Hardness of water is caused by?

Appeared in: KPSC Staff Nurse - 2015

Explanation

Water hardness is caused by dissolved salts of multivalent metallic ions, primarily calcium (Ca²⁺) and magnesium (Mg²⁺).
Calcium bicarbonate is a key compound responsible for what is known as 'temporary hardness' or 'carbonate hardness'.
This type of hardness is significant because it can be removed by simple methods like boiling, which precipitates the calcium as insoluble calcium carbonate.
While other salts cause hardness, calcium bicarbonate is a principal and common cause.

Option A: Salts of sodium, like Sodium Sulphate, are highly soluble and do not contribute to water hardness. Hardness is specifically caused by divalent cations like calcium and magnesium.
Option B: Although Magnesium Chloride does cause water hardness (specifically, permanent hardness), Calcium bicarbonate is also a correct answer and a very common cause of temporary hardness. In questions with multiple correct chemical causes, distinguishing between temporary and permanent hardness is key.
Option D: Similar to sodium salts, salts of potassium, like Potassium Chloride, do not cause water hardness. The property of hardness is associated with divalent, not monovalent, cations.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Causes of Water Hardness as background academic context rather than a clinical decision trigger.
From a public health perspective, community nurses should be aware of the local water quality. While hard water is not generally a health risk, it has significant domestic and economic impacts.
Hard water requires more soap to produce lather and leads to the formation of 'scale' (calcium carbonate deposits) in pipes, water heaters, and boilers, reducing efficiency and lifespan.
A simple health education point for communities is that boiling water can remove temporary hardness, which is useful for domestic purposes, but it does not remove permanent hardness or microbial contamination.

How to Approach the Question

First, identify the core concept of the question, which is 'hardness of water'.
Recall the definition of water hardness: it's caused by dissolved salts of calcium and magnesium.
Differentiate between the two types of hardness: temporary (caused by bicarbonates) and permanent (caused by chlorides and sulfates).
Evaluate each option based on this knowledge.
Option A (Sodium Sulphate) and D (Potassium Chloride) are incorrect because sodium and potassium salts do not cause hardness.
Option B (Magnesium Chloride) and C (Calcium bicarbonate) are both technically correct as they are salts of magnesium and calcium, respectively.

Concept Tested & Keywords

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E6 Parks TextBook of Preventive & Social Medicine part 2 — Subpart B (pp 233-449 of 464) pp. 43-45, 44-46

Practise the full KPSC Staff Nurse - 2015

Attempt every question from this paper in a timed mock, then review the full solution for each one.