Potassium chloride

Potassium-chloride-3D-vdW.png
Potassium chloride

sylvite (mineral form)
muriate of potash

! bgcolor="#ffddaa" colspan="2" | Bulk Properties ethanol: 0.4 g/ cm³acetone: insoluble

General
IUPAC name potassium chloride
Molecular formula	KCl
Molecular weight	74.55 amu
Appearance	white crystalline solid
CAS number	^*
MSDS	Potassium chloride MSDS
Other names

Density	1.987 g/cm³
Solubility	water: 34.4 g/100 cm³ (cold)
Melting point	776 °C (1049 K)
boiling (sublimation) point	1500 °C (1770 K)
Hazards:	see text
Structure
Crystal structure	Face-centred cubic
Hydrates	none believed known
Related Compounds
Other anions	potassium fluoride potassium bromide potassium iodide
Other cations	sodium chloride rubidium chloride
Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) Chemical infobox

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 or colourless vitreous crystal, with a face-centred cubic structure that cleaves easily in three directions. It is also commonly known as "Muriate of Potash". Potash varies in color from pink or red to white depending on the mining and recovery process used. White potash, sometimes referred to as soluble potash, is usually higher in analysis and is used primarily for making liquid starter fertilizers. 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^{^*}, 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, as a sodium-free substitute for table salt (sodium chloride), and in judicial execution through lethal injection. It is sometimes used in water as a completion fluid in oil and gas operations. KCl is useful as beta radiation source for calibration of radiation monitoring equipment because natural potassium contains 0.0118% of the isotope K⁴⁰. One kilogram of KCl yields 16350 becquerels of radiation consisting of 89.28% beta and 10.72% gamma with 1.46083 MeV.

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. Brand names include K-Dur®, Klor-Con®, Micro-K®, and Kaon Cl®. 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.

Physical properties

In chemistry and physics it is a very commonly used as a standard, for example as a calibration standard solution in measuring electrical conductivity of (ionic) solutions, since a carefully prepared KCl solutions have well-reproducible and well-repeatable measureable properties.

Solubility of KCl in various solvents (g KCl / 100g of solvent at 25° C)
H₂O	36
Liquid ammonia	0.04
Liquid sulfur dioxide	0.041
Methanol	0.53
Formic acid	19.2
Sulfolane	0.004
Acetonitrile	0.0024
Acetone	0.000091
Formamide	6.2
Acetamide	2.45
Dimethylformamide	0.017 - 0.05
Reference: Burgess, J. Metal Ions in Solution (Ellis Horwood, New York, 1978) ISBN 0853120277

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. Indeed, a massive overdose of intravenous potassium chloride is used to stop the heart in execution by lethal injection.

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. ISBN 0080220576

External links

Gourt Home::Gourt :: Potassium chloride