is really a disprpportionation reaction of the halate(I)anion: Reaction(11.3)is favoured by the use of dilute alkali and low temperature since the halate(I)anions,are thermally unstable and readily disproportionate(i.e. reaction(11.4)). The stability of the halate(I)anions,decreases from chlorine to iodine and the iodate(I)ion disproportionates very rapidly even at room temperature.
The formation of halate(V)and halide ions by reaction(11.4)is favoured by the use of hot concentrated solutions of alkali and an excess of the halogen.
When chlorine is passed over molten sodium or potassium hydroxide,oxygen is evolved,the high temperature causing the chlorate(V)ion to decompose: