In a village, on analysis of bore well water it has been found to contain impurities such as permanent and temporary Ca 2+ , Mg 2+ , Acids, CO 2 and H 2 S. Suggest the method for softening of this water by using lime and soda with chemical reactions involved in it.
Question
In a village, on analysis of bore well water it has been found to contain impurities such as permanent and temporary Ca 2+ , Mg 2+ , Acids, CO 2 and H 2 S. Suggest the method for softening of this water by using lime and soda with chemical reactions involved in it.
Solution
The process of softening hard water involves the removal of calcium (Ca2+) and magnesium (Mg2+) ions. Lime and soda are commonly used for this purpose. Here's how it works:
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Lime-Soda Process: This is the most commonly used method for softening of permanent hardness of water. The process involves the addition of calculated quantities of lime (Ca(OH)2) and soda (Na2CO3).
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Lime is used to remove the temporary hardness while soda is used to remove the permanent hardness.
The chemical reactions involved are as follows:
For Temporary Hardness (due to the presence of Ca(HCO3)2 and Mg(HCO3)2):
Ca(HCO3)2 + Ca(OH)2 → 2CaCO3↓ + 2H2O Mg(HCO3)2 + 2Ca(OH)2 → 2CaCO3↓ + Mg(OH)2↓ + 2H2O
For Permanent Hardness (due to the presence of CaCl2, MgCl2, CaSO4, MgSO4):
CaCl2 + Na2CO3 → CaCO3↓ + 2NaCl MgCl2 + 2NaOH → Mg(OH)2↓ + 2NaCl CaSO4 + Na2CO3 → CaCO3↓ + Na2SO4 MgSO4 + 2NaOH → Mg(OH)2↓ + Na2SO4
The precipitates of CaCO3 and Mg(OH)2 are removed by filtration.
For the removal of gases like CO2 and H2S, aeration can be used. Aeration is a simple process where water is brought in contact with air which leads to the escape of gases.
CO2 + Ca(OH)2 → CaCO3↓ + H2O H2S + 2H2O → 2H2O + SO2↑
The precipitate of CaCO3 is removed by filtration. The SO2 gas escapes into the air.
This is a basic overview of the process. The actual implementation would require careful monitoring and control to ensure the correct amounts of lime and soda are used, and that the process is carried out safely.
Similar Questions
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You want to test for hardness of water but hard water is not available inthe laboratory. Which of the following compounds may be dissolved inpure water to make it hard ?(i) Hydrogen Carbonate of Sodium(ii) Sulphate of Magnesium(iii) Chloride of Calcium(iv) Carbonate of Sodium
Calculate quantities of lime and soda required for softening of 20,000 litres of water containing following salts in ppm (16.4 ppm NaAlO2 used as a coagulant) Ca+2 = 160 ppm Mg+2 = 72 ppm HCO3 – = 73.2 ppm CO2 = 44 ppm Al2(SO4)3 = 34.2 ppm HCl = 36.5 ppm.a.Lime = 7.84 mg, Soda = 15.05 mgb.Lime = 7.84 g, Soda = 15.05 gc.None of thesed.Lime = 7.84 kg, Soda = 15.05 kg
The Lime-Soda process involves the addition of lime (calcium hydroxide) and soda ash (sodium carbonate) to hard water. The chemicals react with the calcium and magnesium compounds in the water, precipitating them as insoluble solids that can be removed by sedimentation and filtration.Process StepsPre-treatment: Raw water is screened to remove large particles and debris.Chemical Addition:Lime is added to the water to remove temporary hardness and part of the permanent hardness.Soda ash is added to remove the remaining permanent hardness.Mixing: The water is mixed thoroughly to ensure a complete reaction of the chemicals with the hardness ions.Sedimentation: The water is allowed to settle in sedimentation tanks where the precipitated calcium carbonate (CaCO₃) and magnesium hydroxide (Mg(OH)₂) settle out.Filtration: The clarified water is filtered to remove any remaining suspended particles.Post-treatment: The treated water may be further processed, such as disinfection or pH adjustment, before distribution.
A water sample using FeSO4.7H20 as a coagulant at the rate of 139 ppm, gave the following results for raw water: Ca2+=320 ppm; Mg2+=120 ppm, CO2=88ppm; HCO3-=732 ppm. Calculate the lime and soda required for softening of 1000 litres of raw water.
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