Potassium hydroxide
| Potassium hydroxide | |
|---|---|
| Other names | Potash lye |
| Identifiers | |
| CAS number | |
| RTECS number | TT2100000 |
| Properties | |
| Molecular formula | KOH |
| Molar mass | 56.10564 g/mol |
| Appearance | white solid, deliquescent |
| Density | 2.044 g/cm³, solid |
| Melting point |
360 °C |
| Boiling point |
1320 °C |
| Solubility in water | 1100 g/L (25 °C) |
| Basicity (pKb) | -2.29 |
| Structure | |
| Crystal structure | monoclinic |
| Hazards | |
| EU classification | Corrosive (C) |
| R-phrases | R22, R35 |
| S-phrases | (S1/2), S26, S36/37/39, S45 |
| Flash point | non flammable |
| Related Compounds | |
| Other anions | Potassium oxide; Potassium peroxide; Potassium superoxide |
| Other cations | Lithium hydroxide; Sodium hydroxide; Rubidium hydroxide; Caesium hydroxide |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references | |
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Overview
The chemical compound potassium hydroxide (KOH), sometimes known as caustic potash, potassa, potash lye, and potassium hydrate, is a metallic base. It is very alkaline and is a "strong base", along with sodium hydroxide, lithium hydroxide, calcium hydroxide, barium hydroxide and strontium hydroxide.
Properties
Pure potassium hydroxide is a colorless, highly hygroscopic, solid crystalline compound, having density of about 2.04 g/cm3, readily soluble in water (1 g KOH dissolves in 0.5 g water) and lower alcohols (methanol, ethanol, propanols; solubility in ethanol being about 1 g KOH/2.5 mL EtOH), as well as other polar solvents. The dissolution in water is strongly exothermic, producing substantial amounts of energy in form of heat, leading to temperature rise, sometimes up to boiling point and over; concentrated aqueous solutions are called potassium lyes. Potassium hydroxide forms solid hydrates, namely the monohydrate KOH·H2O, the dihydrate KOH·2H2O, and the tetrahydrate KOH·4H2O; it is used therefore as a highly intensive desiccant agent, e.g. for drying liquid amines or their solutions in indifferent, nonpolar solvents (such as hydrocarbons). It is a highly basic compound, forming strongly alkali solutions in water and other polar solvents, capable of deprotonating many acids, even weak ones, and decompose some inorganic as well as organic materials (e.g. dissolution and hydrolysis of broken glass or fats in concentrated KOH solutions). It is an important industrial chemical, used to manufacture many industrial as well as commercial goods and products, for example, most potassium salts; it's also an important laboratory chemical and reagent, again, used to prepare potassium salts, to neutralize acids, further as basic standard in analytics and many more applications. As every strong base/alkali, potassium hydroxide is strongly corrosive, both towards inorganic as well as organic materials, including living tissues; care must be therefore taken, when handling the substance and its solutions. Its corrosivity is sometimes used in cleaning and disinfection of resistant surfaces and materials.[1]
Manufacture
Of historical relevance is the old method of boiling a solution of potassium carbonate (potash) with calcium hydroxide (slaked lime); the ion transfer reaction takes place, because forming calcium carbonate is less soluble than lime, precipitating out of the reaction mixture:
Ca(OH)2 (s), (aq) + K2CO3 (aq) → ↓CaCO3 (s) + 2 KOH (aq)
precipitated calcium carbonate was than filtered out and the resulting KOH solution boiled down, leaving solid potassium hydroxide ("calcinated or caustic potash"). This method, using potash extracted from wood ashes and slaked lime was known probably already in antique times and was the most important method of producing potassium hydroxide until the late 19th century, when it was largely replaced by the modern method of electrolysis of potassium chloride solutions, analogous to the method of manufacturing sodium hydroxide:
- 2 K+ (aq) + 2H2O (l) + 2e− → ↑H2 (g) + 2 KOH (aq)
Hydrogen gas forms as by-product on the cathode; concurrently, an anodic oxidation of the chloride ion takes place:
- 2 Cl– — 2e− → ↑Cl2 (g),
forming chlorine gas as another byproduct. Separation of the anodic and cathodic spaces in the electrolysis cell is essential for this process. For details, see chloralkali process.[2]
Uses
AgricultureMedicine (human and veterinary)
Food preparationFood uses of KOH include:
|
Manufacturing and commercial chemical processesKOH is a major industrial chemical because it is used as a base in a wide variety of chemical processes. Some uses of KOH include:
|
See also
References
- ↑ Römpp Chemie-Lexikon, 9th Ed. (in German)
- ↑ Römpp Chemie-Lexikon, 9th Ed. (in german)
- ↑ http://www.potassium-hydroxide.com
- ↑ http://www.weichtiere.at/Mollusks/Schnecken/weinberg.html
- ↑ http://www.hydroponicsearch.com/Explore_the_Science_of_Hydroponics/Plants/Potassium_hydroxide/
- ↑ http://dermatology.about.com/library/bldefpothyrox.htm
- ↑ http://www.jabfm.org/cgi/content/full/18/6/561
- ↑ http://www.p2pays.org/ref%5C02/01258.pdf
- ↑ http://www.codexalimentarius.net/gsfaonline/additives/details.html?id=311
- ↑ http://biodieselmagazine.com/article.jsp?article_id=462
- ↑ http://www.howtobrew.com/section1/chapter2-2-1.html
- ↑ http://www.powerstream.com/BatteryFAQ.html
- ↑ http://snf.stanford.edu/Materials/ChemFiles/KOHEtch.html
- ↑ http://dx.doi.org/10.1016/j.sna.2003.11.013
- ↑ http://www3.interscience.wiley.com/cgi-bin/abstract/112577341/ABSTRACT
External links
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| Cost Effectiveness of Potassium hydroxide | AND (Cost effectiveness) |
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