Potassium

Occurrence

 

Potassium makes up about 1.5% of the weight of the Earth's crust and is the seventh most abundant element. As it is very electropositive, potassium metal is difficult to obtain from its minerals. It is never found free in nature, as it reacts violently with water. Potassium salts such as sodium.

Potassium can be isolated through potassium chloride.

See also potassium minerals.

Isotopes

Main article: isotopes of potassium

There are 24 known half-life of 1.250×10⁹ years. The decay of ⁴⁰K to ⁴⁰Ar enables a commonly used method for dating rocks. The conventional feldspar; whole rock samples from volcanic flows and shallow instrusives can also be dated if they are unaltered.

Outside of dating, potassium isotopes have been used extensively as tracers in studies of weathering. They have also been used for nutrient cycling studies because potassium is a macronutrient required for life.

⁴⁰K occurs in natural potassium (and thus in some commercial salt substitutes) in sufficient quantity that large bags of those substitutes can be used as a radioactive source for classroom demonstrations. In healthy animals and people, ⁴⁰K represents the largest source of radioactivity, greater even than ¹⁴C. In a human body of 70 kg mass, about 4,400 nuclei of ⁴⁰K decay per second.^[1]

The activity of natural potassium is 31 Bq/g.

Properties

Physical properties

  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 and its compounds emit a ion selective electrodes.

Chemical properties

Potassium must be protected from air for storage to prevent disintegration of the metal from oxide and hydroxide corrosion. Often samples are maintained under a kerosene.

Like the other alkali metals, potassium reacts violently with water producing hydrogen. The reaction is notably more violent than that of lithium or sodium with water, and is sufficiently exothermic that the evolved hydrogen gas ignites.

2K(s) + 2H₂O(l) → H₂(g) + 2KOH(aq)

Because potassium reacts quickly with even traces of water, and its reaction products are nonvolatile, it is sometimes used alone, or as NaK (an alloy with desiccant.

Potassium hydroxide reacts strongly with carbon dioxide to produce potassium carbonate, and is used to remove traces of CO₂ from air.

Potassium compounds generally have excellent water solubility, due to the high hydration energy of the K⁺ ion. The potassium ion is colorless in water.

Methods of separating potassium by dihydrogen hexachloroplatinate (IV) hexahydrate, and sodium cobaltinitrite.

Potassium in the body

Biochemical function

Potassium is important in nerve function and in influencing osmotic balance between cells and the interstitiual fluid.^[2]

Potassium may be detected by taste because it triggers three of the five types of tastebuds, according to concentration. Dilute solutions of potassium ion taste sweet (allowing moderate concentrations in milk and juices), while higher concentrations become increasingly bitter/alkaline, and finally also salty to the taste. The combined bitterness and saltiness of high potassium content solutions makes high-dose potassium supplementation by liquid drinks a palatability challenge.^{[citation needed]}

Membrane polarization

Potassium is also important in allowing muscle contraction and the sending of all nerve impulses in animals through action potentials. Because of the interaction of the charge on a potassium ion and its surrounding water molecules, K⁺ ions are larger than Na⁺ ions, and ion channels and pumps in cell membranes can easily distinguish between the two types of ions, actively pumping or passively allowing one of the two ions to pass, while blocking the other.

A shortage of potassium in body fluids may cause a potentially fatal condition known as alkalosis and cardiac arrhythmia.

Filtration and excretion

Potassium is an essential mineral Donnan equilibrium,^[7] the urine can never sink below the concentration of potassium in serum except sometimes by actively excreting water at the end of the processing. Potassium is secreted twice and reabsorbed three times before the urine reaches the collecting tubules.^[8] At that point, it usually has about the same potassium concentration as plasma. If potassium were removed from the diet, there would remain a minimum obligatory kidney excretion of about 200 mg per day when the serum declines to 3.0-3.5 milliequivalents per liter in about one week,^[9] and can never be cut off completely. Because it cannot be cut off completely, death will result when the whole body potassium declines to the vicinity of one-half full capacity. At the end of the processing, potassium is secreted one more time if the serum levels are too high.

