Which of these statements about the common-ion effect is most correct? (a) The solubility of a salt MA is decreased in a solution that already contains either M+ or A-. (b) Common ions alter the equilibrium constant for the reaction of an ionic solid with water. (c) The common-ion effect does not apply to unusual ions like SO32 - . (d) The solubility of a salt MA is affected equally by the addition of either A- or a noncommon ion.

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Identify the definition of the common-ion effect: The common-ion effect occurs when the solubility of an ionic compound decreases due to the presence of one of its ions in the solution from another source.

Analyze statement (a): Consider if the presence of either ion M+ or A- from another source in the solution would affect the solubility of the salt MA.

Evaluate statement (b): Determine if the common-ion effect actually changes the equilibrium constant (K) or just shifts the equilibrium position.

Assess statement (c): Reflect on whether the common-ion effect is limited to common ions or if it can also apply to less common ions like SO32-.

Review statement (d): Think about whether the addition of a common ion (A-) and a noncommon ion would have the same effect on the solubility of the salt MA.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Common-Ion Effect

The common-ion effect refers to the decrease in solubility of a salt when a common ion is added to the solution. This phenomenon occurs because the addition of a common ion shifts the equilibrium of the dissolution reaction, according to Le Chatelier's principle, favoring the formation of the solid salt and reducing the concentration of dissolved ions.

Le Chatelier's Principle

Le Chatelier's principle states that if a dynamic equilibrium is disturbed by changing the conditions, the system will adjust to counteract the change and restore a new equilibrium. In the context of the common-ion effect, adding a common ion shifts the equilibrium position, leading to decreased solubility of the salt.

Equilibrium Constant

The equilibrium constant (K) is a numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium for a given reaction. It remains constant at a specific temperature, but the presence of common ions does not change the value of K; instead, it affects the concentrations of the ions involved, thereby influencing solubility.

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Equilibrium Constant K

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