Permanent hardness is removed by :(a) Lime soda process(b) Boiling(c) Demineralisation process(d) Base exchange processa)(a) onlyb)(b) onlyc)All of the aboved)(a), (c) and (d) onlyCorrect answer is option 'D'. Can you explain this answer?

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Permanent hardness is removed by :
(a) Lime soda process
(b) Boiling
(c) Demineralisation process
(d) Base exchange process

a)
(a) only
b)
(b) only
c)
All of the above
d)
(a), (c) and (d) only

Correct answer is option 'D'. Can you explain this answer?

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Permanent hardness is removed by :(a) Lime soda process(b) Boiling(c) ...

The hardness of water:

Hardness in water is that characteristic which prevents the formation of sufficient leather or foam when such hard water is mixed with soap.
It is usually caused by the presence of calcium and magnesium salts present in water, which form scum by reaction with soap.

Water softening:

The process of removal of hardness from water is known as Water softening.

Removal of hardness;
1. Temporary hardness:

The temporary or carbonate hardness is caused by carbonates and bicarbonates of Ca and Mg or bivalent cations.

The methods of removing temporary hardness:

Boiling
Addition of lime.

2. Permanent hardness:
The permanent or non-carbonate hardness, which is caused by the sulphates, chlorides and nitrates of Ca and Mg is removed by special methods.
The methods of removing permanent hardness

Lime soda process
Base exchange process
Demineralization

Lime Soda Process

Chemicals normally used are lime {calcium hydroxide, Ca(OH)₂} and soda ash (sodium carbonate, Na₂CO₃).
Lime is used to remove chemicals that cause carbonate hardness.
Soda ash is used to remove chemicals that cause non-carbonate hardness.
Lime soda softening cannot produce water completely free of hardness because of the solubility of CaCO₃ and Mg(OH)2.
Thus the minimum calcium hardness that can be achieved is about 30 mg/L as CaCO₃, and the magnesium hardness is about 10 mg/L as CaCO₃.

Ion-exchange method:

This method is also called the zeolite/permutit process.
In this method, the permanent hardness of water is removed by using resins.
Ca⁺⁺/Mg⁺⁺ ions are exchanged with Cl-, SO^-2₄ ions are exchanged with anion exchange resin (RNH₂OH).
Demineralized water is formed in this process.
Hydrated sodium aluminium silicate is zeolite/permutit.
For the sake of simplicity, sodium aluminium silicate (NaAlSiO₄) can be written as NaZ.
When this is added to hard water, exchange reactions take place.

Permanent hardness can also be removed by:-
Treatment with washing soda (sodium carbonate):-

Washing soda reacts with soluble calcium and magnesium chlorides and sulphates in hard water to form insoluble carbonates.
Sodium carbonate is water-soluble in nature and hence, adds a large number of carbonate ions to the water.
Because of this, the calcium ions come from hard water and the carbonate ions from sodium carbonate.

Note: Permanent Hardness is not removed by Boiling.

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Permanent hardness is removed by :(a) Lime soda process(b) Boiling(c) Demineralisation process(d) Base exchange processa)(a) onlyb)(b) onlyc)All of the aboved)(a), (c) and (d) onlyCorrect answer is option 'D'. Can you explain this answer?

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