Potassium / Kalium [K]

Characteristics

An: 19 N: 20
Am: 39.0983 g/mol
Group No: 1
Group Name: Alkali metal
Block: s-block Period: 4
State: solid at 298 K
Colour: silvery white
Classification: Metallic
Boiling Point: 1032K (759oC)
Melting Point: 336.53K (63.38oC)
Critical temperature: 2223K (1950oC)
Density: 0.89g/cm3

Discovery Information

Who: Sir Humphrey Davy
When: 1807
Where: England

Name Origin

From potash (pot ash); K from latin: kalium "Potassium" in different languages.

Sources

Found in minerals like carnallite [(KMgCl3).6H2O] and sylvite (KCl). Potassium makes up about 2.40% of the weight of the Earth’s crust, it is the seventh most abundant element. The main sources of potash are mined in USA (California, New Mexico and Utah) and Germany. Around 200 tons are produced annually.

Abundance

Universe: 3 ppm (by weight)
Sun: 4 ppm (by weight)
Carbonaceous meteorite: 710 ppm
Earth’s Crust: 15000 ppm
Human: 2 x 106 ppb by weight; 3.2 x 105 ppb by atoms

Uses

Used as potash (potassium carbonate) in making glass, soap, lenses and salt substitute. Also as potassium nitrate (KNO3, also called saltpeter) it is used to make explosives and to colour fireworks in mauve.
Glass treated with liquid potassium is much stronger than regular glass.
Potassium chloride (KCl) is used as a substitute for table salt and is also used to stop the heart, e.g. in cardiac surgery and in executions by lethal injection in solution.

History

Potassium was discovered in 1807 by Sir Humphry Davy, who derived it from caustic potash (KOH). Potassium was the first metal that was isolated by electrolysis.

Notes

Potassium is the second least dense metal; only lithium is less dense. It is a soft, low-melting solid that can easily be cut with a knife. Freshly cut potassium is silvery in appearance, but in air it begins to tarnish toward grey immediately.
Potassium is a necessary mineral in daily nutrition; it assists in muscle contraction and in maintaining fluid and electrolyte balance in body cells.
Formerly called kalium hence the symbol ’K’.

Hazards

Solid potassium reacts violently with water, and should therefore be kept under a mineral oil such as kerosene and handled with care. When in water, it may catch fire spontaneously, burning with a purple flame. Unlike lithium and sodium however, potassium cannot be stored under oil indefinitely. If stored longer than 6 months to a year, dangerous shock-sensitive peroxides can form on the metal and under the lid of the container that can detonate upon opening.
Potassium is very harmful by ingestion or through the skin or eye contact, it may cause irreversible eye damage.

Potassium Compounds

Potassium alginate KC6H7O6
It is an extract of seaweed and is used as a thickener in the food industry and as a gelling agent and emulsifier.

Potassium benzoate A food preservative that inhibits the growth of mold, yeast and some bacteria. It works best in low-pH products, below 4.5, where it exists as benzoic acid. Acidic food and beverage like fruit juice (citric acid), sparkling drinks (carbon dioxide), soft drinks (phosphoric acid), pickles (vinegar) or other acidified food are preserved with potassium benzoate.

Potassium chlorate KClO3 [Oxidizer] It is used in some recipes for gunpowder, generally replacing the less powerful ingredient potassium nitrate. Potassium chlorate is used also as a pesticide.
Potassium chlorate is used in the oxygen-supply systems of aircraft, and has been responsible for at least one plane crash. A fire on the space station MIR was also traced to this substance. The decomposition of potassium chlorate was also used to provide the oxygen supply for limelights.

Potassium chloride KCl
The majority of the potassium chloride produced is used for making fertilizer[2], since the growth of many plants is limited by their potassium intake. As a chemical feedstock it is used for the manufacture of potassium hydroxide and potassium metal. It is also used in medicine, scientific applications, food processing, as a sodium-free substitute for table salt (sodium chloride), and in judicial execution through lethal injection.

Potassium cyanate KCNO It is a general chemical reagent and it is used as a herbicide.

Potassium fluoride KF Used for etching glass and also as a preservative and insecticide.

Potassium nitrate KNO3
One of the most useful applications of potassium nitrate is in the production of nitric acid, by adding concentrated sulfuric acid to an aqueous solution of potassium nitrate, yielding nitric acid and potassium sulfate which are separated through fractional distillation.
is also used as a fertilizer, in model rocket propellant, and in several fireworks such as smoke bombs, in which a mixture with sugar produces a smoke cloud of 600 times their own volume.
In the process of food preservation, potassium nitrate is a common ingredient of salted meat, but heart patients need to take care with it. As a preservative it can be known as E249.
It has also been used in the manufacture of ice cream and can be found in some toothpastes for sensitive teeth. Recently, the use of potassium nitrate in toothpastes for sensitive teeth has increased dramatically, despite the fact that it has not been conclusively shown to help dental hypersensitivity.

Potassium sorbat C6H7O2K
Used to inhibit molds, and yeasts in many foods, such as cheese, wine, yogurt, and baked goods. It can also be found in the ingredients list of many dried fruit products. In addition, herbal dietary supplement products generally contain potassium sorbate, which acts to prevent mold and microbes and to increase shelf life, and is used in such tiny quantities that there is no known adverse health effect. Labeling of this preservative can either read as "potassium sorbate," or "sorbic acid," or "preservatives."

Potassium sulfate K2SO4 The principal use of potassium sulfate is as a fertilizer. The crude salt is also used occasionally in the manufacture of glass.

Reactions of Potassium

Reactions with water
Potassium reacts very rapidly with water to form a colourless solution of potassium hydroxide and hydrogen gas. The resulting solution is basic because of the dissolved hydroxide. This reaction is exothermic. Early in the reaction, the potassium becomes so hot that it catches fire and burns with a characteristic pale lilac colour.
2K(s) + 2H2O --> 2KOH(aq) + H2(g)

Reactions with air
Potassium tarnishes quickly in air due to a reaction of oxygen and moisture. If potassium is burned in air, the result is mainly formation of orange potassium superoxide.
K(s) + O2(g) --> KO2(s)

Reactions with halogens
Potassium metal reacts vigorously with all the halogens to form potassium(I) halides.
2K(s) + F2(g) --> KF(s)
2K(s) + Cl2(g) --> KCl(s)
2K(s) + Br2(g) --> KBr(s)

Reactions with acids
Potassium dissolves readily in dilute sulphuric acid to form solutions containing the aquated K(I) ion together with hydrogen gas.

Reactions with bases
Potassium reacts very rapidly with water to form a colourless solution of potassium hydroxide and hydrogen gas. The resulting solution is basic because of the dissolved hydroxide. This reaction is exothermic. Early in the reaction, the potassium becomes so hot that it catches fire and burns with a characteristic pale lilac colour.
2K(s) + 2H2O --> 2KOH(aq) + H2(g)

Occurrence of Potassium

Potassium makes up about 1.5% of the weight of the Earth’s crust and is the seventh most abundant element in it. As it is very electropositive, potassium metal is difficult to obtain from its minerals. It is never found free in nature. Potassium salts such as carnallite, langbeinite, polyhalite, and sylvite are found in ancient lake and sea beds. These minerals form extensive deposits in these environments, making extracting potassium and its salts more economical. The principal source of potassium, potash, is mined in Saskatchewan, California, Germany, New Mexico, Utah, and in other places around the world. 3000 feet below the surface of Saskatchewan are large deposits of potash which are important sources of this element and its salts, with several large mines in operation since the 1960s. Saskatchewan pioneered the use of freezing of wet sands (the Blairmore formation) in order to drive mine shafts through them. The oceans are another source of potassium, but the quantity present in a given volume of seawater is relatively low compared with sodium.
Potassium can be isolated through electrolysis of its hydroxide in a process that has changed little since Davy. Thermal methods also are employed in potassium production, using potassium chloride.

Isotopes of Potassium

39K [20 neutrons]
Abundance: 93.26%
Stable with 20 neutrons

40K [21 neutrons]
Abundance: 0.012%
Half life: 1.277 x 109 years [ beta- ]
Decay Energy: 1.311 MeV
Decays to 40Ca.
Half life: 1.277 x 109 years [ Electron Capture ]
Decay Energy: 1.505 MeV
Decays to 40Ar.
Half life: 1.277 x 109 years [ beta+ ]
Decay Energy: 1.505 MeV
Decays to 40Ar.
In healthy animals and people, 40K represents the largest source of radioactivity, greater even then 14C. In a human body of 70 kg mass, about 170,000 nuclei of 40K decay per second.

41K [22 neutrons]
Abundance: 6.73%
Stable with 22 neutrons

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