Dictionary:
po·tas·si·um (pə-tăs'ē-əm)  |
A soft, silver-white, highly or explosively reactive metallic element that occurs in nature only in compounds. It is obtained by electrolysis of its common hydroxide and found in, or converted to, a wide variety of salts used especially in fertilizers and soaps. Atomic number 19; atomic weight 39.098; melting point 63.65°C; boiling point 774°C; specific gravity 0.862; valence 1.
[From POTASH (from which it was first obtained).]
potassic po·tas'sic adj.| Sci-Tech Encyclopedia: Potassium |
A chemical element, K, atomic number 19, and atomic weight 39.102. It stands in the middle of the alkali metal family, below sodium and above rubidium. This lightweight, soft, low-melting, reactive metal (see table) is very similar to sodium in its behavior in metallic forms. See also Alkali metals; Periodic table; Rubidium; Sodium.
Temperature | ||||
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Property | °C | °F | SI units | Customary (engineering) units |
Density | 100 | 212 | 0.819 g/cm3 | 51.1 lb/ft3 |
400 | 752 | 0.747 g/cm3 | 46.7 lb/ft3 | |
700 | 1292 | 0.676 g/cm3 | 42.2 lb/ft3 | |
Melting point | 63.7 | 147 | ||
Boiling point | 760 | 1400 | ||
Heat of fusion | 63.7 | 147 | 14.6 cal/g | 26.3 Btu/lb |
Heat of vaporization | 760 | 1400 | 496 cal/g | 893 Btu/lb |
Viscosity | 70 | 158 | 5.15 millipoises | 6.5 kinetic units |
400 | 752 | 2.58 millipoises | 3.5 kinetic units | |
800 | 1472 | 1.36 millipoises | 2 kinetic units | |
Vapor pressure | 342 | 648 | 1 mm | 0.019 lb/in.2 |
696 | 1285 | 400 mm | 7.75 lb/in.2 | |
Thermal conductivity | 200 | 392 | 0.017 cal/(s)(cm2)(cm)(°C) | 26.0 Btu(h)(ft2)(°F) |
400 | 752 | 0.09 cal/(s)(cm2)(cm)(°C) | 21.7 Btu/(h)(ft2)(°F) | |
Heat capacity | 200 | 392 | 0.19 cal/(g)(°C) | 0.19 Btu/(lb)(°F) |
800 | 1472 | 0.19 cal/(g)(°C) | 0.19 Btu/(lb)(°F) | |
Electrical resistivity | 150 | 302 | 18.7 microhm-cm | |
300 | 572 | 28.2 microhm-cm | ||
Surface tension | 100–150 | 212–302 | About 80 dynes/cm | |
Potassium chloride, KCl, finds its main use in fertilizer mixtures. It also serves as the raw material for the manufacture of other potassium compounds. Potassium hydroxide, KOH, is used in the manufacture of liquid soaps, and potassium carbonate in making soft soaps. Potassium carbonate, K2CO3, is also an important raw material for the glass industry. Potassium nitrate, KNO3, is used in matches, in pyrotechnics, and in similar items which require an oxidizing agent.
Potassium is a very abundant element, ranking seventh among all the elements in the Earth's crust, 2.59% of which is potassium in combined form. Seawater contains 380 parts per million, making potassium the sixth most plentiful element in solution.
Potassium is even more reactive than sodium. It reacts vigorously with the oxygen in air to form the monoxide, K2O, and the peroxide, K2O2. In the presence of excess oxygen, it readily forms the superoxide, KO2.
Potassium does not react with nitrogen to form a nitride, even at elevated temperatures. With hydrogen, potassium reacts slowly at 200°C (392°F) and rapidly at 350–400°C (662–752°F). It forms the least stable hydride of all the alkali metals.
The reaction between potassium and water or ice is violent, even at temperatures as low as −100°C (−148°F). The hydrogen evolved is usually ignited in reaction at room temperature. Reactions with aqueous acids are even more violent and verge on being explosive.
The potassium ion (K+) is the most common intracellular cation and is essential for maintaining osmotic pressure and electrodynamic cellular properties in organisms. The intracellular potassium ion concentrations are typically high for most cells, whereas the potassium ion concentrations present in extracellular fluids are significantly lower. The hydrolysis of the coenzyme adenosine triphosphate (ATP) is mediated by the membrane-bound enzyme Na+, K+-ATPase. This enzyme is called the sodium pump and it is activated by both potassium and sodium ions; however, many enzymes are activated by potassium ions alone (for example, pyruvate kinase, aldehyde dehydrogenase, and phosphofructokinase). See also Adenosine triphosphate (ATP).
