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Permanent hardness of water is caused by the presence of dissolved salts such as calcium sulfate and magnesium sulfate. Unlike temporary hardness, which can be removed by boiling, permanent hardness cannot be eliminated by simple heating.
To remove permanent hardness, a chemical called washing soda (sodium carbonate) is commonly added to the water. Washing soda reacts with the calcium and magnesium salts present in hard water to form insoluble carbonates. These carbonates then precipitate out of the water, reducing hardness.
The chemical reactions involved are:
Calcium sulfate reacts with sodium carbonate to form calcium carbonate (insoluble) and sodium sulfate (soluble).
Magnesium sulfate similarly reacts to form magnesium carbonate (insoluble) and sodium sulfate.
This process effectively softens the water, making it suitable for domestic and industrial use. Soft water improves soap efficiency, reduces scale formation in pipes and boilers, and protects appliances.
Other substances like chlorine and bleaching powder are used for disinfection and bleaching purposes, respectively, but they do not remove water hardness.
Understanding how washing soda removes permanent hardness is important in chemistry and environmental science. It explains how chemical treatment improves water quality and makes it safer for daily use.
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