Removal of Hardness of Water
Subject: Science
Overview
Heating and treatment with lime water can remove temporary hardness of water. But permanent hardness is removed by treating water with washing soda or permutit method. This note provides us the information about Removal of Temporary Hardness.Removal of Hardness of Water
Removal of Temporary Hardness
Temporary hardness present in the water can be removed by using the following methods: -
By heating:
Salts like calcium bicarbonate and magnesium bicarbonate, when dissolved in water causes temporary hardness. While heating, soluble salts of calcium and magnesium (bicarbonates) change into insoluble salts. The chemical equations are as follows:
Calcium bicarbonate → Calcium carbonate + Carbon dioxide + Water
Ca(HCO3)2 → CaCO3 + CO2 + H2O
Magnesium bicarbonate → Magnesium carbonate + Carbon dioxide + Water
Mg(HCO3)2 → MgCO3 + CO2 + H2O
Treating with lime water:
The temporary hardness of water can be removed by treating it with lime water. The chemical equations are as follows:
Calcium Bicarbonate + Calcium Hydroxide → Calcium Carbonate + Water
Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 + 2H2O
Magnesium Bicarbonate + Calcium Hydroxide → Calcium Carbonate + Magnesium Carbonate + Water
Mg(HCO3)2 + Ca(OH)2 → CaCO3 + MgCO3 + 2H2O
Removal of Permanent Hardness
Permanent hardness cannot be removed by heating only. Soluble salts of calcium and magnesium are turned to insoluble salts by the following methods.
Treatment with washing soda
Soluble salts of calcium and magnesium change into insoluble salts due to the treatment with sodium carbonate (washing soda).
Calcium Chloride + Sodium Carbonate → Calcium Carbonate + Sodium Chloride
CaCl2 + Na2CO3 → CaCO3 + 2NaCl
Magnesium Sulphate + Sodium Carbonate → Magnesium Carbonate + Sodium Sulphate
MgSO4 + Na2CO3 → MgCO3 + Na2SO4
Permutit Process:
Permutit is the trade name for an artificially prepared sodium zeolite or sodium aluminium orthosilicate obtained by fusing together sodium carbonate silica and alumina. Its composition resembles Na2Al2SiO8 or Na2Z, where, Z stands for Zeolite = Al2SiO8. It possesses the higher quality of reactivity with calcium and magnesium ions forming insoluble calcium or magnesium zeolites.
2Na2Z + Ca++ → CaZ2 +4Na
Thus by passing hard water through a cylinder packed with permutit, all the ions of soluble salts of calcium and magnesium responsible for the hardness of water are retained and replaced by sodium ions. In due course, however, the permutit is exhausted or losses its capacity of reacting with these salts by having given up all its sodium ions. This can be regenerated by soaking in a 10% solution of common salt when the reverse change takes place and calcium and magnesium ions pass into solution and sodium zeolite is formed again.
CaZ2 + 2NaCl → Na2Z + CaCl2
MgZ2 + 2NaCl → Na2Z + MgCl2
The resulting calcium and magnesium chlorides are washed out and the regenerated permutit is used over again.
Things to remember
- Salts like calcium bicarbonate and magnesium bicarbonate when dissolved in water causes temporary hardness.
- Temporary hardness present in the water can be removed by heating hard water and treating it with lime water.
- Permanent hardness present in the water can be removed by treating it with soda water and using permutit process.
- Soluble salts of calcium and magnesium change into insoluble salts due to the treatment with sodium carbonate (washing soda).
- Permutit is the trade name for an artificially prepared sodium zeolite or sodium aluminium orthosilicate obtained by fusing together sodium carbonate silica and alumina
- It includes every relationship which established among the people.
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Questions and Answers
What causes temporary hardness of water?
The temporary hardness of water is caused by calcium and magnesium bicarbonate.
How can boiling water remove temporary hardness?
On heating temporary hard water, the soluble salts like calcium bicarbonate and magnesium bicarbonate get changed into insoluble carbonate salts and these settle down to the bottom of the container and can be filter away. Example: Ca (HCO3)2 →CaCO3 + CO2+ H2O
How can slake lime can remove temporary hardness?
Slaked lime converts bicarbonates of calcium and magnesium into carbonates which removetemporary hardness of water.
What is the temporary hardness of water?
The temporary hardness of water is thehardness of thewater which is caused due to the presence of soluble bicarbonates of calcium and magnesium which can be removed by boiling.
What is slaked lime process of removing hardness of water called?
Slaked lime water of process removing hardness of water called Clark's process.
How permanent hardness of water be removed by washing soda?
Soluble salts of calcium and magnesium change into insoluble salts due to the treatment with sodium carbonate (washing soda).
Calcium Chloride + Sodium Carbonate → Calcium Carbonate + Sodium Chloride
CaCl2 + Na2CO3 → CaCO3 + 2NaCl
Magnesium Sulphate + Sodium Carbonate → Magnesium Carbonate + Sodium Sulphate
MgSO4 + Na2CO3 → MgCO3 + Na2SO4
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