AP Chemistry 7.12: Common-Ion Solubility

Practice AP Chemistry questions on explaining how a common ion changes salt solubility and using Ksp or Q to predict precipitation and ion concentration.

Exam points

Explain how electron transfer and oxidation states define redox reactions and electrochemical processes.
Apply oxidation numbers and half-reaction methods to balance redox equations and analyze cells.

[Maximum number: 1]

Strontium hydroxide dissolves in water according to the following equation. The $K_{s p}$ expression for strontium hydroxide is provided.

\mathrm{Sr}(\mathrm{OH})_{2}(s) \rightleftarrows \mathrm{Sr}^{2+}(a q)+2 \mathrm{OH}^{-}(a q) \quad K_{s p}=\left[\mathrm{Sr}^{2+}\right]\left[\mathrm{OH}^{-}\right]^{2}

Figure for Question 7.12.A—Identify the solubility of a salt, and/or the value of Ksp for the salt, based on the concentration of a common… question 1 — AP Chemistry

The student prepares a second saturated solution of $\mathrm{Sr}(\mathrm{OH})_{2}$ in aqueous $0.10 M \mathrm{Sr}\left(\mathrm{NO}_{3}\right)_{2}$ instead of water. Will the value of $\left[\mathrm{OH}^{-}\right]$ in the second solution be greater than, less than, or equal to the value in the first solution? Justify your answer. (Assume constant temperature.)

For the correct answer and a valid justification: 1 point
Less than. Because the $\mathrm{Sr}\left(\mathrm{NO}_{3}\right)_{2}(a q)$ solution already contains a common ion, $\mathrm{Sr}^{2+}(a q)$ , the solubility of $\mathrm{Sr}(\mathrm{OH})_{2}$ will be decreased, resulting in a lower value of $\left[\mathrm{OH}^{-}\right]$ .

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7.12.A—Identify the solubility of a salt, and/or the value of Ksp for the salt, based on the concentration of a common… question 1