Topic: Valence, oxidation states and chemical reactivity· Classification of Elements and Periodicity in Properties

The method used to remove temporary hardness of water is :

1. Calgon's method

2. Clark's method

3. Ion-exchange method

4. Synthetic resins method

Doubtly Asked 30 Oct 2026 NEET UG 2019 neet Save WhatsApp Report

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Answer: 2. Clark's method

Key idea: temporary hardness is due to bicarbonates of Ca and Mg, and the method meant specifically for it is Clark's method.

In Clark's method slaked lime is added: \(\mathrm{Ca(HCO_3)_2 + Ca(OH)_2 \to 2CaCO_3\downarrow + 2H_2O}\). The insoluble carbonate (and \(\mathrm{Mg(OH)_2}\) for Mg salts) settles out.

Calgon, ion-exchange and synthetic resin methods work for hardness in general (mainly used for permanent hardness), so the method named for temporary hardness is Clark's, option (2).

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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The method used to remove temporary hardness of water is :

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