Potassium chlorate

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Potassium chlorate
KClO3 by No Tears Only Dreams Now.jpg
Crystals of potassium chlorate made from bleach.
Names
IUPAC name
Potassium chlorate
Other names
Berthollet's salt
Potcrate
Potassium chlorate(V)
Properties
KClO3
Molar mass 122.55 g/mol
Appearance White crystalline solid
Odor Odorless
Density 2.32 g/cm3
Melting point 356 °C (673 °F; 629 K)
Boiling point 400 °C (752 °F; 673 K) (decomposes)
3.13 g/100 ml (0 °C)
4.46 g/100 ml (10 °C)
8.15 g/100 ml (25 °C)
13.21 g/100 ml (40 °C)
53.51 g/100 ml (100 °C)
Solubility Reacts with sulfuric acid
Slightly soluble in liq. ammonia, glycerol
Almost insoluble in acetone, alcohols
Insoluble in alkanes, halocarbons
Solubility in glycerol 1 g/100 ml (20 °C)
Vapor pressure ~ 0 mmHg
Thermochemistry
142.97 J·mol-1·K-1
−391.2 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
1870 mg/kg (oral, rat)
Related compounds
Related compounds
Potassium chloride
Potassium hypochlorite
Potassium chlorite
Potassium perchlorate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Potassium chlorate, also known as Berthollet's salt, is the inorganic chemical compound with the formula KClO3, and is the potassium salt of chloric acid. It is a strong oxidizing agent.

Properties

Chemical

Potassium chlorate is a powerful oxidizer.

If sulfuric acid is added to potassium chlorate, chloric acid is formed:

2 KClO3 + H2SO4 → 2 HClO3 + K2SO4

The chloric acid decomposes immediately to perchloric acid and chlorine dioxide. The latter will spontaneously ignite any combustible material (sugar, paper, dust). As a fun project, various sweets, often gummy bears (jelly babies) are dropped into molten potassium chlorate to produce intense pink flames and, if in a narrow container, a screaming sound.

Potassium chlorate will decompose if heated in the presence of a catalyst, usually manganese dioxide, releasing oxygen and leaving potassium chloride behind. This effect can be taken advantage of in order to quickly add oxygen to a system.

2 KClO3(s) → 3 O2(g) + 2 KCl(s)

If the heating occurs without a catalyst, potassium perchlorate will be formed (although in practice, this is difficult to do):

4 KClO3 → 3 KClO4 + KCl

The temperature should be controlled, such that the compound just melts. Too strong heating leads to decomposition with loss of oxygen.

Physical

Potassium chlorate is a transparent to white salt that precipitates as well-formed, lustrous crystals which have a silky texture and are moderately soluble in water and poorly soluble in glycerol. Similar to potassium nitrate, it is not hygroscopic, making it useful as an oxidizer for pyrotechnics. In modern times, however, the use of potassium perchlorate in pyrotechnics has declined strongly, because many compositions with potassium chlorate are unstable and sensitive, leading to unacceptable risk of early ignition.
Unlike hypochlorites, potassium chlorate has no odor, so a 'bleachy' smell is an indication of impure samples.

Availability

Potassium chlorate was available in the past as a fruit growth fertilizer as well as weed killer, but in recent years it has become restricted, due to its powerful oxidizing properties, as it was used in many bombings.

It can also be found in safety match heads, where it is mixed with sulfur and glue, though one would need a large amount of safety matches. It's much cheaper to make it.

Preparation

Potassium chlorate can be prepared by boiling bleach (sodium hypochlorite or calcium hypochlorite solution), for about 10-20 minutes, which causes the hypochlorite to disproportionate into chlorate and chloride. Since sodium chloride is less soluble than the chlorate, it will crystallize, while the chlorate will remain in solution. Crystallization begins at about the same time that the bleach reaches one third of the original volume. This chlorate solution is then added to an equivalent amount of saturated potassium chloride solution, to precipitate the potassium chlorate. Carefully cooling the solution to about 0 degrees C will yield more product. The flat, shiny crystals should then be filtered out and washed multiple times with ice cold water.[1]

Potassium chlorate can also be produced more efficiently via electrolysis of a saturated solution of potassium chloride with inert electrodes. This procedure is known as alkali chlorate cell. A detailed procedure of the process can be found on both the Sciencemadness board as well as in other places online, like YT.

Recrystallization of KClO3 is easy, as it is very soluble in hot water but sparingly soluble in freezing water

Projects

Handling

Safety

When mixed with combustible materials, even those normally slightly flammable (such as dust and lint), it will burn vigorously in combination and the fires are extremely hard to put out, as the chlorate provides the oxygen for the fire. Sulfur and red phosphorus, should be avoided in pyrotechnic compositions containing potassium chlorate, as well as any acidic salts, as these mixtures are shock and friction sensitive and prone to spontaneous deflagration (in the safety head matches, such mixture is stabilized with glue). Molten potassium chlorate will ignite any combustible material and can burn even through standard lab safety clothing.

Storage

Potassium chlorate should be stored in closed containers and away from any organic sources, as well as strong acidic vapors. Since it is not hygroscopic, it is not necessary to keep it air tight.

Disposal

Potassium chlorate can be neutralized with a reducing agent, such as sodium metabisulfite, sodium bisulfite, sodium sulfite or a mixture of sulfuric acid and ferrous ammonium sulfate. The resulting products should be neutralized with a base and safely poured down the drain.[2]

References

  1. http://www.youtube.com/watch?v=JtxQT7aVDeg
  2. http://www.oocities.org/capecanaveral/campus/5361/chlorate/destroy.html

Relevant Sciencemadness threads