Potassium perchlorate

Potassium perchlorate is the inorganic salt with the chemical formula KClO₄. Like other perchlorates, this salt is a strong oxidizer when the solid is heated at high temperature, although it usually reacts very slowly in solution with reducing agents or organic substances. This colorless crystalline solid is a common oxidizer used in fireworks, ammunition percussion caps, and explosive primers, and is used variously in propellants, flash compositions, stars, and sparklers. It has been used as a solid rocket propellant, although in that application it has mostly been replaced by the more performant ammonium perchlorate.

KClO₄ has a relatively low solubility in water (1.5 g in 100 mL of water at 25 °C).

Potassium perchlorate is prepared industrially by treating an aqueous solution of sodium perchlorate with potassium chloride. This single precipitation reaction exploits the low solubility of KClO₄, which is about 1/100 as much as the solubility of NaClO₄ (209.6 g/100 mL at 25 °C).

It can also be produced by bubbling chlorine gas through a solution of potassium chlorate and potassium hydroxide,^{[citation needed]} and by the reaction of perchloric acid with potassium hydroxide; however, this is not used widely due to the dangers of perchloric acid.

Another preparation involves the electrolysis of a potassium chlorate solution, causing KClO₄ to form and precipitate at the anode. This procedure is complicated by the low solubility of both potassium chlorate and potassium perchlorate, the latter of which may precipitate onto the electrodes and impede the current.

KClO₄ is an oxidizer, greatly increasing the rate of combustion of combustible materials relative to burning in air. Combustion with glucose gives carbon dioxide, water molecules and potassium chloride:

The conversion of solid glucose into hot gaseous CO₂ is the basis of the explosive force of this and other such mixtures. With sugar, KClO₄ yields a low explosive, provided a necessary confinement. Otherwise such mixtures simply deflagrate with an intense purple flame characteristic of potassium. Flash compositions used in firecrackers, defined in the US as containing 50 mg of powder or less, usually consist of a mixture of aluminium powder and potassium perchlorate, although this is one of the few instances where potassium chlorate is still allowed as a major component. This mixture, called flash powder, is also used in ground and air fireworks.

As an oxidizer, potassium perchlorate can be used safely in the presence of sulfur, whereas potassium chlorate cannot. The greater reactivity of chlorate is typical – perchlorates are kinetically poorer oxidants. Chlorate can produce chloric acid (HClO₃) in contact with impure acidic sulfur or certain sulfur compounds, which is highly unstable and can lead to premature ignition of the composition. Otherwise the sensitivity of perchlorate / sulfur mixtures is about the same as chlorate / sulfur mixtures, although it lowers the ignition temperature of chlorate mixtures more. Correspondingly, perchloric acid (HClO₄) is quite stable.^{[page needed]}