1. HARD WATER AND SOFT WATER
Soft water- Gives ready and permanent lather with soap
Eg: rain water , distilled water
Hard water- Does not give ready and permanent lather with soap
Eg- sea water, river water, tap water

2. Hard 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.

3. Hardness 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.

4. Removal of Temporary Hardness
Boiling- on boiling the bicarbonates of Ca and Mg decompose into insoluble carbonates, removed by filtration.
Ca(HCO3 )2  CaCO3 +CO2 + H2O
Mg(HCO3 )2  MgCO3 +CO2 + H2O
b)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 + 2H2O
Mg(HCO3 )2 + Ca(OH)2  2 CaCO3 + Mg(OH)2 +2H2O

5. Removal of Permanent Hardness
By adding washing soda- Ca and Mg ions are precipitated as insoluble carbonates which are removed by filtration
CaCl2 + Na2CO3 CaCO3 +2NaCl
MgSO4+ Na2CO3  MgCO3 +Na2SO4
b) Ion-exchange method- the ions responsible for hardness are exchanged with ions which do not cause precipitation.
1.Inorganic ion exchange(permutit) method
2.Organic ion exchangers ( ion exchange resins)

6. Permutit method
Sodium 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+

7. Organic 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)

8. Method
When 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.

9. The exhausted cation exchange resin is regenerated by treatment with moderately conc. Sulphuric acid and the anion exchange resin with moderately conc. Sodium hydroxide solution.

10. c) 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 NaCl
2MgSO4 + Na2[Na4(PO3)6] Na2[Mg2(PO3)6]+4 Na2SO4

11. Disadvantages 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.