Cation Exchange Resin

• An ion is an atom or molecule that has a net electrical charge.The positively charged ions are called cations while the negatively charged ions are called anions.The number of positive charge is equal to the number of negative charge.Soluble ionized substances can be removed by ion exchange. 
• An ion exchange resin is a very small plastic bead with a diameter 0.6 mm are porous and contain invisible water in the beads
• The structure of the resin is a polymer on which a fixed ion has been permanently attached. This ion cannot be removed or displaced as it is a part of the structure..
• Cation exchange resins are phenol aldehyde condensation products, which on sulphonation produce resinous mass having base exchange properties.
• The water coming out of cation-exchanger contains dilute carbonic acid, hydrochloric acid, sulphuric acid etc which can be removed by passing the water through of anion-exchange resin.
• The chemical reactions involved in the process are shown below:

Ca(HCO3)2 + H2R -->  CaR + 2H2O + 2CO2

CaCl2 + H2R --> CaR + 2HCl

MgSO4 + H2R --> MgR + H2SO4

2NaCl + H2R -->  Na2R + 2HCl

H2R is a generic manner of representing cation exchange resins where H represents the Hydrogen ions and R represents the organic part of the substance. From tje reactions listed above, it is evident that the water coming out of the cation-exchanger contains Carbonic acid, Hydrochloric acid, Sulphuric acid, etc. These can be removed by passing the water through a bed of anion exchange resin