Potassium deficiency may occur in several conditions, including malnutrition and excessive vomiting or diarrhea, and in patients undergoing dialysis; supplementation with potassium salts is sometimes required.
| Food and Nutrition: potassium |
An essential mineral, widespread in nature; the human body contains about 125 g, mostly present inside the cells.
| Food and Fitness: potassium |
An important mineral element in the human body. Optimal levels of potassium in the blood help to strengthen arteries, may reduce the damage to blood vessels associated with ageing, and are essential for the efficient functioning of the heart. Potassium-rich diets may reduce blood pressure and counteract some of the harmful effects of high sodium intakes. Some nutritionists suggest that the addition of one piece of potassium-rich fruit or vegetable per day may reduce the risk of a fatal stroke by 40 per cent.
Although deficiencies are rare, they may result from severe diarrhoea, sweating, or vomiting. Mild deficiencies can lead to muscular weakness, increased heart rates, and nausea. Severe deficiencies may lead to heart failure unless supplements are given.
Potassium is found in many foods (including apricots, meat, fish, and poultry). Fruit and vegetables are especially valuable sources of potassium because they tend be relatively low in sodium. Bananas are an excellent recovery food for replacing potassium lost in sweat and they are very convenient (the original prewrapped food!). For these reasons, many professional cyclists eat bananas during races.
Potassium toxicity is rare, but excessively high intakes can lead to muscular weakness and heart complaints, and may accompany kidney disease. The daily potassium requirement is about 2-4 grams (UK recommended level for adults is 3.5 g per day).
| Dental Dictionary: potassium |
An alkali metal element, the seventh most abundant element in the earth’s crust. Its atomic number is 19 and its atomic weight is 39.1. Potassium in the body constitutes the predominant intracellular cation, helping to regulate neuromuscular excitability and muscle contraction. The average adequate daily intake of potassium for most adults is 2 to 4 grams.
| Alternative Medicine Encyclopedia: Potassium |
Description
Potassium is one of the electrolytes essential to the smooth running of the human body; in fact just about all bodily functions depend on it to some extent. It is also one of the most abundant minerals in the body, constituting 70% of the positive ions inside cells; the rest are a mixture of sodium, magnesium, calcium, arginine, and others. Potassium is distributed to the cells by a process of passive diffusion and is regulated by an enzyme called adenosinetriphosphatase together with the level of sodium concentration inside the cell. Potassium and sodium are antagonistic, which means that an imbalance of one will automatically cause an imbalance of the other; normally potassium should predominate inside the cell.
General Use
Potassium is necessary for normal cell respiration; a deficiency can cause decreased levels of oxygen, which will reduce the efficiency of cell function. Adequate supplies of potassium are also required to regulate heartbeat, facilitate normal muscle contraction, regulate the transfer of nutrients to cells, and regulate kidney function and stomach juice secretion, among other things. One of the most important uses of potassium in the body is in the process of nerve transmission, as it is a cofactor catalyst for the activation of several enzyme systems, but since only minute amounts are required for these processes, deficiency in this respect is unlikely.
Potassium is thought to be therapeutically useful in many ways, including assisting in the treatment of alcoholism, acne, alleviating allergies, promoting the healing of burns, and preventing high blood pressure. It can also help with such problems as congestive heart failure, chronic fatigue syndrome, or kidney stones. People suffering from any of the above should consider increasing their intake of potassium after talking to a professional.
Symptoms of Potassium Deficiency
A deficiency of potassium in the blood is referred to as hypokalemia and manifests itself in many ways. Among the most serious are arthritis, high blood pressure, heart disease, stroke, cancer, and even infertility, as potassium constitutes a vital element of seminal fluid.
Potassium deficiency will increase acid levels in the body, lowering the natural pH, which will have far reaching effects. Lack of potassium can also aggravate problems caused by lack of protein. If potassium levels are down, the liver cannot operate normally, particularly regarding transformation of glucose to glycogen. A healthy liver should have about twice as much potassium as sodium.
Potassium deficiency can cause problems with the formation of connective tissue, and can render normally strong body tissue vulnerable to all kinds of problems. The collagen of a healthy person is approximately as strong as steel, and the strength of bone tissue can be likened to that of cast iron. Lack of potassium may create a susceptibility to fractures, skin lesions that do not heal, or other connective tissue problems. So important is potassium for the protection of collagen that many natural health gurus claim that along with other vital nutrients, it constitutes an essential element of protection against premature aging. As long ago as the 1920s, Max Gerson was the first person ever to cure lupus lesions with a diet designed to reduce abnormally high sodium levels and raise potassium levels to normal, which was entirely raw fruit and vegetables.
Potassium is essential to the efficient processing of foods in the body; without it they cannot be broken down into the proper compounds. This can lead to rheumatism, and is one reason why adequate potassium prevents rheumatism.
Potassium Requirements
In the past potassium was more plentiful in the diet than salt, but gradually, the situation has been reversed. The widespread lack of potassium in modern diets is largely due to modern processing and high levels of salt added to most processed foods. Cooking and processing destroy potassium, and added salt further robs the body of vital potassium. This departure from traditional cooking of fresh homegrown fruit and vegetables is likely the cause of many health problems faced by modern society.
Who Needs Potassium Supplements?
