Q. Ca⁺² = 20 ppm, Mg⁺² = 25 ppm, CO₂ = 30 ppm, HCO^-₃ = 150, K⁺ = 10 ppm. Calculate the lime (87% pure) and soda (91% pure) required softening 1 million litters of water sample.

Ans.

Calculation of CaCO₃ equivalent of given impurities:

Lime required:

74/100[Mg⁺⁺ + CO₂ + HCO^-₃ as CaCO₃ equivalent] mg/L *Volume of water*100/%purity

74/100[104.16 + 68.181 + 122.95] mg/L*1000000l*100/86

74/100[295.29] mg/L * 100000*100/87

= 251.16*10⁶ mg

= 251.16*10⁶ mg*1Kg/10⁶

= 251.16

Soda required = 106/100[50 + 104.16 – 122.95] mg/L *1000000*100/91

   = 100/106[31.21] mg/L*106*100/91

   = 36.35*10⁶ mg

   = 36.35*10⁶ mg*1Kg/10⁶

    = 36.35Kg