Bleaching Powder and Sodium Hydroxide

Dhristi JEE 2022-24

Bleaching Powder - What is the Chemical Name for Bleaching Powder?

Calcium Hypochlorite is the chemical name for bleaching powder. It is an inorganic compound. The formula of Calcium hypochlorite is CaO(Cl)₂. It is a vital component of commercial products called bleaching powder, chlorinated lime, or chlorine powder, used for water treatment, and as a bleaching agent. This compound is comparatively constant and has more chlorine than sodium hypochlorite (liquid bleach). It is a white solid, but the commercial samples mostly appear yellow. It does not dissolve in hard water and is instead used more in soft water treatment. It has two forms, hydrated (hydrous) and dry (anhydrous).

 

What is the Formula for Bleaching Powder?

The formula of bleaching powder (Calcium Hypochlorite) is CaO(Cl)₂. Bleaching powder is formed with the action of chlorine gas (produced from the Chlor-alkali method) on dry slaked lime, Ca(OH)₂.     

            

Ca(OH)₂             +            Cl₂            →       CaO(Cl)₂                 +         H₂O 

Calcium Hydroxide      Chlorine               Calcium Oxychloride       Water

(Slaked Lime)                                             (Bleaching Powder)

 

What is the Use of Bleaching Powder?

  • It is used for bleaching linen, cotton in textile industries, and for bleaching washed clothes in the laundry.

  • In many chemical industries, bleaching powder, CaO(Cl)₂, is used as an oxidizing agent. 

  • It is used as a germicide and disinfectant, especially in the sterilization of drinking water, to free water from harmful microorganisms.

  • It is used for the production of chloroform.

  • It makes wool unshrinkable.


Sodium Hydroxide

Sodium hydroxide is also called caustic soda. It is an inorganic compound. The formula for sodium hydroxide is NaOH. It is a white solid ionic compound composed of hydroxide anions, OH⁻ , and sodium cations, Naᐩ. Sodium hydroxide is a highly erosive alkali and base that decays proteins at room temperature and may induce severe chemical burns. It is highly dispersible in water and quickly absorbs moisture and carbon dioxide from the air. It develops a series of hydrates NaOH.nH2O. The monohydrate NaOH.nH2O crystallizes in water solutions between 12.3°C and 61.8°C.


Common Salt Chemical Formula

Sodium hydroxide acts with protic acids to give the corresponding salts and water. For example, when sodium hydroxide works with hydrochloric acid, sodium chloride is produced.   

       

 NaOH(aq) + HCl(aq) -> NaCl(aq) +H2O(l)


Preparation of Sodium Hydroxide

Sodium hydroxide is usually prepared by the electrolysis of sodium chloride in the Castner-Kellner cell. A brine solution is electrolyzed using carbon anode and mercury cathode. Sodium metal, released at the cathode, merges with mercury to create a sodium amalgam. Chlorine gas emerges at the cathode. The amalgam is treated with water to produce hydrogen gas and sodium hydroxide.


Uses of Common Salt - Sodium Chloride

Sodium chloride is necessary to sustain the electrolyte balance of fluids in the human body. If levels of electrolytes become too high or low, the person can become over-hydrated or dehydrated. Sodium chloride has been used to store and flavour foods for thousands of years. As a preservative, salt helps to restrict decay and helps to keep foods safe to eat. Salt is also used in fermenting methods for foods like pickles, sauerkraut, and kefir. It is also used in the refining of vegetable oils and petroleum. It also helps in purifying bauxite for the elimination of aluminium. It can also be used as a cleansing agent and in washing powder for machines, metal sheets, etc.


Properties of Sodium Chloride

It is quickly dissolvable in water and partly soluble or insoluble in other liquids.It is persistent towards heat. Sodium chloride resembles white crystals which do not have an odour but maintain a taste. NaCl acts as a good conductor of electricity due to the free movement of the ions in its aqueous state. The melting point of NaCl is 801°C and its boiling point is 1,413°C.

FAQs on Bleaching Powder and Sodium Hydroxide

1. Define the Physical Properties of Sodium Hydroxide?

Pure sodium hydroxide melts at 318°C (604°F) without breakdown, and with a boiling point of 1,388°C (2,530°F). It is a colourless crystalline solid. It is highly dispersible in water, with less solubility in cold solvents such as methanol and ethanol. NaOH is insoluble in non-polar solvents. The dissolution of solid sodium hydroxide in water is a highly exothermic reaction where a large amount of heat is released. The resulting solution is usually colourless and odourless. Due to the method of saponification that occurs between NaOH and natural skin oils, it feels slippery on touching.

2. Why is Calcium Hypochlorite Highly Used in Industries?

Calcium hypochlorite is an inorganic compound. As a mixture with calcium chloride and lime, it is sold as bleaching powder or chlorine powder. It is one of the most extensively used sanitation and disinfecting agents in the world. Calcium hypochlorite is also regarded to be the best product to be used for water treatment. Calcium hypochlorite is mainly used in large-scale industrial facilities, pharmaceutical plants, power plants, paper mills, automotive assembly facilities, mines, and other manufacturing units to sanitize water for rinsing, washing, spraying, coating, or cooling during processing.

3. What is the chemical formula of bleaching powder?

Calcium hypochlorite is the chemical name of bleaching powder and the formula for bleaching powder is CaO(Cl2). It is an inorganic compound and appears as a white solid.

4. How is sodium hydroxide prepared?

Sodium hydroxide or NaOH is prepared by electrolysis of brine solution in the Castner-Kellner cell. There is a carbon anode and a mercury cathode. The sodium molecules are released at the cathode end and the chlorine gas at the anode end. Sodium merges with mercury at the cathode forming an amalgam which reacts with H2O to release hydrogen gas and sodium hydroxide.

5. What are the uses of bleaching powder?

Bleaching powder has a wide variety of uses especially in industries and households as a bleaching agent as well as in the laundry. It is used in the chemical industry as an oxidizing agent and in the production of chloroform and in the chemical treatment of water to make it drinkable, thus, acting as a disinfectant.

6. What are the properties of sodium chloride?

Sodium chloride is a white crystalline solid that does not have a smell but has a taste and is easily soluble in water but dissoluble in other liquids. It is a good conductor of electricity in its aqueous state due to availability of free electrons. It doesn't change the structure on being heated and has a boiling point of 1413°C. Its melting point is 801°C.

7. What is liquid bleach?

Liquid bleach or simply bleach is a chemical liquid used in households as a bleaching agent. Its chemical name is sodium hypochlorite (NaClO) and releases chlorine very easily. Powder bleach, ie, calcium hypochlorite is more stable than sodium hypochlorite and has more chlorine in the comparison.

Comment