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JEE Main levelOne or more correct optionsDifficulty 2 of 3eq100

Which of the following statements about hardness of water are correct?

  1. A1 ppm of hardness corresponds to 1 mg of equivalent per litre of dilute aqueous solution.
  2. BSodium and potassium salts are the chief cause of hardness.
  3. CTemporary hardness is removed by boiling because bicarbonates decompose to insoluble carbonates.
  4. D mol/L of gives a hardness of 100 ppm as (molar mass 100).

Answer: A, C, D

Hardness is due to dissolved Ca2+ and Mg2+, not Na+ or K+. Boiling converts Ca(HCO3)2 into CaCO3, and 1 ppm = 1 mg/L. Each mole of Mg2+ counts as one mole of CaCO3 equivalent, so 1.0e-3 mol/L = 0.100 g/L = 100 ppm. Correct: first, second and fourth.
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