Potassium hydroxide

Potassium hydroxide is an inorganic compound with the formula KOH, and is commonly called caustic potash.

Along with sodium hydroxide (NaOH), this colorless solid is a prototypical strong base. It has many industrial and niche applications, most of which exploit its caustic nature and its reactivity toward acids. An estimated 700,000 to 800,000 tonnes were produced in 2005. About 100 times more NaOH than KOH is produced annually. KOH is noteworthy as the precursor to most soft and liquid soaps, as well as numerous potassium-containing chemicals. It is a white solid that is dangerously corrosive. Most commercial samples are ca. 90% pure, the remainder being water and carbonates.[10]

Potassium hydroxide
Crystal structure of KOH
Pellets of potassium hydroxide
IUPAC name
Potassium hydroxide
Other names
Caustic potash, Lye, Potash lye, Potassia, Potassium hydrate, KOH
3D model (JSmol)
ECHA InfoCard 100.013.802
EC Number 215-181-3
E number E525 (acidity regulators, ...)
RTECS number TT2100000
UN number 1813
Molar mass 56.11 g mol−1
Appearance white solid, deliquescent
Odor odorless
Density 2.044 g/cm3 (20 °C)[1]
2.12 g/cm3 (25 °C)[2]
Melting point 360[3] °C (680 °F; 633 K)
Boiling point 1,327 °C (2,421 °F; 1,600 K)
85 g/100 g (-23.2 °C)
97 g/100 mL (0 °C)
121 g/100 mL (25 °C)
138.3 g/100 mL (50 °C)
162.9 g/100 mL (100 °C)[1][4]
Solubility soluble in alcohol, glycerol
insoluble in ether, liquid ammonia
Solubility in methanol 55 g/100 g (28 °C)[2]
Solubility in isopropanol ~14 g / 100 g (28 °C)
Basicity (pKb) −0.7[5](KOH(aq) = K+ + OH)
−22.0·10−6 cm3/mol
1.409 (20 °C)
65.87 J/mol·K[2]
79.32 J/mol·K[2][6]
-425.8 kJ/mol[2][6]
-380.2 kJ/mol[2]
Safety data sheet ICSC 0357
GHS pictograms The corrosion pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)[7]
GHS signal word Danger
H302, H314[7]
P280, P305+351+338, P310[7]
NFPA 704
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
273 mg/kg (oral, rat)[9]
US health exposure limits (NIOSH):
PEL (Permissible)
REL (Recommended)
C 2 mg/m3[8]
IDLH (Immediate danger)
Related compounds
Other anions
Potassium hydrosulfide
Potassium amide
Other cations
Lithium hydroxide
Sodium hydroxide
Rubidium hydroxide
Caesium hydroxide
Related compounds
Potassium oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Properties and structure

Potassium hydroxide is usually sold as translucent pellets, which become tacky in air because KOH is hygroscopic. Consequently, KOH typically contains varying amounts of water (as well as carbonates - see below). Its dissolution in water is strongly exothermic. Concentrated aqueous solutions are sometimes called potassium lyes. Even at high temperatures, solid KOH does not dehydrate readily.[11]


At higher temperatures, solid KOH crystallizes in the NaCl crystal structure. The OH group is either rapidly or randomly disordered so that the OH group is effectively a spherical anion of radius 1.53 Å (between Cl
and F
in size). At room temperature, the OH groups are ordered and the environment about the K+
centers is distorted, with K+
distances ranging from 2.69 to 3.15 Å, depending on the orientation of the OH group. KOH forms a series of crystalline hydrates, namely the monohydrate KOH{{hydrate}}, the dihydrate KOH · 2H2O and the tetrahydrate KOH · 4H2O.[12]

Thermal stability

Like NaOH, KOH exhibits high thermal stability. The gaseous species is dimeric. Because of its high stability and relatively low melting point, it is often melt-cast as pellets or rods, forms that have low surface area and convenient handling properties.


Basicity, solubility and desiccating properties

About 121 g of KOH dissolve in 100 mL water at room temperature, which contrasts with 100 g/100 mL for NaOH. Thus on a molar basis, KOH is slightly less soluble than NaOH. Lower molecular-weight alcohols such as methanol, ethanol, and propanols are also excellent solvents.They participate in an acid-base equilibrium. In the case of methanol the potassium methoxide (methylate) forms: [13]


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.

