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Potassium hydroxide is an inorganic compound with the formula potassiumhydroxide, and is commonly called caustic potash.
Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which utilize its nature and its reactivity toward acids. About 2.5 million were produced in 2023. KOH is noteworthy as the precursor to most soft and liquid , as well as numerous potassium-containing chemicals. It is a white solid that is dangerously corrosive. (2025). 9783527306732, Wiley-VCH. ISBN 9783527306732
Because of its high affinity for water, KOH serves as a desiccant in the laboratory. It is often used to dry basic solvents, especially amines and pyridines.
When R is a long chain, the product is called a potassium soap. This reaction is manifested by the "greasy" feel that KOH gives when touched; on the skin are rapidly converted to soap and glycerol.
Molten KOH is used to displace halides and other . The reaction is especially useful for aromaticity reagents to give the corresponding .
Filtering off the precipitated calcium carbonate and boiling down the solution gives potassium hydroxide ("calcinated or caustic potash"). This method of producing potassium hydroxide remained dominant until the late 19th century, when it was largely replaced by the current method of electrolysis of potassium chloride solutions. The method is analogous to the manufacture of sodium hydroxide (see chloralkali process):
Hydrogen gas forms as a byproduct on the cathode; concurrently, an anodic oxidation of the chloride ion takes place, forming chlorine gas as a byproduct. Separation of the anodic and cathodic spaces in the electrolysis cell is essential for this process.Römpp Chemie-Lexikon, 9th Ed. (in German)
In chemical synthesis, the choice between the use of KOH and the use of NaOH is guided by the solubility or keeping quality of the resulting salt.
The corrosive properties of potassium hydroxide make it a useful ingredient in agents and preparations that clean and Disinfection surfaces and materials that can themselves resist corrosion by KOH.
KOH is also used for semiconductor chip fabrication (for example anisotropic wet etching).
Potassium hydroxide is often the main active ingredient in chemical "cuticle removers" used in manicure treatments.
Because aggressive bases like KOH damage the cuticle of the hair shaft, potassium hydroxide is used to chemically assist the removal of hair from animal hides. The hides are soaked for several hours in a solution of KOH and water to prepare them for the unhairing stage of the tanning process. This same effect is also used to weaken human hair in preparation for shaving. Preshave products and some shave creams contain potassium hydroxide to force open the hair cuticle and to act as a hygroscopic agent to attract and force water into the hair shaft, causing further damage to the hair. In this weakened state, the hair is more easily cut by a razor blade.
Potassium hydroxide is used to identify some species of fungi. A 3–5% aqueous solution of KOH is applied to the flesh of a mushroom and the researcher notes whether or not the color of the flesh changes. Certain species of gilled mushrooms, boletes, polypores, and lichens
The caustic effects arise from being highly alkaline, but if potassium hydroxide is neutralised with a non-toxic acid then it becomes a non-toxic potassium salt. It is approved as a food additive under the code E525.
Uses
KOH and NaOH can be used interchangeably for a number of applications, although in industry, NaOH is preferred because of its lower cost.
Purity requirements
Manufactured KOH are used in various applications that need various purities. For industrial uses, like cleaning metals or treating waste gases, only 90% purity, minimal, is required. Food grade ones also require 90%, except it must have arsenic less than 3 ppm and lead less than 5 ppm. KOH at this purity is used to debitterate olive and the manufacture of cocoa. Electronic grade ones which are used to etch semiconductors and treat silicon wafers in photovoltaic cells require at least 99.9% purity and less than 1 ppm for total metal ion concentration. Reagent level ones that are used in pharmaceutical applications and professional analytical labs require purity higher than 99.99% and Heavy metals less than 0.1 ppm for safety to use.
Catalyst for hydrothermal gasification process
In industry, KOH is a good catalyst for hydrothermal gasification process. In this process, it is used to improve the yield of gas and amount of hydrogen in process. For example, production of coke from coal often produces much coking wastewater. In order to degrade it, supercritical water is used to convert it to the syngas containing carbon monoxide, carbon dioxide, hydrogen and methane. Using pressure swing adsorption, various gases could be separated, and then power-to-gas technology is used to convert them to fuel. On the other hand, the hydrothermal gasification process could degrade other waste such as sewage sludge and waste from food factories.
Precursor to other potassium compounds
Many potassium salts are prepared by neutralization reactions involving KOH. The potassium salts of carbonate, cyanide, permanganate, phosphate, and various silicates are prepared by treating either the oxides or the acids with KOH. The high solubility of potassium phosphate is desirable in .
Manufacture of soft soaps
The saponification of with KOH is used to prepare the corresponding "potassium Soap", which are softer than the more common sodium hydroxide-derived soaps. Because of their softness and greater solubility, potassium soaps require less water to liquefy, and can thus contain more cleaning agent than liquefied sodium soaps.
As an electrolyte
Aqueous solution potassium hydroxide is employed as the electrolyte in Alkaline battery based on nickel-cadmium, nickel-hydrogen, and manganese dioxide-zinc. Potassium hydroxide is preferred over sodium hydroxide because its solutions are more conductive. The nickel–metal hydride batteries in the Toyota Prius use a mixture of potassium hydroxide and sodium hydroxide. Nickel–iron batteries also use potassium hydroxide electrolyte.
Food industry
In food products, potassium hydroxide acts as a food thickener, pH control agent and food stabilizer. The FDA considers it generally safe as a direct food ingredient when used in accordance with Good Manufacturing Practices. It is known in the E number system as E525.
Niche applications
Like sodium hydroxide, potassium hydroxide attracts numerous specialized applications, virtually all of which rely on its properties as a strong chemical base with its consequent ability to degrade many materials. For example, in a process commonly referred to as "chemical cremation" or "resomation", potassium hydroxide hastens the decomposition of soft tissues, both animal and human, to leave behind only the bones and other hard tissues. Entomologists wishing to study the fine structure of insect anatomy may use a 10% aqueous solution of KOH to apply this process.
(2025). 9780521692168, Cambridge University Press. ISBN 9780521692168 are identifiable based on this color-change reaction. Testing Chemical Reactions at MushroomExpert.com
Safety
Potassium hydroxide is a Chemical burn alkali and its solutions range from irritating to skin and other tissue in low concentrations, to highly corrosive in high concentrations. Eyes are particularly vulnerable, and dust or mist is severely irritating to lungs and can cause pulmonary edema. Safety considerations are similar to those of sodium hydroxide.
See also
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