Potassium chlorate, KClO₃

The Potassium chlorate, KClO₃, is obtained by methods similar to those employed for the corresponding sodium salt. The electrolysis of the chloride affords a means of manufacture, and it is also obtained by the interaction of potassium chloride and calcium chlorate. Large quantities are made by the electrolytic oxidation of sodium chloride to chlorate, and conversion of this salt into potassium chlorate by treatment with potassium chloride. Sodium chlorate is much more soluble than potassium chlorate, so that the electrolytic process is not impeded by crystallization of the salt.

The electrochemical formation of chlorate from hypochlorite is regarded by Knibbs and Palfreeman as involving two reactions, represented by the equations

OCl' + 2HOCl = ClO₃' + 2H^• + 2Cl';
2OCl' + 2H^• + 2Cl' = 2HOCl + 2Cl'.

The net result is the disappearance of three hypochlorite ions, with formation of 1 chlorate ion and 2 chloride ions. Although apparently termolecular, the first reaction is unimolecular, since the concentration of the hypochlorous acid remains constant. The second reaction is practically instantaneous. Chloride can be produced by the electrolysis of chlorate, possibly in accordance with the equation

4MClO₃ = 3MClO₄ + MCl,

M representing an atom of a univalent metal. The formation of chloride is promoted by rise of temperature, but is almost inhibited by the presence of a chromate.

Potassium chlorate forms monoclinic crystals, its melting-point being given as 357.10° C., 370° C., and 372° C. When a solution obtained by treatment of crude Californian petroleum with concentrated sulphuric acid and dilution with water is added to a solution in water of the ordinary tabular potassium chlorate, and the mixture concentrated on the water-bath, the salt separates in long fibrous crystals of silky appearance.

The density of potassium chlorate is 2.344 at 17° C., 2.3384, or in mean 2.331. The specific heat is given as 0.194 between 16° and 49° C., and 0.2096 between 16° and 98° C. The values recorded for the heat of formation from the elements are 93.8 Cal. and 95.8 Cal.

Temperature. °C.	0	10	20	30	40	50	60	70	80	90	100	120	136	160	190
Solubility of KClO3 in 100 gr of water °C.	3.3	5.0	7.1	10.1	14.5	19.7	26.0	32.5	39.6	47.5	56.0	73.3	99	148	183

Potassium chlorate is employed for various purposes as an oxidizer, examples being the manufacture of dyes such as aniline-black, and the production of safety matches and fireworks.

With concentrated hydrochloric acid potassium chlorate evolves chlorine and chlorine peroxide, a reaction useful in certain analytical operations. The mixture is called " euchlorine."

When heated to 357° C., potassium chlorate undergoes no perceptible decomposition, but the particles cake together, and under the microscope exhibit signs of incipient fusion. At a slightly higher temperature the salt melts, and there is rapid evolution of oxygen between 370° and 380° C., several reactions being initiated.

1. Potassium perchlorate is formed by autoxidation, the exothermic reaction corresponding with the equation
   
   KClO₃ + 3KClO₃ = 3KClO₄ + KCl + 61.3 Cal.
   
   Scobai has proved the reaction to take place in accordance with this equation by measuring the velocity of formation of potassium perchlorate at 395° C., and has also demonstrated its quadrimolecular nature.
2. Simultaneously, a unimolecular reaction occurs, potassium chlorate decomposing with formation of potassium chloride, and evolution of oxygen:
   
   2KClO₃ = 2KCl + 3O₂.
3. A sufficient rise in temperature initiates the decomposition of the potassium perchlorate, chiefly in accordance with the equation
   
   KClO₄ = KCl + 2O₂;
   
   and at 445° C. there is complete decomposition in the sense indicated, except for a small proportion of potassium chlorate simultaneously regenerated.

The decomposition is much facilitated by the presence of certain oxides, such as manganese dioxide. The part played by these agents has been the subject of considerable controversy. Repeated use of the oxide produces no measurable diminution in its activity. The action has been suggested to be entirely mechanical, and analogous to that of sand and other substances in promoting the ebullition of water. On this assumption, all bodies in a fine state of division might be expected to exert a similar influence, a view at variance with the results of experiment. The oxides of metals capable of yielding more than one oxide, such as iron, nickel, copper, and cobalt, facilitate the reaction; but the oxides of zinc and magnesium are without effect. Probably higher and lower oxides of manganese are formed alternately at the expense of the chlorate. In presence of the oxide there is no apparent formation of potassium perchlorate, the manganese dioxide inducing the decomposition of the chlorate into chloride and oxygen at a temperature lower than that necessary for the autoxidation of the chlorate to perchlorate with appreciable velocity.