Potassium chloride

Not to be confused with Potassium chlorate.

"KCl" redirects here. For other uses, see KCL (disambiguation).

This article is about the salt. For the use of potassium chloride as a medication, see Potassium chloride (medical use). For the use of potassium in biology, see Potassium in biology.

Potassium chloride (KCl, or potassium salt) is a metal halide salt composed of potassium and chlorine. 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. Potassium chloride can be obtained from ancient dried lake deposits.^[7] KCl is used as a fertilizer,^[8] in medicine, in scientific applications, domestic water softeners (as a substitute for sodium chloride salt), and in food processing, where it may be known as E number additive E508.

Potassium chloride

Names
Other names Sylvite Muriate of potash
Identifiers
CAS Number	7447-40-7 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:32588 Y
ChEMBL	ChEMBL1200731 N
ChemSpider	4707 Y
DrugBank	DB00761 Y
ECHA InfoCard	100.028.374
E number	E508 (acidity regulators, ...)
KEGG	D02060 Y
PubChem CID	4873
RTECS number	TS8050000
UNII	660YQ98I10 Y
CompTox Dashboard (EPA)	DTXSID5021178
InChI InChI=1S/ClH.K/h1H;/q;+1/p-1 Y Key: WCUXLLCKKVVCTQ-UHFFFAOYSA-M Y InChI=1/ClH.K/h1H;/q;+1/p-1 Key: WCUXLLCKKVVCTQ-REWHXWOFAZ
SMILES [Cl-].[K+]
Properties
Chemical formula	KCl
Molar mass	74.555 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)
Solubility in water	27.77 g/100mL (0 °C) 33.97 g/100mL (20 °C) 54.02 g/100mL (100 °C)
Solubility	Soluble in glycerol, alkalies Slightly soluble in alcohol Insoluble in ether[1]
Solubility in ethanol	0.288 g/L (25 °C)[2]
Acidity (pKa)	~7
Magnetic susceptibility (χ)	−39.0·10−6 cm3/mol
Refractive index (nD)	1.4902 (589 nm)
Structure
Crystal structure	face centered cubic
Space group	Fm3m, No. 225
Lattice constant	a = 629.2 pm[3]
Coordination geometry	Octahedral (K+) Octahedral (Cl−)
Thermochemistry
Std molar entropy (S⦵298)	83 J·mol−1·K−1[4]
Std enthalpy of formation (ΔfH⦵298)	−436 kJ·mol−1[4]
Pharmacology
ATC code	A12BA01 (WHO) B05XA01 (WHO)
Routes of administration	Oral, IV, IM
Pharmacokinetics:
Excretion	Kidney: 90%; Fecal: 10%[5]
Hazards
NFPA 704 (fire diamond)	1 0 0
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	2600 mg/kg (oral, rat)[6]
Safety data sheet (SDS)	ICSC 1450
Related compounds
Other anions	Potassium fluoride Potassium bromide Potassium iodide
Other cations	Lithium chloride Sodium chloride Rubidium chloride Caesium chloride Ammonium chloride
Related compounds	Potassium hypochlorite Potassium chlorite Potassium chlorate Potassium perchlorate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

It occurs naturally as the mineral sylvite, which is named after salt's historical designations sal degistivum Sylvii and sal febrifugum Sylvii,^[9] and in combination with sodium chloride as sylvinite.^[10]

Uses

Fertilizer

Potassium chloride, compacted, fertilizer grade

The majority of the potassium chloride produced is used for making fertilizer, called potash, since the growth of many plants is limited by potassium availability.^[11][12] The term "potash" refers to various mined and manufactured salts that contain potassium in water-soluble form. Potassium chloride sold as fertilizer is known as "muriate of potash"—it is the common name for potassium chloride (KCl) used in agriculture.^{[13][14][15][16]} The vast majority of potash fertilizer worldwide is sold as muriate of potash.^[17][18] The dominance of muriate of potash in the fertilizer market is due to its high potassium content (approximately 60% K
₂O equivalent) and relative affordability compared to other potassium sources like sulfate of potash (potassium sulfate).^[16][19] Potassium is one of the three primary macronutrients essential for plant growth, alongside nitrogen and phosphorus. Potassium plays a vital role in various plant physiological processes, including enzyme activation, photosynthesis, protein synthesis, and water regulation.^[20][21] For watering plants, a moderate concentration of potassium chloride (KCl) is used to avoid potential toxicity: 6 mM (millimolar) is generally effective and safe for most plants, that is approximately 0.4 grams (0.014 oz) per liter of water.^[22][23]

Medical use

Main article: Potassium chloride (medical use)

Potassium is vital in the human body, and potassium chloride by mouth is the standard means to treat low blood potassium, although it can also be given intravenously. It is on the World Health Organization's List of Essential Medicines.^[24] It is also an ingredient in Oral Rehydration Therapy (ORT)/solution (ORS) to reduce hypokalemia caused by diarrhoea.^[25] This is another medicine on the WHO's List of Essential Medicines.^[24] Overdose causes hyperkalemia which can disrupt cell signaling to the extent that the heart will stop, reversibly in the case of some open heart surgeries.

