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HARD
WATER
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"Water
that produces curd with soap and produces very little lather
is called hard water. Hard water affects cleaning ability of soap." |
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| Hard water contains bicarbonate, chlorides and sulphates ( any one or all ) of calcium and magnesium . | |||
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SOFT
WATER
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"Water
that produces lather with soap easily is called soft water.
Soft water does not affect cleaning action of soap" |
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TYPES
OF HARD WATER
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| There
are two types of hard water. 1. Temporary hard water 2. Permanent hard water |
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TEMPORARY
HARD WATER
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| "Water that contains bicarbonate of calcium and magnesium or of both is called temporary hard water." | |||
| These bicarbonate are soluble in water and produce corresponding ions. | |||
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Mg(HCO3)2
è Mg+2
+2HCO3-1
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Ca(HCO3)2
è Ca+2
+ 2HCO3-1
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PERMANENT
HARD WATER
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| Water that contains chlorides or sulphates of calcium or magnesium or of both is called Permanent water. | |||
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CaCl2è
Ca+2 + 2Cl-1
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MgSO4
è Mg+2
+ SO4-2
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| These compounds are soluble in water and produce corresponding ions. | |||
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REMOVAL
OF HARDNESS OF WATER
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| Hardness of water can be removed by the following two methods: | |||
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CLARK'S
METHOD
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| In Clark’s method a calculated amount of calcium hydroxide Ca (OH)2 is added to hard water. Due to reaction, insoluble carbonates are obtained which are separated by filtration. | |||
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Ca(HCO3)2
+ Ca(OH)2 è 2CaCO3
+ 2H2O
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Mg(HCO3)2
+ Ca(OH)2 è
CaCO3 + MgCO3 + 2H2O
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ION-EXCHANGE
METHOD
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| In this method sodium zeolite is used as ion-exchanger. Na-zeolite is passed through the pipes containing hard water. Sodium zeolite is converted into calcium-zeolite or magnesium-zeolite. These are insoluble in water and are separated from water by filtration. | |||
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Ca+2
+ Na2-zeolite è
Ca-zeolite + 2Na+1
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Mg+2
+Na2-zeolite è
Mg-zeolite + 2Na+1
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DISADVANTAGE
OF HARD WATER
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| Domestic: Hard water affect cleaning ability of soap. When hard water is used for washing, large amount of soap is consumed. Industrial: Hard water can cause "Scaling" inside the pipes that transport water . Therefore if we use hard water in turbines and heat exchangers, their pipes will be corroded Health: Hard water when used for drinking for long period can lead to stomach disorders. Especially hard water contains magnesium sulphate can weaken the stomach permanently. |
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