As a nucleophile in organic chemistry

KOH, like NaOH, serves as a source of OH, a highly nucleophilic anion that attacks polar bonds in both inorganic and organic materials. Aqueous KOH saponifies esters:


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 — fats on the skin are rapidly converted to soap and glycerol.

Molten KOH is used to displace halides and other leaving groups. The reaction is especially useful for aromatic reagents to give the corresponding phenols.[14]

Reactions with inorganic compounds

Complementary to its reactivity toward acids, KOH attacks oxides. Thus, SiO2 is attacked by KOH to give soluble potassium silicates. KOH reacts with carbon dioxide to give bicarbonate:



Historically, KOH was made by adding potassium carbonate to a strong solution of calcium hydroxide (slaked lime) The salt metathesis reaction results in precipitation of solid calcium carbonate, leaving potassium hydroxide in solution:

Ca(OH)2 + K2CO3 → CaCO3 + 2 KOH

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.[10] The method is analogous to the manufacture of sodium hydroxide (see chloralkali process):

2 KCl + 2 H2O → 2 KOH + Cl2 + H2

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.[15]


KOH and NaOH can be used interchangeably for a number of applications, although in industry, NaOH is preferred because of its lower cost.

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.[10] The high solubility of potassium phosphate is desirable in fertilizers.

Manufacture of soft soaps

The saponification of fats with KOH is used to prepare the corresponding "potassium soaps", 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.[16]

As an electrolyte

LeakedBattery 2701a
Potassium carbonate, formed from the hydroxide solution leaking from an alkaline battery

Aqueous potassium hydroxide is employed as the electrolyte in alkaline batteries based on nickel-cadmium, nickel-hydrogen, and manganese dioxide-zinc. Potassium hydroxide is preferred over sodium hydroxide because its solutions are more conductive.[17] The nickel–metal hydride batteries in the Toyota Prius use a mixture of potassium hydroxide and sodium hydroxide.[18] 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 (as a direct human food ingredient) as generally safe when combined with "good" manufacturing practice conditions of use.[19] 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.[20] Entomologists wishing to study the fine structure of insect anatomy may use a 10% aqueous solution of KOH to apply this process.[21]

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 disinfect surfaces and materials that can themselves resist corrosion by KOH.[15]

KOH is also used for semiconductor chip fabrication. See also: 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[22] are identifiable based on this color-change reaction.[23]


Potassium hydroxide and its solutions are severe irritants to skin and other tissue.[24]

