Bleaching Powder and Sodium hydroxide: Common Salt

Common Salt (Sodium Chloride)

  • Common salt is formed by the reaction between hydrochloric acid and sodium hydroxide.
  • Its chemical name is sodium chloride (\(NaCl\)).
Common Salt

Common Salt

It exists as an important raw material for the production of various chemical compounds such as caustic soda (sodium hydroxide), bleaching powder (\(CaOCl_2\)), etc.

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Let us have a look at the production of these compounds from common salt:

Bleaching Powder

  • Bleaching powder is a pale yellowish powder existing with a strong smell of chlorine.
  • It is soluble in water but due to the presence of impurities, we never observe a clear solution.
  • Its chemical formula is \(CaOCl_2\) with its chemical name as Calcium hypochlorite.
Calcium Hypochlorite - Bleaching Powder

Calcium Hypochlorite Structure

1. Preparation of Bleaching Powder

Bleaching powder is synthesized by the action of chlorine gas (produced from the chlor-alkali process) on dry slaked lime (\(Ca (OH)_2\)).

\(Ca(OH)_2 ~+ ~Cl_2~ → ~CaOCl_2 ~+~ H_2O\)

2. Uses of Bleaching Powder

  • It is used for bleaching dirty clothes in the laundry, as a bleaching agent for cotton and linen in the textile industry.
  • It is a strong oxidizing agent hence used as an oxidizer in many industries.
  • It is used as a disinfectant which is used for disinfecting water to make potable water.

Sodium Hydroxide

  • Sodium hydroxide is a whitish solid, available in flakes, pellets, and granules.
  • It is popularly known as caustic soda.
  • It is soluble in a polar solvent such as water but insoluble in non-polar solvents such as ether.
Sodium hydroxide

Sodium hydroxide crystal 3D ball structure

1. Preparation of Sodium Hydroxide

  • Sodium hydroxide is synthesized through the chloralkali process. In this process, electricity is passed through an aqueous solution of sodium chloride (commonly called brine), and the decomposition of brine takes place.
  • Chlorine gas is deposited at the anode while hydrogen at the cathode. The final solution of sodium hydroxide is formed at the cathode.
  • As NaOH (an alkali) and chlorine gas are present in the final product, this process is known as the chloralkali process.

\(2NaCl~ (aq)~ + ~2H_2O ~(l)~ \rightarrow~ 2NaOH ~(aq)~ + ~Cl_2~(g)~ + ~H_2~(g)\)

Sodium Hydroxide

Sodium Hydroxide (NaOH)

2. Uses of Sodium Hydroxide

  • It is used for manufacturing of paper, soaps, and detergents.
  • It is used for degreasing metals.
  • It is used to remove sulfurous impurities from poor quality crude oil by the process called caustic washing.

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