|Molecular formula||K 2 CO 3|
|External identifiers / databases|
|Molar mass||138.20 g mol −1|
2.428 g cm −3
891 ° C
very light in water (1120 g l −1 at 20 ° C)
|ΔH f 0||
−1151.0 kJ / mol
|As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .|
Potassium carbonate (in technical terms) or potassium carbonate (common name : potash ), K 2 CO 3 , is an alkali and the potassium salt of carbonic acid . It forms a white, hygroscopic powder with a melting temperature of 891 ° C and a density of 2.428 g · cm −3 . The name potash comes from the old method of enriching potassium carbonate from plant ash (especially wood ash , but also seaweed ash ) by washing it out with water (hence the name “lye salt”) and then evaporating it in pots. The traditional name was also the inspiration for the English names potash and potassium , whereby potash includes many mineral potassium salts (e.g. potassium chloride ) and should better be translated as potassium salt .
The world's largest potash salt deposits are in Canada , Russia , Eritrea , Belarus and Germany ; Potassium carbonate is also found in some inland waters such as the Dead Sea or the Lop Nor desert . In the past, potash was mainly obtained from wood ash by leaching . The content of mineral components in wood ash is around 85%; about 14-19% of this is potassium carbonate and sodium carbonate.
Extraction and presentation
- Carbonization of potassium hydroxide :
- Combustion gases are predominantly used as a CO 2 source.
- Reaction of milk of lime ( calcium hydroxide solution) with potassium sulfate and carbon monoxide at 30 bar (formate process). The separated potassium formate is then oxidatively calcined:
- Leaching of plant ash and subsequent evaporation in ash houses (historically, technically no longer relevant)
- Potassium carbonate reacts with water to form potassium hydrogen carbonate and potassium hydroxide.
With acids, the corresponding potassium salts are formed with the evolution of carbon dioxide . At room temperature it crystallizes as a dihydrate from the aqueous solution.
Anhydrous potassium carbonate crystallizes monoclinically , space group P 2 1 / c (space group no. 14) with the lattice parameters a = 5.640 Å , b = 9.839 Å, c = 6.874 Å and β = 98.70 °. At 250 ° C this changes into the monoclinic β-form (space group C 2 / c (No. 15) , a = 5.675 Å, b = 9.920 Å, c = 7.018 Å and β = 96.8 °). At 450 ° C this changes into a hexagonal shape.
- Additive in the manufacture of glass
- Additive to soft soaps
- Manufacture of potash glasses
- Manufacture of colors
- Manufacture of photographic developers
- Manufacture of fertilizers (potassium-supplying component)
- Anhydrous potassium carbonate is occasionally used as a drying agent in the laboratory .
- Raising agent for flat baked goods ( cookies and gingerbread , especially Christmas bakery ) and dough with a high sugar content.
- Additive to cocoa as an acidity regulator
- Neutralizing agent when using hydrochloric acid (E 507) as an aroma enhancer .
- Rapid drying of raisins: By removing the natural wax layer from the grapes, the moisture evaporates more easily.
- Base product for other potassium compounds.
- To remove crusts from pots: put 1 tablespoon on the crust in the pot, let stand overnight and boil the next day with a cup of water; the residues loosen from the bottom of the pot.
- Release agent for plaster casts ( sculpture )
- Electrolyte component in molten carbonate fuel cells
- Approved tobacco additive for snuff according to the Tobacco Ordinance
- Additive for the intake of certain addictive substances
- Additive in some hand washing liquid soaps
- Environmentally friendly de-icing agent (instead of de-icing salt ) for black ice on streets and sidewalks
- Because it always contains radioactive potassium-40, potash can be used for student experiments on radioactivity
- For many centuries in Europe, potassium carbonate in the form of beech ash was used to bump clothes and other textiles made of linen and later also of cotton . The ashes are filled into bags and added to a wooden barrel filled with layered laundry. By pouring hot water over the sachet, a lye was released that had a cleansing and slightly bleaching effect. The lye was then washed out with water at the wash fountain or the river. The advent of curd soap and later synthetic detergents at the beginning of the 20th century made this method obsolete.
- Part of fire extinguishing agents
The soda- potash digestion is used for poorly soluble (alkaline earth) sulfates, highly annealed (acidic or amphoteric) oxides, silicates and silver halides; the digestion takes place in a Na 2 CO 3 / K 2 CO 3 melt. ZrO 2 , Zr 3 (PO 4 ) 4 , Al 2 O 3 , Cr 2 O 3 and Fe 2 O 3 are only partially dissolved. A mixture of soda and potash is used for this melt digestion, because this means that the melting point is lower than that of pure salts ( eutectic mixture ). In addition, the enormous carbonate excess forces the reaction equilibrium onto the product side.
An example of sulfates:
- Entry on E 501: Potassium carbonate in the European database on food additives, accessed on July 1, 2020.
- Entry on POTASSIUM CARBONATE in the CosIng database of the EU Commission, accessed on August 11, 2020.
- Entry on Potassium carbonate in the ChemIDplus database of the United States National Library of Medicine (NLM)
- David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Standard Thermodynamic Properties of Chemical Substances, pp. 5-20.
- USGS (US Mineral Resources Program): Potash. (PDF; 88 kB) As of January 2010.
- Entry on wood ash. In: Lexicon of Chemistry. Spektrum der Wissenschaft Verlagsgesellschaft, accessed on September 3, 2018 .
- Entry on potassium carbonate. In: Römpp Online . Georg Thieme Verlag, accessed on November 12, 2014.
- Y. Idemoto, JW Richardson, N. Koura, S. Kohara, CK Loong: Crystal structure of (Li x K 1-x ) 2 CO 3 (x = 0,0.43,0.5,0.62,1) by neutron powder diffraction analysis. In: Journal of Physics and Chemistry of Solids , 59, 1998, pp. 363-376, doi: 10.1016 / S0022-3697 (97) 00209-6 .
- HY Becht, B. Struikmans: A mono Clinic High-Temperature Modification ot Potassium Carbonate. In: Acta Crystallographica , B32, 1976, pp. 3344-3346, doi: 10.1107 / S0567740876010303 .
- SJ Schneider, EM Levin: Polymorphism of K 2 CO 3 . In: Journal of the American Ceramic Society , 56 (4), 1973, pp. 218-219, doi: 10.1111 / j.1151-2916.1973.tb12461.x .
- Study by the University of Natural Resources and Life Sciences, Vienna on the effects of nitrogen-containing thawing agents Thawing agent study 2000 (PDF; 1.6 MB)
- LVR Institute for Regional Studies and Regional History: Baking laundry with beech ash
- Georg Pleß: Substitution of certain environmentally harmful fire extinguishing agents in selected areas of application . Ed .: Institute of the Fire Brigade Saxony-Anhalt. Heyrothsberge 2003 ( Umweltbundesamt.de [PDF]).