Potassium chlorate
 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 | |
| Std molar
entropy (S |
142.97 J·mol-1·K-1 |
| Std enthalpy of
formation (ΔfH |
−391.2 kJ/mol |
| Hazards | |
| Safety data sheet | Sigma-Aldrich |
| Flash point | Non-flammable |
| Lethal dose or concentration (LD, LC): | |
| LD50 (Median dose)
|
1,870 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.
Contents
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 chlorate 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 terror 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 from the electrolysis of KCl (see below).
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 Celsius will yield more product. The flat, shiny crystals should then be filtered out and washed multiple times with ice cold water.[1]
If you already have access to another chlorate, for example, a sodium chlorate weed killer, preparation of potassium chlorate is very easy. Make a saturated solution of the weed killer at high temperature, cool down the solution to precipitate any sodium chloride adulterant, and perform a metathesis as written above.
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. Woelen's page also details this process very well.[2]
Recrystallization of KClO3 is easy, as it is very soluble in hot water but sparingly soluble in freezing water
Projects
- Screaming jelly baby (gummy bear)
- Burning hearts
- Cockroach cremation
- Flash powder
- Chloric acid and perchloric acid synthesis
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.[3]
References
- ↑ http://www.youtube.com/watch?v=JtxQT7aVDeg
- ↑ http://woelen.homescience.net/science/chem/exps/miniature_chlorate_cell/index.html
- ↑ http://www.oocities.org/capecanaveral/campus/5361/chlorate/destroy.html