See also


  1. ^ a b Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. p. 4-80. ISBN 0-8493-0486-5.
  2. ^ a b c d e f "potassium hydroxide". chemister.ru. Archived from the original on 18 May 2014. Retrieved 8 May 2018.
  3. ^ "A18854 Potassium hydroxide". Alfa Aesar. Thermo Fisher Scientific. Archived from the original on 19 October 2015. Retrieved 26 October 2015.
  4. ^ Seidell, Atherton; Linke, William F. (1952). Solubilities of Inorganic and Organic Compounds. Van Nostrand. Retrieved 2014-05-29.
  5. ^ Popov, K.; et al. (2002). "7Li, 23Na, 39K and 133Cs NMR comparative equilibrium study of alkali metal cation hydroxide complexes in aqueous solutions. First numerical value for CsOH formation". Inorganic Chemistry Communications. 3 (5): 223–225. doi:10.1016/S1387-7003(02)00335-0. ISSN 1387-7003. Retrieved October 20, 2018.
  6. ^ a b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A22. ISBN 978-0-618-94690-7.
  7. ^ a b c Sigma-Aldrich Co., Potassium hydroxide. Retrieved on 2014-05-18.
  8. ^ a b c NIOSH Pocket Guide to Chemical Hazards. "#0523". National Institute for Occupational Safety and Health (NIOSH).
  9. ^ Chambers, Michael. "ChemIDplus - 1310-58-3 - KWYUFKZDYYNOTN-UHFFFAOYSA-M - Potassium hydroxide [JAN:NF] - Similar structures search, synonyms, formulas, resource links, and other chemical information". chem.sis.nlm.nih.gov. Archived from the original on 12 August 2014. Retrieved 8 May 2018.
  10. ^ a b c Schultz, Heinz; Bauer, Günter; Schachl, Erich; Hagedorn, Fritz; Schmittinger, Peter (2005). "Potassium Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim, Germany: Wiley-VCH. doi:10.1002/14356007.a22_039. ISBN 978-3-527-30673-2.
  11. ^ Holleman, A. F; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. ISBN 978-0-12-352651-9.
  12. ^ Wells, A.F. (1984). Structural Inorganic Chemistry. Oxford: Clarendon Press. ISBN 978-0-19-855370-0.
  13. ^ Platonov, Andrew Y.; Kurzin, Alexander V.; Evdokimov, Andrey N. (2009). "Composition of Vapor and Liquid Phases in the Potassium Hydroxide + Methanol Reaction System at 25 °С". J. Solution Chem. 39 (3): 335–342. doi:10.1007/s10953-010-9505-1.
  14. ^ W. W. Hartman (1923). "p-Cresol". Organic Syntheses. 3: 37. doi:10.15227/orgsyn.003.0037.; Collective Volume, 1, p. 175
  15. ^ a b Römpp Chemie-Lexikon, 9th Ed. (in German)
  16. ^ K. Schumann; K. Siekmann (2005). "Soaps". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a24_247. ISBN 978-3527306732.
  17. ^ D. Berndt; D. Spahrbier (2005). "Batteries". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a03_343. ISBN 978-3527306732.
  18. ^ "Toyota Prius Hybrid 2010 Model Emergency Response Guide" (PDF). Toyota Motor Corporation. 2009. Archived from the original (PDF) on 2011-10-29.
  19. ^ "Compound Summary for CID 14797 - Potassium Hydroxide". PubChem.
  20. ^ Green, Margaret (January 1952). "A RAPID METHOD FOR CLEARING AND STAINING SPECIMENS FOR THE DEMONSTRATION OF BONE". The Ohio Journal of Science. 52 (1): 31–33. Archived from the original on 8 January 2015. Retrieved 20 November 2012.
  21. ^ Thomas Eisner (2003). For the Love of Insects. Harvard University Press. p. 71.
  22. ^ Elix, J.A.; Stocker-Wörgötter, Elfie (2008). "Chapter 7: Biochemistry and secondary metabolites". In Nash III, Thomas H. Lichen Biology (2nd ed.). New York: Cambridge University Press. pp. 118–119. ISBN 978-0-521-69216-8.
  23. ^ Testing Chemical Reactions Archived 2009-10-15 at the Wayback Machine at MushroomExpert.com
  24. ^ Potassium hydroxide, SIDS Initial Assessment Report For SIAM 13. Bern, Switzerland, 6-9 November 2001. Archived 3 January 2018 at the Wayback Machine By Dr. Thaly LAKHANISKY. Date of last Update: February 2002

External links

Acid value

In chemistry, acid value (or neutralization number or acid number or acidity) is the mass of potassium hydroxide (KOH) in milligrams that is required to neutralize one gram of chemical substance. The acid number is a measure of the number of carboxylic acid groups in a chemical compound, such as a fatty acid, or in a mixture of compounds. In a typical procedure, a known amount of sample dissolved in an organic solvent (often isopropanol) and titrated with a solution of potassium hydroxide (KOH) of known concentration using phenolphthalein as a color indicator.

The acid number is used to quantify the acidity of a substance e.g. biodiesel. It is the quantity of base, expressed in milligrams of potassium hydroxide, that is required to neutralize the acidic constituents in 1 g of sample.

Veq is the volume of titrant (ml) consumed by the crude oil sample and 1 ml of spiking solution at the equivalent point, beq is the volume of titrant (ml) consumed by 1 ml of spiking solution at the equivalent point, and 56.1 g/mol is the molecular weight of KOH. WOil is the mass of the sample in grams.

The molar concentration of titrant (N) is calculated as such:

In which WKHP is the mass (g) of KHP in 50 ml of KHP standard solution, Veq is the volume of titrant (ml) consumed by 50 ml KHP standard solution at the equivalent point, and 204.23 g/mol is the molecular weight of KHP.

There are standard methods for determining the acid number, such as ASTM D 974 and DIN 51558 (for mineral oils, biodiesel), or specifically for biodiesel using the European Standard EN 14104 and ASTM D664 are both widely used worldwide. Acid number (mg KOH/g oil) for biodiesel should to be lower than 0.50 mg KOH/g in both EN 14214 and ASTM D6751 standard fuels. This is since the FFA produced may corrode automotive parts and these limits protect vehicle engines and fuel tanks.

