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Potassium-argon dating , method of determining the time of origin of rocks by measuring the ratio of radioactive argon to radioactive potassium in the rock. This dating method is based upon the decay of radioactive potassium to radioactive argon in minerals and rocks; potassium also decays to calcium Thus, the ratio of argon and potassium and radiogenic calcium to potassium in a mineral or rock is a measure of the age of the sample. The calcium-potassium age method is seldom used, however, because of the great abundance of nonradiogenic calcium in minerals or rocks, which masks the presence of radiogenic calcium. On the other hand, the abundance of argon in the Earth is relatively small because of its escape to the atmosphere during processes associated with volcanism. The potassium-argon dating method has been used to measure a wide variety of ages.
Naturally occurring 40 K has a half-life of 1. It decays to stable 40 Ar by electron capture or positron emission 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 40 Ar was quantitatively retained.
Minerals are dated by measurement of the concentration of potassium and the amount of radiogenic 40 Ar that has accumulated. The minerals best suited for dating include biotitemuscovitemetamorphic hornblendeand volcanic feldspar ; whole rock samples from volcanic flows and shallow instrusives can also be dated if they are unaltered.
In healthy animals and people, 40 K represents the largest source of radioactivity, greater even than 14 C. Potassium is formed in supernovae by nucleosynthesis from lighter atoms. Potassium is principally created in Type II supernovae via an explosive oxygen-burning process. Potassium is the 20th most abundant element in the solar system and the 17th most abundant element by weight in the Earth. It makes up about 2.
Potash is primarily a mixture of potassium salts because plants have little or no sodium content, and the rest of a plant's major mineral content consists of calcium salts of relatively low solubility in water.
While potash has been used since ancient times, its composition was not understood. Georg Ernst Stahl obtained experimental evidence that led him to suggest the fundamental difference of sodium and potassium salts in and Henri Louis Duhamel du Monceau was able to prove this difference in Potassium metal was first isolated in by Humphry Davy, who derived it by electrolysis of molten KOH with the newly discovered voltaic pile.
Potassium was the first metal that was isolated by electrolysis. Because of the sensitivity of potassium to water and air, air-free techniques are normally employed for handling the element. It is unreactive toward nitrogen and saturated hydrocarbons such as mineral oil or kerosene. Depending on the concentration, the ammonia solutions are blue to yellow, and their electrical conductivity is similar to that of liquid metals.
Potassium slowly reacts with ammonia to form KNH 2but this reaction is accelerated by minute amounts of transition metal salts. Elemental potassium does not occur in nature because of its high reactivity. It reacts violently with water see section Precautions below  and also reacts with oxygen. Orthoclase potassium feldspar is a common rock-forming mineral.
The deposits often show layers starting with the least soluble at the bottom and the most soluble on top. Potassium is the eighth or ninth most common element by mass 0. Potassium levels influence multiple physiological processes, including   . Potassium homeostasis denotes the maintenance of the total body potassium content, plasma potassium level, and the ratio of the intracellular to extracellular potassium concentrations within narrow limits, in the face of pulsatile intake mealsobligatory renal excretion, and shifts between intracellular and extracellular compartments.
Plasma potassium is normally kept at 3. Levels outside this range are associated with an increasing rate of death from multiple causes,  and some cardiac, kidney,  and lung diseases progress more rapidly if serum potassium levels are not maintained within the normal range. Hypokalemiaa deficiency of potassium in the plasma, can be fatal if severe. Common causes are increased gastrointestinal loss vomitingdiarrheaand increased renal loss diuresis.
Potassium content in the plasma is tightly controlled by four basic mechanisms, which have various names and classifications.
The four are 1 a reactive negative-feedback system, 2 a reactive feed-forward system, 3 a predictive or circadian system, and 4 an internal or cell membrane transport system. Collectively, the first three are sometimes termed the "external potassium homeostasis system";  and the first two, the "reactive potassium homeostasis system".
Define potassium-argon dating. potassium-argon dating synonyms, potassium-argon dating pronunciation, potassium-argon dating translation, English dictionary definition of potassium-argon dating. n a technique for determining the age of minerals based on the occurrence in natural potassium of a small fixed amount of radioisotope 40K that decays.
Renal handling of potassium is closely connected to sodium handling. Sodium is reabsorbed to maintain extracellular volume, osmotic pressure, and serum sodium concentration within narrow limits. Potassium is reabsorbed to maintain serum potassium concentration within narrow limits.
