Presentation on theme: "HARD WATER AND SOFT WATER"— Presentation transcript:
1HARD WATER AND SOFT WATER Soft water- Gives ready and permanent lather with soapEg: rain water , distilled waterHard water- Does not give ready and permanent lather with soapEg- sea water, river water, tap water
2Hard water does not give ready lather with soap. WHY ? Soaps are sodium salt of higher fatty acids. They react with Ca and Mg ions present in hard water to form salts and produce a curdy precipitate.Hence they are not suitable washing purposes.
3Hardness of water of two types Temporary Hardness- Can be easily removed by simply by boiling. Due to the presence of bicarbonates of Ca and Mg dissolved in it.Permanent hardness- cannot be easily removed. Due to the presence of chlorides and sulphates of Ca and Mg dissolved in water.
4Removal of Temporary Hardness Boiling- on boiling the bicarbonates of Ca and Mg decompose into insoluble carbonates, removed by filtration.Ca(HCO3 )2 CaCO3 +CO2 + H2OMg(HCO3 )2 MgCO3 +CO2 + H2Ob)Clark’s Process-Lime is added to precipitate out as Calcium carbonate and Magnesium hydroxide which are removed by filtration.Ca(HCO3 )2 + Ca(OH)2 2 CaCO3 + 2H2OMg(HCO3 )2 + Ca(OH)2 2 CaCO3 + Mg(OH)2 +2H2O
5Removal of Permanent Hardness By adding washing soda- Ca and Mg ions are precipitated as insoluble carbonates which are removed by filtrationCaCl2 + Na2CO3 CaCO3 +2NaClMgSO4+ Na2CO3 MgCO3 +Na2SO4b) Ion-exchange method- the ions responsible for hardness are exchanged with ions which do not cause precipitation.1.Inorganic ion exchange(permutit) method2.Organic ion exchangers ( ion exchange resins)
6Permutit methodSodium aluminium silicate (Na2Al2Si2O8.x.H2O) are known as zeolites or permutit.(Na2 Z). When hard water is passed through zeolites , Na+ ions from zeolites repalce Ca2+ and Mg2+ ions from hard water.Na2 Z + Ca2+ Ca Z +2 Na+Na2 Z + Mg2+ Mg Z +2 Na+
7Organic ion exchangers Organic polymers having –COOH or –SO3H or–NH3+OH- groups act as ion exchange resins.These are of two types.Cation ion exchange resin ( Resin-H)Anion ion exchange resin ( Resin –OH)
8MethodWhen hard water is passed through tanks filled with resins successively , the resins exchange the ions which cause hardness.2Resin-H + Ca2+ (Resin)2 Ca+ 2 H+Resin-OH + Cl - Resin- Cl + OH-2Resin-OH + SO (Resin)2 SO OH-OH- ions liberated from anion exchange resin, neutralise H+ ions from cation exchange resin.
9The exhausted cation exchange resin is regenerated by treatment with moderately conc. Sulphuric acid and the anion exchange resin with moderately conc. Sodium hydroxide solution.
10c) Calgon process Calgon (Sodium hexameta phosphate [(NaPO3)6]) React with Ca or Mg ions to form soluble complex salts. Na+ ions repalce Ca2+ and Mg2+ ions. Hence they are not available as free ions to cause hardness.2CaCl2 + Na2[Na4(PO3)6] Na2[Ca2(PO3)6]+ 4 NaCl2MgSO4 + Na2[Na4(PO3)6] Na2[Mg2(PO3)6]+4 Na2SO4
11Disadvantages of Hard Water 1.Not suitable for laundry work ( wastage of soap and poor cleaning)2.Ca carbonate or sulphate deposit in boilers. More fuel is consumed for heating water.3.Corrodes boiler.