Question

bleaching powder lost its chlorine content after a month although kept in air tight container ? what could be the reason ?

Answer 1

Bleaching powder loses its chemical activity due to loss of chlorine even if kept in air tight container. This is due to high temperature and does not matter whether container is air tight or not because it is thermally not very stable. Each of the bleaching powder has a shelf life. Beyond that time period the chlorine component gets lost and thus it lose its activity.The changes that are responsible for reducing the percentage of available chlorine content in an old sample of bleaching powder is :

On long standing, CaOCl₂.H₂O decomposes slowly to give a mixture of Ca(ClO₃)₂ and CaCl₂ or CaCl₂ and O₂.
6[​CaOCl₂.H₂O] $\to$Ca(ClO₃)₂ + 5CaCl₂ + 6H₂O​
2[​CaOCl₂.H₂O] $\to$2CaCl₂ +O₂+ 2H₂O​​