The following methods can not be used to remove permanent hardness of water

The following methods can not be used to remove permanent hardness of water
  1. Treatment with washing soda
  2. Ion-exchange method
  3. Treating with Calgon
  4. Adding calculated amount of lime

Solution

(d) Lime is added to hard water to remove temporary hardness. (Clark's method) $\mathrm{Ca}\left(\mathrm{HCO}_3\right)_2+\mathrm{Ca}(\mathrm{OH})_2 \Rightarrow 2 \mathrm{Ca} \mathrm{CO}_3 \downarrow+2 \mathrm{H}_2 \mathrm{O}$

Asked in: AP EAMCET 2023 (17 May Shift 1)

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