GATE 2018 CE (CE1) – Question 61
Water contains Ca²⁺ 60 mg/L (atomic weight 40), Mg²⁺ 30 mg/L (atomic weight 24.31) and HCO₃⁻ 400 mg/L (formula weight 61). Carbonate hardness expressed as CaCO₃, to one decimal, is ______ mg/L.
Practise this question in The GATE Grind →
Show answer and explanation
Correct answer: 272.0 to 274.0
Explanation
Ca hardness is $60(100)/40=150$ mg/L as CaCO₃ and Mg hardness $30(100)/24.31=123.406$ mg/L. Total hardness is 273.406 mg/L. Bicarbonate alkalinity is $400(50)/61=327.869$ mg/L. Carbonate hardness is the smaller of hardness and alkalinity: 273.4 mg/L.