Those who may need to take potassium supplements include women who take oral contraceptives, abusers of alcohol or drugs, smokers, athletes, workers whose job involves physical exertion, patients who have had their gastrointestinal tract surgically removed, anyone suffering from any degree of malabsorption syndrome, and vegetarians. People who have eating disorders, especially bulimia and anorexia, are particularly at risk from damage due to low potassium levels. Also, individuals who have been ill, anyone who has undergone surgery and those who are taking cortisone or digitalis preparations, and those suffering from high levels of stress will probably also have low potassium levels.
No RDA has been officially established for potassium, but practitioners recommend that the optimal daily intake should be in the region of 3,500 mg. The average daily intake is about 2,500 mg. However, in general, nutritionists recommend reducing salt intake and ensuring adequate supply by increasing the amount of fresh fruit and vegetables in the diet.
If a person feels that he or she may be suffering from a potassium deficiency, but would like to make sure before taking supplements, there are a variety of laboratory tests that can be conducted. They include serum-potassium determinations (although these may be unreliable unless levels are very low), serum creatinine, electrocardiograms, serum-pH determinations, whole blood, sublingual cell smears, and red blood cell potassium level determinations.
Preparations
Absolutely the best sources of potassium are fresh natural foods. Supplements may have side effects and large doses must be taken to approach the levels of potassium that can be obtained from food; the average tablet contains about 90 mg, for example, and a medium banana contains 500 mg. Vegetables containing the highest levels of potassium are generally those containing the lowest levels of starch. Seaweed has an amazingly high potassium content, containing roughly ten times as much as leafy vegetables, but also contains a large amount of mineral salt. Green coconut milk is another source of potassium.
Plentiful Sources of Potassium
There is a great variety of natural foods that are an excellent source of potassium. These include avocados; bananas; chard; citrus fruits; juices such as grapefruit, tomato, and orange; dried lentils; green leafy vegetables; milk; molasses; nuts such as almonds, brazils, cashews, peanuts, pecans and walnuts; parsnips; dried peaches; potatoes; raisins; sardines; spinach; and whole-grain cereals.
Cooking
Boiling food in water is a sure way to lose the potassium in it, unless it is to make soup. Baking and broiling are ways in which food can be cooked while at the same time preserving the potassium content, indeed, these methods preserve all the nutrients apart from vitamin C and some of the B vitamins which are destroyed by heat. Broiling also oxidizes essential fatty acids. Stir-frying is also a good way of preserving nutrients. It is important to vary the intake of potassium rich foods in order to ensure adequate intake of other nutrients and to avoid the possibility of toxicity, as some vegetables contain elements that are toxic if they are eaten in large amounts (oxalic acid in rhubarb for example). It is important to note that freezing also depletes potassium levels in foods.
RECIPE FOR POTASSIUM BROTH. Many variations are to be found under the heading "potassium broth," and most natural health practitioners recommend one version or another, but the main constituents are the following vegetables, generally any vegetable of choice can be added to this base.
Ingredients
First, in a stainless steel pan, boil the stock bones, if using them. After about one hour, add the remaining ingredients and continue to simmer in plenty of water for about another hour. It is preferable to use the potatoes and carrots well scrubbed, but with their skins on, as this retains valuable nutrients. Keep any unused soup in the refrigerator.
Potassium Supplements
Potassium supplements come in either tablet or liquid form, and anything over 390 mg needs a prescription in the United States. Enteric coated tablets have been known to cause ulcers, as they do not dissolve until they reach the intestines and may prove too concentrated for the undefended intestinal wall. To be on the safe side, supplements should be taken with a glass of juice. Slow-release enteric-coated supplements are now available, which decrease the danger of ulcers. Potassium gluconate is the ideal supplement, as it more closely resembles the potassium found in plants. Small divided doses should be taken, as opposed to one large dose, when treating a potassium deficiency. Athletic drinks are an electrolyte replacement and as such contain potassium. Potassium supplements should be kept in a cool, dry place, out of direct light. They should not be frozen and should not be kept in the bathroom medicine cabinet as heat and moisture may reduce effectiveness.
Precautions
In general, the multitude of nutrients that humans require in order to stay healthy are synergistic, which means they are interdependent. If depleted of one, it is highly likely that there are deficiencies in others. Many nutrients, for example, require the presence of either calcium or vitamin C for efficient use by the body, and if suffering from a deficiency of any of the B vitamins, there is almost certainly a deficiency in the B vitamins in general, as they occur together in nature. With this in mind, it is very unwise to take large amounts of any one nutrient without making sure that the full spectrum of nutrients is plentifully available for the body to make use of. This can best be achieved by making sure that a large proportion of the daily diet is in the form of raw fruit and vegetables, whole grains, and unroasted nuts.
Of all the essential nutrients that are commonly taken as supplements, potassium is perhaps the most dangerous. Only 14 grams of potassium can cause death under certain circumstances, particularly when intake is low at other times, as it has been found that when potassium intake is restricted, somehow the mechanism for utilizing it is altered, so that large amounts cannot be processed.
