METHODS OF SOFTENING HARD WATER, std 8 to 10 CBSE

Methods of removal of temporary hardness.

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.

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.

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. 

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 : 

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’.

This is carried out by passing hard water through the layers of zeolite or permutit. This method removes both temporary hardness and permanent hardness.

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.

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 ?

Types of hardness, water for std 8 to 10 CBSE

TYPES OF HARDNESS
Depending on the kind of negative ions present along with Mg++ and Ca++ ions, hard water is classified into two types namely temporary hard water and permanent hard water.
The water that contains bicarbonate ions along with Mg++ and Ca++ ions could be softened by mere boiling. Hence, such water is called temporary hard water.
The water that contains chloride or sulphate ions along with Mg++ and Ca++ ions is called permanent hard water.
This means the hardness causes by dissolved magnesium bicarbonate and calcium bicarbonate is temporary hardness.
The hardness caused by dissolved magnesium chloride, calcium chloride, magnesium sulphate or calcium sulphate is called permanent hardness.
Water samples may contain more that one salt that causes hardness.

DISADVANTAGES OF HARD WATER
We use water daily for a number of activities such as washing clothes, cleaning utensils, bathing, drinking, cooking and so on.
Hard water is not so suitable for these activities.

1. Pulses and vegetables are not cooked properly in hard water.
2. Hard water used for bathing makes the skin dry and leaves a whitish residue on the skin.
3. The utensils lose shine and get stained when washed with hard water.
4. Hard water is not suitable even for washing. Clothes are not cleaned in hard water.
5. Soap is also wasted.
6. The salts present in hard water from a yellow stain on clothes.
7. The salts accumulated on the inner walls of the cooking utensils makes their cleaning difficult.
8. It also wastes fuel energy.

Hard water causes in Industrial pipe lines etc.

Video presentation 

how hard water develops insoluble carbonates in pipes 

• Hard water poses many problems in industries such as paper, dye, printing, textiles, sugar etc.
• Hard water forms a scale on the inner walls of industrial boilers.
• Why does hard water causes scales on the walls of boilers ?
• Hard water usually contains dissolved bicarbonates.
• The dissolved bicarbonates, on boiling, dissociate to form insoluble carbonates which go on depositing on the inner walls of the boiler.
• This results in scaling.
• The scale not only corrodes the boiler but wastes fuel as well.
• Hard water sometimes causes foaming and explosions of the boiler. 
• The scales formed inside the pipes reduce the size of the pipes and corrode them (fig). 
• Therefore hard water is not suitable for use in boilers.
• Hence we need to soften water and then use it. 
• There are many methods of softening water.
• Some methods remove only temporary hardness while others remove both types of hardness.

Activity
Take some amount of hard water in a glass beaker and boil it. Allow the water to cool. Observe the walls of the beaker closely. Repeat the experiment with soft water. What difference do you notice ? Why ? Explain.

Examining impurities in glass