Potassium persulfate

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Potassium persulfate
Potassium peroxydisulfate bottle and sample.jpg
Potassium persulfate sample and original bottle
Names
Systematic IUPAC name
Potassium peroxydisulfate
Other names
Dipotassium peroxodisulfate
Potassium perdisulfate
Potassium peroxydisulfate
Identifiers
Jmol-3D images Image
Properties
K2S2O8
Molar mass 270.322 g/mol
Appearance White solid
Density 2.477
Melting point 186–250 °C (367–482 °F; 459–523 K) (decomposes)
Boiling point Decomposes
1.75 g/100 mL (0 °C)
4.49 g/100 ml (20 °C)
Solubility Soluble in conc. hydrogen peroxide[1], hydrogen fluoride[2]
Insoluble in benzene, chloroform, ethanol, methanol
Vapor pressure ~0 mmHg
Thermochemistry
-1,916 kJ/mol[3]
Hazards
Safety data sheet ScienceLab
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
802 mg/kg (oral, rat)
Related compounds
Related compounds
Potassium peroxymonosulfate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Potassium persulfate, also known as potassium peroxydisulfate is a chemical compound used as an oxidizing agent, with the formula K2S2O8.

Properties

Chemical

When potassium persulfate is heated in a 50% aqueous solution of sulfuric acid, hydrogen peroxide results, which, due to the high temperature, distills from the solution. The H2O2 obtained this way has a concentration of 40-60%. This method was previously used in the manufacturing of hydrogen peroxide on industrial scale before being replaced by the quinone process.

Potassium persulfate will react with silver nitrate to form silver(I,III) oxide (silver peroxide):[4]

K2S2O8 + AgNO3 → Ag4O4 + K2SO4 + SOx + NOx + Ox

Potassium peroxydisulfate oxidizes acetone in the presence of diluted sulfuric acid and silver metal to acetic acid, releasing carbon dioxide:[5]

2 K2S2O8 + (CH3)2CO → CH3COOH + KHSO4 + CO2

Reaction with nitric acid gives off oxygen and ozone fumes, and nitrogen as byproduct.[6]

Physical

A sample of potassium persulfate

Potassium persulfate is a white crystalline solid, poorly soluble in water. It decomposes if heated to temperatures over 125°C. It has a density of 2.477 g/cm3.

Availability

Potassium persulfate can be bought from chemical suppliers and eBay.

Preparation

The most common way to synthesize potassium persulfate is via the electrolysis of a cold solution potassium bisulfate in sulfuric acid, at a high current density[7]:

2 KHSO4 → K2S2O8 + H2

Tantalum electrodes can be used in this reaction.[8]

Bubbling elemental fluorine through an aqueous solution of KHSO4 or K2SO4 will also yield potassium peroxydisulfate. The reaction also works in the absence of water.[9][10]

It can also be prepared by adding KHSO4 to a solution of the more soluble salt ammonium peroxydisulfate. Potassium persulfate will precipitate from this reaction.

Projects

  • Make silver peroxide
  • Make hydrogen peroxide

Handling

Safety

Potassium peroxydisulfate is a strong oxidizer and should be handled with care.

Potassium persulfate will slowly decompose in wet environment.

Storage

Potassium persulfate should be stored in closed bottles, away from any acidic vapors or organic materials.

If kept in a dark and dry environment, it will remain stable for years.[11]

Disposal

Heating the salt will cause it to decompose.

References

  1. Skogareva; Ippolitov; Russian Journal of Inorganic Chemistry; vol. 43; nb. 11; (1998); p. 1668 - 1670
  2. Fredenhagen, H.; Z. Anorg. Chem.; vol. 242; (1939); p. 23 - 32
  3. Balej, Jan; Zeitschrift fur Physikalische Chemie; vol. 224; nb. 6; (2010); p. 883 - 892
  4. Marshall, H.; Journal of the Chemical Society; vol. 59; (1891); p. 775
  5. Broensted, J. N.; Z. phys. Ch.; vol. 102; (1922); p. 169 - 207
  6. Baeyer, A.; Villiger, V.; Ber.; vol. 34; (1901); p. 853 - 862
  7. F. Feher, "Potassium Peroxydisulfate", Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 392.
  8. Gmelin, vol. O: MVol.2; 46, page 276 - 278
  9. Fichter, F.; Humpert, K.; Helvetica Chimica Acta; vol. 9; (1926); p. 521 - 525
  10. Mueller, E.; Zeitschrift fuer Elektrochemie; vol. 10; (1904); p. 753 - 776
  11. Elbs, K.; Neher, P.; Chemiker-Zeitung; vol. 45; (1921); p. 1113 - 1114

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