As oil-fats rancidify, triglycerides are converted into fatty acids and glycerol, causing an increase in acid number. A similar observation is observed with biodiesel aging through analogous oxidation processes and when subjected to prolonged high temperatures (ester thermolysis) or through exposure to acids or bases (acid/base ester hydrolysis). Low Acid value indicates good cleansing by soap.

Alkali hydroxide

The alkali hydroxides are a class of chemical compounds which are composed of an alkali metal cation and the hydroxide anion (OH−). The alkali hydroxides are:

Lithium hydroxide (LiOH)

Sodium hydroxide (NaOH)

Potassium hydroxide (KOH)

Rubidium hydroxide (RbOH)

Caesium hydroxide (CsOH)The most common alkali hydroxide is sodium hydroxide, which is readily available in most hardware stores in products such as a drain cleaner. Another common alkali hydroxide is potassium hydroxide. This is available as a solution used for cleaning terraces and other areas made out of wood.

All alkali hydroxides are very corrosive, being strongly alkaline.

A typical school demonstration demonstrates what happens when a piece of an alkali metal is introduced to a bowl of water. A vigorous reaction occurs, producing hydrogen gas and the specific alkali hydroxide. For example, if sodium is the alkali metal:

Sodium + water → sodium hydroxide + hydrogen gas

2 Na + 2 H2O → 2 NaOH + H2

Alkaline battery

An alkaline battery (IEC code: L) is a type of primary battery which derives its energy from the reaction between zinc metal and manganese dioxide.

Compared with zinc-carbon batteries of the Leclanché cell or zinc chloride types, alkaline batteries have a higher energy density and longer shelf-life, with the same voltage.

The alkaline battery gets its name because it has an alkaline electrolyte of potassium hydroxide, instead of the acidic ammonium chloride or zinc chloride electrolyte of the zinc-carbon batteries. Other battery systems also use alkaline electrolytes, but they use different active materials for the electrodes.

Alkaline batteries account for 80% of manufactured batteries in the US and over 10 billion individual units produced worldwide. In Japan alkaline batteries account for 46% of all primary battery sales. In Switzerland alkaline batteries account for 68%, in the UK 60% and in the EU 47% of all battery sales including secondary types. Alkaline batteries contain Zinc and Manganese dioxide (Health codes 1), which can be toxic in higher concentrations. However, compared to other battery types, the toxicity of alkaline batteries is moderate. Alkaline batteries are used in many household items such as MP3 players, CD players, digital cameras, pagers, toys, lights, and radios.

Caesium hydroxide

Caesium hydroxide or cesium hydroxide (CsOH) is a chemical compound consisting of caesium ions and hydroxide ions. It is a strong base (pKb=-1.76), much like the other alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. In fact, caesium hydroxide is corrosive enough to quickly corrode through glass.

Due to its high reactivity, caesium hydroxide is extremely hygroscopic. Laboratory caesium hydroxide is typically a hydrate.

It is an anisotropic etchant of silicon, exposing octahedral planes. This technique can form pyramids and regularly shaped etch pits for uses such as Microelectromechanical systems. It is known to have a higher selectivity to etch highly p-doped silicon than the more commonly used potassium hydroxide.

This compound is not commonly used in experiments due to the high extraction cost of caesium and its reactive behaviour. It acts in similar fashion to the compounds rubidium hydroxide and potassium hydroxide, although more reactive.

Cannizzaro reaction

The Cannizzaro reaction, named after its discoverer Stanislao Cannizzaro, is a chemical reaction that involves the base-induced disproportionation of two molecules of a non-enolizable aldehyde to give a primary alcohol and a carboxylic acid.

Cannizzaro first accomplished this transformation in 1853, when he obtained benzyl alcohol and potassium benzoate from the treatment of benzaldehyde with potash (potassium carbonate). More typically, the reaction would be conducted with sodium hydroxide or potassium hydroxide, giving the sodium or potassium carboxylate salt of the carboxylic-acid product:

2 C6H5CHO + KOH → C6H5CH2OH + C6H5COOKThe process is a redox reaction involving transfer of a hydride from one substrate molecule to the other: one aldehyde is oxidized to form the acid, the other is reduced to form the alcohol.

Chemical test in mushroom identification

Chemical tests in mushroom identification are methods that aid in determining the variety of some fungi. The most useful tests are Melzer's reagent and potassium hydroxide.

