Boiling : You already know that temporary hardness is causes due to dissolved bicarbonates of calcium and magnesium.
Boiling is a method of removal of temporary hardness.
When water is boiled, the bicarbonates that cause temporary hardness are converted into insoluble carbonates, leading to the removal of Ca++ and Mg++ from water.
Boiling is a method of removal of temporary hardness.
When water is boiled, the bicarbonates that cause temporary hardness are converted into insoluble carbonates, leading to the removal of Ca++ and Mg++ from water.
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| Calcium and Magnesium carbonate reaction with water |
The precipitates that are formed are removed by filtering.
Boiling is the easiest method of softening a small quantity of water.
Softening a large quantity of water by boiling is highly expensive.
The Process is also time consuming.
Temporary hardness is rare.
Boiling removes the bicarbonate component only.
Therefore, we need to consider other methods of softening.
Boiling is the easiest method of softening a small quantity of water.
Softening a large quantity of water by boiling is highly expensive.
The Process is also time consuming.
Temporary hardness is rare.
Boiling removes the bicarbonate component only.
Therefore, we need to consider other methods of softening.
Do if yourself
It the water you use at home is hard, can it be softened by boiling ? Boil and examine.
Methods of removal of permanent hardness.
1. Distillation :
Water obtained from any source. However hard it may be, can be softened by distillation. Distilled water is both soft and pure. The condensation of water vapours produced on heating is the principle involved in this process. This method removes both temporary and permanent hardness.
Think it over
Why is the process purification of seawater through distillation not so feasible ?
2. Soda process :
Both temporary hardness and permanent hardness of water can be removed by adding sodium carbonate.
This method is called Soda process.
Sodium carbonate reacts with salts that causes hardness to give their respective carbonates.
The following chemical equations clarify these reactions.
This method is called Soda process.
Sodium carbonate reacts with salts that causes hardness to give their respective carbonates.
The following chemical equations clarify these reactions.
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| Different Chemical reacts with salt equation. |
The insoluble carbonates present in the softened water are removed by filtration.
The water softened by this method.
However, contains salts such as sodium sulphate, sodium chloride and so on.
The presence of these salts does not pose serious problems.
These salts do not come in the way of formation of lather with soap.
3. Permutit process :
The water softened by this method.
However, contains salts such as sodium sulphate, sodium chloride and so on.
The presence of these salts does not pose serious problems.
These salts do not come in the way of formation of lather with soap.
3. Permutit process :
Permutit is used in softening hard water.
Naturally occurring sodium aluminium silicate is called zeolite.
This compound can also be prepared artificially. Artificially prepared sodium aluminium silicate is called permutit.
Permutit is prepared by heating quartz, sand, china clay and sodium carbonate.
Fusing sodium silicate and sodium aluminates is another method of preparing permutit.
Permutit is in the from of a porous gel.
The principle involved in this process is to convert the dissolved salts of calcium and magnesium into insoluble calcium and magnesium permutits, respectively.
This is done by exchanging the base ion radicals such as Ca++ and Mg++ with the base ion Na+ of sodium aluminium silicate.
Hence this process is also known as ‘base exchange process’.
Naturally occurring sodium aluminium silicate is called zeolite.
This compound can also be prepared artificially. Artificially prepared sodium aluminium silicate is called permutit.
Permutit is prepared by heating quartz, sand, china clay and sodium carbonate.
Fusing sodium silicate and sodium aluminates is another method of preparing permutit.
Permutit is in the from of a porous gel.
The principle involved in this process is to convert the dissolved salts of calcium and magnesium into insoluble calcium and magnesium permutits, respectively.
This is done by exchanging the base ion radicals such as Ca++ and Mg++ with the base ion Na+ of sodium aluminium silicate.
Hence this process is also known as ‘base exchange process’.
This is carried out by passing hard water through the layers of zeolite or permutit. This method removes both temporary hardness and permanent hardness.
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| Permutit process removes temp. as well as permanent hardness. |
In the permutit process, there will be a column in which gravel, sand and permutit are placed in alternate layers.
Hard water is made to rise up through the various layers.
As water passes through the permutit, the ions of calcium (Ca++) and magnesium (Mg++) which causes hardness are exchanged with the sodium ions of the permutit.
Permutit is changed eventually into calcium aluminium silicate and magnesium aluminium silicate.
These are called calcium permutit and magnesium permutit respectively. We shall discuss two examples to understand how this happens.
Hard water is made to rise up through the various layers.
As water passes through the permutit, the ions of calcium (Ca++) and magnesium (Mg++) which causes hardness are exchanged with the sodium ions of the permutit.
Permutit is changed eventually into calcium aluminium silicate and magnesium aluminium silicate.
These are called calcium permutit and magnesium permutit respectively. We shall discuss two examples to understand how this happens.
Sodium permutit + Calcium chloride " Calcium permutit + Sodium chloride
Sodium permutit + Magnesium sulphate " Magnesium permutit + Sodium sulphate
Water that comes out of the permutit column contains neither calcium ions nor magnesium ions.
However, the water softened by this method contains sodium ions.
The presence of these ions, however, will not make water hard.
Permutit process is an economical way of softening water.
The hardness is more or less completely removed by this method.
This method is not so appropriate if the hard water contains sodium salts or suspended matter in large quantities.
Lead, if present in water, is not removed in this method.
The permutit process is useless if the water contains iron or manganese impurities.
What we get through permutit process is only soft water and not pore water.
Justify
Pure water is soft However, soft water need not be pure. It this possible ? How ?
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