The potassium moves passively through pores in the cell wall. When ions move through pumps there is a gate in the pumps on either side of the cell wall and only one gate can be open at once. As a result 100 ions are forced through per second. Pores have only one gate and there one kind of ion only can stream through at 10 million to 100 million ions per second.^[10] The pores require calcium in order to open^[11] although it is thought that the calcium works in reverse by blocking at least one of the pores.^[12] Carbonyl groups inside the pore on the amino acids mimics the water hydration that takes place in water solution^[13] by the nature of the electrostatic charges on four carbonyl groups inside the pore.^[14]

Potassium in the diet

Adequate intake can generally be guaranteed by eating a variety of foods containing potassium and deficiency is rare in healthy individuals eating a balanced diet. Foods with high sources of potassium include in order from highest to lowest avocados, potatoes, bananas, broccoli, orange juice, soybeans and apricots, although it is also common in most fruits, vegetables and meats. Diets high in potassium can reduce the risk of hypertension and a potassium deficiency combined with an adequate DRI of 4,000mg of potassium, though most Americans consume only half that amount per day.^[16] Similarly, in the European Union, particularly in Germany and Italy, insufficient potassium intake is somewhat common.^[17]

Supplements of potassium in medicine are most widely used in conjunction with beriberi.^[18][19] A vitamin B-1 deficiency is possible if food containing sulfite or sulfur dioxide is eaten or an alcoholic drink fermented with sulfur dioxide is consumed during the meal, since sulfite destroys vitamin B-1 in the intestines.^[20]

Individuals suffering from kidney diseases may suffer adverse health effects from consuming large quantities of dietary potassium. End stage renal failure patients undergoing therapy by renal dialysis must observe strict dietary limits on potassium intake, since the kidneys control potassium excretion, and buildup of blood concentrations of potassium may trigger fatal cardiac arrhythmia. Acute glucose,^[22][23] hyperventilation^[24] and perspiration.^[25]

Applications

Agriculture and health

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• It is primarily used in oxide.
• Potassium is an essential component needed in plant growth and is found in most soil types.
• In animal cells, potassium ions are vital to keeping cells alive (see Na-K pump)
• table salt and is also used to stop the heart, e.g. in cardiac surgery and in executions by lethal injection in a solution.
• Potassium bisulfite (KHSO₃) is used as a food preservative (but not in meats), straw, wine and beer-making and in the tanning of leathers.
• Potassium bromate (KBrO₃) is used as a flour improver (E924).
• Potassium sodium tartrate, or Rochelle salt (KNaC₄H₄O₆) is used in baking powder and medicine.
• Potassium pyrophosphate (K₄P₂O₇) is used in detergents.
• Potassium fluorosilicate (K₂SiF₆) is used as an insecticide.

Industrial

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• Potassium hydroxide is an important industrial chemical used as a strong base.
• saltpeter.
• potash, is used in glass manufacturing.
• Toughened glass treated with molten potassium nitrate is much stronger than regular glass.
• Potassium vapor is used in several types of magnetometers*NaK (usually pronounced "nack"), an desiccant for producing dry and air-free solvents.
• The superoxide KO₂ is used as a portable source of oxygen and as a carbon dioxide absorber. It is useful in portable respiration systems.
• Potassium bromide (KBr) is used in photographic film and in engraving.
• Potassium chromate (K₂CrO₄) is used in dyes and stains (bright yellowish-red colour), in explosives and fireworks, in safety matches, in the tanning of leather and in fly paper.
• Potassium fluorosilicate (K₂SiF₆) is used in specialized glasses, ceramics, and enamels.
• Potassium sodium tartrate, or Rochelle salt (KNaC₄H₄O₆) is used in the silvering of mirrors.

Many potassium salts are very important, and include: potassium sulfate.

History

Potassium was discovered in London England by Sir electrolysis.

Potassium was not known in Roman times, and its names are not Classical Latin but rather neo-Latin.

• The name kalium was taken from the word "alkali", which came from Arabic al qalīy = "the calcined ashes".
• The name potassium was made from the word "alkali extracted in a pot from the ash of burnt wood or tree leaves.

Precautions

 

Solid potassium reacts violently with water, and should therefore be kept under a mineral oil such as caesium not be stored for longer than three months unless stored in an inert (oxygen free) atmosphere, or under vacuum.^[26]

The extremely alkaline potassium hydroxide (KOH) residue on the surface of potassium which has been exposed to moisture, is a caustic hazard. As with sodium metal, the "soapy" feel of potassium metal on skin is due to caustic breakdown of the fats in skin into crude soft potassium soap, and represents the beginning of an alkali burn. Potassium should obviously be handled with care, with full skin and eye protection.

Potassium fires are exacerbated by water, and only a few dry chemicals are effective for them. Potassium has also been discovered to react violently with iodine.

References

See also

• Potassium compounds
• Potassium in biology