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Potassium must be conserved, but because the amount of potassium in the blood plasma is very small and the pool of potassium in the cells is about 30 times as large, the situation is not so critical for potassium. Since potassium is moved passively   in counter flow to sodium in response to an apparent but not actual Donnan equilibrium 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 excreted twice and reabsorbed three times before the urine reaches the collecting tubules. 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 membrane.
When ions move through Ion transporters pumps there is a gate in the pumps on both sides of the cell membrane and only one gate can be open at once. As a result, approximately ions are forced through per second.
Ion channel have only one gate, and there only one kind of ion can stream through, at 10 million to million ions per second. The U. As for safety, the NAM also sets tolerable upper intake levels ULs for vitamins and minerals, but for potassium the evidence was insufficient, so no UL was established. Most Americans consume only half that amount per day. Likewise, in the European Unionin particular in Germany and Italyinsufficient potassium intake is somewhat common.
Potassium is present in all fruits, vegetables, meat and fish.
Foods with high potassium concentrations include yamparsleydried apricotsmilkchocolateall nuts especially almonds and pistachiospotatoesbamboo shootsbananasavocadoscoconut watersoybeansand bran. The USDA lists tomato pasteorange juicebeet greenswhite beanspotatoesplantainsbananasapricots, and many other dietary sources of potassium, ranked in descending order according to potassium content.
Potassium-argon dating definition: a technique for determining the age of minerals based on the occurrence in natural | Meaning, pronunciation, translations and examples Log In Dictionary. Potassium-argon dating definition, a method for estimating the age of a mineral or rock, based on measurement of the rate of decay of radioactive potassium into argon. See more. The potassium-argon dating method has been used to measure a wide variety of ages. The potassium-argon age of some meteorites is as old as 4, years, and volcanic rocks as young as 20, years old have been measured by this method. Argonargon dating. Radiometric dating. Additional Information. External Websites.
A day's worth of potassium is in 5 plantains or 11 bananas. Diets low in potassium can lead to hypertension  and hypokalemia. Supplements of potassium are most widely used in conjunction with diuretics that block reabsorption of sodium and water upstream from the distal tubule thiazides and loop diureticsbecause this promotes increased distal tubular potassium secretion, with resultant increased potassium excretion. A variety of prescription and over-the counter supplements are available.
Potassium is also available in tablets or capsules, which are formulated to allow potassium to leach slowly out of a matrix, since very high concentrations of potassium ion that occur adjacent to a solid tablet can injure the gastric or intestinal mucosa.
Since the kidneys are the site of potassium excretion, individuals with impaired kidney function are at risk for hyperkalemia if dietary potassium and supplements are not restricted. The more severe the impairment, the more severe is the restriction necessary to avoid hyperkalemia.
Potassium can be detected by taste because it triggers three of the five types of taste sensations, according to concentration. The combined bitterness and saltiness of high-potassium solutions makes high-dose potassium supplementation by liquid drinks a palatability challenge.
Potassium salts such as carnallitelangbeinitepolyhaliteand sylvite form extensive evaporite deposits in ancient lake bottoms and seabeds making extraction of potassium salts in these environments commercially viable. The principal source of potassium - potash - is mined in CanadaRussiaBelarusKazakhstanGermanyIsraelUnited StatesJordanand other places around the world.
They are located in the Zechstein and were deposited in the Middle to Late Permian. The largest deposits ever found lie 1, meters 3, feet below the surface of the Canadian province of Saskatchewan. Saskatchewan, where several large mines have operated since the s pioneered the technique of freezing of wet sands the Blairmore formation to drive mine shafts through them. The main potash mining company in Saskatchewan until its merge was the Potash Corporation of Saskatchewannow Nutrien.
Several methods are used to separate potassium salts from sodium and magnesium compounds. The most-used method is fractional precipitation using the solubility differences of the salts. Electrostatic separation of the ground salt mixture is also used in some mines. The resulting sodium and magnesium waste is either stored underground or piled up in slag heaps. Most of the mined potassium mineral ends up as potassium chloride after processing.
The mineral industry refers to potassium chloride either as potash, muriate of potash, or simply MOP. Pure potassium metal can be isolated by electrolysis of its hydroxide in a process that has changed little since it was first used by Humphry Davy in Although the electrolysis process was developed and used in industrial scale in the s, the thermal method by reacting sodium with potassium chloride in a chemical equilibrium reaction became the dominant method in the s.
The production of sodium potassium alloys is accomplished by changing the reaction time and the amount of sodium used in the reaction. The Griesheimer process employing the reaction of potassium fluoride with calcium carbide was also used to produce potassium. Lower purity metal is considerably cheaper.
