Chemistry:Potassium chloride

Short description: Ionic compound (KCl)

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
KEGG	D02060 Y
PubChem CID	4873
RTECS number	TS8050000
UNII	660YQ98I10 Y
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
Solubility in ethanol	0.288 g/L (25 °C)
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
Coordination geometry	Octahedral (K+) Octahedral (Cl−)
Thermochemistry
Std molar entropy (So298)	83 J·mol−1·K−1
Std enthalpy of formation (ΔfH⦵298)	−436 kJ·mol−1
Pharmacology
1=ATC code }}	A12BA01 (WHO) B05XA01 (WHO)
Routes of administration	Oral, IV, IM
Pharmacokinetics:
Excretion	Kidney: 90%; Fecal: 10%
Hazards
Safety data sheet	ICSC 1450
NFPA 704 (fire diamond)	0 1 0
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	2600 mg/kg (oral, rat)
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

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. KCl is used as a fertilizer, 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.

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

Uses

Fertilizer

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. Potassium chloride sold as fertilizer is known as muriate of potash. The vast majority of potash fertilizer worldwide is sold as muriate of potash.

Potassium chloride, compacted, fertilizer grade.

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 is on the World Health Organization's List of Essential Medicines. 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

It 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. Complaints of bitterness or a chemical or metallic taste are also reported with potassium chloride used in food.

Industrial

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, soaps, and as a sodium-free substitute for table salt for people concerned about the health effects of sodium.

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.

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.

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.

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. In order to use off-the-shelf materials, it needs to be crystallized sequentially, using controlled temperature, in order to extract KCl, which is the subject of ongoing research. It also emits a relatively low level of 511 keV gamma rays from positron annihilation, which can be used to calibrate medical scanners.

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 [lowest usable temperature 12 °F (−11 °C) v. −25 °F (−32 °C)]. It is also used in various brands of bottled water.

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.

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 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, it has been entirely replaced by much tougher crystals such as zinc selenide.

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

Toxicity

The typical amounts of potassium chloride found in the diet appear to be generally safe. In larger quantities, however, potassium chloride is toxic. The -1">50 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 -1">50 of sodium chloride (table salt) is 3.75 g/kg.

Intravenously, the -1">50 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) by the proportion by mass of potassium ions in potassium chloride (about 0.52445 mg K⁺/mg KCl).

Chemical properties

Solubility

KCl is soluble in a variety of polar solvents.

Solubility

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):

[math]\ce{ KCl_{(l)}{} + Na_{(l)} <=> NaCl_{(l)}{} + K_{(g)} }[/math]

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.

Other potassium chloride stoichiometries

Potassium chlorides with formulas other than KCl have been predicted to become stable under pressures of 20 GPa or more. 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.

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.

The vast majority of potassium chloride is produced as agricultural and industrial grade potash in Saskatchewan, Canada, as well as Russia and Belarus. Saskatchewan alone accounted for over 25% of the world's potash production in 2017.

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:

[math]\ce{ KOH + HCl -> KCl + H2O }[/math]

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:

[math]\ce{ 2 K + Cl2 -> 2 KCl }[/math]

Further reading

• Lide, D. R., ed (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5. 
• Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. ISBN 978-0-08-022057-4. https://books.google.com/books?id=OezvAAAAMAAJ&q=0-08-022057-6&dq=0-08-022057-6&source=bl&ots=m4tIRxdwSk&sig=XQTTjw5EN9n5z62JB3d0vaUEn0Y&hl=en&sa=X&ei=UoAWUN7-EM6ziQfyxIDoCQ&ved=0CD8Q6AEwBA. 

External links

• "Potassium chloride". Drug Information Portal. U.S. National Library of Medicine. https://druginfo.nlm.nih.gov/drugportal/name/potassium%20chloride.