Calcium hydroxide canot be used to remove permanent hardness of water why
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Chemical Water Softeners which lead to precipitation - these are chemical substances added to the water to remove dissolved calcium, magnesium or iron(II) salt by forming precipitate or undissolved solids. The precipitate is then removed by filtration.
Calcium hydroxide, Ca(OH)2 - addition of calculated amount of Ca(OH)2 will remove only temporary hardness from water. Ca(OH)2 precipitates the insoluble trioxocarbonate(IV).
Example, Ca(OH)2(s) + Ca(HCO3)2(aq) → 2CaCO3(s) + 2H2O
Note: Ca(OH)2 is slightly soluble; Ca(HCO3)2 is soluble; CaCO3is insoluble.
Also, notice that excess of Ca(OH)2 could cause hardness, hence the amount added is measured.
Chemical Water Softeners which lead to precipitation - these are chemical substances added to the water to remove dissolved calcium, magnesium or iron(II) salt by forming precipitate or undissolved solids. The precipitate is then removed by filtration.
Calcium hydroxide, Ca(OH)2 - addition of calculated amount of Ca(OH)2 will remove only temporary hardness from water. Ca(OH)2 precipitates the insoluble trioxocarbonate(IV).
Example, Ca(OH)2(s) + Ca(HCO3)2(aq) → 2CaCO3(s) + 2H2O
Note: Ca(OH)2 is slightly soluble; Ca(HCO3)2 is soluble; CaCO3is insoluble.
Also, notice that excess of Ca(OH)2 could cause hardness, hence the amount added is measured.
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