If a salt forms an acidic cation, increasing the pH will cause its solubility to:

If a salt forms an acidic cation, increasing the pH will cause its solubility to:

• A. Increase
• B. Decrease
• C. Stay the same
• D. First increase then decrease

Answer: (A)

A salt with an acidic cation is one whose cation can act as a weak acid in water. In solution, that acidic cation tends to hydrolyze, helping to make the solution more acidic. When you raise the pH by adding base, the base reacts with and removes the acidic cation (for example, NH4+ reacts with OH− to give NH3 and H2O). This removal of the acidic species shifts the dissolution equilibrium of the solid to the right in order to replenish the cation, so more of the salt dissolves. In other words, increasing pH reduces the amount of the acidic cation in solution, driving more solid to dissolve to restore balance, and the solubility goes up.

A salt with an acidic cation is one whose cation can act as a weak acid in water. In solution, that acidic cation tends to hydrolyze, helping to make the solution more acidic. When you raise the pH by adding base, the base reacts with and removes the acidic cation (for example, NH4+ reacts with OH− to give NH3 and H2O). This removal of the acidic species shifts the dissolution equilibrium of the solid to the right in order to replenish the cation, so more of the salt dissolves. In other words, increasing pH reduces the amount of the acidic cation in solution, driving more solid to dissolve to restore balance, and the solubility goes up.