When permanent hard water is treated with slaked lime or calcium hydroxide [Ca(OH)2], the calcium ions [Ca2+] in the water react with the hydroxide ions [OH-] in the slaked lime to form insoluble calcium carbonate [CaCO3] and water [H2O].
The chemical equation for this reaction is:
Ca2+ (aq) + 2OH- (aq) → Ca(OH)2 (s)
Ca2+ (aq) + 2OH- (aq) → Ca(OH)2 (s)Ca(OH)2 (s) + CO2 (g) → CaCO3 (s) + H2O (l)
The resulting calcium carbonate precipitates out of the water and can be removed by filtration or sedimentation, leaving the water softened.
When permanent hard water is treated with washing soda or sodium carbonate [Na2CO3], the calcium and magnesium ions [Ca2+ and Mg2+] in the water react with the carbonate ions [CO32-] in the washing soda to form insoluble calcium carbonate [CaCO3] and magnesium hydroxide [Mg(OH)2].
The resulting calcium carbonate and magnesium hydroxide can be removed by filtration or sedimentation, leaving the water softened.
In both cases, the addition of the slaked lime or washing soda to the hard water causes a chemical reaction that results in the removal of the calcium and magnesium ions, which are responsible for causing the hardness of the water.
Permanent hard water contains calcium and magnesium ions in the form of bicarbonates, sulfates, and chlorides.
When slaked lime (calcium hydroxide) is added to permanent hard water, the calcium and magnesium ions react with the hydroxide ions to form insoluble carbonates and hydroxides.
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Verified answer
When permanent hard water is treated with slaked lime or calcium hydroxide [Ca(OH)2], the calcium ions [Ca2+] in the water react with the hydroxide ions [OH-] in the slaked lime to form insoluble calcium carbonate [CaCO3] and water [H2O].
The chemical equation for this reaction is:
Ca2+ (aq) + 2OH- (aq) → Ca(OH)2 (s)
Ca2+ (aq) + 2OH- (aq) → Ca(OH)2 (s)Ca(OH)2 (s) + CO2 (g) → CaCO3 (s) + H2O (l)
The resulting calcium carbonate precipitates out of the water and can be removed by filtration or sedimentation, leaving the water softened.
When permanent hard water is treated with washing soda or sodium carbonate [Na2CO3], the calcium and magnesium ions [Ca2+ and Mg2+] in the water react with the carbonate ions [CO32-] in the washing soda to form insoluble calcium carbonate [CaCO3] and magnesium hydroxide [Mg(OH)2].
The chemical equation for this reaction is:
Ca2+ (aq) + CO32- (aq) → CaCO3 (s)
Ca2+ (aq) + CO32- (aq) → CaCO3 (s)Mg2+ (aq) + 2OH- (aq) → Mg(OH)2 (s)
The resulting calcium carbonate and magnesium hydroxide can be removed by filtration or sedimentation, leaving the water softened.
In both cases, the addition of the slaked lime or washing soda to the hard water causes a chemical reaction that results in the removal of the calcium and magnesium ions, which are responsible for causing the hardness of the water.
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SOLUTION
1) TREATED WITH SLAKED LIME
REACTION
[tex] \orange{ \sf \: Ca(HCO_3)_2 + Ca(OH)_2\:➞\:2CaCO_3 + 2H_2O }[/tex]
[tex] \orange{ \sf \: Mg(HCO_3)_2 + Ca(OH)_2 \: ➞ \: MgCO_3 + CaCO_3 + 2H_2O }[/tex]
2) TREATED WITH WASHING SODA
[tex] \orange{ \sf \: Ca(HCO_3)_2 + Na_2CO_3 \: ➞ \:CaCO_3 + 2NaHCO_3 }[/tex]
[tex] \orange{ \sf \: Mg(HCO_3)_2 + Na_2CO_3 \: ➞ \: MgCO_3 + 2NaHCO_3 }[/tex]