3 Hard waterGroundwater dissolves rocks and minerals releasing calcium, magnesium, and other ions that cause water to be hard. These dissolved ions give hard water its characteristics.
4 Hard water"Water that produces curd with soap and produces very little lather is called hard water.Hard water affects cleaning ability of soap."Hard water contains bicarbonate, chlorides and sulphates ( any one or all ) of calcium and magnesium .
5 Soft water"Water that produces lather with soap easily is called soft water.Soft water does not affect cleaning action of soap"
8 TEMPORARY HARD WATER Mg(HCO3)2 è Mg+2 +2HCO3-1 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.Mg(HCO3)2 è Mg+2 +2HCO3-1Ca(HCO3)2 è Ca+2 + 2HCO3-1
9 PERMANENT HARD WATERWater that contains chlorides or sulphates of calcium or magnesium or of both is called Permanent water.CaCl2è Ca+2 + 2Cl-1MgSO4 è Mg+2 + SO4-2These compounds are soluble in water and produce corresponding ions.
11 There are two methods to remove hardness of water CLARK'S METHOD.ION-EXCHANGE METHOD.
12 CLARK'S METHODIn 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.Ca(HCO3)2 + Ca(OH)2 è 2CaCO3 + 2H2OMg(HCO3)2 + Ca(OH)2 è CaCO3 + MgCO3 + 2H2O
13 ION-EXCHANGE METHODIn 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.Ca+2 + Na2-zeolite è Ca-zeolite + 2Na+1Mg+2 +Na2-zeolite è Mg-zeolite + 2Na+1
23 Some people prefer the taste. Calcium ions in the water are good for children's teeth and bones.It helps to reduce heart disease.Some brewers prefer using hard water for making beer.A coating of limescale inside copper pipes, or especially old lead pipes, stops poisonous salts dissolving into water.
24 summaryHard water contains calcium ions, Ca2+(aq), or magnesium ions, Mg2+(aq). These ions react with soap, making it difficult to form a lather and producing scum. Hard water can be softened by adding calcium hydroxide which makes insoluble carbonates which are separated by filtration . Alternatively, the hard water can be passed through an ion-exchange resin in a column. Sodium ions replace the calcium ions in the water as it passes through the column.
25 Resources www.tutorvista.com www.citycollegiate.com en.Wikipedia.orgText books by sindh text book board