + It can maintain the normal structure of thylakoid membrane in chloroplasts, lacking K + Thylakoid membrane structure is loose, affecting the normal progress of photosynthesis. At the same time, it can promote the formation of proton gradient on thylakoid membrane and photosynthetic phosphorylation.

(3) It is conducive to normal respiration of plants and improves energy metabolism.

(4) Enhance the synthesis and transport of substances in plants. For example, the synthesis and operation of carbohydrates; Enhance the synthesis of protein and nucleoprotein; Promote nitrogen fixation of legume rhizobia.

(5) Enhance plant resistance.

(6) Enhance the ability of frost resistance, drought resistance and salt resistance;

(7) Enhance the resistance of plants to diseases and pests. The experiment showed that increasing the amount of potassium fertilizer could effectively reduce the leaf spot disease, rice blast, sheath blight, etc. of rice; Wheat powdery mildew, scab and wheat rust, etc.

(8) Reduce the harm of reducing substances to rice.^[1]

Storage method

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Potassium metal is very active and needs to be stored in isolation from air and water. Potassium and sodium are generally stored in kerosene and liquid paraffin. The storage room shall be ventilated, low temperature and dry. Store separately from acid and oxidant.

Safety shall be paid attention to during storage and use. The fire caused by metallic potassium shall not be extinguished with water or foam extinguishing agent, but with sodium carbonate dry powder. Potassium is also very corrosive to the skin.

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