Doisynolic acid

Doisynolic acid is a synthetic, nonsteroidal, orally active estrogen that was never marketed. The reaction of estradiol or estrone with potassium hydroxide, a strong base, results in doisynolic acid as a degradation product, which retains high estrogenic activity, and this reaction was how the drug was discovered, in the late 1930s. The drug is a highly active and potent estrogen by the oral or subcutaneous route. The reaction of equilenin or dihydroequilenin with potassium hydroxide was also found to produce bisdehydrodoisynolic acid, the levorotatory isomer of which is an estrogen with an "astonishingly" high degree of potency, while the dextrorotatory isomer is inactive. Doisynolic acid was named after Edward Adelbert Doisy, a pioneer in the field of estrogen research and one of the discoverers of estrone.Doisynolic acid is the parent compound of a group of synthetic, nonsteroidal estrogens with high oral activity. The synthetic, nonsteroidal estrogens methallenestril, fenestrel, and carbestrol were all derived from doisynolic acid and are seco-analogues of the compound. Doisynoestrol, also known as fenocycline, is cis-bisdehydrdoisynolic acid methyl ether, and is another estrogenic derivative.

Edison–Lalande cell

The Edison–Lalande cell was a type of alkaline primary battery developed by Thomas Edison from an earlier design by Felix Lalande and Georges Chaperon. It consisted of plates of copper oxide and zinc in a solution of potassium hydroxide. The cell voltage was low (about 0.75 volts) but the internal resistance was also low so these cells were capable of delivering large currents.

Hydroxyl value

In analytical chemistry, the hydroxyl value is defined as the number of milligrams of potassium hydroxide required to neutralize the acetic acid taken up on acetylation of one gram of a chemical substance that contains free hydroxyl groups. Hydroxyl value is a measure of the content of free hydroxyl groups in a chemical substance, usually expressed in units of the mass of potassium hydroxide (KOH) in milligrams equivalent to the hydroxyl content of one gram of the chemical substance. The analytical method used to determine hydroxyl value traditionally involves acetylation of the free hydroxyl groups of the substance with acetic anhydride in pyridine solvent. After completion of the reaction, water is added, and the remaining unreacted acetic anhydride is converted to acetic acid and measured by titration with potassium hydroxide.

The hydroxyl value can be calculated using the following equation. Note that a chemical substance may also have a measurable acid value affecting the measured end point of the titration. The acid value (AV) of the substance, determined in a separate experiment, enters into this equation as a correction factor in the calculation of the hydroxyl value (HV):

Where HV is the hydroxyl value; VB is the amount (ml) potassium hydroxide solution required for the titration of the blank; Vacet is the amount (ml) of potassium hydroxide solution required for the titration of the acetylated sample; Wacet is the weight of sample (in grams) used for acetylation; N is the normality of the titrant; 56.1 is the molecular weight of potassium hydroxide; AV is a separately determined acid value of the chemical substance.

The content of free hydroxyl groups in a substance can also be determined by methods other than acetylation. Determinations of hydroxyl content by other methods may instead be expressed as a weight percentage (wt. %) of hydroxyl groups in units of the mass of hydroxide functional groups in grams per 100 grams of substance. The conversion between hydroxyl value and other hydroxyl content measurements is obtained by multiplying the hydroxyl value by the factor 17/560. The chemical substance may be a fat, oil, natural or synthetic ester, or other polyol.

ASTM D 1957 and ASTM E222-10 describe several versions of this method of determining hydroxyl value.

KOH test

The KOH Test for Candida albicans, also known as a potassium hydroxide preparation or KOH prep, is a quick, inexpensive fungal test to differentiate dermatophytes and Candida albicans symptoms from other skin disorders like psoriasis and eczema.Dermatophytes are a type of fungus that invades the top layer of the skin, hair, or nails. There are three genera of fungi commonly implicated: Trichophyton (found in skin, nail, and hair infections), Epidermophyton (skin and nail infections), and Microsporum (skin and hair infections).

Dermatophytes produce an infection commonly known as ringworm or tinea. It can appear as "jock itch" in the groin or inner thighs (tinea cruris); on the scalp and hair (tinea capitis) resulting in brittle hair shafts that fall out easily. Tinea unguium affects the nails and athlete's foot (tinea pedis) affects the feet. Tinea versicolor refers to a fungal infection of the skin caused by Malassezia furfur. It appears anywhere on the skin and produces red or gray, scaly patches of itchy skin. Deeper infections may be discoloured, ulcerative and purulent.