Just the right amount of potassium is essential. Too much or too little can cause muscle spasms and cramps if a calcium deficiency also exists. With this in mind, it is important to ensure adequate intake of calcium and vitamin D, which will promote the uptake of calcium in the body.
Many sufferers of degenerative diseases such as tuberculosis, cancer, and arthritis, suffer from high serum potassium levels. This is not because they have too much serum, but because the disease affects body functions in such a way that it throws off this valuable nutrient instead of using it. In such cases, natural sources of potassium, such as fresh fruit or vegetable juice, can be more effective than supplements.
Potassium and Heart Disease
Potassium has been implicated in the treatment of heart disease since the 1930s, but some heart disease that is due to malnutrition does not respond to potassium. Indeed, because of the impaired ability of the body to take up potassium, it can be dangerous. Most heart disease patients of the Western world, however, can benefit from an increase in potassium levels.
Potassium and Arthritis
For many, when they begin to eat a well balanced selection of fresh vegetables and fruits, and eliminate a large proportion of processed, denatured foods, they begin to feel amazingly well very quickly, as the potassium/sodium balance in the body is restored. Tiredness and other symptoms, such as arthritis, are soon replaced with renewed energy and vigor, and the body is able to replenish itself and finds new strength. However, potassium is only partially successful at treating osteoarthritis.
Side Effects
Those who are taking potassium-sparing diuretics, such as spironolactone, triamterene, or amiloride should not take potassium supplements. Anyone allergic to potassium supplements or those who have kidney disease should not take them either. Those suffering from Addison's disease, heart disease, intestinal blockage, stomach ulcers, those using medication for heart disease, or taking diuretics, or who are above the age of 55, should consult a doctor before taking potassium supplements. There are no contradictions for pregnant or breast feeding women, although they should not take mega-doses.
ECG and kidney function tests can be affected by potassium supplementation, the doctor should be informed if potassium supplements are being taken. However, supplementation will not affect blood tests, unless they are to measure serum-potassium levels.
Symptoms of Potassium Overdose
Overdose symptoms of potassium include listlessness, mental confusion, tingling of limbs, weakness, pallid complexion, low blood pressure, and an irregular or fast heartbeat. These symptoms can progress to a drop in blood pressure, convulsion, coma, and eventually cardiac arrest, and can also be triggered by any kind of shock to the system. If any of the above symptoms occur, or in cases of bloody stool (may appear black and tarry), or difficulty in breathing or nausea, medical help should be sought immediately. High serum-potassium is the major problem with shock and is the major cause of death in cases of shock or injury. This is a life-threatening situation, and self treatment is not appropriate.
If such an emergency occurs and medical help is not available, a glass of water containing half a teaspoon of salt, a quarter of a teaspoon of bicarbonate soda and a little honey will help. Potassium supplements should be taken with extreme care in cases of dehydration, as this can be fatal. Adequate liquids, particularly juice, should always accompany the supplement.
Interactions
Care should be taken when taking potassium supplements in conjunction with diuretics. A practitioner should be consulted. A doctor should be informed when a patient is taking potassium supplements. In addition, the following are known to react with potassium:
Resources
Books
Gerson, Max. A Cancer Therapy. California, Totality books: 1977.
Other
Weber, Charles. "Roles of Potassium in the Body." http://www.members.tripod.com/~charles_W/arthritis4.html.
"Potassium." In Vitamins Plus.com. http://www.vitaminsplus.com/library/minerals/potassium.asp.
[Article by: Patricia Skinner]
| Britannica Concise Encyclopedia: potassium |
For more information on potassium, visit Britannica.com.
| Sports Science and Medicine: potassium |
An essential mineral that forms the main cations (negative ions) in intracellular fluid. Potassium plays an important role in muscle and nerve function. Although deficiencies are rare, they can lead to muscle weakness, irregularities of heart rate, and nausea. Severe deficiencies may lead to heart failure. Toxicity due to an excessive intake of potassium is also rare, but it can lead to muscle weakness, and heart and kidney disorders. The best dietary sources of potassium are fruit (especially bananas) and vegetables because they are high in potassium, but relatively low in sodium.
| Columbia Encyclopedia: potassium |
Potassium is a soft, silver-white metal. Physically and chemically it resembles the other alkali metals in Group 1 of the periodic table. It is extremely reactive, more so than sodium. It combines so readily with oxygen that it is usually stored submerged in kerosene or some other hydrocarbon, out of contact with air. It reacts violently with water to form potassium hydroxide, KOH, releasing hydrogen, which usually ignites. It combines directly with the halogens, sulfur, and other nonmetallic elements (except nitrogen). It reacts with many organic compounds.
