>> Study Material
>> IIT JEE Chemistry
>> Physical Chemistry
>> Ionic Equilibrium
>> Applications of Solubility Product-Part1
Applications of Solubility Product
(i) Purification of common salt
Natural common salt consists of many insoluble and soluble impurities. Saturated solution of common salt is prepared and insoluble impurities are filtered off. Hydrogen chloride gas (HCl) is circulated through the saturated solution. HCl and NaCl dissociate into their respective ions as:
NaCl ↔ Na+ + Cl-
HCl ↔ H+ + Cl-
The concentration of Cl- ions increases considerably in solution due to ionization HCl. Hence, the ionic product [Na+][Cl-] exceeds the solubility product of sodium chloride and, therefore, pure sodium chloride precipitates out from solution.
(ii) Salting out of soap
Soap is a sodium salt of higher acids. From the solution, soap is precipitated by the addition of concentrated solution of sodium chloride. Soap and sodium chloride are present in the form of ions.
CnH2n+1 COONa ↔ CnH2n+1 COO- + Na+
NaCl ↔ Na+ + Cl-
Thus, the concentration of Na+ ions increases considerably on addition of NaCl solution. Hence, the ionic product [CnH2n+1COO-] [Na+] exceeds the solubility product of soap and, therefore, soap precipitates out from the solution.
(iii) Manufacture of sodium bicarbonate (baking soda):
In Solvay's soda process. CO2 gas is passed through ammonical brine to precipitate out NaHCO3.
NH4OH + CO2 → NH4HCO3
NH4HCO3 + NaCl → NaHCO3 + NH4Cl
NaHCO3 is precipitated first because of its lower solubility product as compared to those of NH4Cl, NH3HCO3 and NaCl.
Thus, baking soda (NaHCO3) can be quantifiably estimated.
(iv) Application of solubility product in quantitative analysis
1. Estimation of barium as barium sulphate:
H2SO4 as precipitating agent is added to the aqueous solution of BaCl2.
BaCl2 + H2SO4 → BaSO4 + 2HCl
Precipitation of BaSO4 takes place when its ionic product exceeds solubility product. H2SO4 is added in slight excess to ensure complete precipitation. Large excess of H2SO4 is harmful for complex formation.