A Candida yeast infection can also be identified by a KOH test by taking scrapings from the mouth (oral thrush), vagina (vaginitis) and skin (candidiasis). There are over 40 different fungus species known to cause disease in humans, of which Candida albicans is the most common and most frequently tested for.


A kaliapparat is a laboratory device invented in 1831 by Justus von Liebig (1803–1873) for the analysis of carbon in organic compounds. The device, made of glass, consists of a series of five bulbs connected and arranged in a triangular shape.

To determine the carbon in an organic compound with a kaliapparat, the substance is first burned, converting any carbon present into carbon dioxide (CO2). The vaporous products are passed through the kaliapparat, which is filled with potassium hydroxide (KOH) solution. The potassium hydroxide reacts with the CO2 to make potassium carbonate. The reaction, ignoring ionic dissociation, can be written as follows:

2 KOH + CO2 → K2CO3 + H2O.

Subtracting the mass of the kaliapparat before the combustion from that found after the combustion gives the amount of CO2 absorbed. From the mass of CO2 thus found, standard stoichiometric calculations then give the mass of carbon in the original sample.

A stylized symbol of a kaliapparat is used in the American Chemical Society logo, originally designed in the early 20th century by Tiffany's Jewelers.


A lye is a metal hydroxide traditionally obtained by leaching ashes, or a strong alkali which is highly soluble in water producing caustic basic solutions. "Lye" is commonly an alternative name of sodium hydroxide (NaOH) or historically potassium hydroxide (KOH), though the term "lye" refers most commonly to sodium hydroxide.

Today, lye is commercially manufactured using a membrane cell chloralkali process. It is supplied in various forms such as flakes, pellets, microbeads, coarse powder or a solution.

Nickel–hydrogen battery

A nickel–hydrogen battery (NiH2 or Ni–H2) is a rechargeable electrochemical power source based on nickel and hydrogen. It differs from a nickel–metal hydride (NIMH) battery by the use of hydrogen in gaseous form, stored in a pressurized cell at up to 1200 psi (82.7 bar) pressure. The Nickel–hydrogen battery was patented on Feb 25, 1971 by Alexandr Ilich Kloss and Boris Ioselevich Tsenter in the United States.NiH2 cells using 26% potassium hydroxide (KOH) as an electrolyte have shown a service life of 15 years or more at 80% depth of discharge (DOD)

The energy density is 75 Wh/kg, 60 Wh/dm3 specific power 220 W/kg. The open-circuit voltage is 1.55 V, the average voltage during discharge is 1.25 V.While the energy density is only around one third as that of a lithium battery, the distinctive virtue of the nickel–hydrogen battery is its long life: the cells handle more than 20,000 charge cycles with 85% energy efficiency and 100% faradaic efficiency.

NiH2 rechargeable batteries possess properties which make them attractive for the energy storage of electrical energy in satellites and space probes. For example, the ISS, Mercury Messenger, Mars Odyssey and the Mars Global Surveyor are equipped with nickel–hydrogen batteries. The Hubble Space Telescope, when its original batteries were changed in May 2009 more than 19 years after launch, led with the highest number of charge and discharge cycles of any NiH2 battery in low earth orbit.

Potassium hydrosulfide

Potassium hydrosulfide is the inorganic compound with the formula KHS. This colourless salt consists of the cation K+ and the bisulfide anion [SH]−. It is the product of the half-neutralization of hydrogen sulfide with potassium hydroxide. The compound is used in the synthesis of some organosulfur compounds. It is prepared by neutralizing aqueous KOH with H2S. Aqueous solutions of potassium sulfide consist of a mixture of potassium hydrosulfide and potassium hydroxide.

The structure of the potassium hydrosulfide resembles that for potassium chloride. Their structure is however complicated by the non-spherical symmetry of the SH− anions, but these tumble rapidly in the solid high temperatures.Addition of sulfur gives dipotassium pentasulfide.

Potassium peroxide

Potassium peroxide is an inorganic compound with the molecular formula K2O2. It is formed as potassium reacts with oxygen in the air, along with potassium oxide (K2O) and potassium superoxide (KO2).

Potassium peroxide reacts with water to form potassium hydroxide and oxygen:

Potassium sulfide

Potassium sulfide is the inorganic compound with the formula K2S. The colourless solid is rarely encountered, because it reacts readily with water, a reaction that affords potassium hydrosulfide (KSH) and potassium hydroxide (KOH). Most commonly, the term potassium sulfide refers loosely to this mixture, not the anhydrous solid.