The metal has limited use since it so closely resembles sodium, which is readily available at lower cost. Nonetheless, potassium compounds are widely used in industry, although they are usually more expensive than the similar sodium compound. Potassium carbonate, or potash, K2CO3, is used principally in soap and glass manufacture. The chloride, KCl, is used in fertilizers and in the production of other potassium compounds. The chlorate, KClO3, and perchlorate, KClO4, are used in explosives and fireworks. The hydroxide, or caustic potash, KOH, is used in soaps. The nitrate, saltpeter (or niter), KNO3, is used in matches and explosives. Other commercially useful compounds include the bromide, KBr, the cyanide, KCN, the chromate, K2CrO4, the dichromate, K2Cr2O7, and the iodide, KI.
Javelle water contains potassium hypochlorite, KClO, a compound found only in solution. The metasilicate, K2SiO3, is used in water glass. Potassium has several useful tartaric acid salts, e.g., Rochelle salt (sodium potassium tartrate), tartar (argol) and cream of tartar (potassium hydrogen tartrate), and tartar emetic (potassium antimony tartrate). Potassium aluminum sulfate, KAl(SO4)2·12H2O, is a compound used in tanning, in water purification, and in baking powder; usually called alum, it is also called potash alum to distinguish it from other alkali aluminum sulfates. Potassium permanganate, KMnO4, a purple-black, crystalline compound that forms deep purple, aqueous solutions, is used in the chemical laboratory as a powerful oxidizing agent and in medicine as an antiseptic and disinfectant.
With sodium the metal forms alloys that are liquid at room temperature; these alloys are sometimes used in chemical reactions. Substances containing potassium impart a purple color to a flame. Potassium does not occur uncombined in nature but is found widely distributed in sylvite (KCl), carnallite (MgCl2·KCl), feldspar, mica, and other minerals. It is the seventh most abundant element in the earth's crust and the sixth most abundant of the elements in solution in the oceans. It is found in mineral waters, brines, and salt deposits. Potassium is an essential nutrient for plants and animals.
Potassium metal is produced commercially by a thermochemical process in which molten potassium chloride is reacted with sodium vapor; this method is also used to produce liquid sodium-potassium alloys. The metal may be produced electrolytically from fused potassium hydroxide, but, unlike sodium and lithium, it reacts with carbon electrodes and may form explosive compounds. Potassium was discovered in 1807 by Humphry Davy, who decomposed potash with an electric current. Potassium was the first metal so discovered; Davy discovered sodium a few days later by a similar experiment.
| Veterinary Dictionary: potassium |
A chemical element, atomic number 19, atomic weight 39.102, symbol K. In combination with other minerals, potassium forms alkaline salts that are important in body processes and play an essential role in maintenance of its acid–base and water balance. All body cells, especially muscle tissue, require a high content of potassium. A proper balance between sodium, calcium and potassium in the blood plasma is necessary for proper cardiac function. Alfalfa meal, molasses and soyabean meal are good sources for herbivores.
| Gardener's Dictionary: K |
The chemical symbol for potassium. Used in the formula NPK of a complete fertilizer.
| Wikipedia: Potassium |
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silvery white |
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| Name, symbol, number | potassium, K, 19 | ||||||||||||||||||||||||||||||
| Element category | alkali metal | ||||||||||||||||||||||||||||||
| Group, period, block | 1, 4, s | ||||||||||||||||||||||||||||||
| Standard atomic weight | 39.0983(1) g·mol−1 | ||||||||||||||||||||||||||||||
| Electron configuration | [Ar] 4s1 | ||||||||||||||||||||||||||||||
| Electrons per shell | 2, 8, 8, 1 (Image) | ||||||||||||||||||||||||||||||
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| Phase | solid | ||||||||||||||||||||||||||||||
| Density (near r.t.) | 0.89 g·cm−3 | ||||||||||||||||||||||||||||||
| Liquid density at m.p. | 0.828 g·cm−3 | ||||||||||||||||||||||||||||||
| Melting point | 336.53 K, 63.38 °C, 146.08 °F | ||||||||||||||||||||||||||||||
| boiling point | 1032 K, 759 °C, 1398 °F | ||||||||||||||||||||||||||||||
| Triple point | 336.35 K (63°C), kPa | ||||||||||||||||||||||||||||||
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| Oxidation states | 1 (strongly basic oxide) |
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| Electronegativity | 0.82 (Pauling scale) | ||||||||||||||||||||||||||||||
| Ionization energies (more) |
1st: 418.8 kJ·mol−1 | ||||||||||||||||||||||||||||||
| 2nd: 3052 kJ·mol−1 | |||||||||||||||||||||||||||||||
| 3rd: 4420 kJ·mol−1 | |||||||||||||||||||||||||||||||
| Atomic radius | 227 pm | ||||||||||||||||||||||||||||||
| Covalent radius | 203±12 pm | ||||||||||||||||||||||||||||||
| Van der Waals radius | 275 pm | ||||||||||||||||||||||||||||||
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| Crystal structure | body-centered cubic | ||||||||||||||||||||||||||||||
| Magnetic ordering | paramagnetic | ||||||||||||||||||||||||||||||
| Thermal conductivity | (300 K) 102.5 W·m−1·K−1 | ||||||||||||||||||||||||||||||
| Thermal expansion | (25 °C) 83.3 µm·m−1·K−1 | ||||||||||||||||||||||||||||||
| Speed of sound (thin rod) | (20 °C) 2000 m/s | ||||||||||||||||||||||||||||||
| Young's modulus | 3.53 GPa | ||||||||||||||||||||||||||||||
| Shear modulus | 1.3 GPa | ||||||||||||||||||||||||||||||
| Bulk modulus | 3.1 GPa | ||||||||||||||||||||||||||||||
| Mohs hardness | 0.4 | ||||||||||||||||||||||||||||||
| Brinell hardness | 0.363 MPa | ||||||||||||||||||||||||||||||
| CAS registry number | 7440-09-7 | ||||||||||||||||||||||||||||||
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Potassium (pronounced /pɵˈtæsiəm/) is a chemical element. It has the symbol K (Latin: kalium, from Arabic: القَلْيَه al-qalyah “plant ashes”, cf. Alkali from the same root), atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash. Elemental potassium is a soft silvery-white metallic alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the evolved hydrogen.
