Permanent hardness of water can be removed by adding?

ESIC Nursing Officer 2016 (shift-1)

Non Nursing Subjects

Easy

Appeared in: ESIC Nursing Officer 2016 (shift-1)

Explanation

Permanent hardness is caused by soluble salts like calcium and magnesium chlorides and sulfates.
Washing soda (sodium carbonate, Na₂CO₃) is used to remove permanent hardness.
It works by chemical precipitation. The carbonate ions from washing soda react with calcium and magnesium ions to form insoluble calcium carbonate and magnesium carbonate.
These insoluble precipitates are then removed from the water, making it soft.

Option A: Bleaching powder (calcium hypochlorite) is a disinfectant. Its primary role is to kill bacteria and other pathogens in water, not to remove mineral hardness.
Option B: Chlorine is a powerful gaseous disinfectant used in large-scale water treatment plants. It effectively kills microorganisms but has no effect on the dissolved mineral salts that cause hardness.
Option C: Potassium permanganate is a strong oxidizing agent. It is used in water treatment to remove impurities like iron and manganese and to control taste and odor, but it does not remove calcium and magnesium salts.

Visual 1: Diagram - A simple diagram showing a beaker of hard water (containing Ca²⁺ ions). An arrow shows washing soda (Na₂CO₃) being added, leading to a second beaker where solid calcium carbonate (CaCO₃) has precipitated at the bottom, illustrating the softening process.
Visual 2: Table - A comparison table outlining the differences between temporary and permanent hardness, including their chemical causes and respective removal methods.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Water treatment and removal of permanent hardness as background academic context rather than a clinical decision trigger.
Understanding water purity is fundamental to community health nursing. Nurses often educate communities on safe water practices to prevent waterborne diseases like cholera, typhoid, and gastroenteritis.
Knowledge of water hardness is relevant for sterilization procedures. Using hard water in autoclaves can lead to mineral deposits (scale) on instruments and the chamber, reducing efficiency and potentially compromising sterility.
What if? - If the question asked about removing temporary hardness, the correct answer would be boiling or adding lime (calcium hydroxide), as these methods target the bicarbonates responsible for temporary hardness.

How to Approach the Question

First, identify the key term in the question: 'Permanent hardness'.
Recall the definition of permanent hardness (caused by chlorides and sulfates of Ca/Mg) and differentiate it from temporary hardness (caused by bicarbonates).
Analyze the options to determine their primary function in water treatment.
Differentiate between methods for 'softening' (removing hardness minerals) and 'disinfection' (killing germs).
Bleaching powder, chlorine, and potassium permanganate are primarily disinfectants or oxidants. Washing soda is a known water-softening agent.
Select the option that chemically removes the salts responsible for permanent hardness.

Concept Tested & Keywords

Qk8M0591e5PObxgRkof8-t