Types of Hardness in Water for std 8 to 10 GSEB CBSE Course.

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.

Pulses and vegetables are not cooked properly in hard water.

Hard water used for bathing makes the skin dry and leaves a whitish residue on the skin.

The utensils lose shine and get stained when washed with hard water.

Hard water is not suitable even for washing. Clothes are not cleaned in hard water.

Soap is also wasted.

The salts present in hard water from a yellow stain on clothes.

The salts accumulated on the inner walls of the cooking utensils makes their cleaning difficult.

It also wastes fuel energy.

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.

Hard water contains bicarbonates.

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.