Bleaching powder is chemically, calcium oxychloride (CaOCl2). Bleaching powder is manufactured using Backmann’s plant in which slack lime and Chlorine are made to react to create Bleaching Powder.
Bleaching powder is a yellowish white powder with a strong smell of chlorine. When exposed to air, bleaching powder gives a smell of chlorine. This is because bleaching powder reacts with carbon dioxide from the atmosphere to produce calcium carbonate and chlorine.
How bleaching Powder bleaches?
In the presence of a very small amount of dilute acid, it gives nascent oxygen. Due to the evolution of nascent oxygen, it acts as an oxidising and a bleaching agent.
2CaOCl2 + H2SO4 → CaCl2 + CaSO4 + 2HOCl
2HOCl → 2 HCl + 2 [O]
When it is treated with excess of dilute acids, chlorine is evolved. Chlorine gas produced in this way is known as, “available chlorine” which is responsible for the bleaching action of bleaching power. Available chlorine in bleaching powder is usually 35 – 38% by weight. The strength of bleaching powder is estimated on the basis of available chlorine content.
CaOCl2 + H2SO4→ CaSO4 + H2O + Cl2
CaOCl2 + 2HCl→ CaCl2 + H2O + Cl2
Bleaching powder is used to bleach cotton and linen in textile industry and wood pulp in paper industry. It is also used to bleach washed clothes in laundry. Bleaching powder is also used as a disinfectant and germicide, since it liberates chlorine on exposure to the atmosphere which destroys the germs. It is also used for disinfecting water for the same reason. It is also used as an oxidising agent in many chemical industries