Hardness as CaCO₃

Ca hardness = 2.5 [Ca^{2 +}], Mg hardness = 4.12 [Mg^{2 +}]

Hardness is reported as mg/L as CaCO₃. Multiply dissolved Ca²⁺ (mg/L as ion) by 2.50 (≡ 50/20.04) and Mg²⁺ by 4.12 (≡ 50/12.15). Total hardness = Ca + Mg hardness. Carbonate hardness is the lesser of total hardness and alkalinity; the remainder is noncarbonate hardness.

$Ca^{2 +}$ (mg/L): Calcium ion
$Mg^{2 +}$ (mg/L): Magnesium ion
$TH$ (mg/L): Total hardness as CaCO₃

Step-by-step solved example

Ca²⁺ = 48 mg/L, Mg²⁺ = 10 mg/L. Total hardness as CaCO₃?

Hardness titration of a water sample (meq as CaCO3).

1. Calcium
Ca hardness = 48 × 2.50 = 120 mg/L as CaCO₃.
2. Magnesium + total
Mg hardness = 10 × 4.12 = 41.2. TH = 120 + 41.2 = 161 mg/L as CaCO₃.
$T H = 161 mg/L as CaCO_{3}$

Answer: 161 mg/L as CaCO₃

10 practice questions

0/10 correct

1.Ca²⁺ = 80 mg/L as the ion. Ca hardness =

2.The factor 2.5 is

3.Water with TH = 40 mg/L as CaCO₃ is classified as

4.Mg²⁺ = 12 mg/L. Mg hardness ≈

5.Carbonate hardness is

6.Lime–soda softening is aimed at

7.TH = 180 mg/L as CaCO₃, Alk = 120 mg/L as CaCO₃. NCH =

8.Hardness ions of primary concern are

9.Ca²⁺ = 40 mg/L, Mg²⁺ = 0. Total hardness =

10.Ion-exchange water softeners typically replace Ca²⁺/Mg²⁺ with