Potassium

Potassium is a chemical element on the periodic table whose chemical symbol is K (from the Latin Kalium and from the Arabic القلية, DMG al-qalya, "plant ash"), whose atomic number is 19. It is a silvery-white alkali metal, abundant in nature in elements related to salt water and other minerals. It oxidizes rapidly in air, is highly reactive, especially in water, and chemically resembles sodium.

Main features

Potassium.

It is the fifth lightest and lightest metal; It is a soft solid that is easily cut with a knife, has a very low melting point, burns with a violet flame and is silvery on surfaces exposed to air, in contact with which it oxidizes rapidly, forcing it to be stored. oil coated.

Like other alkali metals, it reacts violently with water, giving off hydrogen, and can even ignite spontaneously in the presence of water.

Applications

• Potassium metal is used in photoelectric cells.
• Chloride and nitrate are used as fertilizers.
• Potassium peroxide is used in self-sustained fire and miner breathing devices.
• Nitrate is used in the manufacture of powder and chromat and dicromato in pyrotecnia.
• The potassium carbonate is used in the manufacture of crystals.
• NaK alloy, a sodium alloy and potassium, is a material used for heat transfer.
• Potassium chloride is used to cause cardiac arrest in lethal injection executions.

Other important potassium salts are bromide, cyanide, hydroxide, iodide, and sulfate.

The K⁺ ion is present at the ends of the chromosomes (in the telomeres) stabilizing the structure. Likewise, the hexahydrate ion (like the corresponding magnesium ion) stabilizes the structure of DNA and RNA by compensating for the negative charge of the phosphate groups.

The sodium pump is a mechanism by which the required concentrations of K⁺ and Na⁺ ions are achieved inside and outside the cell—K ion concentrations ⁺ higher inside the cell than outside—to enable the transmission of the nerve impulse.

Vegetables (broccoli, beets, eggplant and cauliflower), beans and fruits (bananas and stone fruits such as avocado, apricot, peach, cherry, plum) are foods rich in potassium.

Decreased blood potassium levels cause hypokalemia.

It is one of the essential elements for plant growth —it is one of the three consumed in the greatest quantity— since the potassium ion, which is found in most types of soil, is involved in respiration.

History

Potassium (from the scientific Latin potassium, and this from the German pottasche, pot ash) name given by Humphry Davy when he discovered it in 1807, was the first metallic element isolated by electrolysis, in its case from potassium hydroxide (KOH), a compound from whose Latin name, Kalĭum, comes the chemical symbol for potassium.

Davy himself gave the following account of his discovery before the Royal Society of London on November 19, 1807: «I placed a small fragment of potash on an isolated disk of platinum which communicated with the negative side of an electric battery of 250 copper and zinc plates in full activity. A platinum wire that communicated with the positive side was brought into contact with the upper face of the potash. The whole apparatus worked outdoors. In these circumstances a very lively activity was manifested; the potash began to melt at its two electrifying points. On the upper face (positive) there was a lively effervescence, determined by the detachment of an elastic fluid; on the underside (negative) no elastic fluid was released, but small globules of vivid metallic luster completely similar to mercury globules. Some of these globules, as they were formed, burned with explosion and bright flame; others gradually lost their shine and were finally covered with a white crust. These globules formed the substance that I was looking for; it was a particular combustible principle, it was the base of potash: potassium."

The importance of the discovery lies in the fact that it confirmed Antoine Lavoisier's hypothesis that if soda and potash reacted with acids in the same way as lead and silver oxides, it was because they were formed from the combination of a metal with the oxygen, an extreme that was confirmed by isolating potassium and only a week later sodium by electrolysis of soda. In addition, obtaining potassium allowed the discovery of other elements, since given its great reactivity it is capable of decomposing oxides to combine and remain with oxygen; in this way silicon, boron and aluminum could be isolated.

