![]() ![]() ![]() The common ion affects the solubility of the compound in a solution. The mathematical product of silver(I) and iodide ion molarities is constant in an equilibrium mixture regardless of the source of the ions, and so an increase in one ion’s concentration must be balanced by a proportional decrease in the other. This effect may also be explained in terms of mass action as represented in the solubility product expression: In solutions that already contain either of these ions, less AgI may be dissolved than in solutions without these ions. This solubility equilibrium may be shifted left by the addition of either silver(I) or iodide ions, resulting in the precipitation of AgI and lowered concentrations of dissolved Ag + and I –. ![]() Consider the dissolution of silver iodide: This is an example of a phenomenon known as the common ion effect, which is a consequence of the law of mass action that may be explained using Le Châtelier’s principle. Therefore, the presence of the common ion, ammonium ion, causes decreased dissociation of ammonia and thereby reduces the pH of the solution from 10.97 to 9.34.Ĭompared with pure water, the solubility of an ionic compound is less in aqueous solutions containing a common ion (one also produced by dissolution of the ionic compound). The pOH and pH of the solution can be calculated using the standard equations and equal 4.66 and 9.34, respectively. The approximation is valid as the hydroxide concentration is less than 5% of 0.040 molar. Substituting these values into the expression for K b, x equals 2.2 × 10 −5 molar. COMMON ION EFFECT ON SOLUBILITY POGIL WORKSHEET PLUSThe values for the initial, change, and equilibrium concentrations are placed in the ICE table, with changes in the concentration denoted by x.ĭue to the small value of x, 0.050 minus x is approximately equal to 0.050, and 0.040 plus x is approximately equal to 0.040, which can be verified later by the 5% rule. The K b for this reaction is 1.76 × 10 −5 and is equal to the concentration of ammonium times the concentration of hydroxide divided by the concentration of the ammonia. As chloride ions are pH-neutral, they can be ignored.Īmmonia partially dissociates to produce ammonium and hydroxide ions. If 0.040 molar ammonium chloride is added into the solution, the new pH can be determined using the base dissociation constant of ammonia and an ICE table.Īmmonium chloride ionizes completely to produce 0.040 molar of both ammonium and chloride ions. The pH of a 0.050 molar ammonia solution is 10.97. The common ion effect can be explained with the help of Le Châtelier’s principle, which states that a change in the concentration of the reactants or products at equilibrium will cause the system to shift in a direction that counterbalances the change. This phenomenon is known as the common ion effect. ![]() In this case, the presence of the common ion results in the decreased dissociation of a compound. To counterbalance that change, the equilibrium shifts to the left and causes production of acetic acid until the equilibrium is reestablished. When sodium acetate is added to an acetic acid solution, it increases the total concentration of acetate ions and disturbs the equilibrium. Both acetic acid and sodium acetate have the acetate ion in common. Acetic acid, a weak acid, partially dissociates in solution to produce hydronium and acetate ions, while its salt, sodium acetate, dissociates completely to produce sodium ions and acetate. ![]()
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