The chemical compound potassium chloride (KCl) is a metal halide composed of potassium and chlorine. In its pure state it is odourless. It has a white to colourless vitreous crystal, with a face-centred cubic structure that cleaves easily in three directions. KCl is used in medicine, scientific applications, food processing and in judicial execution through lethal injection. It occurs naturally as the mineral sylvite and in combination with sodium chloride as sylvinite .

Chemical Properties

Potassium chloride can react as a source of chloride ion. As with any other soluble ionic chloride, it will precipitate insoluble chlorides when added to a solution of an appropriate metal salt such as silver nitrate:

KCl(aq) + Ag(NO₃)(aq) -----> AgCl(s) + KNO₃(aq)

Although potassium is more electropositive than sodium, KCl can be reduced to the metal by reaction with metallic sodium if the potassium is removed by distillation, due to Le Chatelier's principle:

This method is the main method for producing metallic potassium. Electrolysis (used for sodium) fails because of the high solubility of potassium in molten KCl.

Manufacture/Extraction

Potassium chloride occurs naturally as sylvite, and it can be extracted from sylvinite . It is also extracted from salt water and can be manufactured by crystallization from solution, flotation or electrostatic separation from suitable minerals. It is a by-product of the making of nitric acid from potassium nitrate and hydrochloric acid.

Uses

The majority of the potassium chloride produced is used for making fertilizer^[2], since the growth of many plants is limited by their potassium intake. As a chemical feedstock it is used for the manufacture of potassium hydroxide and potassium metal. It is also used in medicine, scientific applications, food processing and in judicial execution through lethal injection.

Biological/Medical Properties

Potassium is vital in the human body and oral potassium chloride is the common means to replenish it, although it can also be diluted and given intravenously. It can be used as a salt substitute for food, but due to its weak, bitter, unsalty flavor, it is usually mixed with regular salt, sodium chloride, for this purpose to improve the taste. Medically it is used in the treatment of hypokalemia and associated conditions, for digitalis poisoning, and as an electrolyte replenisher. Side effects can include gastrointestinal discomfort including nausea and vomiting, diarrhea and bleeding of the gut. Overdoses cause hyperkalemia which can lead to paresthesia, cardiac conduction blocks, fibrillation and arrhythmias, also sclerotic effects.

Precautions

Orally it is toxic in excess; the LD₅₀ is around 2500 mg/kg (meaning that a 150-lb person would have to consume about six ounces; regular salt is about as toxic). Intravenously this is reduced to just over 100 mg/kg but of more concern are its severe effects on cardiac muscles; high doses can cause cardiac arrest and rapid death.

Suppliers/Manufacturers

• Sigma Aldrich
• Alfa Aesar
• VWR International
• Fisher Scientific

References

• Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990.
• N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press, 1984.