Potassium chloride
Potassium chloride 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. It could be obtained from ancient dried lake deposits. KCl is used as a fertilizer, in medicine, in scientific applications, and in food processing, where it may be known as E number additive E508.
In a few states of the United States, it is 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.
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. The two main types of potash are muriate of potash and sulphate of potash. While SOP typically sells at a premium to MOP, the vast majority of potash fertilizer worldwide is sold as MOP.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, the safest and most effective medicines needed in a health system. Overdose causes hyperkalemia which can disrupt cell signalling to the extent that the heart will stop, reversibly in the case of some open heart surgeries, or to induce death in the case of lethal injections.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 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 amount of nutrients in the feed, which in turn promotes healthy growth in animals. As an added benefit, it is known to increase milk production.
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.
Glass manufacturers use granular potash as a flux, lowering the temperature at which a mixture melts. Because potash confers 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.
There are also a small number 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 that are 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, 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 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 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 has also been used to produce heat packs which employ exothermic chemical reactions, but these have mostly been discontinued with the advent of cheaper and more efficient methods, such as the oxidation of metals or the crystallization of sodium acetate.
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. In larger quantities, however, potassium chloride is toxic. The of orally ingested potassium chloride is approximately 2.5 g/kg, or for a body mass of. In comparison, the of sodium chloride is 3.75 g/kg.Intravenously, the 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 by the proportion by mass of potassium ions in potassium chloride. In such quantities, it has severe consequences on the cardiac muscles, potentially causing cardiac arrest and rapid death. For this reason, it is used in surgical abortion, and as the third and final drug delivered in the lethal injection process.
Chemical properties
Solubility
KCl is soluble in a variety of polar solvents.| Solvent | Solubility |
| 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 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 :This method is the main method for producing metallic potassium. Electrolysis fails because of the high solubility of potassium in molten KCl.
Physical properties
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
- 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
- dN/dT = −33.2×10−6/°C
- dL/dT = 40×10−6/°C
- Thermal conductivity = 0.036 W/
- Damage threshold : 4 GW/cm2 or 2 J/cm2 ; 4.2 J/cm2
Production
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 with hydrochloric acid: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: