Potassium chlorate

Potassium chlorate is a compound containing potassium, chlorine and oxygen, with the chemical formula K[ClO₃]. In pure form, it is a white crystalline substance. It is the most common chlorate in industrial use, and is usually present in well-stocked laboratories. It is used

• as an oxidizing agent,
• to prepare oxygen,
• as a disinfectant,
• in safety matches, and
• in explosives and fireworks.

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Uses

Potassium chlorate (also named chlorate of potash) was one key ingredient in early firearms percussion caps (primers) . It continues in that application, where not supplanted by potassium perchlorate.

Chlorate-based propellants are more efficient than traditional gunpowder and are less susceptible to damage by water. However, they can be extremely unstable in the presence of sulfur or phosphorus and are much more expensive. Chlorate propellants must be used only in equipment designed for them; failure to follow this precaution is a common source of accidents. Potassium chlorate, often in combination with silver fulminate, is used in trick noise-makers known as "crackers", "snappers", "pop-its", or "bang-snaps", a popular type of novelty firework.

When mixed with other materials, it may form a high explosive. The hygroscopic and slightly weaker sodium chlorate is sometimes used as a safer and less expensive substitute for potassium chlorate. In World War I, mixes of potassium chlorate with plasticizers (such as wax) were the most common type of plastic explosive used, often filling grenades and other munitions. When used in explosives as an oxidizer, the explosive is low order meaning it burns rapidly rather than explodes. When mixed with a plasticizer, it may become high order, requiring a blasting cap (generally a commercial #8) to detonate properly. Potassium chlorate is also used in some formulas of gunpowder, generally replacing the less powerful potassium nitrate.

Potassium chlorate is often used in highschool and college laboratories to generate oxygen gas; it is a far cheaper source than a pressurized or cryogenic oxygen tank. Potassium chlorate will readily decompose if heated in contact with a catalyst, typically manganese (IV) dioxide (MnO₂). Thus, it may be simply placed in a test tube and heated over a burner. If the test tube is equipped with a one-holed stopper and hose, warm oxygen can be drawn off. The reaction is as follows:

2KClO₃(s) → 3O₂(g) + 2KCl(s)

The safe performance of this reaction requires very pure reagents and careful temperature control. Molten potassium chlorate is an extremely powerful oxidizer and will spontaneously react with many common materials. Explosions have resulted from liquid chlorates spattering into the latex or PVC tubes of oxygen generators, as well as from contact between chlorates and hydrocarbon sealing greases. Impurities in potassium chlorate itself can also cause problems. When working with a new batch of potassium chlorate, it is advisable to take a small sample (~ 1 gram) and heat it strongly on an open glass plate. Contamination may cause this small quantity to explode, indicating that the chlorate should be discarded. Potassium chlorate is used in the oxygen-supply systems of aircraft, and has been responsible for at least one plane crash. A fire on the space station MIR was also traced to this substance. The decomposition of potassium chlorate was also used to provide the oxygen supply for limelights.

Potassium chlorate is used also as a pesticide. In Finland it is sold under trade name Fegabit. Finland also used potassium chlorate as the main ingredient—approximately 60%—of a refined version of the Molotov Cocktail.

Safety

Potassium chlorate should be handled with care. It reacts vigorously, and in some cases spontaneously ignites or explodes, when mixed with many combustible materials. Sulfur should be avoided in compositions of gunpowder containing potassium chlorate, as these mixtures are prone to spontaneous deflagration.

Production

On an industrial scale, potassium chlorate is produced by the electrolysis of a sodium chloride solution to form sodium chlorate, which is reacted with potassium chloride to precipitate potassium chlorate. The resultant sodium chloride is returned to the mother liquor for electrolysis.

KClO₃ can also be produced on a smaller scale by the thermal disproportionation of a hypochlorite to its respective chlorate and chloride by boiling, then adding KCl. This reaction should be done in a fume hood due to the production of chlorine and chlorine dioxide gas. Potassium chlorate's insolubility means it is easy to separate from soluble contaminants, but relatively difficult to separate from insoluble ones, for example electrode or cell matter.

See also

• Chloric acid
• Potassium perchlorate
• Potassium nitrate

References

• "Chlorate de potassium. Chlorate de sodium", Fiche toxicol. n° 217, Paris:Institut national de recherche et de sécurité, 2000. 4pp.
• Continuous process for the manufacture of potassium chlorate by coupling with a sodium chlorate production plant