Question:
Temporary hardness of water is mainly due to the presence of :
Temporary hardness of water is mainly due to the presence of :
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Carbonate Hardness = Temporary Hardness (Removed by boiling).
Non-Carbonate Hardness = Permanent Hardness (Requires chemical softeners).
Updated On: May 20, 2026
- Nitrates of calcium and magnesium
- Bicarbonates of calcium and magnesium
- Sulphates
- Chlorides
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The Correct Option is B
Solution and Explanation
Concept:
Hardness in water is defined as the concentration of multivalent cations, primarily calcium ($Ca^{2+}$) and magnesium ($Mg^{2+}$). It is classified into two types: temporary and permanent.
Step 1: Define Temporary Hardness.
Temporary hardness, also known as carbonate hardness, is caused by the presence of dissolved bicarbonate minerals of calcium and magnesium, specifically $Ca(HCO_3)_2$ and $Mg(HCO_3)_2$. It is called "temporary" because it can be easily removed by boiling the water.
Step 2: Analyze the removal process.
When water containing these bicarbonates is boiled, a chemical reaction occurs: \[ Ca(HCO_3)_2 \xrightarrow{\Delta} CaCO_3 \downarrow + H_2O + CO_2 \uparrow \] The soluble bicarbonates decompose into insoluble carbonates, which precipitate out of the water, thus removing the hardness.
Step 3: Distinguish from Permanent Hardness.
Permanent hardness is caused by the sulfates, chlorides, and nitrates of calcium and magnesium (Options 1, 3, and 4). These cannot be removed by boiling and require chemical treatment like ion exchange or lime-soda processes.
Step 1: Define Temporary Hardness.
Temporary hardness, also known as carbonate hardness, is caused by the presence of dissolved bicarbonate minerals of calcium and magnesium, specifically $Ca(HCO_3)_2$ and $Mg(HCO_3)_2$. It is called "temporary" because it can be easily removed by boiling the water.
Step 2: Analyze the removal process.
When water containing these bicarbonates is boiled, a chemical reaction occurs: \[ Ca(HCO_3)_2 \xrightarrow{\Delta} CaCO_3 \downarrow + H_2O + CO_2 \uparrow \] The soluble bicarbonates decompose into insoluble carbonates, which precipitate out of the water, thus removing the hardness.
Step 3: Distinguish from Permanent Hardness.
Permanent hardness is caused by the sulfates, chlorides, and nitrates of calcium and magnesium (Options 1, 3, and 4). These cannot be removed by boiling and require chemical treatment like ion exchange or lime-soda processes.
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