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Temporary hardness in water, often due to the presence of dissolved carbonated & bicarbonates of heavy metals such as calcium and magnesium, it can be removed by boiling. When the water is boiled, the bicarbonates decompose and form insoluble carbonates or hydroxides, which precipitate out. Filtering the water afterward helps remove these precipitates, effectively reducing temporary hardness.
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| Temporary Hardness | Permanent Hardness | |
|---|---|---|
| Cause | Temporary hardness is caused by the presence of bicarbonates of calcium and magnesium in water. | Permanent hardness is caused by the presence of sulfates and chlorides of calcium and magnesium in water. |
| Removal | It can be removed by boiling the water. Upon boiling, the bicarbonates decompose to form insoluble carbonates that precipitate out, making the water softer. | It cannot be removed by boiling alone. Other methods like ion exchange or chemical treatment are required to eliminate permanent hardness. |
| Reversibility | Temporary hardness can be easily removed and is reversible. | Permanent hardness is challenging to remove and typically irreversible through simple processes like boiling. |
→ PPM: It is defined as the number of parts by weight of calcium carbonate per million (10^6) parts by weight of water. (it represents the number of parts of calcium carbonate (CaCO3) per million parts of water. For instance, 1 ppm of hardness means there is 1 milligram of calcium carbonate dissolved in one liter of water.)
→ Degree Clarke (°Cl) : It is defined as the of grains og CaCO3 equivalent present per gallon of water or it is number of parts of CaCO3 equivalent hardness in 70,000 parts of water.
→ Degree French (°Fr) : It is defined as the parts of CaCO3 Equivalent present in 10^5 parts of water
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Hardness is the soap consuming capacity of water and caused mainly due to dissolved salts of calcium and magnesium.
Water which does not forms lather with a soap easily on shaking is called hard water.