Bleaching powder in cold water is an excellent bleaching agent. But it cannot act as a good bleaching agent when dissolved in hot water.Why?

Explanation

Bleaching powder reacts with cold water to produce chloride and hypochlorite ions. Hypochlorite ions dissociate producing nascent oxygen which is responsible for bleaching:
`CaOCl_(2) +H_(2)O hArr Ca^(+2) +Cl^(-) +ClO^(-) +H^(+) + OH^(-)`
Bleaching powder reacts with hot water and produces chloride and chlorate ions:
`3ClO^(-) to 2Cl^(-) +ClO_(3)^(-)`