The chemical compound potassium chloride (KCl) is a metal halide salt composed of potassium and chlorine. In its pure state it is odorless. It has a white or colorless vitreous crystal, with a crystal structure that cleaves easily in three directions. Potassium chloride crystals are face-centered cubic. Potassium chloride 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.
Although potassium is more electropositive than sodium, KCl can be reduced to the metal by reaction with metallic sodium at 850 °C because the potassium is removed by distillation (see 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.
As with other compounds containing potassium, KCl in powdered form gives a lilac flame test result:)
Potassium chloride is also used as the third of a three drug combination in judicial execution through lethal injection. Additionally, KCl is used to terminate the life of the unborn fetus in induced abortion procedures by lethal injection to the heart, which induces cardiac arrest.
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 makes up 70% of Ace Hardware's pet and vegetation-friendly "Ice Melt" though inferior in melting quality to calcium chloride (0°F v. -25°F). It is also used in Dasani 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 60s, which was much less corrosive and more effective. Rated for B and C fires.
Potassium chloride is also an optical crystal with a wide transmission range from 210nm to 20um. It was often used in the infrared spectrum range and it is still used some time.
KCl crystal is hygroscopic and cheap. This limits its application to protected environment or for short term uses (prototyping ). Exposed to free air KCl optics will "rot".
Today other crystals much more tough like ZnSe has overcome KCl (for the IR spectral range).
Transmission Range: 210nm to 20um
Transmitivity = 92% @ 450nm and rises linearly to 94% @ 16um
Refractive Index = 1.456 @ 10um
Reflection Loss = 6.8% @ 10um (2 surfaces)
dN/dT (Expansion Coefficient)= -33.2 x 10-6/°C
dL-dT (Refractive Index Gradient)= 40 x 10-6/°C
Coefficient of Absorption: 0.001 cm-1
Thermal Conductivity = 0.036 (W/cm K):
Damage Threshold (Newman & Novak): 4GW/cm2 or 2j/cm2 (0.5-1ns pulse rate)
Damage Threshold (Kovalev & Faizullov)= 4.2j/cm2 (1.7ns pulse rate)
Dr. Jack Kevorkian's thanatron machine injected a lethal dose of potassium chloride into the patient, which caused the heart to stop functioning, after a sodium thiopental-induced coma was achieved. A similar device, the German 'Perfusor', also uses potassium chloride as a suicide aid.
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 carefully prepared KCl solutions have well-reproducible and well-repeatable measurable properties.
| Solubility of KCl in various solvents|
(g KCl / 100 g of solvent at 25 °C)
|Liquid sulfur dioxide||0.041|
|Dimethylformamide||0.017 - 0.05|
Burgess, J. Metal Ions in Solution
(Ellis Horwood, New York, 1978)