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Preparation, Properties & Uses of bleaching powder

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Published on Apr 13, 2013

Preparation
It is manufactured by the calcium process: ~\mathrm{2Cl_2 + 2Ca(OH)_2\longrightarrow \ Ca(OCl)_2 + CaCl_2 + 2H_2O}.

"Bleaching powder" is a mixture of calcium hypochlorite (Ca(OCl)2) and the basic chloride CaCl2, H2O with some slaked lime, Ca(OH)2. [1]
Properties

Calcium hypochlorite is a yellow white solid which has a strong smell of chlorine. It is not highly soluble in water, and is more preferably used in soft to medium-hard water. It has two forms: a dry form and a hydrated form. The hydrated form is safer to handle.

Calcium hypochlorite reacts with carbon dioxide to form calcium carbonate and release dichlorine monoxide: ~\mathrm{Ca(ClO)_2 + CO_2\longrightarrow \ CaCO_3 + Cl_2O \uparrow}.

A calcium hypochlorite solution is basic. This is due to the hydrolysis performed by the hypochlorite ion, as hypochlorous acid is weak, but calcium hydroxide is a strong base. As a result, the hypochlorite ion is a strong conjugate base, and the calcium ion is a weak conjugate acid: ClO− + H2O → HClO + OH−

Similarly, calcium hypochlorite reacts with hydrochloric acid to form calcium chloride, water and gaseous chlorine: Ca(OCl)2 + 4 HCl → CaCl2 + 2 H2O + 2 Cl2

Uses

Calcium hypochlorite is used for the disinfection of drinking water or swimming pool water. It is used as a sanitizer in outdoor swimming pools in combination with a cyanuric acid stabilizer, which reduces the loss of chlorine due to ultraviolet radiation. The calcium content hardens the water and tends to clog up some filters; hence, some products containing calcium hypochlorite also contain anti-scaling agents.

Calcium hypochlorite is also an ingredient in bleaching powder, used for bleaching cotton and linen. It is also used in bathroom cleaners, household disinfectant sprays, moss and algae removers, and weedkillers.

In addition, calcium hypochlorite may be used to manufacture chloroform.

Bleaching powder is used also in sugar industry for bleaching sugar cane juice before its crystallization.

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