---
title: "A saturated solution of calcium fluoride is in dynamic equilibrium with undissolved solid at \\(25^\\circ\\text{C}\\), as represented by the following equation:  \\[\\text{CaF}_2(s) \\rightleftharpoons \\text{Ca}^{2+}(aq) + 2\\,\\text{F}^-(aq)\\]  A student adds a small amount of solid potassium fluoride, \\(\\text{KF}\\), to the mixture at constant temperature. The \\(\\text{KF}\\) dissolves completely. Which of the following statements best predicts and explains the effect of adding \\(\\text{KF}(s)\\) to the mixture?"
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url: "https://nerd-notes.com/ubq/120279/"
date_modified: "2026-08-23T04:04:15+00:00"
---

# A saturated solution of calcium fluoride is in dynamic equilibrium with undissolved solid at \(25^\circ\text{C}\), as represented by the following equation:

\[\text{CaF}_2(s) \rightleftharpoons \text{Ca}^{2+}(aq) + 2\,\text{F}^-(aq)\]

A student adds a small amount of solid potassium fluoride, \(\text{KF}\), to the mixture at constant temperature. The \(\text{KF}\) dissolves completely. Which of the following statements best predicts and explains the effect of adding \(\text{KF}(s)\) to the mixture?

A saturated solution of calcium fluoride is in dynamic equilibrium with undissolved solid at \(25^\circ\text{C}\), as represented by the following equation:

\[\text{CaF}_2(s) \rightleftharpoons \text{Ca}^{2+}(aq) + 2\,\text{F}^-(aq)\]

A student adds a small amount of solid potassium fluoride, \(\text{KF}\), to the mixture at constant temperature. The \(\text{KF}\) dissolves completely. Which of the following statements best predicts and explains the effect of adding \(\text{KF}(s)\) to the mixture?

- **A.** The mass of \(\text{CaF}_2(s)\) increases because \(\text{K}^+(aq)\) ions react with \(\text{Ca}^{2+}(aq)\) ions to form an insoluble solid that co-precipitates from solution.
- **B.** The mass of \(\text{CaF}_2(s)\) increases because the added \(\text{F}^-(aq)\) causes the reaction quotient \(Q\) to exceed \(K_{sp}\), shifting the equilibrium toward the reactants.
- **C.** The mass of \(\text{CaF}_2(s)\) decreases because the added \(\text{F}^-(aq)\) reacts with undissolved \(\text{CaF}_2(s)\) to form a soluble complex ion.
- **D.** The mass of \(\text{CaF}_2(s)\) decreases because adding a soluble salt increases the numerical value of \(K_{sp}\) for \(\text{CaF}_2\) at constant temperature.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120279/*