JEE Main · 2020 · 05 Sep 2020 · Shift 2 · Hydrogen

The one that is NOT suitable for the removal of permanent hardness of water is:

(A)Calgon's method
(B)Clark's method✓ Correct
(C)Treatment with sodium carbonate
(D)Ion-exchange method

Answer: (B)

Solution

Permanent hardness comes from the chlorides and sulphates of calcium and magnesium, which boiling cannot remove. Clark's method adds a measured amount of slaked lime and works only on temporary hardness due to bicarbonates, so it is the one unsuited to permanent hardness. Treatment with washing soda, the Calgon process and ion exchange all remove the

Ca X^{2 +}

and

Mg X^{2 +}

responsible for permanent hardness.

JEE Main · 2020 · 05 Sep 2020 · Shift 2 · Single correct option

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