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Bleaching Powder – Definition, Structure, Preparation, Properties

  • Last Updated : 06 Oct, 2021

Bleaching powder, also known as calcium hypochlorite, is a visible chemical that has shown to be extremely beneficial to people. It is a potent and poisonous chemical that can be harmful if not handled appropriately. Because it is an oxidising agent, it has a high value in organic chemistry. It has been used to oxidise thiol and sulphide by-products of organic synthesis, decreasing their odour and making them safe to dispose of.

It is utilised on a wide basis by the fabric, paper pulp, and petrochemical sectors. It is also commonly utilised in the home. Bleaching powder has a strong base and the characteristics of acido-basic and oxydo-reduction.

Bleaching Powder (Calcium Oxychloride)

Bleaching Powder, also known as chloride of lime, is solid in texture and yellowish-white in colour. Bleaching powder can be recognised by the smell of chlorine. Bleaching powder is generally used for the removal of colour, as indicated by its name. It is also known as a bleaching agent.  

Bleaching powder, when dissolved in water, form an aqueous solution, which is basic in nature. Bleaching powder works on the principle of oxidation. The bleaching action of the bleaching powder is caused due to the presence of chlorine in it. A compound of calcium hydroxide exists, which is known as slaked lime reacts to form bleaching powder. 

Slaked Lime reacts with the chemical compound chlorine, it gives a compound, bleaching powder (calcium oxychloride) and gives water as a by-product. Bleaching powder is an inorganic compound with the formula Ca(OCl)2. The compound is soluble in water but due to the presence of impurities, the solution obtained by mixing this compound in water is not a clear solution. 

Structure of Bleaching Powder

The structural formula of bleaching powder contains two atoms of chlorine. Among these two atoms, one of them is properly bonded to the atoms of the chemical compound Calcium. The other atom of Chlorine results in the formation of a bond with the atom of Oxygen.

Preparation of Bleaching Powder

The manufacture of bleaching powder is carried out in Bachmann’s plant as follows:

The entire system is prepared for the manufacturing of bleaching powder, containing a vertical cast-iron tower packed with a hopper at the top, two inlets near the base (one for chlorine and the other for hot air) and an exit for waste gases near the top. This tower is then fitted with shelves that are placed at varying heights with rotating rakes. The shelves are a total of eight in number. Slaked lime is introduced into the hopper. It eventually comes in contact with chlorine moving slowly in the upward direction. The bleaching powder is then collected at the base in the barrel area of the tower. 

Conditions to be looked after during the manufacture: 

  • The chlorine used should be dilute in nature. 
  • The temperature should be maintained below 40°C.

Properties of Bleaching Powder:

Bleaching Powder is a pale yellowish powder that possesses a strong smell of chlorine. 

  • It performs a reaction with dilute acids to produce chlorine. 
  • It is soluble in cold water. The lime is left as an insoluble residue on dilution.
  • On reaction with an excess of a dilute, for instance, dilute sulphuric acid, the chlorine from the bleaching powder gets liberated. 

Thereby, the chlorine that is produced as a result of the action of dilute acid on bleaching powder acts as a bleaching agent. Therefore, chlorine is the bleaching agent in bleaching powder. 



Ca(OH)2 (aq) + Cl2(aq) ⇢ CaOCl2(aq) + H2O(l)

Slaked lime + Chlorine ⇢  Bleaching powder + Water

Uses of Bleaching Powder

Bleaching Powder has the following uses: 

  1. Used as an oxidising agent in chemical industries.
  2. Used for disinfection of drinking water.
  3. Used for bleaching of washed clothes in the laundry.
  4. Used for bleaching wood pulp in the paper manufacturing industry.
  5. Used as a bleaching agent in the textile industry for bleaching cotton and linen. 

Sample Questions 

Question 1: What is the main aim of bleaching powder?

Answer:

Bleaching powder is mainly used for removing colours from materials. 

Question 2: Describe what happens when bleaching powder is subjected to air?

Answer:

On keeping in the air, bleaching powder absorbs the atmospheric moisture and becomes watery. Upon reaction with oxygen, bleaching powder produces calcium carbonate and chlorine gas.

Question 3: Describe the pH value of bleaching powder. 



Answer:

Bleaching powder is considered to be basic in nature. It gives calcium chloride, chlorine and water upon reaction with hydrochloric acid. Bleach is considered to contain about 5% sodium hypochlorite, giving the skin a pH of about 11. Hence, it is mildly irritating.

Question 4: Why does bleaching powder act as an oxidising agent? 

Answer:

The bleaching powder reacts in the presence of a very small amount of dilute acid to release nascent oxygen. The release of the nascent oxygen causes the bleaching powder to act as both an oxidising and a bleaching agent.

Question 5: State some harmful effects of bleaching powder. 

Answer: 

Some harmful effects of bleaching powder are:

  • The fumes from bleaching powder are really strong in nature which on inhalation may cause a large number of health problems.
  • It is highly irritating and corrosive to the skin.
  • It may even result in the formation of lumps on the eyes.
  • It may burn human tissue both internally and externally.

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