The market is volatile because long-term storage of the metal is difficult. It must be stored in a dry inert gas atmosphere or anhydrous mineral oil to prevent the formation of a surface layer of potassium superoxidea pressure-sensitive explosive that detonates when scratched.
The resulting explosion often starts a fire difficult to extinguish. Potassium is now quantified by ionization techniques, but at one time it was quantitated by gravimetric analysis. Reagents used to precipitate potassium salts include sodium tetraphenylboratehexachloroplatinic aci and sodium cobaltinitrite into respectively potassium tetraphenylboratepotassium hexachloroplatinateand potassium cobaltinitrite.
Potassium ions are an essential component of plant nutrition and are found in most soil types. Modern high- yield agriculture depends upon fertilizers to replace the potassium lost at harvest. Most agricultural fertilizers contain potassium chloride, while potassium sulfate is used for chloride-sensitive crops or crops needing higher sulfur content. Only a very few fertilizers contain potassium nitrate. Potassium, in the form of potassium chloride is used as a medication to treat and prevent low blood potassium.
Potassium sodium tartrate KNaC 4 H 4 O 6Rochelle salt is the main constituent of baking powder ; it is also used in the silvering of mirrors.
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Potassium bromate KBrO 3 is a strong oxidizer Eused to improve dough strength and rise height. Potassium bisulfite KHSO 3 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. Major potassium chemicals are potassium hydroxide, potassium carbonate, potassium sulfate, and potassium chloride.
Megatons of these compounds are produced annually. Potassium hydroxide KOH is a strong base, which is used in industry to neutralize strong and weak acidsto control pH and to manufacture potassium salts. It is also used to saponify fats and oilsin industrial cleaners, and in hydrolysis reactions, for example of esters.
Potassium nitrate KNO 3 or saltpeter is obtained from natural sources such as guano and evaporites or manufactured via the Haber process ; it is the oxidant in gunpowder black powder and an important agricultural fertilizer. Potassium cyanide KCN is used industrially to dissolve copper and precious metals, in particular silver and gol by forming complexes.
Its applications include gold miningelectroplatingand electroforming of these metals ; it is also used in organic synthesis to make nitriles. Potassium carbonate K 2 CO 3 or potash is used in the manufacture of glass, soap, color TV tubes, fluorescent lamps, textile dyes and pigments. Potassium chlorate KClO 3 is added to matches and explosives. Potassium bromide KBr was formerly used as a sedative and in photography.
Potassium chromate K 2 CrO 4 is used in inksdyesstains bright yellowish-red color ; in explosives and fireworks ; in the tanning of leather, in fly paper and safety matchesbut all these uses are due to the chemistry of the chromate ion, rather than the potassium ion.
There are thousands of uses of various potassium compounds.
One example is potassium superoxideKO 2an orange solid that acts as a portable source of oxygen and a carbon dioxide absorber. It is widely used in respiration systems in mines, submarines and spacecraft as it takes less volume than the gaseous oxygen. Another example is potassium cobaltinitriteK 3 [Co NO 2 6 ]which is used as artist's pigment under the name of Aureolin or Cobalt Yellow.
The stable isotopes of potassium can be laser cooled and used to probe fundamental and technological problems in quantum physics. The two bosonic isotopes possess convenient Feshbach resonances to enable studies requiring tunable interactions, while 40 K is one of only two stable fermions amongst the alkali metals.
An alloy of sodium and potassium, NaK is a liquid used as a heat-transfer medium and a desiccant for producing dry and air-free solvents.
It can also be used in reactive distillation. Metallic potassium is used in several types of magnetometers. Potassium metal can react violently with water producing potassium hydroxide KOH and hydrogen gas. This reaction is exothermic and releases sufficient heat to ignite the resulting hydrogen in the presence of oxygen. Finely powdered potassium ignites in air at room temperature.
The bulk metal ignites in air if heated. Because its density is 0. Many common fire extinguishing agents, including water, either are ineffective or make a potassium fire worse. Nitrogenargonsodium chloride table saltsodium carbonate soda ashand silicon dioxide sand are effective if they are dry.
Some Class D dry powder extinguishers designed for metal fires are also effective. These agents deprive the fire of oxygen and cool the potassium metal. During storage, potassium forms peroxides and superoxides.
These peroxides may react violently with organic compounds such as oils. Both peroxides and superoxides may react explosively with metallic potassium. Because potassium reacts with water vapor in the air, it is usually stored under anhydrous mineral oil or kerosene.
