Bleaching Powder and Sodium hydroxide: Common Salt

Common salt – Sodium Chloride

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

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

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

Preparation of sodium hydroxide:

Sodium hydroxide is synthesized through the chlor-alkali 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 final product, this process is known as the chlor-alkali process.

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

sodium hydroxide

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.

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

Calcium Hypochlorite Structure

Preparation of bleaching powder:

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

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

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.

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Practise This Question

What is the reaction takes place at the cathode in the standard hydrogen electrode?