Potassium chloride

Potassium chloride
Names
Other names
Sylvite
Muriate of potash
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
DrugBank
ECHA InfoCard 100.028.374
E number E508 (acidity regulators, ...)
KEGG
RTECS number TS8050000
UNII
Properties
KCl
Molar mass 74.5513 g·mol−1
Appearance white crystalline solid
Odor odorless
Density 1.984 g/cm3
Melting point 770 °C (1,420 °F; 1,040 K)
Boiling point 1,420 °C (2,590 °F; 1,690 K)
21.74% (0 °C)
25.39% (20 °C)
36.05% (100 °C)
Solubility Soluble in glycerol, alkalies
Slightly soluble in alcohol Insoluble in ether[1]
Acidity (pKa) ~7
39.0·10−6 cm3/mol
1.4902 (589 nm)
Structure
face centered cubic
Fm3m, No. 225
a = 629.2 pm [2]
Octahedral (K+)
Octahedral (Cl)
Thermochemistry
83 J·mol−1·K−1[3]
−436 kJ·mol−1[3]
Pharmacology
A12BA01 (WHO) B05XA01 (WHO)
  • US: C (Risk not ruled out)
Oral, IV, IM
Pharmacokinetics:
Renal: 90%; Fecal: 10% [4]
Hazards
Safety data sheet ICSC 1450
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
0
1
0
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
2600 mg/kg (oral, rat)[5]
Related compounds
Other anions
Potassium fluoride
Potassium bromide
Potassium iodide
Potassium astatide
Other cations
Lithium chloride
Sodium chloride
Rubidium chloride
Caesium chloride
Francium chloride
Related compounds
Potassium chlorate
Potassium perchlorate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Potassium chloride (KCl) is a metal halide salt composed of potassium and chloride. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water and its solutions have a salt-like taste. KCl is used as a fertilizer,[6] in medicine, scientific applications, food processing, and used to cause cardiac arrest as the third drug in the "three drug cocktail" for executions by lethal injection. It occurs naturally as the mineral sylvite and in combination with sodium chloride as sylvinite.[7]

The version for injection is on the World Health Organization's List of Essential Medicines, the most important medications needed in a basic health system.[8]

Uses

Fertilizer

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, lethal injections, scientific applications, food processing, and as a sodium-free substitute for table salt for people concerned about the health effects of sodium.

Medical use

Potassium is vital in the human body, and potassium chloride by mouth is the common means to treat low blood potassium, although it can also be 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 ordinary table salt (sodium chloride) to improve the taste. The addition of 1 ppm of thaumatin considerably reduces this bitterness.[9] Complaints of bitterness or a chemical or metallic taste are also reported with potassium chloride used in food.[10]

Other

It is sometimes used in water as a completion fluid in petroleum and natural gas operations, as well as being an alternative to sodium chloride in household water softener units.

KCl is useful as a beta radiation source for calibration of radiation monitoring equipment, because natural potassium contains 0.0118% of the isotope 40K. One kilogram of KCl yields 16350 becquerels of radiation consisting of 89.28% beta and 10.72% gamma with 1.46083 MeV.

Potassium chloride is used in some de-icing products that are designed to be safer for pets and plants, though these are inferior in melting quality to calcium chloride [lowest usable temperature 12 °F (−11 °C) v. −25 °F (−32 °C)]. It is also used in various brands of bottled water, as well as in bulk quantities for fossil fuel drilling purposes.

Potassium chloride was once used as a fire extinguishing agent, used in portable and wheeled fire extinguishers. Known as Super-K dry chemical, it was more effective than sodium bicarbonate-based dry chemicals and was compatible with protein foam. This agent fell out of favor with the introduction of potassium bicarbonate (Purple-K) dry chemical in the late 1960s, which was much less corrosive and more effective. It is rated for B and C fires.

Along with sodium chloride and lithium chloride, potassium chloride is used as a flux for the gas welding of aluminium.

Potassium chloride is also an optical crystal with a wide transmission range from 210 nm to 20 µm. While cheap, KCl crystal is hygroscopic. This limits its application to protected environments or short-term uses such as prototyping. Exposed to free air, KCl optics will "rot". Whereas KCl components were formerly used for infrared optics, it has been entirely replaced by much tougher crystals such as zinc selenide.

Potassium chloride has also been used to produce heat packs which employ exothermic chemical reactions,[11] but these have mostly been discontinued with the advent of cheaper and more efficient methods, such as the oxidation of metals ('Hot Hands' one-time-use products) or the crystallization of sodium acetate (multiple-use products).

Potassium chloride is used as a scotophor with designation P10 in dark-trace CRTs, e.g. in the Skiatron.

