Sodium chlorate is an inorganic compound with the chemical formula NaClO3. It is a white crystalline powder that is readily soluble in water. It is hygroscopic. It decomposes above 300 °C to release oxygen and leaves sodium chloride. Several hundred million tons are produced annually, mainly for applications in bleaching pulp to produce high brightness paper.
Unit cell of sodium chlorate
3D model (JSmol)
|UN number||1495, 2428|
CompTox Dashboard (EPA)
|Molar mass||106.44 g mol−1|
|Appearance||Colorless or white solid, hygroscopic|
|Density||2.49 g/cm3 (15 °C)|
2.54 g/cm3 (20.2 °C)
|Melting point||248–261 °C (478–502 °F; 521–534 K)|
|Boiling point|| 300–400 °C (572–752 °F; 573–673 K) |
|79 g/100 mL (0 °C)|
89 g/100 mL (10 °C)
105.7 g/100 mL (25 °C)
125 g/100 mL (40 °C)
220.4 g/100 mL (100 °C)
|Solubility||Soluble in glycerol, hydrazine, methanol|
Slightly soluble in ethanol, ammonia
|Solubility in acetone||Sparingly soluble|
|Solubility in glycerol||20 g/100 g (15.5 °C)|
|Solubility in ethanol||14.7 g/100 g|
|Vapor pressure||<0.35 mPa|
Refractive index (nD)
|1.515 (20 °C)|
a = 6.57584 Å
Formula units (Z)
Heat capacity (C)
Std enthalpy of
Gibbs free energy (ΔfG˚)
|Safety data sheet||ICSC 1117|
|GHS Signal word||Danger|
|H271, H302, H411|
|NFPA 704 (fire diamond)|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|6500 mg/kg (rats, oral)|
700 mg/kg (dogs, oral)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
- NaCl + 3 H2O → NaClO3 + 3 H2
- 2 NaCl + H2O → NaClO + NaCl + H2
The sodium chlorate process is not to be confused with the Chloralkali process, which is an industrial process for the electrolytic production of sodium hydroxide and chlorine gas.
The main commercial use for sodium chlorate is for making chlorine dioxide (ClO2). The largest application of ClO2, which accounts for about 95% of the use of chlorate, is in bleaching of pulp. All perchlorate compounds are produced industrially by the oxidation of solutions of sodium chlorate by electrolysis.
Sodium chlorate may be used to control a variety of plants including morning glory, canada thistle, johnson grass, bamboo, Ragwort, and St John's wort. The herbicide is mainly used on non-crop land for spot treatment and for total vegetation control on areas including roadsides, fenceways, and ditches. Sodium chlorate is also used as a defoliant and desiccant for:
If used in combination with atrazine, it increases the persistence of the effect. If used in combination with 2,4-D, performance is improved. Sodium chlorate has a soil sterilant effect. Mixing with other herbicides in aqueous solution is possible to some extent, so long as they are not susceptible to oxidation.
The sale of sodium chlorate as a weedkiller was banned in the European Union in 2009 citing health dangers, with existing stocks to be used within the following year.
Chemical oxygen generationEdit
Chemical oxygen generators, such as those in commercial aircraft, provide emergency oxygen to passengers to protect them from drops in cabin pressure. Oxygen is generated by high-temperature decomposition of sodium chlorate:
- 2 NaClO3 → 2 NaCl + 3 O2
Heat required to initiate this reaction is generated by oxidation of a small amount of iron powder mixed with the sodium chlorate, and the reaction consumes less oxygen than is produced. Barium peroxide (BaO2) is used to absorb the chlorine that is a minor product in the decomposition. An ignitor charge is activated by pulling on the emergency mask. Similarly, the Solidox welding system used pellets of sodium chlorate mixed with combustible fibers to generate oxygen.
Sodium chlorate can be mixed with sucrose sugar to make a highly explosive fuel, similar to that of gunpowder, that burns in airtight spaces. This is the reaction:
8 NaClO3 + C12H22O11 → 8 NaCl + 12 CO2 + 11 H2O
Toxicity in humansEdit
Sodium chlorate is toxic: "doses of a few grams of chlorate are lethal". The oxidative effect on hemoglobin leads to methaemoglobin formation, which is followed by denaturation of the globin protein and a cross-linking of erythrocyte membrane proteins with resultant damage to the membrane enzymes. This leads to increased permeability of the membrane, and severe hemolysis. The denaturation of hemoglobin overwhelms the capacity of the G6PD metabolic pathway. In addition, this enzyme is directly denatured by chlorate.
Acute severe hemolysis results, with multi-organ failure, including DIC and kidney failure. In addition there is a direct toxicity to the proximal renal tubule. The treatment will consist of exchange transfusion, peritoneal dialysis or hemodialysis.
Marketed formulations contain a fire retardant. Most commercially available chlorate weedkillers contain approximately 53% sodium chlorate with the balance being a fire depressant such as sodium metaborate or ammonium phosphates.
Sodium chlorate is the active ingredient in a variety of commercial herbicides. Some trade names for products containing sodium chlorate include Atlacide, Defol, De-Fol-Ate, Drop-Leaf, Fall, Harvest-Aid, Kusatol, Leafex, and Tumbleaf. The compound may be used in combination with other herbicides such as atrazine, 2,4-D, bromacil, diuron, and sodium metaborate.
Sodium chlorate was an extensively used weed killer within the EU, until 2009 when it was withdrawn after a decision made under terms of EU Regulations. Its use as a herbicide outside the EU remains unaffected, as does its use in other non-herbicidal applications, such as in the production of chlorine dioxide biocides and for pulp and paper bleaching.
Historian James Watson of Massey University in New Zealand wrote a widely reported article, "The Significance of Mr. Richard Buckley's Exploding Trousers" about accidents with sodium chlorate when used as a herbicide to control ragwort in the 1930s. This later won him an Ig Nobel Prize in 2005, and was the basis for the May 2006 "Exploding Pants" episode of MythBusters.
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