Potassium

Here are some selected, pertinent facts about potassium courtesy of Wikipedia.

With a density less than that of water, potassium is the second least dense metal after lithium. 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 gray visibly and immediately. Potassium must be protected from air for storage to prevent disintegration of the metal from oxide and hydroxide corrosion. Often samples are maintained under an inert medium such as kerosene.

It has the symbol K (Arabic: al qalja‎ → Latin: kalium), and atomic number 19. The name "potassium" comes from the word "potash", as potassium was first isolated from potash. Potassium is a soft silvery-white metallic alkali metal that occurs naturally bound to other elements in seawater and many minerals. It oxidizes rapidly in air and is very reactive, especially towards water. In many respects, potassium and sodium are chemically similar, although organisms in general, and animal cells in particular, treat them very differently.

• Potassium is an essential element for all living organisms.
• Potassium and its compounds emit a violet color in a flame. This fact is the basis of the flame test for the presence of potassium in a sample.
• Potassium compounds generally have excellent water solubility, due to the high hydration energy of the K+ ion. The potassium ion is colorless in water.
• Potassium may be detected by taste because it triggers all the 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.

• It is primarily used in fertilizer as either the chloride, sulfate or carbonate - not as the oxide.
• Potassium hydroxide is an important industrial chemical used as a strong base.
• Potassium nitrate is used in gunpowder (black powder). An older term for KNO3 is saltpeter.
• Potassium carbonate, known as potash, is used in glass manufacturing.
• Glass treated with liquid potassium is much stronger than regular glass.
• NaK, pronounced "nack", an alloy of sodium and potassium which is liquid at room temperature, is used as a heat-transfer medium. It can also be used as a desiccant for producing dry and air-free solvents.
• 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)
• Potassium chloride 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.
• The superoxide KO2 is used as a portable source of oxygen and as a carbon dioxide absorber. It is useful in portable respiration systems.
• Many potassium salts are very important, and include: potassium bromide, potassium carbonate, potassium chlorate, potassium chloride, potassium chromate, potassium cyanide, potassium dichromate, potassium iodide, potassium nitrate, potassium sulfate.

Solid potassium reacts violently with water, and should therefore be kept under a mineral oil such as kerosene and handled with care. 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, which can detonate upon opening. DO NOT store potassium, rubidium or caesium for longer than a year unless stored in an inert (argon) atmosphere or in a vacuum.

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 only with careful skin and eye protection.

Potassium fires are exacerbated by water, and only a few dry chemicals are effective for them. For a fire discussion which applies to alkali metals in general, see the precaution section for sodium.

Potassium is an essential mineral micronutrient in human nutrition; it is the major cation (positive ion) inside animal cells, and it is thus important in maintaining fluid and electrolyte balance in the body. Potassium is also important in allowing muscle contraction and the sending of all nerve impulses in animals. See action potential for an explanation of the interplay of sodium and potassium in all excitable animal cells. Because of the interaction of the charge on a potassium ion and its surrounding water molecules, K+ ions are actually a little smaller 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 hypokalemia (see article for detail), typically resulting from diarrhea, increased diuresis and vomiting. Deficiency symptoms include muscle weakness, paralytic ileus, ECG abnormalities, decreased reflex response and (in severe cases) respiratory paralysis, alkalosis and arrhythmia.
Eating a variety of foods that contain potassium is the best way to get an adequate amount. Healthy individuals who eat a balanced diet rarely need supplements. Foods with high sources of potassium include orange juice, potatoes, bananas, avocados, apricots, parsnips and turnips, although many other fruits, vegetables, and meats contain potassium. Research has indicated that diets high in potassium can reduce the risk of hypertension.

The 2004 guidelines of the Institute of Medicine specify an RDA of 4,700 mg of potassium. However, it is thought that most Americans consume only half that amount per day. Similarly, in the European Union, particularly in Germany and Italy, insufficient potassium intake is widespread. Supplements of potassium in medicine are most widely used in conjunction with the most powerful classes of diuretics, which rid the body of sodium and water, but have the side effect of also causing potassium loss in urine. A variety of medical supplements are available.

Some people with kidney disease are advised to avoid 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 heart dysrhythmias.