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GATE 2020 CE (CE2) – Question 47

Water and Waste Water Quality and Treatment · Water quality standards, parameters and water quality index · 2 marks · Multiple choice

Alkalinity (eq/L) is $\{HCO_3^-\}+2\{CO_3^{2-}\}+\{OH^-\}-\{H^+\}$, with braces denoting mol/L. A sample has bicarbonate $2\times10^{-3}$ mol/L, carbonate $3.04\times10^{-4}$ mol/L and pH 9.0. Atomic weights Ca = 40, C = 12, O = 16. Neglect OH⁻ and H⁺. Find alkalinity as CaCO₃ (mg/L).

  1. 130.4
  2. 100.0
  3. 50.0
  4. 65.2

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Correct answer: (A) 130.4

Explanation

Alkalinity is $0.002+2(0.000304)=0.002608$ eq/L. CaCO₃ equivalent mass is 50 g/eq. Thus alkalinity is $0.002608(50000)=130.4$ mg/L as CaCO₃. **A**.