Question

A sample of hard water contains 1 mg CaCl₂ and 1 mg MgCl₂ per litre. Calculate the hardness of water in terms of CaCO₃ present in per 10⁶ parts of water.

Answer 1

Hardness of soluble salt equivalent to CaCO₃ = (w x Molar mass of CaCO₃) / Molar mass of soluble salt

Hardness of CaCl₂ = (1x100) / 111 = 0.901 mg/L

Hardness of MgCl₂ = (1x100) / 95 = 1.052 mg/L

Hardness = 0.90 + 1.053 = 1.953 mg/L

1mg/L = 1 mg of CaCO₃ equivalent to hardness of 1L of water or 10⁶ mg of water

Therefore, hardness in the sample is 1.953 ppm.