Page 86 - Chemistry ICSE Class IX
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74 ICSE Chemistry – 9
Soft water when passed through pipe lines does not leave mineral
deposits on the inner surfaces of the pipes. This allows pipelines
to remain undamaged.
Disadvantages of soft water. Soft water is almost totally devoid of
essential minerals, such as calcium and magnesium. This de ciency
of minerals is known to have caused heart ailments and/or coronary
diseases.
What do you mean by hard water
Water which does not form lather with soap or soap solution is called hard
water. Hard water forms curdy precipitate with soap.
Hardness of water is due to the presence of dissolved calcium and
magnesium bicarbonates, sulphates and chlorides in it.
Advantages of Hard Water. The National Academy of Sciences
suggest that somewhat hard water is good for health because it
supplements the required minerals like calcium and magnesium.
Disadvantages of Hard Water.
Hard water does not give quick and good lather with soap.
Hard water leaves some minerals on the skin, leading to dryness
and roughness. Such invisible layer of minerals prevent the
removal of harmful bacteria from the skin while washing. The
soap curd left behind may cause skin irritation and eruption.
Minerals in hard water combine with dirt in clothes and cannot be
removed easily during next wash.
Washing hair with hard water leads to reddish ting in tresses
which is dif cult to remove.
The pipes through which hard water is passed have to be replaced
more often. This is due to deposit of hard layer of minerals on its
inner walls, which ultimately leads to choking and corroding of
the pipe.
If hard water is used in boilers, lime scale is formed on the inner
wall of the boilers. This increases the consumption of electricity. So,
the use of hard water in boilers increases expenditure. Apart from
it, the boiler’s body get corroded and hence require replacement
of boilers.
Considering the advantages and disadvantages of soft water and hard
water, an ideal water should be a combination of both soft and hard water.
Types and Causes of Hardness
There are two types of hardness of water: Temporary hardness and
Permanent hardness.
Temporary hardness. Water is said to be temporary hard
when it contains calcium and magnesium bicarbonates [or
hydrogencarbonates, Ca(HCO ) , Mg(HCO ) ]. This type of hardness
3 2
3 2
can be easily removed simply by boiling.
boil
Ca(HCO ) (aq) o CaCO (s)p + H O(l) + CO (g)
3 2
2
2
3
Permanent hardness. Water is said to be permanent hard when it
contains sulphates and chlorides of calcium and magnesium, (CaCl ,
2
CaSO , MgCl , MgSO ). Permanent hardness cannot be removed by
4
2
4
boiling. Permanent hardness can be removed by adding washing
soda solution (dropwise) to the water.
