Temporary Hardness Vs. Permanent Hardness of Water
Hardness of water is caused by the presence of dissolved salts of calcium and magnesium. It is classified into two types: temporary hardness and permanent hardness.
| Aspect | Temporary Hardness | Permanent Hardness |
|---|---|---|
| Cause | Due to dissolved bicarbonates of calcium and magnesium (Ca(HCO3)2, Mg(HCO3)2). | Due to dissolved chlorides and sulphates of calcium and magnesium (CaCl2, MgSO4). |
| Removal Method | Can be removed by boiling, which decomposes bicarbonates into insoluble carbonates. | Cannot be removed by boiling; requires chemical treatment such as addition of washing soda, ion-exchange resins, or lime-soda process. |
| Nature | Temporary and reversible. | Permanent and irreversible without chemical treatment. |
| Effect on Soap Lathering | Reduces soap lathering ability. | Does not significantly affect soap lathering. |
| Example | Water containing Ca(HCO3)2. | Water containing MgSO4. |
Key Point: Temporary hardness can be easily removed by simple boiling, while permanent hardness requires advanced chemical methods for treatment.
Read also Methods to Determine Hardness of Water
Test Your Knowledge: Hardness of Water
1. Temporary hardness of water is mainly caused by the presence of:
View Answer & Explanation
Correct Answer: (a) Calcium and magnesium bicarbonates
Temporary hardness arises due to bicarbonates of calcium and magnesium, which can be removed by boiling.
2. Permanent hardness of water cannot be removed by:
View Answer & Explanation
Correct Answer: (a) Boiling
Permanent hardness is due to chlorides and sulphates of calcium and magnesium, which cannot be removed by boiling but require chemical treatment.
3. Which of the following statements correctly distinguishes temporary and permanent hardness?
View Answer & Explanation
Correct Answer: (d) All of the above
All listed distinctions are correct: causes, removal methods, and reversibility differentiate temporary and permanent hardness.