Question

A zeolite softener was completely exhausted and was generated by passing 1000 litres of NaCl .How many litres of a sample of hardness 500 ppm can be softened by this softener ?

Answer 1

The total amount of NaCl required for the softening process is

1000 litres x 100 mg/lit =100000 mg .
CaCl₂ + Na₂Ze → 2NaCl + CaZe 
1CaCl₂ → 2NaCl 
1CaCl₂ → 1CaCO₃ 
Hence 1CaCO₃ → 2NaCl 
100 mg of CaCO₃ = 2 x 58.5 mg of NaCl
2 x 58.5 mg of NaCl = 100 mg of CaCO₃ 
100000 mg of NaCl = 100000 x 100/2 x 58.5 mg of CaCO₃ 
The hardness of the water sample is 500 ppm , i.e. 500 mg of CaCO₃ is required for 1 litre of water . 
Volume of water required for 100000 x 100 /2 x 58.5 mg of CaCO₃ is 
= 100000 x 100 /2 x 58.5 x 500 Litres
= 170.94 Litres
170.94 Litres of a sample of water can be softened by this softener .