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Questions
Give reason for the following:
Hardness in temporary water can be removed by boiling, but hardness in permanent hard water cannot.
Temporary hardness in water can be removed by boiling.
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Solution 1
Temporary hardness is due to the presence of bicarbonate of calcium or magnesium, on boiling bicarbonate decomposes to CO2, carbonate which is in soluble and can be filtered out. Where as permanent hard water contains [SO2]2- or Cl–– of calcium and magnesium, cannot be removed by boiling.
Solution 2
Temporary hardness in water is due to the presence of HCO3 of calcium or magnesium.
On boiling bicarbonate changes to carbonate which is insoluble in water and is filtered out, CO2 gas escapes and water becomes soft.
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