Points to Remember:
- Permanent hardness in water is caused by dissolved minerals that are not easily removed by boiling.
- The main culprits are salts of calcium and magnesium.
- Bicarbonates are associated with temporary hardness.
Introduction:
Water hardness is a measure of the mineral content, primarily calcium and magnesium ions, dissolved in water. Hardness is categorized as temporary or permanent. Temporary hardness is caused by the presence of bicarbonate salts of calcium and magnesium (e.g., Ca(HCOâ??)â??, Mg(HCOâ??)â??), which can be removed by boiling. Permanent hardness, however, is due to the presence of other salts of calcium and magnesium that are not removed by boiling. This question focuses on identifying the salt primarily responsible for permanent hardness. The approach required is factual, drawing upon established chemical principles of water hardness.
Body:
Types of Water Hardness and their Causes:
Water hardness arises from the dissolution of minerals in water as it percolates through the ground. The two main types are:
Temporary Hardness: Caused by the presence of soluble bicarbonates of calcium and magnesium. Boiling the water converts these bicarbonates into insoluble carbonates, which precipitate out, thus softening the water.
Permanent Hardness: Caused by the presence of chlorides, sulfates, and nitrates of calcium and magnesium. These salts remain dissolved even after boiling. They are more difficult to remove and require methods like ion exchange or reverse osmosis.
Analysis of Options:
Let’s analyze the given options:
(A) Magnesium bicarbonate (Mg(HCOâ??)â??): This is a bicarbonate salt and is responsible for temporary hardness, not permanent hardness.
(B) Magnesium sulfate (MgSOâ??): This is a sulfate salt of magnesium. Sulfate salts of calcium and magnesium are major contributors to permanent hardness.
(C) Magnesium carbonate (MgCOâ??): While magnesium carbonate is insoluble in water, it can contribute to hardness if it’s present in a soluble form like a complex ion. However, it’s not the primary cause of permanent hardness compared to sulfates.
(D) None of the above: This is incorrect as magnesium sulfate is a significant contributor.
Conclusion:
In summary, magnesium sulfate (MgSOâ??) is the main cause of permanent hardness among the given options. While other salts of calcium and magnesium can also contribute to permanent hardness, sulfates are particularly significant. Magnesium bicarbonate contributes to temporary hardness, and magnesium carbonate, while potentially impacting hardness, is not the primary cause of permanent hardness. Therefore, the correct answer is (B). Effective water softening strategies need to address both temporary and permanent hardness, employing appropriate techniques like boiling for temporary hardness and ion exchange or reverse osmosis for permanent hardness to ensure safe and efficient water usage, promoting public health and environmental sustainability.
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