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Facts About Potassium

Potassium
Credit: Greg Robson/Creative Commons, Andrei Marincas | Shutterstock
Atomic Number: 19
Atomic Symbol: K
Atomic Weight: 39.0983
Melting Point: 149.9 F (65.5 C)
Boiling Point: 1,398 F (759 C)

Word origin: The etymology of the word potassium can be traced from English, Latin and Arabic. It comes from the English potash (pot ashes) and Arabic qali (alkali). The origin of its symbol K comes from the Latin word kalium.

Discovery: Potassium was discovered in 1807 by Humphry Davy, who isolated it from caustic potash. It was the first metal isolated by electrolysis.

Properties

Potassium, classified as an alkali metal, is the lightest known metal after lithium. It is soft and can be cut easily with a knife. It has a silvery appearance immediately after a fresh surface is exposed. It is one of the most reactive and electroresponsive of metals. It oxidizes quickly when exposed to air, so in order to be preserved it must be placed in a mineral oil such as kerosene. [See Periodic Table of the Elements]

As with other metals of the alkali group, potassium decomposes in water with the evolution of hydrogen. It usually catches fire spontaneously when reacting with water. Potassium’s salts give their flames a violet color.

There are 17 known isotopes of potassium. Ordinary potassium is composed of three isotopes. One — 40°K (0.0118 percent) — is radioactive with a half-life of 1.28 x 109 years.

Despite its radioactivity, potassium presents no significant hazard when handled.

Sources of Potassium

Potassium is the seventh most abundant metal in the world. It makes up about 2.4 percent of the earth’s crust by weight.

potash
A large sample of potash, a source of potassium.
Credit: farbled | Shutterstock

However, potassium is never found free in nature. It is obtained through electrolysis of the hydroxide — the same technique that Davy first used when isolating it. Potassium can also be acquired through thermal methods, such as the reduction of potassium compounds with calcium carbide (CaC2), carbon, silicon or sodium. This is a common process.

Most potassium minerals are insoluble and it is very difficult to obtain metal from them. The exceptions are certain minerals that are found in ancient lake and sea beds. These minerals, such as sylvite, carnallite, langbeinite, and polyhalite, form extensive deposits in these ancient sites, and potassium and its salts can be obtained from them with relative ease.

Potash is mined in Germany, New Mexico, California, Utah, Saskatchewan and elsewhere. Potassium is found in the ocean but only in relatively small amounts.

Foods with potassium

Potassium is important to healthy nutrition. Potassium is found in a wide range of foods, such as leafy greens, tomatoes, cucumbers, zucchini, eggplant, pumpkins, potatoes, carrots, beans, dairy foods, bananas, meat, poultry, fish and nuts. The Institute of Medicine of the National Academies of Science encourages adults to consume of at least 4,700 milligrams of potassium every day.

Uses of potassium

Potassium is an essential material for plant growth and it is found in most soils. Therefore, the greatest demand for potash is for use in fertilizers.

Many potassium salts are very important and commonly used, including hydroxide, nitrate, carbonate, chlorate, bromide, iodide, cyanide, sulfate, chromate, and dichromate.

An alloy of sodium and potassium (NaK) is used as a heat-transferring medium.

(Source: Los Alamos National Laboratory)

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