Culinary use

Potassium chloride can be used as a salt substitute for food, but due to its weak, bitter, unsalty flavor, it is often mixed with ordinary table salt (sodium chloride) to improve the taste, to form low sodium salt. The addition of 1 ppm of thaumatin considerably reduces this bitterness.^[26] Complaints of bitterness or a chemical or metallic taste are also reported with potassium chloride used in food.^[27]

Execution

In the United States, potassium chloride is used as the final drug in the three-injection sequence of lethal injection as a form of capital punishment. It induces cardiac arrest, ultimately killing the inmate.^[28]

Industrial

As a chemical feedstock, the salt is used for the manufacture of potassium hydroxide and potassium metal. It is also used in medicine, lethal injections, scientific applications, food processing, soaps, and as a sodium-free substitute for table salt for people concerned about the health effects of sodium.^{[citation needed]}

It is used as a supplement in animal feed to boost the potassium level in the feed. As an added benefit, it is known to increase milk production.^{[citation needed]}

It is sometimes used in solution as a completion fluid in petroleum and natural gas operations, as well as being an alternative to sodium chloride in household water softener units.^{[citation needed]}

Glass manufacturers use granular potash as a flux, lowering the temperature at which a mixture melts. Because potash imparts excellent clarity to glass, it is commonly used in eyeglasses, glassware, televisions, and computer monitors.^{[citation needed]}

Because natural potassium contains a tiny amount of the isotope potassium-40, potassium chloride is used as a beta radiation source to calibrate radiation monitoring equipment. It also emits a relatively low level of 511 keV gamma rays from positron annihilation, which can be used to calibrate medical scanners.^{[citation needed]}

Potassium chloride is used in some de-icing products designed to be safer for pets and plants, though these are inferior in melting quality to calcium chloride. It is also used in various brands of bottled water.^{[citation needed]}

Potassium chloride was once used as a fire extinguishing agent, and 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, as well as more effective. It is rated for B and C fires.^{[citation needed]}

Along with sodium chloride and lithium chloride, potassium chloride is used as a flux for the gas welding of aluminium.^{[citation needed]}

Potassium chloride is also an optical crystal with a wide transmission range from 210 nm to 20 μm. While cheap, KCl crystals are 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, they have been entirely replaced by much tougher crystals such as zinc selenide.^{[citation needed]}

Potassium chloride is used as a scotophor with designation P10 in dark-trace CRTs, e.g. in the Skiatron.^{[citation needed]}

Toxicity

The typical amounts of potassium chloride found in the diet appear to be generally safe.^[29] 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 of potassium chloride is far smaller, at about 57.2 mg/kg to 66.7 mg/kg; this is found by dividing the lethal concentration of positive potassium ions (about 30 to 35 mg/kg)^[30] by the proportion by mass of potassium ions in potassium chloride (about 0.52445 mg K⁺/mg KCl).^[31]

Chemical properties

Solubility

KCl is soluble in a variety of polar solvents.

Solubility^[32]

Solvent	Solubility (g/kg of solvent at 25 °C)
Water	360
Liquid ammonia	0.4
Liquid sulfur dioxide	0.41
Methanol	5.3
Ethanol	0.37
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):

${\displaystyle {\ce {KCl_{(l)}{}+ Na_{(l)}<=> NaCl_{(l)}{}+ K_{(g)}}}}$

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.^[10]

Other potassium chloride stoichiometries

Potassium chlorides with formulas other than KCl have been predicted to become stable under pressures of 20 GPa or more.^[33] Among these, two phases of KCl₃ were synthesized and characterized. At 20-40 GPa, a trigonal structure containing K⁺ and Cl₃⁻ is obtained; above 40 GPa this gives way to a phase isostructural with the intermetallic compound Cr₃Si.

Physical properties

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

Under ambient conditions, the crystal structure of potassium chloride is like that of NaCl. It adopts a face-centered cubic structure known as the B1 phase with a lattice constant of roughly 6.3 Å. Crystals cleave easily in three directions. Other polymorphic and hydrated phases are adopted at high pressures.^[34]

Some other properties are

• Transmission range: 210 nm to 20 μm
• Transmittivity = 92% at 450 nm and rises linearly to 94% at 16 μm
• Refractive index = 1.456 at 10 μm
• Reflection loss = 6.8% at 10 μm (two surfaces)
• dN/dT (expansion coefficient)= −33.2×10⁻⁶/°C
• dL/dT (refractive index gradient)= 40×10⁻⁶/°C
• Thermal conductivity = 0.036 W/(cm·K)
• Damage threshold (Newman and Novak): 4 GW/cm² or 2 J/cm² (0.5 or 1 ns pulse rate); 4.2 J/cm² (1.7 ns pulse rate Kovalev and Faizullov)

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

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.

Most potassium chloride is produced as agricultural and industrial-grade potash in Saskatchewan, Canada, Russia, and Belarus. Saskatchewan alone accounted for over 25% of the world's potash production in 2017.^[35]

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:

${\displaystyle {\ce {KOH + HCl -> KCl + H2O}}}$

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:

${\displaystyle {\ce {2 K + Cl2 -> 2 KCl}}}$

References

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Further reading

• Lide DR, ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.
• Greenwood NN, Earnshaw A (1984). Chemistry of the Elements. Oxford: Pergamon Press. ISBN 978-0-08-022057-4.

External links