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GATE 2022 CE (CE1) – Question 22

Water and Waste Water Quality and Treatment · Water quality standards, parameters and water quality index · 1 mark · Multiple choice

The total hardness in raw water is 500 milligram per liter as CaCO3. The total hardness of this raw water, expressed in milligram equivalent per liter, is (Consider the atomic weights of Ca, C, and O as 40 g/mol, 12 g/mol, and 16 g/mol, respectively.)

  1. 10
  2. 100
  3. 1
  4. 5

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Correct answer: (A) 10

Explanation

The molar mass of CaCO₃ is $40+12+3(16)=100$ g/mol. Since calcium has valence 2, the equivalent weight is $100/2=50$ g/equivalent.

Hence $500\ \mathrm{mg/L}\div50\ \mathrm{mg/meq}=\mathbf{10\ \mathrm{meq/L}}$, **A**.