Potassium

Potassium

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melting point: 63.38°C
boiling point: 759°C
density: 0.862 g/cm³
most common ions: K⁺

Potassium is a soft, silvery alkali metal that reacts strongly with water to produce hydrogen gas. The word "potassium" is derived from "potash" or "pot ashes," as Humphry Davy isolated the element in 1807 via the electrolysis of caustic potash, KOH. The element's symbol is derived from kalium (Latin), which originated from qali (Arabic for "alkali"). Currently, potassium metal is generated by the reduction of molten potassium chloride, KCl, with sodium and the use of fractional distillation to separate the resulting mixture. In nature it is never found in its elemental form. Compounds of potassium are found primarily in the minerals sylvite, carnallite, langbeinite, and polyhalite, as well as in the brines of the Dead Sea in Jordan and the Great Salt Lake in Utah. Potassium is the second most abundant alkali metal and the eighth most abundant element in Earth's crust (18,400 ppm). Potassium burns violet in the flame test.

The industrial demand for potassium metal is much smaller than that for sodium. Potassium-sodium alloys (which are liquid at room temperature) serve as heat-exchange liquids in the cooling systems of nuclear reactors. Strong bases such as potassium amides and alkoxides are formed from the reaction of potassium with amines and alcohols, respectively.

Compounds of potassium are economically more important than the metal. KCl is used extensively in fertilizers. KOH is used to make liquid soaps and detergents. Potassium nitrate, KNO₃, serves primarily as an oxidizing agent in gunpowder and pyrotechnics. Potassium superoxide, KO₂, is used in backup ventilation equipment as it generates oxygen gas in the presence of CO₂. Potassium ions are essential to plants and animals as many metabolic reactions and pathways depend on their presence.

see also Alkali Metals.

Nathan J. Barrows

Bibliography

Emsley, John (2001). Nature's Building Blocks: An A-Z Guide to the Elements. New York: Oxford University Press.

Greenwood, N. N., and Earnshaw, A. (1997). Chemistry of the Elements, 2nd edition. Boston: Butterworth-Heinemann.

Lide, David R., ed. (2000). CRC Handbook of Chemistry & Physics, 81st edition. New York: CRC Press.