Side effects

The typical amounts of potassium chloride found in the diet appear to be generally safe.[12] In larger quantities, however, potassium chloride is toxic. The LD50 of orally ingested potassium chloride is approximately 2.5 g/kg, or 190 grams (6.7 oz) for a body mass of 75 kilograms (165 lb). In comparison, the LD50 of sodium chloride (table salt) is 3.75 g/kg. Intravenously, the LD50 is around 80 times smaller at just over 30 mg/kg[13] In such quantities, potassium chloride has severe consequences on the cardiac muscles, potentially causing cardiac arrest and rapid death. For this reason, it is used as the third and final drug delivered in the lethal injection process.

Chemical properties

Solubility

KCl is soluble in a variety of polar solvents.

Solubility[14]
Solvent Solubility
(g/kg of solvent at 25 °C)
H2O 360
Liquid ammonia 0.4
Liquid sulfur dioxide 0.41
Methanol 5.3
Formic acid 192
Sulfolane 0.04
Acetonitrile 0.024
Acetone 0.00091
Formamide 62
Acetamide 24.5
Dimethylformamide 0.17–0.5

Solutions of KCl are common standards, for example for calibration of the electrical conductivity of (ionic) solutions, since KCl solutions are stable, allowing for reproducible measurements. In aqueous solution, it is essentially fully ionized into solvated K+ and Cl ions.

Redox and the conversion to potassium metal

Although potassium is more electropositive than sodium, KCl can be reduced to the metal by reaction with metallic sodium at 850 °C because the more volatile potassium can be removed by distillation (see Le Chatelier's principle):

KCl(l) + Na(l) ⇌ NaCl(l) + K(g)

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.[7]

Physical properties

"Raise banana yields using potassium chloride!", an ad above a highway in a banana-growing district of Hekou County, Yunnan, China

The crystal structure of potassium chloride is like that of NaCl. It adopts a face-centered cubic structure. Its lattice constant is roughly 6.3 Å. Crystals cleave easily in three directions.

Some other properties are

As with other compounds containing potassium, KCl in powdered form gives a lilac flame test result.

Production

Sylvite
Sylvinite

Potassium chloride is extracted from minerals sylvite, carnallite, and potash. 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 production of nitric acid from potassium nitrate and hydrochloric acid.

Laboratory methods

Potassium chloride is inexpensively available and is rarely prepared intentionally in the laboratory. It can be generated by treating potassium hydroxide (or other potassium bases) with hydrochloric acid:

KOH + HCl → KCl + H2O

This conversion is an acid-base neutralization reaction. The resulting salt can then be purified by recrystallization. Another method would be to allow potassium to burn in the presence of chlorine gas, also a very exothermic reaction:

2 K + Cl2 → 2 KCl

References

  1. "Potassium chloride (PIM 430)". International Programme on Chemical Safety. 3.3.1 Properties of the substance. Retrieved 2011-01-17.
  2. D.B. Sirdeshmukh; L. Sirdeshmukh; K.G. Subhadra. Alkali Halides: A Handbook of Physical Properties.
  3. 1 2 Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A22. ISBN 0-618-94690-X.
  4. "Compound Summary for CID 4873". Retrieved 17 October 2015.
  5. http://chem.sis.nlm.nih.gov/chemidplus/rn/7447-40-7%5B%5D
  6. "Potassium Fertilizers (Penn State Agronomy Guide)". Penn State Agronomy Guide (Penn State Extension). Retrieved 2016-12-10.
  7. 1 2 Burkhardt, Elizabeth R. (2006). "Potassium and Potassium Alloys". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a22_031.pub2.
  8. "WHO Model List of Essential Medicines (19th List)" (PDF). World Health Organization. April 2015. Retrieved 8 December 2016.
  9. Lorient, Denis; Linden, G. (1999). New ingredients in food processing: biochemistry and agriculture. Boca Raton: CRC Press. p. 357. ISBN 1-85573-443-5. ... in dietary food containing potassium chloride, thaumatin added in the ratio of 1 ppm considerably reduces the sensation of bitterness. ...
  10. Sinopoli, Dominique A.; Lawless, Harry T. (2012). "Taste Properties of Potassium Chloride Alone and in Mixtures with Sodium Chloride Using a Check-All-That-Apply Method". Journal of Food Science. 77 (9): S319–22. PMID 22901084. doi:10.1111/j.1750-3841.2012.02862.x.
  11. U.S. Patent 3,874,504
  12. Nutrition, Center for Food Safety and Applied. "GRAS Substances (SCOGS) Database - Select Committee on GRAS Substances (SCOGS) Opinion: Potassium chloride". www.fda.gov. Retrieved 21 June 2017.
  13. Bhatkhande, C.Y.; Joglekar, V.D. (1977). "Fatal poisoning by potassium in human and rabbit". Forensic Science. 9 (1): 33–6. PMID 838413. doi:10.1016/0300-9432(77)90062-0.
  14. Burgess, J. (1978). Metal Ions in Solution. New York: Ellis Horwood. ISBN 0-85312-027-7.

Further reading

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