Question

A water has an alkalinity of 200 mg/L as CaCO3. The Ca2+ concentration is 160 mg/L as the ion and the Mg2+ concentration is 40 mg/L as the ion. The pH is 8.1. Find the total carbonate and noncarbonate hardness

Answer 1

We first need to express calcium and magnesium hardness as CaCO₃.

Cacium hardness as CaCO₃ = (Conc. of Ca²⁺ ion/Equivalent wt. of Calcium) x Equivalent wt. of CaCO₃

= (160 mg/L / 20) x 50

= 400 mg/L as CaCO₃

Magnesium hardness as CaCO₃ = (Conc. of Mg²⁺ ion / Equivalent wt. of magnesium) x Equivalent wt. of CaCO₃

=(40 mg/L / 12) x 50

= 166. 67 mg/L as CaCO₃

Total Hardness = Calcium Hardness + Magnesium Hardness

= 400 + 166.67 = 566.67 mg/L as CaCO₃

Total Carbonate Hardness = Total Alkalinity = 200 mg/L as CaCO₃

Total Non carbonate Hardness = Total Hardness - Carbonate Hardness = 566.67 - 200 = 366.67 mg/L as CaCO₃