Saponification value

Saponification value number represents the number of milligrams of potassium hydroxide required to saponify 1g of fat under the conditions specified. It is a measure of the average molecular weight (or chain length) of all the fatty acids present. As most of the mass of a fat/tri-ester is in the 3 fatty acids, the saponification value allows for comparison of the average fatty acid chain length. The long chain fatty acids found in fats have a low saponification value because they have a relatively fewer number of carboxylic functional groups per unit mass of the fat as compared to short chain fatty acids.

If more moles of base are required to saponify N grams of fat then there are more moles of the fat and the chain lengths are relatively small, given the following relation:

Number of moles = mass of oil / average molecular mass

The calculated molar mass is not applicable to fats and oils containing high amounts of unsaponifiable material, free fatty acids (>0.1%), or mono- and diacylglycerols (>0.1%).

Handmade soap makers who aim for bar soap use NaOH (sodium hydroxide, lye). Because saponification values are listed in KOH (potassium hydroxide) the value must be converted from potassium to sodium to make bar soap; potassium soaps make a paste, gel or liquid soap. To convert KOH values to NaOH values, divide the KOH values by the ratio of the molecular weights of KOH and NaOH (1.403).

Standard methods for analysis are for example: ASTM D5558 for vegetable and animal fats, ASTM D 94 (for petroleum) and DIN 51559.

Total acid number

The total acid number (TAN) is a measurement of acidity that is determined by the amount of potassium hydroxide in milligrams that is needed to neutralize the acids in one gram of oil. It is an important quality measurement of crude oil.

The TAN value indicates to the crude oil refinery the potential of corrosion problems. It is usually the naphthenic acids in the crude oil that cause corrosion problems. This type of corrosion is referred to as naphthenic acid corrosion (NAC).

TAN values may also be useful in other industries where oils are used as lubricants to determine oxidation and the subsequent corrosion risk to machinery.TAN value can be deduced by various methods, including

Potentiometric titration: The sample is normally dissolved in toluene and propanol with a little water and titrated with alcoholic potassium hydroxide (if sample is acidic). A glass electrode and reference electrode is immersed in the sample and connected to a voltmeter/potentiometer. The meter reading (in millivolts) is plotted against the volume of titrant. The end point is taken at the distinct inflection of the resulting titration curve corresponding to the basic buffer solution.

Color indicating titration: An appropriate pH color indicator e.g. phenolphthalein, is used. Titrant is added to the sample by means of a burette. The volume of titrant used to cause a permanent color change in the sample is recorded and used to calculate the TAN value.

Spectroscopic methods: as with many chemical parameters, spectroscopy can be used to make fast, accurate measurements once calibrated by a reference method. Mid and near infrared spectroscopy are most commonly used for this purpose. Spectroscopic methods are valuable as they can also be used to simultaneously measure a number of other parameters and do away with the need for wet chemistry.

Voges–Proskauer test

Voges–Proskauer or VP is a test used to detect acetoin in a bacterial broth culture. The test is performed by adding alpha-naphthol and potassium hydroxide to the Voges-Proskauer broth which has been inoculated with bacteria. A cherry red color indicates a positive result, while a yellow-brown color indicates a negative result.The test depends on the digestion of glucose to acetylmethylcarbinol. In the presence of oxygen and strong base, the acetylmethylcarbinol is oxidized to diacetyl, which then reacts with

guanidine compounds commonly found in the peptone medium of the broth. Alpha-naphthol acts as a color enhancer, but the color change to red can occur without it.

Procedure: First, add the alpha-naphthol; then, add the potassium hydroxide. A reversal in the order of the reagents being added may result in a weak-positive or false-negative reaction.

VP is one of the four tests of the IMViC series, which tests for evidence of an enteric bacterium. The other three tests include: the indole test [I], the methyl red test [M], and the citrate test [C].VP positive organisms include Enterobacter, Klebsiella, Serratia marcescens, Hafnia alvei, Vibrio cholera biotype eltor, and Vibrio alginolyticus.

VP negative organisms include Citrobacter sp., Shigella, Yersinia, Edwardsiella, Salmonella, Vibrio furnissii, Vibrio fluvialis, Vibrio vulnificus, and Vibrio parahaemolyticus.

Potassium compounds

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