Potassium in nature occurs only as ionic salt. As such, it is found dissolved in seawater, and as part of many minerals. Potassium ion is necessary for the function of all living cells, and is thus present in all plant and animal tissues. It is found in especially high concentrations in plant cells, and in a mixed diet, it is most highly concentrated in fruits.
In many respects, potassium and sodium are chemically similar, although they have very different functions in organisms in general, and in animal cells in particular.
Contents |
Potassium is never found free, as it reacts violently with water, which is abundant in nature.[1] As various compounds, potassium makes up about 1.5% of the weight of the Earth's crust and is the seventh most abundant element.[1] As it is very electropositive, potassium metal is difficult to obtain from its minerals.
Potassium as such 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 "potash", which is English, and originally meant an alkali extracted in a pot from the ash of burnt wood or tree leaves. The structure of potash was not then known,[when?] but is now understood to be mostly potassium carbonate. By heating, the carbonate could be freed of carbon dioxide, leaving "caustic potash", so called because it caused chemical burns in contact with human tissue.
Potassium metal was discovered in 1807 in England by Sir Humphry Davy, who derived it from caustic potash (KOH), by the use of electrolysis of the molten salt with the newly discovered voltaic pile. Before the 18th century, no distinction was made between potassium and sodium. Potassium was the first metal that was isolated by electrolysis.[2] Davy extracted sodium by a similar technique, demonstrating the elements to be different.[3]
Pure potassium metal may be isolated by electrolysis of its hydroxide in a process that has changed little since Davy.[1] Thermal methods also are employed in potassium production, using potassium chloride
Potassium salts such as carnallite, langbeinite, polyhalite, and sylvite form extensive deposits in ancient lake and seabeds, making extraction of potassium salts in these environments commercially viable. The principal source of potassium, potash, is mined in Saskatchewan, California, Germany, New Mexico, Utah, and in other places around the world. It is also found abundantly in the Dead Sea. Three thousand 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 main mining company is the Potash Corporation of Saskatchewan. The oceans are another source of potassium, but the quantity present in a given volume of seawater is relatively low compared with sodium.[4][5]
There are 24 known isotopes of potassium. Three isotopes occur naturally: 39K (93.3%), 40K (0.0117%) and 41K (6.7%). Naturally occurring 40K decays to stable 40Ar (11.2%) by electron capture and by positron emission, and decays to stable 40Ca (88.8%) by beta decay; 40K has a half-life of 1.250×109 years. The decay of 40K to 40Ar enables a commonly used method for dating rocks. The conventional K-Ar dating method depends on the assumption that the rocks contained no argon at the time of formation and that all the subsequent radiogenic argon (i.e., 40Ar) was quantitatively retained. Minerals are dated by measurement of the concentration of potassium and the amount of radiogenic 40Ar that has accumulated. The minerals that are best suited for dating include biotite, muscovite, plutonic/high grade metamorphic hornblende, and volcanic 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.[6]
The activity of natural potassium is 31 Bq/g.
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.[1]
In a flame test, potassium and its compounds emit a pale violet color, which may be masked by the strong yellow emission of sodium if it is also present. Cobalt glass can be used to filter out the yellow sodium color.[7] Potassium concentration in solution is commonly determined by flame photometry, atomic absorption spectrophotometry, inductively coupled plasma, or ion selective electrodes.
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 hydrocarbon medium which does not react with alkali metals, such as mineral oil or 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.
