SSC
Bleaching powder is commonly known by the chemical name:
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Answer: Option A — Calcium hypochlorite (calcium oxychloride)
Detailed Solution
Bleaching powder is a white or pale yellow powder with a strong smell of chlorine. Its formula is usually written as CaOCl2 (calcium oxychloride). Commercial bleaching powder is a mixture, and its active ingredient is calcium hypochlorite, Ca(OCl)2.
Bleaching powder is made by passing chlorine gas over dry slaked lime (calcium hydroxide):
Ca(OH)2 + Cl2 → CaOCl2 + H2O
This process is carried out in Hasenclever's or Bachmann's plant. The chlorine needed comes from the chlor-alkali process, the electrolysis of brine (sodium chloride solution), which also produces sodium hydroxide and hydrogen.
When bleaching powder comes into contact with water or a dilute acid, it releases chlorine, which is responsible for its bleaching and disinfecting action. The chlorine produces nascent oxygen, which bleaches coloured substances by oxidising them.
Uses of bleaching powder:
- To disinfect drinking water and swimming pool water, making it free of germs.
- To bleach cotton and linen in the textile industry, and wood pulp in paper factories.
- To bleach washed clothes in laundries.
- As an oxidising agent in chemical industries.
- To make chloroform and to make wool unshrinkable.
- Bleaching powder should be stored in airtight containers, because it slowly loses its chlorine when exposed to air.
- Household liquid bleach is mainly sodium hypochlorite (NaOCl) solution, which is a different compound.
Why not the other options?
- ✗Calcium carbonate (CaCO3) is limestone, chalk and marble.
- ✗Sodium hypochlorite (NaOCl) is liquid household bleach, not bleaching powder.
- ✗Calcium sulphate is found as gypsum and plaster of Paris.
Quick tip
Remember: Bleaching powder = CaOCl2 (calcium oxychloride or hypochlorite), made from slaked lime and chlorine, used to disinfect water. Liquid bleach = sodium hypochlorite.
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Common Names & Chemical Formulas — Preparation
This question tests your understanding of Common Names & Chemical Formulas, a key topic in the General Knowledge section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.
This topic covers the common names, chemical names and formulas of everyday substances, such as common salt, baking soda, washing soda, bleaching powder, plaster of Paris, gypsum, quicklime and blue vitriol, along with the Latin names and symbols of elements. These are high-frequency memory questions. For example, baking soda is sodium hydrogen carbonate (NaHCO3), washing soda is Na2CO3.10H2O, and blue vitriol is copper sulphate pentahydrate. Remember the elements whose symbols come from Latin names, such as Na (natrium) for sodium, Fe (ferrum) for iron and Ag (argentum) for silver. Practise the common names and chemical formulas questions below, written in the style of the general awareness sections of exams such as SSC, banking, railways, CUET GAT, MAH CET and CLAT. Each question comes with a detailed explanation that adds related facts, so every question helps you revise more than one point.