Potassium hydroxide
| Crystal structure | |||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
|||||||||||||||||||
| __ K + _ _ OH - | |||||||||||||||||||
| General | |||||||||||||||||||
| Surname | Potassium hydroxide | ||||||||||||||||||
| other names |
|
||||||||||||||||||
| Ratio formula | KOH | ||||||||||||||||||
| Brief description |
white, hygroscopic, odorless solid |
||||||||||||||||||
| External identifiers / databases | |||||||||||||||||||
|
|||||||||||||||||||
| properties | |||||||||||||||||||
| Molar mass | 56.11 g mol −1 | ||||||||||||||||||
| Physical state |
firmly |
||||||||||||||||||
| density |
2.04 g cm −3 |
||||||||||||||||||
| Melting point |
360 ° C |
||||||||||||||||||
| boiling point |
1327 ° C |
||||||||||||||||||
| solubility |
good in water (1130 g l −1 at 20 ° C) |
||||||||||||||||||
| safety instructions | |||||||||||||||||||
|
|||||||||||||||||||
| MAK |
Switzerland: 2 mg m −3 (measured as inhalable dust ) |
||||||||||||||||||
| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | |||||||||||||||||||
Potassium hydroxide (also caustic potash , caustic potash ), chemical formula KOH , is a white hygroscopic solid. In water, it dissolves to form the strong base potassium hydroxide, generating a great deal of heat . It reacts with carbon dioxide in the air to form potassium carbonate and is therefore stored in airtight containers. To prevent potassium hydroxide from binding water in the air, it can be stored with a desiccant. As a strong base, the hydroxide ion displaces weaker and volatile bases from their salts .
properties
Potassium hydroxide is a white, strongly hygroscopic substance that is usually sold as cookies or sticks, less often as a powder. It dissolves in water with great heat development due to the negative enthalpy of solution of −57.1 kJ / mol and forms potassium hydroxide , in the solid state it forms mono-, di- and tetrahydrates . It reacts with the carbon dioxide in the air to form potassium carbonate. Potassium hydroxide, called " alcoholic potash ", is also soluble in alcohols such as methanol and ethanol .
synthesis
Earlier potassium hydroxide was causticizing of potassium carbonate produced. This works according to the equation
Today potassium hydroxide is mostly obtained by aqueous electrolysis of potassium chloride and subsequent evaporation of the solution.
use
In microsystem technology , potassium hydroxide is used for the selective anisotropic etching of monocrystalline silicon .
In microbiology it is used to differentiate between gram-positive and gram-negative bacteria in the rapid test method.
It is used as an electrolyte in galvanic oxygen sensors. It fulfills the same purpose in the widespread alkali-manganese cells and the historically important nickel-cadmium accumulators .
It is used as an acidity regulator in the food industry. It is generally approved in the EU as a food additive with the designation E 525 without maximum quantity restriction ( quantum satis ) for food.
It is used in the manufacture of potassium compounds, glass, dyes, batteries and as a drying and absorbing agent for carbon dioxide .
It may alkaline-under excessive heat certain metals oxidative catch .
Potassium hydroxide is used as a catalyst in the production of rapeseed oil and methanol to biodiesel by transesterification .
Household and handicrafts
Potassium hydroxide is used to prepare soft soaps ( soft soaps ) of various vegetable and animal fats and oils , as well as in the detergent manufacture to produce water-softening potassium phosphate used for liquid detergents.
Since soaps made with sodium hydroxide do not dissolve in sea water due to the sodium chloride content of the salt water, special salt water soaps for seafarers are also made with potassium hydroxide.
Potassium saponified also branded and gummy fats and oils into water-soluble salts of fatty acids and is therefore as oven cleaner and the waste liquors of paint - and oil paints used.
Potassium hydroxide is added to pipe cleaning agents , as this both dissolves hair and saponifies the fats adhering to the drain, so that they can be washed away by the water. However, since caustic potash attacks acrylic glass as well as enamelled and glazed surfaces of tubs and sanitary ware , which are made of silicate glass-like material ( glass corrosion ), it should be used with care.
Web links
Individual evidence
- ↑ Entry on E 525: Potassium hydroxide in the European database on food additives, accessed on June 27, 2020.
- ↑ Entry on POTASSIUM HYDROXIDE in the CosIng database of the EU Commission, accessed on February 17, 2020.
- ↑ a b c d e f g h Entry on potassium hydroxide in the GESTIS substance database of the IFA , accessed on January 10, 2017(JavaScript required) .
- ↑ Entry on Potassium hydroxide in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
- ↑ Swiss Accident Insurance Fund (Suva): Limit values - current MAK and BAT values (search for 1310-58-3 or potassium hydroxide ), accessed on November 2, 2015.
- ↑ Prof. Blum's tip of the month August 2004 (tip no. 86): Drain cleaners are dangerous , In: Chemieunterricht.de