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 sodium which is liquid at room temperature) to dry solvents prior to distillation. In this role, it serves as a potent 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 precipitation, sometimes used for gravimetric analysis, include the use of sodium tetraphenylborate, hexachloroplatinic acid, and sodium cobaltinitrite
Potassium cations are important in neuron (brain and nerve) function, and in influencing osmotic balance between cells and the interstitial fluid, with their distribution mediated in all animals (but not in all plants) by the so-called
Potassium may be detected by taste because it triggers three of the five types of taste sensations, 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.[9]
Potassium is also important in allowing muscle contraction and the sending of all nerve impulses in animals through action potentials. By nature of their electrostatic and chemical properties, K+ ions are larger than Na+ ions, and ion channels and pumps in cell membranes can distinguish between the two types of ions, actively pumping or passively allowing one of the two ions to pass, while blocking the other. [10]
A shortage of potassium in body fluids may cause a potentially fatal condition known as hypokalemia, 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 cardiac arrhythmia.
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. Sodium makes up most of the cations of blood plasma at a reference range of about 145 milliequivalents per liter (3345 milligrams) and potassium makes up most of the cell fluid cations at about 150 milliequivalents per liter (4800 milligrams). Plasma is filtered through the glomerulus of the kidneys in enormous amounts, about 180 liters per day.[11] Thus 602,000 milligrams of sodium and 33,000 milligrams of potassium are filtered each day. All but the 1000-10,000 milligrams of sodium and the 1000-4000 milligrams of potassium likely to be in the diet must be reabsorbed. Sodium must be reabsorbed in such a way as to keep the blood volume exactly right and the osmotic pressure correct; potassium must be reabsorbed in such a way as to keep serum concentration as close as possible to 4.8 milliequivalents (about 190 milligrams) per liter.[12]
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 only one kind of ion can stream through, at 10 million to 100 million ions per second.[18] The pores require calcium in order to open[19] although it is thought that the calcium works in reverse by blocking at least one of the pores.[20] Carbonyl groups inside the pore on the amino acids mimics the water hydration that takes place in water solution[21] by the nature of the electrostatic charges on four carbonyl groups inside the pore.[22]
A potassium intake sufficient to support life can generally be guaranteed by eating a variety of foods, especially plant foods. Clear cases of potassium deficiency (as defined by symptoms, signs and a below-normal blood level of the element) are rare in healthy individuals eating a balanced diet. Foods with high sources of potassium include orange juice, potatoes, bananas, avocados, tomatoes, broccoli, soybeans, brown rice, garlic and apricots, although it is also common in most fruits, vegetables and meats.[23]
Epidemiological studies and studies in animals subject to hypertension indicate that diets high in potassium can reduce the risk of hypertension and possibly stroke (by a mechanism independent of blood pressure), and a potassium deficiency combined with an inadequate thiamine intake has produced heart disease in rats.[24] With these findings, the question of what is the intake of potassium consistent with optimal health, is debated. For example, the 2004 guidelines of the Institute of Medicine specify a DRI of 4,000 mg of potassium (100 mEq), though most Americans consume only half that amount per day, which would make them formally deficient as regards this particular recommendation.[25] Similarly, in the European Union, particularly in Germany and Italy, insufficient potassium intake is somewhat common.[26]
Supplements of potassium in medicine are most widely used in conjunction with loop diuretics and thiazides, 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 and non-medical supplements are available. Potassium salts such as potassium chloride may be dissolved in water, but the salty/bitter taste of high concentrations of potassium ion make palatable high concentration liquid supplements difficult to formulate.[9] Typical medical supplemental doses range from 10 milliequivalents (400 mg, about equal to a cup of milk or 6 oz. of orange juice) to 20 milliequivalents (800 mg) per dose. Potassium salts are also available in tablets or capsules, which for therapeutic purposes are formulated to allow potassium to leach slowly out of a matrix, since very high concentrations of potassium ion (which might occur next to a solid tablet of potassium chloride) can kill tissue, and cause injury to the gastric or intestinal mucosa. For this reason, non prescription supplement potassium pills are limited by law in the U.S. to only 99 mg of potassium.
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 (hyperkalemia) may trigger fatal cardiac arrhythmia.
About 93% of the world potassium production was consumed by the fertilizer industry.[5]
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Potassium ions are an essential component of plant nutrition and are found in most soil types. Its primary use in agriculture, horticulture and hydroponic culture is as a fertilizer as the chloride (KCl), sulfate (K2SO4) or nitrate (KNO3).
In animal cells, potassium ions are vital to keeping cells alive (see
Potassium ion is a nutrient necessary for human life and health. Potassium chloride is used as a substitute for table salt by those seeking to reduce sodium intake so as to control hypertension. The USDA lists tomato paste, orange juice, beet greens, white beans, potatoes, bananas and many other good dietary sources of potassium, ranked according to potassium content per measure shown.[27]
Potassium sodium tartrate, or Rochelle salt (KNaC4H4O6) is the main constituent of baking powder. Potassium bromate (KBrO3) is a strong oxidiser, used as a flour improver (E924) to improve dough strength and rise height.
The sulfite compound, potassium bisulfite (KHSO3) is used as a food preservative, for example in wine and beer-making (but not in meats). It is also used to bleach textiles and straw, and in the tanning of leathers.
