Q.What is hard water? Write a note on the Calgon's Method for the removal of hardness of water.
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Start your 14-day free trial to unlock the full solution →Hard water contains Ca2+/Mg2+ salts and does not lather with soap; Calgon (sodium hexametaphosphate) softens it by forming soluble complex ions that keep Ca2+ and Mg2+ out of the way.
Hard water:
Water that does not produce lather (foam) readily with soap is called hard water. This hardness is due to the presence of soluble bicarbonates, chlorides and sulphates of calcium and magnesium. Hard water wastes soap because the Ca2+ and Mg2+ ions first react with soap to form an insoluble scum.
Calgon's method:
Calgon is the commercial name for sodium hexametaphosphate, Na6P6O18, sometimes written as Na2[Na4(PO3)6].
When Calgon is added to hard water, the sodium ions of Calgon are exchanged for the Ca2+ and Mg2+ ions of the hard water, forming soluble complex ions in which the calcium and magnesium are locked up:
Na2[Na4(PO3)6] -> 2Na+ + [Na4(PO3)6]^2-
[Na4(PO3)6]^2- + 2Ca2+ -> [Ca2(PO3)6]^2- + 4Na+
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