Total Hardness as CaCO3
Easyhardnesswater treatment
A water analysis reports calcium at 40 mg/L as Ca2+ and magnesium at 12 mg/L as Mg2+. The total hardness expressed as CaCO3 is most nearly:
- A52 mg/L
- B100 mg/L
- C149 mg/L
- D199 mg/L
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Answer: C. 149 mg/L
Each ion is converted to its CaCO₃ equivalent by multiplying by 50 divided by its equivalent weight. For calcium (equivalent weight 20.04): 40 × 50/20.04 = 99.8 mg/L. For magnesium (equivalent weight 12.15): 12 × 50/12.15 = 49.4 mg/L. Total hardness = 99.8 + 49.4 ≈ 149 mg/L as CaCO₃. Simply adding the raw concentrations gives 52 mg/L, and converting only the calcium gives about 100 mg/L.
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