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Chemistry

Temporary hardness in water can be removed by boiling. Give balanced equations to explain how, hardness in temporary hard water is removed by boiling.

Water

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Answer

Temporary hardness in water is due to the presence of calcium or magnesium bicarbonates.

On boiling temporary hard water, calcium and magnesium bicarbonates in water decompose to give insoluble carbonates, carbon dioxide and water.

The insoluble carbonates are filtered out, CO2 gas escapes and water is rendered soft.

Ca(HCO3)2Calcium bicarbonateBoilCaCO3Calcium carbonate+H2O+CO2[g]\underset{\text{Calcium bicarbonate}}{\text{Ca(HCO}3)2}\xrightarrow{\text{Boil}} \underset{\text{Calcium carbonate}}{\text{CaCO}3↓} + \text{H}2\text{O} + \text{CO}_2 [\text{g}]

Mg(HCO3)2Magnesium bicarbonateBoilMgCO3Magnesium carbonate+H2O+CO2[g]\underset{\text{Magnesium bicarbonate}}{\text{Mg(HCO}3)2}\xrightarrow{\text{Boil}} \underset{\text{Magnesium carbonate}}{\text{MgCO}3↓} + \text{H}2\text{O} + \text{CO}_2 [\text{g}]

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