Question

Which of the following is a correct set for the salts, types of hardness and the common methods used for removing the respective hardness ?

• A. Mg(HCO3)2, temporary hardness, washing soda method
• B. CaCO3, temporary hardness, boiling method
• C. MgSO4, permanet hardness, calgon's method
• D. CaCl2, permanent hardness, Clark's method

Answer 1

Answer: (C)

MgSO4, permanet hardness, calgon's method

Answer 2

Temporary hardness is because of the presence of bicarbonates of Mg2+ and Ca2+. The methods used for their removal are :

(1) boiling method

(2) Clark's method , Ca(HCO3)2 + Ca(OH)2  2CaCO3 + 2H2O Permanent hardness is because of the presence of SO42–, Cl– etc of Mg2+ and Ca2+. The methods used for their removal are :

(1) Washing soda method, MCl2 + Na2CO3 $\rightarrow$MCO3

+ 2NaCl

(2) Calgon's method M+ + Na4 P6O2–18 $\rightarrow$Na2MP6O2–18