Question

1 kg of a sample of water contained 222 mg of CaCl2 and 219 mg of Mg(HCO3)2. The permanent and temporary hardness are in ppm​

Answer 1

The permanent is 200ppm and temporary hardness is 150ppm.

Explanation:

• CaCl2 is responsible for permanent  hardness.  
• Mg(HCO3)2 is responsible for temporary  hardness .
• One litre of water weights =1 kg =1000g = 1000x1000 mg = 106mg = 1 ppm

CaCl2

• Amount of the salt(mg/Lit) = 222
• Molecular weight of salt= 111
• Amounts equivalent toCaCO3(mg/Lit)= 222 x (100/111) = 200

∴ The permanent is 200ppm.

Mg(HCO3)2

• Amount of the salt(mg/Lit) = 219
• Molecular weight of salt= 146
• Amounts equivalent toCaCO3(mg/Lit)= 219 x (100/146) = 150

∴ The temporary hardness is 150ppm.

• Temporary hardness [ Mg(HCO3)2 ]= 150mgs/Lit.
• Permanent hardness [ CaCl2 ] = 200mgs/Lit.
• Total hardness = Temporary hardness+ Permanent hardness

        = 150 + 200

        = 350mgs/Lit.