Which chemical substance is used for the purification of water?

Raj. CHO -2020

Community Health Nursing

Easy

Appeared in: Raj. CHO -2020

Explanation

Bleaching powder, also known as chlorinated lime (CaOCl₂), is a standard chemical used for the disinfection of water.
When mixed with water, it releases 'available chlorine' (about 33% when fresh), which acts as a powerful germicide.
The released chlorine destroys pathogens like bacteria and viruses, making the water safe to drink.
It is an effective, inexpensive, and widely accepted method for purifying water on both small (household) and large (community wells) scales.

Option A: Lime is primarily used in water treatment for softening (reducing hardness) and adjusting pH. While it has some disinfectant properties, it is not the standard or primary agent for making drinking water potable.
Option C: Potassium permanganate is a strong oxidizing agent but a weak disinfectant for water. Its effectiveness is quickly reduced by organic matter in the water, and it can impart an undesirable color, taste, and smell.
Option D: Formaldehyde is a highly toxic chemical used for fumigation, preserving biological specimens, and as an industrial disinfectant. It is not safe for human consumption and is never used to purify drinking water.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Chemical methods of water purification and disinfection as background academic context rather than a clinical decision trigger.
In community health nursing, understanding water purification methods is crucial for preventing waterborne diseases like cholera, typhoid, and gastroenteritis.
Nurses play a key role in educating communities about safe water practices, including the correct procedure for disinfecting wells using bleaching powder (e.g., using Horrock's apparatus to determine the correct dosage).
It is important to advise that bleaching powder loses its chlorine content when exposed to air, light, and moisture. It should be stored in a cool, dark, dry, and corrosion-resistant container.

How to Approach the Question

First, identify the core requirement of the question: a chemical used for the 'purification' of water, which implies making it safe for drinking.
Evaluate each option based on its known primary application in public health and chemistry.
Eliminate Formaldehyde immediately due to its high toxicity and use as a preservative/fumigant, not for ingestion.
Eliminate Lime as its primary role in water treatment is softening and pH control, not disinfection.
Compare Bleaching Powder and Potassium Permanganate. Recall that chlorine-based compounds are the standard for water disinfection due to their potent and reliable germicidal action, while potassium permanganate is considered a weak and unreliable disinfectant for this purpose.
Conclude that Bleaching Powder is the most appropriate and widely used chemical for water purification among the given choices.

Concept Tested & Keywords

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