Potassium persulfate
- Potassium persulfate
- Potassium persulfate
- About Sulphate of potassium
- Potassium persulfuricum
- E 922
Colorless crystals
Fixed
2.48 g · cm -3
Decomposition from ~ 100 ° C
Decomposition
Solubility in water: 50 g / l ( 20 ° C), insoluble in alcohol
Risk
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Potassium, often short potassium persulfate, often abbreviated as KPS, is the potassium salt of peroxodisulfuric acid. The persulfate ion contains oxygen in the unstable oxidation state of -1. Therefore, potassium is a radical and a very strong oxidizing or bleaching agents.
Production and representation
Potassium technically by the electrolysis of the concentrated potassium sulfate or potassium hydrogen sulfate solution at high current densities (~ 1A/dm ² ) was prepared. At the anode are oxidized to sulfate ions peroxodisulfate ions at the cathode, water is reduced to hydrogen. The relatively sparingly soluble potassium crystallizes out.
In the industrial process used for the anodic reaction of the platinum or glassy carbon electrode having a high overpotential for oxygen evolution used. For the cathodic reaction, lead or graphite electrodes are employed. At low current densities and in dilute solutions the formed as an intermediate sulfate radical anions do not react with each other to persulfate ion, but by water with evolution of oxygen.
Properties
If Kaliumperoxodisulfatlösungen heated ( 70-100 ° C) or UV radiation breaks down the persulfate to sulfate radical anions. This reaction can be accelerated by suitable catalysts so that it (20-50 ° C) proceeds already at a lower temperature appreciably. Examples of catalysts are metallic platinum, silver (I) - and copper ( II) ions.
Persulfate among the strongest oxidants and are surpassed only in its oxidizing power of fluorine, ozone and oxygen fluorides. However, the oxidation is relatively slow. They are able to oxidise virtually all organic compounds. Iodide - iodine solution is slowly deposited, manganese ( II) salt solution are oxidized to manganese dioxide in the presence of catalytically active silver (I ) ions, even to the permanganate.
Potassium is stable as a crystalline solid, but decomposes at elevated temperatures under oxygen evolution. At ~ 100 ° C the decomposition is completed. In moist or impure state it tends already at much lower temperatures for the decomposition. Therefore, the compound during storage from direct sunlight and other heat sources must be protected.
Solutions of potassium acid reaction and rapidly disintegrate slowly at room temperature and at elevated temperature. In a strongly acidic medium ( pH <4), the decomposition proceeds autocatalytically. The resulting acid catalyzes the further decomposition of persulfate.
Potassium may react violently with reducing agents. Mixtures of potassium and combustible materials can also burn the absence of air.
Use
Potassium is a common initiator for polymerization in emulsion or in solution, for example in the preparation of polyacrylates, polyvinyl acetate and polyvinyl chloride, and in the copolymerization in emulsion of acrylonitrile, 1,3-butadiene, styrene, and other monomers. These reactions with a required quantity of usually 0.1-0,5 % potassium are usually performed at 75 to 95 ° C. In combination with redox polymerizations at lower temperatures are possible. In cosmetics, potassium is an essential component of bleaching preparations for bleaching hair and as a bleaching component in hair dye use. Potassium is in the textile finishing, used as desizing agent and bleach activator, particularly for cold bleaching process. Furthermore, it is used as oxidizing agent used in chemical synthesis (example Elbs oxidation of phenols to p- diphenols in alkaline solution ) and in the analysis, for example as a disintegrating agent.
Other uses potassium found in laboratories for cleaning glassware in paper production for the modification of starch, as a disinfectant and for the oxidative removal of pollutants (eg, mercury in waste air treatment systems).
In the metal and electronics industry is potassium to a lesser extent for blackening brass ( method according to Erich Groschuff ) and for etching printed circuit boards ( PCBs ) are used. In the latter case, either the surface is cleaned by oxidation ( etching ) or copper removed by oxidation ( etching). Due to the higher solubility in water, however, sodium is preferred for this application.
In photography potassium persulfate may be used as attenuators, to remove traces of thiosulfate from the negatives in the film processing. Previously potassium was used as a flour treatment agent for " flour improvers ". In Germany, this has been prohibited since 1956/57.