Temporary hardness of Water
- Temporary hardness is due to the presence of
calcium hydrogencarbonate Ca(HCO3)2(aq) and magnesium hydrogencarbonate Mg(HCO3)2(aq).
- Both calcium hydrogencarbonate and magnesium hydrogencarbonate decompose when
heated. The original insoluble carbonate is reformed. This happens when water
is boiled. The boiling the water causes the precipitation of
solid calcium carbonate or solid magnesium carbonate. This removes the calcium
ions or magnesium ions from the water, and so removes the hardness. Therefore,
hardness due to hydrogencarbonates is said to be temporary.
- Generally an increase in water temperature
causes an increase in the solubility of most salts. But one should understood from above there are exceptions
like CaCO3, CaSO4, MgCO3, Mg(OH)2 all of which become less soluble as the temperature
increases.
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