Potassium hydroxide
- Caustic potash
- Caustic potash
- Kaliumoxidhydrat
- Caustic potash
- Potassium hydrate
- E 525
- Potassium hydroxide solution (aqueous solution)
White, hygroscopic material
Fixed
2.04 g · cm -3
360 ° C.
1320 ° C
Well in water (1120 g / l at 20 ° C) and in 2.5 parts of alcohol (ethanol )
Risk
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Potassium hydroxide ( caustic potash also, caustic potash ), chemical formula KOH, is a white hygroscopic solid. In water it dissolves to become very hot to the strong base potassium hydroxide solution. With carbon dioxide of the air, it reacts to form potassium carbonate and is, therefore, stored in airtight containers. To prevent potassium binds water from the air, it can be stored with a desiccant. The hydroxide ion displaces the strong base is weaker and volatile bases from their salts.
Properties
Potassium hydroxide is a white, highly hygroscopic material, which is usually, rarely sold as cookies or bars as a powder. In water it dissolves to become very hot, by the negative enthalpy of solution of -57.1 kJ / mol and forms potassium hydroxide solution, in the solid state it forms mono-, di-and tetrahydrate. With the carbon dioxide contained in the air, it reacts to form potassium carbonate.
Potassium contains 0.0118 % to the isotope 40K, this provides 21723 Bq per kg of KOH, which are 89.28 % and 10.72 % Beta radiation Gamma radiation with 1.46083 MeV.
Synthesis
Previously potassium hydroxide was prepared by so-called " caustification " of potassium carbonate. This proceeds according to the equation
Today, potassium hydroxide is usually obtained by aqueous electrolysis of potassium chloride, followed by evaporation of the solution.
Use
Potassium hydroxide is used in the production for the production of soft detergents soaps ( soft soaps ), and for the preparation of water-softening potassium phosphate for liquid detergents.
In microsystems technology (MST ) of KOH is used for selective anisotropic etching of single crystal silicon.
In Microbiology KOH is used to distinguish between gram-positive and gram-negative bacteria in the quick test method.
In galvanic oxygen sensor is used as the electrolyte. Serves the same purpose also in the widespread alkaline manganese cells.
In the food industry, KOH is used as an acidity regulator. It is in the EU as a food additive called E 525 no maximum limit ( quantum satis ) generally approved for food.
KOH is used for the production of potassium compounds, glass, dyes, batteries and as a drying and carbon dioxide absorbent.
KOH can unlock certain metals alkaline - oxidative under strong heating.
In the production by transesterification of rapeseed oil and methanol to biodiesel potassium hydroxide is used as catalyst.