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Important Salts in Daily Life - Preparation and Uses of Bleaching Powder

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Topics

  • Introduction
  • Experiment
  • Properties
  • Uses

Introduction:

Calcium hypochlorite, with the chemical formula Ca(ClO)₂ or Ca(OCl)₂, is an inorganic compound commonly known as bleaching powder or calcium oxychloride. It is a white solid, though commercial samples often appear yellow, with a strong chlorine odour due to its slow decomposition in moist air. This compound is relatively stable in both solid and solution forms and provides a higher chlorine content compared to sodium hypochlorite. Pure calcium hypochlorite contains about 99.2% active chlorine, while industrial-grade samples typically have 65-70% active chlorine. It is widely used for water treatment and as a bleaching agent.

Bleaching powder gets its property because of this release of chlorine gas.

CaOCl₂ + CO₂ → CaCO₃ + Cl₂↑

Bleaching powder is obtained by the reaction of chlorine gas with slaked lime.

Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

Experiment

1. Aim: To observe the bleaching action of bleaching powder on a coloured cloth and understand its reaction mechanism.

2. Requirements: a piece of coloured cloth, a saturated solution of bleaching powder, and a dropper.

3. Procedure

  • Take a piece of coloured cloth.
  • Using a dropper, apply a few drops of the saturated bleaching powder solution to a small part of the cloth.
  • Observe the changes in the colour of the cloth.

4. Observation: The spot where the solution is applied causes the cloth's colour to fade or bleach.

5. Conclusion: Bleaching powder releases chlorine gas when it reacts with air (CO₂). Chlorine is a strong oxidising agent that removes colour from the cloth by breaking down the dye molecules. This property of bleaching powder makes it a useful bleaching and disinfecting agent.

Properties:

  • Bleaching powder is a yellowish-white solid with a strong chlorine-like odour. Its chemical name is calcium oxychloride (CaOCl₂).
  • It releases chlorine gas slowly when exposed to air due to its reaction with carbon dioxide. Reacts rapidly with dilute acids like hydrochloric acid or sulphuric acid, releasing chlorine gas completely.

CaOCl₂ + H₂SO₄ → CaSO₄ + Cl₂ ↑+ H₂O

  • It is stable in dry conditions but decomposes slowly in the presence of moisture and has strong oxidising and disinfecting properties.
  • It can act as a bleaching agent due to the release of chlorine gas, which breaks down colour molecules.

Uses:

  1. It is widely used for disinfecting drinking water in water treatment plants and swimming pools.
  2. Serves as a bleaching agent in the textile and paper industries.
  3. It is used for sanitising roadsides, garbage sites, and other areas requiring disinfection.
  4. Helps in the preparation of chlorine gas in laboratories and industrial settings.
  5. It plays a role in producing other chlorine-based compounds.
  6. It is used in emergency sanitation to neutralise pathogens and contaminants.
  7. Effective for cleaning and deodorising purposes due to its chlorine content.
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