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Bleaching Powder

Bleaching power is an inorganic compound of calcium. Its chemical name is calcium hypochlorite and its chemical formula is Ca (OCl2). It is also known as chloride of lime and calcium oxychloride. In dry form, it is a pale yellowish powder and smells like chlorine. It is soluble in water but its solution is not clear as it contains impurities.

Bleaching Powder

This chemical is very unstable and highly reactive, so, it should be used with proper care and safety. In liquid state, the potency of bleaching power or its effect depends on the concentration of bleaching powder.

Chemical properties of bleaching powder

i) In air, it reacts with CO2 gas to produce chlorine gas and calcium carbonate as shown in the below chemical reaction;

CaOCl2 + CO2 → CaCO3 + Cl2

ii) When it reacts with dilute hydrochloric acid (HCl), the chlorine gas is produced, see the reaction;

CaOCl2 + 2HCl → CaCl2 + Cl2 + H2O

iii) When it reacts with dilute sulphuric acid, it forms calcium sulphate and other products as shown in the below reaction;

CaOCl2 + H2SO4 - → CaSO4 + Cl2 + H2O

The chlorine produced in the above reactions of bleaching powder with dilute acids acts as a bleaching agent. So, it is the chlorine present in the bleaching power, which acts as a real bleaching agent.

Preparation of Bleaching Powder

Bleaching powder is prepared by the reaction of chlorine gas (formed in the Chlor-alkali process) with the dry slaked lime, whose chemical formula is Ca (OH)2. The chlorine gas is passed over the dry slaked lime in this process.

On a large scale it can be manufactured in two different types of manufacturing plants as described below;

  1. Backmann Plant
  2. Hasenclever Plant

1) Preparation of bleaching powder in Hasenclever Plant

The plant is made of four cylinders of cast iron. Each cylinder measures 2 to 3 meters in length and provided with a stirrer or shafts fitted with blades. These shafts can be rotated inside the cylinders to carry out the mixing of substances.

The cylinder at top is provided with an inlet for pouring Ca (OH) 2 or slaked lime and an outlet to release the waster gases. Whereas, the bottom cylinder has an inlet for Cl2 and an outlet for the bleaching powder to come out, produced in this process. The cylinder are connected with each other with pipes.

How Hasenclever Plant works?

The dry slaked lime CaOH2 is poured into the plant through inlet or hopper present in the top most cylinder. Then, the slaked lime moves forward with the help of revolving blades of the shafts. The chlorine gas is made to enter the lowermost cylinder through inlet present on it. The chlorine gas moves up to the upper most cylinder where it reacts with the dry slaked lime to form bleaching power. When bleaching powder is formed, it comes out through the outlet present at the bottom of the middle cylinder and is collected in a vessel.

2) Preparation of bleaching powder in backmann plant

It is made of vertical cast-iron tower provided with a hoper at the tops and two inlets fitted at the base; one inlet is provided for entering chlorine and another one is used for sending hot air into the plant. Apart from this, one exit is present near the top to eject or release waste gases from the plant.

The tower contains eight shelves fitted at different heights. Each shelve is provided with rotating rake. The slaked lime is made to enter through the hopper. The chlorine gas move upwards and comes in contact with slaked lime and leads to the formation of bleaching powder, which is collected at the base in a barrel. The temperature should be below 40 degree centigrade in this process, and the chlorine should be used in dilute form.

Storage of bleaching powder

It is stored in air-tight container so that it does not come in contact with air. If it is left open in air, it reacts with CO2 and forms CaCO3 and Chlorine.

pH value of bleaching powder

  • The bleaching powder that is used for domestic purposes has a pH value of 11. So, it is bit irritating to the skin.
  • The concentrated bleaching powder, which has 10-15% of sodium hypochlorite, has a pH value of 13. The high PH value makes it highly alkaline.

Uses of bleaching powder

Bleaching powder offers lots of uses or it can used in different ways, some of which are described below;

i) Cleaning old items

Old precious items like jewellery or showpieces that are made of metal can be cleaned easily by using bleaching powder.

ii) To whiten clothes and remove stains

It can also be used to whiten clothes and remove stains from clothes as well as from tiles and various other surfaces. It is rubbed over the stain with some water and left for some time, and then washed thoroughly with water.

iii) Bathroom cleaner

It can be used to clean bathroom after mixing with equal amount of water. You may spray this solution over the tiles and wash if after 15 to 20 minutes.

iv) To clean glass dishes

It can be used after mixing with soapy water to clean glass dishware. It makes glass dishware clean, shining, and also disinfect them. It can used to clean and glow other utensils. The garbage cans can be disinfected by cleaning it with a mixture of bleaching powder, water, and dish-washing liquid.

v) For disinfection purposes

It can be used as a disinfection spray after mixing it with hot after. It can be sprayed over surfaces and at various places in your home.

vi) Kill walkways weeds

It can also kill walkways weeds. You can pour bleaching powder over the weeds and left if undisturbed for 2 or 3 days, then you can remove the weed with very ease.

vii) Sanitization of household tools

It is also effective in the sanitization of garden and kitchen tools when used after mixing it with water. Besides this, it also sanitizes and cleans plastic furniture when used after mixing with mild detergent water. Besides this, it can also disinfect the medical tools whey are soaked in warm water mixed with bleaching powder.

Viii) Preservation

You can add some bleaching powder in the flower vase to keep the cut flowers fresh for a long time. Also, you can prevent bacterial growth by adding some bleach and sugar in the water.

ix) Oxidizing Agent:

It is also used as oxidizing agent in various industries. For example, it is used to form chloroform by reacting it with ethanol or acetone.

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