Potassium chlorate is a compound containing potassium, chlorine and
oxygen atoms, with the molecular formula KClO3. In its pure form, it is a white
crystalline substance. It is the most common chlorate in industrial use. It is
used as an oxidizing agent,
to prepare oxygen, as a disinfectant,
in safety matches, in explosives and fireworks,
in cultivation, forcing the blossoming stage of the Longan tree, causing it to
produce fruit in warmer climates. Production
On the industrial scale, potassium chlorate is produced by the Liebig
process: passing chlorine into hot calcium hydroxide, subsequently adding
potassium chloride: . 6Ca(OH)2 + 6Cl2 -> Ca(ClO3)2 + 5CaCl2 +
6H2O Ca(ClO3)2 + 2KCl -> 2KClO3 + CaCl2
The electrolysis of KCl in aqueous solution is also used sometimes, in
which the chloride ions formed at the anode react with KOH in situ. The low
solubility of KClO3 in water causes the salt to conveniently isolate itself from
the reaction mixture by simply precipitating out of solution.
Potassium chlorate can be produced in small amounts by disproportionation in a
sodium hypochlorite solution followed by metathesis reaction with potassium
chloride: 3 NaClO → 2NaCl + NaClO3
KCl + NaClO3 → NaCl + KClO3 It can also be produced by passing
chlorine gas into a hot solution of caustic potash:
3 Cl2(g) + 6 KOH(aq) → KClO3(aq) + 5 KCl(aq) + 3 H2O(l)
Uses Potassium chlorate was one key
ingredient in early firearms percussion caps. 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. Another application of potassium
chlorate is as the oxidizer in a smoke composition such as used in, e.g., smoke
grenades. Since 2005, a cartridge with potassium chlorate mixed with lactose
and rosin is used for generating the white smoke signalling the election of
new pope by a papal conclave. Potassium chlorate is often used in high
school and college laboratories to generate oxygen gas. It is a far cheaper
source than a pressurized or cryogenic oxygen tank. Potassium chlorate readily
decomposes if heated while in contact with a catalyst, typically manganese(IV)
dioxide. 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:
2 KClO3(s) → 3 O2(g) + 2 KCl(s) Heating it in the absence of a catalyst
converts it into potassium perchlorate: 4 KClO3 → 3 KClO4 + KCl
With further heating, potassium perchlorate decomposes to potassium
chloride and oxygen: KClO4 → KCl + 2 O2
The safe performance of this reaction requires very pure reagents and careful
temperature control. Molten potassium chlorate is an extremely powerful
oxidizer and spontaneously reacts with many common materials such as sugar.
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 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 chemical
oxygen generators, employed as oxygen-supply systems of e.g. aircraft,
space stations, and submarines, 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 was sold under trade name Fegabit.
Potassium chlorate can react with sulfuric acid to form a highly reactive
solution of chloric acid and potassium sulfate:
2 KClO3 + H2SO4 → 2 HClO3 + K2SO4 The solution so produced is sufficiently
reactive that it spontaneously ignites if combustible material is present.
In schools, molten potassium chlorate is used in the dramatic screaming jelly
babies demonstration. In chemical labs it is used to oxidize
HCl and release small amounts of gaseous chlorine.
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. It burns
vigorously in combination with virtually any combustible material, even those
normally only slightly flammable. Mixtures of potassium chlorate and a
fuel can ignite by contact with sulfuric acid, so it should be kept away from
this reagent. Sulfur should be avoided in pyrotechnic compositions containing
potassium chlorate, as these mixtures are prone to spontaneous deflagration.
Most sulfur contains trace quantities of sulfur-containing acids, and these can
cause spontaneous ignition - "Flowers of sulfur" or "sublimed sulfur", despite
the overall high purity, contains significant amounts of sulfur acids.
Also, mixtures of potassium chlorate with any compound with ignition
promoting properties sulfide) are very dangerous to prepare, as they are
extremely shock sensitive. See also
Chloric acid 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 External links