---
title: "A student investigates the dissolution equilibrium of calcium fluoride,  (\\text{CaF}_2\\), at \\(25\\ ^\\circ\\text{C}\\): \\[ \\text{CaF}_2(s) \\rightleftharpoons \\text{Ca}^{2+}(aq) + 2\\,\\text{F}^-(aq) \\quad\\quad K_{sp} = 4.0 \\times 10^{-11} \\] The student adds excess \\(\\text{CaF}_2(s)\\) to two separate beakers at \\(25\\ ^\\circ\\text{C}\\). Beaker 1 contains \\(100\\text{ mL}\\) of distilled water, and Beaker 2 contains \\(100\\text{ mL}\\) of \\(0.10\\text{ M NaF}(aq)\\). After both mixtures are thoroughly stirred and reach equilibrium, which of the following statements correctly compares the molar solubility of \\(\\text{CaF}_2\\) in the two beakers and provides the best justification?"
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url: "https://nerd-notes.com/ubq/121464/"
date_modified: "2026-08-23T05:04:42+00:00"
---

# A student investigates the dissolution equilibrium of calcium fluoride, 
(\text{CaF}_2\), at \(25\ ^\circ\text{C}\):
\[
\text{CaF}_2(s) \rightleftharpoons \text{Ca}^{2+}(aq) + 2\,\text{F}^-(aq) \quad\quad K_{sp} = 4.0 \times 10^{-11}
\]
The student adds excess \(\text{CaF}_2(s)\) to two separate beakers at \(25\ ^\circ\text{C}\). Beaker 1 contains \(100\text{ mL}\) of distilled water, and Beaker 2 contains \(100\text{ mL}\) of \(0.10\text{ M NaF}(aq)\). After both mixtures are thoroughly stirred and reach equilibrium, which of the following statements correctly compares the molar solubility of \(\text{CaF}_2\) in the two beakers and provides the best justification?

A student investigates the dissolution equilibrium of calcium fluoride, 
(\text{CaF}_2\), at \(25\ ^\circ\text{C}\):
\[
\text{CaF}_2(s) \rightleftharpoons \text{Ca}^{2+}(aq) + 2\,\text{F}^-(aq) \quad\quad K_{sp} = 4.0 \times 10^{-11}
\]
The student adds excess \(\text{CaF}_2(s)\) to two separate beakers at \(25\ ^\circ\text{C}\). Beaker 1 contains \(100\text{ mL}\) of distilled water, and Beaker 2 contains \(100\text{ mL}\) of \(0.10\text{ M NaF}(aq)\). After both mixtures are thoroughly stirred and reach equilibrium, which of the following statements correctly compares the molar solubility of \(\text{CaF}_2\) in the two beakers and provides the best justification?

- **A.** The molar solubility of \(\text{CaF}_2\) is lower in Beaker 2 because the initial presence of \(\text{F}^-(aq)\) causes the reaction quotient \(Q\) to reach \(K_{sp}\) at a lower concentration of dissolved \(\text{Ca}^{2+}(aq)\).
- **B.** The molar solubility of \(\text{CaF}_2\) is lower in Beaker 2 because the presence of the dissolved spectator ion \(\text{Na}^+(aq)\) decreases the value of the equilibrium constant \(K_{sp}\).
- **C.** The molar solubility of \(\text{CaF}_2\) is higher in Beaker 2 because the added \(\text{F}^-(aq)\) ions increase the rate of the forward dissolution reaction relative to the precipitation reaction.
- **D.** The molar solubility of \(\text{CaF}_2\) is higher in Beaker 2 because the additional \(\text{F}^-(aq)\) ions increase the strength of ion-dipole attractions between the solid salt and water molecules.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/121464/*