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Question

Permanent hardness is removed by boiling water with:
  1. CaO
  2. Na2CO3
  3. CaCO3
  4. Ca(OH)2

A
Ca(OH)2
B
Na2CO3
C
CaCO3
D
CaO
Solution
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Temporary hardness is removed by boiling water with NaOH.

Ca(HCO3)2+2NaOHCaCO3+Na2CO3+2H2O.

Permanent hardness is removed by boiling water with sodium carbonate.

CaCl2+Na2CO3CaCO3+2NaCl.

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Similar Questions
Q1
Permanent hardness is due to SO24 and Cl of Ca2+ and Mg2+ and is removed by the addition of Na2CO3.
CaSO4+Na2CO3CaCO3+Na2SO4
CaCl2+Na2CO3CaCO3+2NaCl
If hardness is 100 ppm CaCO3, amount of Na2CO3 required to soften 10 L of hard water is :
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Q2
Permanent hardness is removed by boiling water with:
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Q3
Presence of CaSO4 causes permanent hardness in water. It can be removed by precipitating it as CaCO3 by adding Na2CO3. If the amount of Na2CO3 required to soften 100 L of hard water, which is 200 ppm CaCO3, is x g, then value of x is:
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Q4
Following reaction is used to remove temporary hardness which is due to dissolved bicarbonates of Ca2+ and Mg2+.

Ca(HCO3)2+Ca(OH)22CaCO3+2H2O

Actually lime (CaO) is added which in H2O forms Ca(OH)2 and precipitates CaCO3 CaO+H2OCa(OH)2

If 10 L of hard water requires 0.56 g of CaO, temporary hardness of CaCO3 is x×102 ppm. Find x.
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Q5
Permanent hardness is due to Cl and SO24 of Mg2+ and Ca2+ and is removed by adding Na2CO3.

CaSO4+Na2CO3CaCO3+Na2SO4
CaCl2+Na2CO3CaCO3+2NaCl

Which of the following statements is/are correct?

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