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Note on Removal of Hardness of Water

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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.

  • 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
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Very Short Questions

The temporary hardness of water is caused by calcium and magnesium bicarbonate.

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

Slaked lime converts bicarbonates of calcium and magnesium into carbonates which removetemporary 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.

Slaked lime water of process removing hardness of water called Clark's process.

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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  • Temporary hardness can be removed by

    hydrolith
    epsom salt
    plaster of paris
    slaked lime
  • Temporary hardness can be removed from water by adding

    HCl
    Ca(HCO3)2
    Ca(OH)2
    H2SO4
  • Tem porary hardness of water is due to the presence of

    H2SO4
    Ca(HCO3)2
    Ca(OH)2
    HCl
  • Temporary hardness is removed by

    Permutit process
    Organic ion exchange
    Soda lime process
    Clark's method
  • Temporary hardness is due to presence of

    sulphates of Ca and Mg


    bicarbonates of Ca and Mg


    bicarbonates of Cl and Mg


    sulphates of Ca and Cl


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