Bleaching powder is a yellowish white powder, which is also called chloride of lime It is a mixture of calcium CaCl2 and calcium hypochlorite Ca(OCl)2 On standing for a long time in air, bleaching powder undergoes slow auto - oxidation and loses the available chlorine The reaction can be represented as
6CaOCl2
bleaching‌powder
→
Ca(ClO3)2
calcium‌chlorate
+
5CaCl2
calcium‌chloride
Thus, on keeping for a long time CaOCl2 forms a mixture of Ca(ClO3)2+CaCl2