Abundance

Potassium constitutes around 2.4% by weight of the earth's crust, being the seventh most abundant. Due to its solubility it is very difficult to obtain the pure metal from its ores. Even so, large deposits of potassium minerals (carnallite, langbeinite, polyhalite, and silvin) exist on ancient seabeds and lakes where extraction of the metal and its salts is economically viable.

Chemical properties

Potassium must be protected from the air to prevent such corrosion of metal by oxide and hydroxide. Often the samples are kept under a reducing medium such as kerosene. Like 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 exothermic enough that the evolved hydrogen gas ignites. Because potassium reacts rapidly with even traces of water, and its reaction products are permanent, it is sometimes used alone, or as NaK (an alloy with sodium that is liquid at room temperature) to dry solvents before distillation. In this role, potassium serves as a powerful drying agent. Potassium hydroxide reacts strongly with carbon dioxide, due to the high energy of the K⁺ ion. The K⁺ ion is colorless in water. Potassium separation methods include precipitation, sometimes by gravimetric analysis.

Isotopes

Seventeen isotopes of potassium are known, three of them naturally occurring ³⁹K (93.3%), ⁴⁰K (0.01%) and ⁴¹ K (6.7%). Isotope ⁴⁰K, with a half-life of 1.278x10⁹ years, decays to stable ⁴⁰Ar (11.2%) by capture electronics and emission of a positron, and the remaining 88.8% at ⁴⁰Ca by β-decay.

The decay of ⁴⁰K into ⁴⁰Ar is used as a method for rock dating. The conventional K-Ar method is based on the hypothesis that the rocks did not contain argon when they formed and that the formed one did not escape from them but was retained so that the present comes completely and exclusively from the disintegration of the original potassium. The measurement of the amount of potassium and ⁴⁰Ar and application of this dating procedure is adequate to determine the age of minerals such as volcanic feldspar, muscovite, biotite and hornblende and in general samples of volcanic rocks and intrusive that have not undergone alteration.

Beyond verification, potassium isotopes have been widely used in climate studies as well as nutrient cycling studies as a macro-nutrient required for life.

The isotope ⁴⁰K is present in natural potassium in sufficient quantity that bags of commercial potassium compounds can be used in school demonstrations as a radioactive source.

Biological function

Potassium in the body

Potassium is the major cation in the intracellular fluid of the human body. It is involved in maintaining normal water balance, the osmotic balance between cells and interstitial fluid, and the acid-base balance, determined by pH of the organism. Potassium is also involved in muscle contraction and the regulation of neuromuscular activity, by participating in the transmission of the nerve impulse through the action potentials of the human organism. Due to the nature of their electrostatic and chemical properties, potassium ions are smaller than sodium ions, so ion channels and pumps in cell membranes can distinguish between the two types of ions; actively or passively pump allowing one of these ions to pass, while blocking the other. Potassium promotes cell development and is partly stored at the muscle level, therefore if the muscle is being formed) an adequate supply of potassium is essential. A significant decrease in serum potassium levels (below 3.5 meq/L) can cause a potentially fatal condition known as hypokalemia, often resulting in conditions such as diarrhea, increased urine output, vomiting, and dehydration. Deficiency symptoms include: muscle weakness, fatigue, asthenia, cramps, at the gastrointestinal level: ileus, constipation, electrocardiogram abnormalities, cardiac arrhythmias, and in severe cases respiratory paralysis and alkalosis.

Hyperkalemia, or increased potassium levels above 5.5 meq/L, is one of the most serious electrolyte disorders and can be caused by increased intake (oral or parenteral: blood), redistribution (from intracellular to extracellular fluid) or decreased renal excretion. In general, the clinical manifestations appear with levels greater than 6.5 meq/L, the main ones being: cardiovascular: with changes in the electrocardiogram, ventricular arrhythmias and asystole (cardiac arrest), at the neuromuscular level: paresthesias, weakness, respiratory failure and at the gastrointestinal level nausea and vomiting.

Absorption, filtration and excretion

Potassium is rapidly absorbed from the small intestine. Between 80 and 90% of ingested potassium is excreted in the urine, the rest is lost in the feces. The kidneys maintain normal serum potassium levels through their ability to filter, reabsorb, and excrete potassium under the influence of the hormone aldosterone. Together with sodium, both regulate the balance between fluids and electrolytes in the body, since they are the major intracellular (potassium) and extracellular (sodium) fluid cations of the organism's total body fluids. The concentration of sodium in plasma is about 145 meq/L, while that of potassium is 3.5 to 4.5 meq/L (in plasma). Plasma is filtered through the glomeruli of the kidneys in enormous amounts, about 180 L/day. Daily sodium and potassium ingested in the diet must be reabsorbed; sodium must be reabsorbed as much as necessary to maintain proper plasma volume and osmotic pressure, while potassium must be reabsorbed to maintain serum cation concentrations at 4.8 meq/L (about 190 milligrams) (6). The sodium pump must always be kept operational to conserve sodium. Potassium must sometimes be conserved, but since the amounts of potassium in plasma are so small, and the concentration of potassium at the cellular level is about three times as great, the situation is not so critical for potassium. Since potassium is transported passively in response to a reverse flow to sodium, urine can never decrease serum potassium concentrations, except a few times where active excretion of water is observed. Potassium is secreted doubly and reabsorbed three times before urine reaches the collecting ducts of the kidney. At this point the same concentration is usually reached in plasma. If potassium were removed from the diet, it would force the kidney into a minimal excretion of potassium around 200 mg/day when serum potassium declines to 3.0 meq/L in about a week. The sodium/potassium pump is a mechanism by which the required concentrations of K⁺ and Na⁺ ions are achieved inside and outside the cell—K⁺ ion concentrations higher inside the cell than outside—to enable the transmission of the nerve impulse.

Potassium in the diet

Adequate potassium intake can generally be ensured by consuming a variety of potassium-containing foods, and deficiency is very rare in individuals eating a balanced diet. Foods that are a high source of potassium include: vegetables (potato or potato, broccoli, beets, eggplant and cauliflower) and fruits (bananas or plantains) and stone fruits (such as grapes, apricots, peach, cherry, plum, etc.), are foods rich in potassium. Potassium is the third most abundant mineral in our body. It is involved in the reaction of the nerves, in the muscular movement and in its healthy maintenance.

The foods that have the most potassium are beans, which provide 1,300 mg of potassium per 100 g; wheat germ, which provides about 842 mg of potassium every 100 g; avocado, which provides 600 mg every 100 g; soy provides 515 mg per 100 g; walnuts, which provide 441 mg of potassium every 100 g; the potato or potato, which provides 421 mg of potassium per 100 g, and the banana or plantain, which provides 396 mg per 100 g.

Diets high in potassium may reduce the risk of hypertension, and potassium deficiency (hypokalemia) combined with inadequate thiamine intake has resulted in deaths in experimental mice.

Potassium salts, as they have a salty taste, can easily replace sodium salts in those diets where this last element must be restricted.

Potassium supplements in medicine are used mostly in conjunction with loop and thiazide diuretics, a class of diuretics that lower sodium and body water levels when necessary, but also cause potassium loss in the urine. Individuals with kidney disease or kidney disease may experience adverse health effects from consuming large amounts of potassium. In chronic renal failure, patients undergoing treatment receiving renal dialysis must follow a strict diet in the content of potassium provided, since the kidneys control the excretion of potassium and the accumulation of potassium due to renal failure can cause serious problems such as a fatal cardiac arrhythmia. Acute hyperkalemia (excess potassium) can be reduced through treatment with oral soda, glucose, hyperventilation, and perspiration.

Precautions

Solid potassium reacts violently with water, even more so than sodium, so it must be kept immersed in a suitable liquid such as oil or kerosene.