Bleacing powder is calcium hypochlorite ( Ca(OCl)2 ). It is a one of the major chemical industry in the world. Limestone and chlorine gas are used as raw materials to manufacture bleaching powder which is used as a disinfectant and as an oxidizing agent. Bleaching powder show different reactions.
In this tutorial, we study about followings.
Bleaching powder is a white - yellowish powder which very well dissolves in water. The active ingredient of bleaching powder is calcium hypochlorite ( Ca(OCl)2 ). It is an inorganic compound.
Bleaching Powder chemical composition: Ca(ClO)2CaCl2Ca(OH)2.2H2O
Ca(OCl)2 is a white, corrosive solid that comes either in tablet form or as a granular powder in the market. It easily emits chlorine gas easily when it contacts with water or moisture.
Steps, reactions, materials of bleaching powder and physical conditionsin manufacturing process is explained below.
First, slaked lime (CaO) is produced by heating limestine. As a by product carbon dioxide is given.
Calcium oxide and water reaction
Calcium oxide is mixed with water to take calcium hydroxide ( Ca(OH)2 ). Ca(OH)2 is precipitated in concentrated solutions.
Reason to bleaching property is hypochlorite ion (OCl-). Colourful things are oxidized by atomic oxygen ('O') which is formed by OCl- ion. Atomic oxygen is very reactive.
when atomic oxygen is reduced, Colorful things are oxidized simultaneously.
Fe2+, I-, Br- ions can be oxidized by bleaching powder.
A suspension of bleaching powder in water is added dropwise to water and stirred. In earlier times, chlorine gas (Cl2) was used. But due to inconvenience of transporting heavy gas cylinders of chlorine, this method is abandoned.
When bleaching powder is heated with a dilute acid, chlorine gas is emitted.
Gaseous CO2 dissolve well in the water. That forms carbonic (H2CO2) acid. Carbonic acid can release Cl2 from bleaching powder.
Bleaching powder hydrolysis to hypochlorous acid ( HOCl ) and calcium hydroxide ( Ca(OH)2 ). Hypochlorous acid is not stable and again hydrolysis to chlorine gas.
Bleaching powder can oxidize another substances. Therefore bleaching powder can behave as an oxidizing agent.
Add bleaching powder to acidic KI solution. Purple colour I2 is emitted. When I2 contact with farina, you can see purple colour.
Ferrous ions ( Fe2+ ) are oxidized to ferric ( Fe3+ ) ions. You can identify Fe3+ ions by adding KSCN. Then red colour [Fe(SCN)]2+ is given.
Bleaching powder reacts with ammonia and give calcium chloride ( CaCl2 ), nitrogen gas (N2 ) and water as the products.
Sodium hypochlorite (NaClO) can be used as a disinfectant. But HOCl is more efficient than NaClO and Ca(OCl)2 in disinfecting process.
HOCl decomposes to HCl, atomic oxygen atom and water. Atomic oxygen is very reactive and is reduced to O2- readily. With that step, coloured thing is oxidized to get colourless.