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Removal of temporary hardness by Clark's process

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Clark's process involves the addition of a controlled quantity of slaked lime (calcium hydroxide)

Ca(HCO₃)₂(aq) + Ca(OH)₂(aq)2CaCO₃(s) + 2H₂O(l)

Mg(HCO₃)₂(aq) + Ca(OH)₂(aq)CaCO₃(s) + MgCO₃(s) + 2H₂O(l)

Slaked lime is itself a source of calcium ions (and hence hardness) so care must be taken to avoid adding an excess.