Unlike lithium and sodium, however, potassium should not be stored under oil for longer than six months, unless in an inert oxygen free atmosphere, or under vacuum. After prolonged storage in air dangerous shock-sensitive peroxides can form on the metal and under the lid of the container, and can detonate upon opening. Ingestion of large amounts of potassium compounds can lead to hyperkalemiastrongly influencing the cardiovascular system.
From Wikipedia, the free encyclopedia. Chemical element with atomic number This article is about the chemical element.
For the use of potassium as a medication, see Potassium chloride medical use. Main article: Isotopes of potassium. Main article: Potash.
Main article: Potassium in biology. See also: Potassium chloride medical use. GHS hazard statements.
GHS precautionary statements. Play media. Pure and Applied Chemistry. Encyclopedia Britannica. Retrieved April The Journal of Experimental Biology 2 : Chymische Schriften. Philosophical Transactions of the Royal Society. From p. The name of "potash" potassewhich the new French nomenclature has bestowed as the name of the entire species [i. Indeed, it is taken from [the vessels] that one formerly used for the roasting of washing powder concentrated from cinders: iron pots pott in the dialect of Lower Saxonyfor which roasting ovens have been substituted since then.
Thus I now propose to substitute for the until now common words of "plant alkali", "vegetable alkali", "potash", etc. Annalen der Physik. Bibcode : AnP In our German nomenclature, I would suggest the names Kalium and Natroniumif one would not rather continue with the appellations Kali-metalloid and Natron-metalloid which are used by Mr. Erman [i. Or perhaps one finds it yet more advisable for the present to create two classes, metals and metalloidsand to place Kalium and Natronium in the latter - Gilbert.
Stockholm, Sweden: A. Compendium of Chemical Terminology2nd ed. Blackwell Scientific Publications, Oxford. Angewandte Chemie International Edition. Bradley G. The Journal of Organic Chemistry. Handbook of Chemistry and Physics 87th ed.
McCleverty and T. Meyer eds. In Anatoly Agulyanski ed. Chemistry of Tantalum and Niobium Fluoride Compounds 1st ed. Burlington: Elsevier.
Isotopes in the Earth Sciences. Improved crop quality by nutrient management. Radioactive Human Body". Harvard Natural Sciences Lecture Demonstrations. Potassium naturally occurs in 3 isotopes: 39 K Two are stable, while the radioactive isotope 40 K decays with a half-life of 1. Conversion to stable 40 Ca occurs via electron emission beta decay in Conversion to stable 40 Ar occurs via electron capture in the remaining Argon, being a noble gasis a minor component of most rock samples of geochronological interest: it does not bind with other atoms in a crystal lattice.
When 40 K decays to 40 Ar argonthe atom typically remains trapped within the lattice because it is larger than the spaces between the other atoms in a mineral crystal. Entrained argon-diffused argon that fails to escape from the magma-may again become trapped in crystals when magma cools to become solid rock again. After the recrystallization of magma, more 40 K will decay and 40 Ar will again accumulate, along with the entrained argon atoms, trapped in the mineral crystals.
Measurement of the quantity of 40 Ar atoms is used to compute the amount of time that has passed since a rock sample has solidified. Despite 40 Ca being the favored daughter nuclide, it is rarely useful in dating because calcium is so common in the crust, with 40 Ca being the most abundant isotope.
Thus, the amount of calcium originally present is not known and can vary enough to confound measurements of the small increases produced by radioactive decay. The ratio of the amount of 40 Ar to that of 40 K is directly related to the time elapsed since the rock was cool enough to trap the Ar by the equation.
The scale factor 0. In practice, each of these values may be expressed as a proportion of the total potassium present, as only relative, not absolute, quantities are required. To obtain the content ratio of isotopes 40 Ar to 40 K in a rock or mineral, the amount of Ar is measured by mass spectrometry of the gases released when a rock sample is volatilized in vacuum.
The potassium is quantified by flame photometry or atomic absorption spectroscopy.
The amount of 40 K is rarely measured directly. The amount of 40 Ar is also measured to assess how much of the total argon is atmospheric in origin. Both flame photometry and mass spectrometry are destructive tests, so particular care is needed to ensure that the aliquots used are truly representative of the sample.
Ar-Ar dating is a similar technique which compares isotopic ratios from the same portion of the sample to avoid this problem. Due to the long half-life of 40 Kthe technique is most applicable for dating minerals and rocks more thanyears old. For shorter timescales, it is unlikely that enough 40 Ar will have had time to accumulate in order to be accurately measurable.
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