Non-dietary uses of potassium chloride include its use to stop the heart, e.g. in cardiac surgery and in a solution used in executions by lethal injection.
Potassium vapor is used in several types of magnetometers. An alloy of sodium and potassium, NaK (usually pronounced "nack"), that 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 metal reacts vigorously with all of the halogens to form the corresponding potassium halides, which are white, water-soluble salts with cubic crystal morphology. Potassium bromide (KBr), potassium iodide (KI) and potassium chloride (KCl) are used in photographic emulsion to make the corresponding photosensitive silver halides.
Potassium hydroxide KOH is a strong base, used in industry to neutralize strong and weak acids and thereby finding uses in pH control and in the manufacture of potassium salts. Potassium hydroxide is also used to saponify fats and oils and in hydrolysis reactions, for example of esters and in industrial cleaners.
Potassium nitrate KNO3 or saltpeter is obtained from natural sources such as guano and evaporites or manufactured by the Haber process and is the oxidant in gunpowder (black powder) and an important agricultural fertilizer. Potassium cyanide KCN is used industrially to dissolve copper and precious metals particularly silver and gold by forming complexes; applications include gold mining, electroplating and electroforming of these metals. It is also used in organic synthesis to make nitriles. Potassium carbonate K2CO3, also known as potash, is used in the manufacture of glass and soap and as a mild desiccant.
Potassium chromate (K2CrO4) is used in inks, 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.
The superoxide KO2 is an orange-colored solid used as a portable source of oxygen and as a carbon dioxide absorber. It is useful in portable respiration systems. It is widely used in submarines and spacecraft as it takes less volume than O2 (g).
4KO2 + 2CO2 --> 2K2CO3 + 3O2
Potassium chlorate KClO3 is a strong oxidant, used in percussion caps and safety matches and in agriculture as a weedkiller. Glass may be treated with molten potassium nitrate KNO3 to make toughened glass, which is much stronger than regular glass.
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This section requires expansion with: additional citations. |
Potassium reacts very violently with water producing hydrogen gas which then usually catches fire. Potassium is usually kept under a hydrocarbon oil such as mineral oil or kerosene to stop the metal from reacting with water vapour present in the air. Unlike lithium and sodium, however, potassium should not 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. It is recommended that potassium, rubidium or caesium not be stored for longer than three months unless stored in an inert (oxygen free) atmosphere, or under vacuum.[28]
As potassium reacts with water to produce highly flammable hydrogen gas, a potassium fire is only exacerbated by the addition of water, and only a few dry chemicals are effective for putting out such a fire (see the precaution section in sodium).
Potassium also produces potassium hydroxide (KOH) in the reaction with water. Potassium hydroxide is a strong alkali and so is a caustic hazard, causing burns.
Due to the highly reactive nature of potassium metal, it must be handled with great care, with full skin and eye protection being used and preferably an explosive resistant barrier between the user and the potassium.
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Look up potassium in Wiktionary, the free dictionary. |
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| Periodic table | |||||||||||||||||||||||||||||||||||||||||
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| H | He | ||||||||||||||||||||||||||||||||||||||||
| Li | Be | B | C | N | O | F | Ne | ||||||||||||||||||||||||||||||||||
| Na | Mg | Al | Si | P | S | Cl | Ar | ||||||||||||||||||||||||||||||||||
| K | Ca | Sc | Ti | V | Cr | Mn | Fe | Co | Ni | Cu | Zn | Ga | Ge | As | Se | Br | Kr | ||||||||||||||||||||||||
| Rb | Sr | Y | Zr | Nb | Mo | Tc | Ru | Rh | Pd | Ag | Cd | In | Sn | Sb | Te | I | Xe | ||||||||||||||||||||||||
| Cs | Ba | La | Ce | Pr | Nd | Pm | Sm | Eu | Gd | Tb | Dy | Ho | Er | Tm | Yb | Lu | Hf | Ta | W | Re | Os | Ir | Pt | Au | Hg | Tl | Pb | Bi | Po | At | Rn | ||||||||||
| Fr | Ra | Ac | Th | Pa | U | Np | Pu | Am | Cm | Bk | Cf | Es | Fm | Md | No | Lr | Rf | Db | Sg | Bh | Hs | Mt | Ds | Rg | Uub | Uut | Uuq | Uup | Uuh | Uus | Uuo | ||||||||||
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This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
| Translations: Potassium |
Français (French)
n. - potassium
Ελληνική (Greek)
n. - (χημ.) κάλιο
Português (Portuguese)
n. - potássio (m) (Quím.)
Español (Spanish)
n. - potasio
中文（简体）(Chinese (Simplified))
钾
中文（繁體）(Chinese (Traditional))
n. - 鉀
한국어 (Korean)
n. - 칼륨, 포타슘(금속원소:기호 k; 번호 19)
العربيه (Arabic)
(الاسم) بوتاسيوم : نوع من المعادن
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 | saltpetre |
| KOH |
| saltpeter, saltpetre |
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