common ion effect

1. COMMON ION
EFFECT
MAIN POINTS ARE:

2. DEFINITIONS
The solubility of an ionic precipitate
decreases when a soluble compound
containing one of the ions of the
precipitate is added to the solution.
Hg2Cl2 (s) Hg2+2 + 2Cl-
The shifts in equilibrium that occurs
because of the addition of an ion
already involved in the equilibrium
reaction.
AgCl(s) Ag+(aq) + Cl-(aq)

3. Explanation of an example:
A saturated solution of calcium sulphate. CaSO4(s) Ca2+(S) + 2Cl-
 Ksp = [Ca2+] [SO42-] = 2.4 into 10-3 mol dm-6 at 298K
When a solution that contains the same ion is added to the
saturated CaSO4 solution for e:g dilute H2SO4 : equilibrium shift to left,CaSO4 will
precipitate out.
In presence of the additional COMMON ION (SO42-) the CaSO4 becomes less
soluble. In solution ca ions are used and CaSO4 will precipitate out.

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6. PARTCIPATION
OF COMMON
ION EFFECT
PARTICIPATION OF COMMON ION EFFECT
OF CRUDE COMMON SALT:
The PURIFICATION common ion effect can
make insoluble substances more insoluble.
An example of common ion effect is when
sodium chloride is added to a solution
Of HCl and water. The hydrochloric acid and
water are in equilibrium with the products
Being H3O+ and Cl-. Then some sodium chloride
is added to the solution.
HCl(g) + H2O H3O+ + Cl-

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8. SALTING – OUT OF SOAP:
The salting out process used in the manufacturing of soaps benefits
from the common ion
Effect. Soaps are sodium salts of fatty acids. Addition of sodium
chloride reduces the solubility
Of soap salts. In the presence of excess Na+ the reduced making the
soap less effective.
RCOONa Na+ + RCOO-
NaCl Na+ + Cl-

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