#common ion effect

[biology-geology-beaches-india]

The Science Research Diaries of S. Sunkavally. Page 169.

[whats-in-a-sentence]

The common ion effect is not limited to solutions of slightly soluble salts; for example, figure 10.17 shows that even the relatively soluble salt NaCl can be precipitated from solution on addition of concentrated HCl, a source of the common ion Cl-.

"Chemistry" 2e - Blackman, A., Bottle, S., Schmid, S., Mocerino, M., Wille, U.

[babewegotchemistry]

Solubility

Solubility, the ability of a species do dissolve in a liquid or aqueous solution, is quantifiable by equilibriums. Dissolution is a chemical reaction with the general formula

Solid (c) --> cation (aq) + anion (aq)

Taking the equilibrium expression of this gives us

K = ([cation][anion]) since pure solids are not involved in equilibria

Here we use K_sp, called the solubility product constant, instead of the equilibrium constant K_eq, but otherwise it is the same concept. If Q < K_sp, the solid will dissolve. If Q > K_sp, the solid either does not dissolve, or, if it previously already had, it precipitates out. If Q = K_sp, the solution is saturated, which is a kind of equilibrium wherein the maximum amount of solute has been dissolved in the solvent. 

Common Ion Effect

Using equilibriums to chart solubilities explains a phenomenon called the common ion effect, wherein a solution already containing one ion that the solid will dissociate into causes the solid’s solubitity product constant to lower. For example, if you dissolve table salt (NaCl), it dissociates into Cl- and Na+. If you dissolve it in a chloride solution, as in water that already has Cl- ions in it, you will be able to dissolve less salt.