Chapter 2 · Question 12

How is bleaching powder prepared? Write the chemical equation and give its uses.

Q12

How is bleaching powder prepared? Write the chemical equation and give its uses.

Answer Revealed

Direct Answer:

Bleaching powder is produced by the action of chlorine gas on dry slaked lime (

\text{Ca(OH)}_2

2\text{Ca(OH)}_2 + 2\text{Cl}_2 \rightarrow \text{Ca(OCl)}_2 + \text{CaCl}_2 + 2\text{H}_2\text{O}

. Although the actual composition is complex, it is represented as

\text{Ca(OCl)}_2

and commonly called calcium oxychloride. Uses: (i) bleaching cotton and linen in the textile industry, wood pulp in paper factories, and washed clothes in laundries; (ii) as an oxidising agent in chemical industries; (iii) making drinking water free from germs.

Simple Explanation

Bleaching powder is made by passing chlorine gas over dry slaked lime. The chlorine from the chlor-alkali process is used to make it — a nice example of one industrial product feeding another. The reaction:

2\text{Ca(OH)}_2 + 2\text{Cl}_2 \rightarrow \text{Ca(OCl)}_2 + \text{CaCl}_2 + 2\text{H}_2\text{O}

. The product, calcium oxychloride, is a white powder with a smell of chlorine. It bleaches clothes, whitens paper, and kills germs in water — this is why you might smell chlorine in swimming pool water or freshly laundered white clothes.

Exam-Ready Structure

Bleaching powder is an important industrially manufactured chemical derived from the chlorine produced during the chlor-alkali process. 1. Chemical identity: Though the actual chemical composition is complex, bleaching powder is represented in this chapter by the formula

\text{Ca(OCl)}_2

(calcium oxychloride). 2. Preparation: Chlorine gas produced during the electrolysis of brine is utilised to manufacture bleaching powder. It is produced by the action of chlorine gas on dry slaked lime (

\text{Ca(OH)}_2

2\text{Ca(OH)}_2 + 2\text{Cl}_2 \rightarrow \text{Ca(OCl)}_2 + \text{CaCl}_2 + 2\text{H}_2\text{O}

. 3. Uses: (a) Used for bleaching cotton and linen in the textile industry, wood pulp in paper factories, and washed clothes in laundries. (b) Used as an oxidising agent in many chemical industries. (c) Used to make drinking water free from germs. 4. The chlorine used as a raw material for bleaching powder comes from the chlor-alkali process, linking these two industrial chemical production pathways.

Key Points

Bleaching powder: $\text{Ca(OCl)}_2$ (calcium oxychloride), also known by the common name bleaching powder
Preparation: $2\text{Ca(OH)}_2 + 2\text{Cl}_2 \rightarrow \text{Ca(OCl)}_2 + \text{CaCl}_2 + 2\text{H}_2\text{O}$
Made by passing chlorine gas over dry slaked lime
Uses: bleaching cotton/linen/paper pulp, oxidising agent in chemical industries, disinfecting drinking water

How is bleaching powder prepared? Write the chemical equation and give its uses.