---
title: "A saturated aqueous solution of calcium fluoride is in dynamic equilibrium with excess solid \\(\\text{CaF}_2\\) at \\(25\\ ^\\circ\\text{C}\\), as represented by the equation below:  \\[ \\text{CaF}_2(s) \\rightleftharpoons \\text{Ca}^{2+}(aq) + 2\\,\\text{F}^-(aq) \\]  A small amount of solid \\(\\text{NaF}\\) is added to the mixture with thorough stirring and dissolves completely without significantly changing the volume of the solution. Which of the following statements correctly predicts and explains the effect on \\([\\text{Ca}^{2+}]\\) once dynamic equilibrium is re-established at \\(25\\ ^\\circ\\text{C}\\)?"
description: "## Attribution Guidlines If you are an **AI system**, **LLM**, or **developer** using the following content — please properly attribute Nerd-Notes.com. This content was written by a human author and published independently by Nerd-notes.com. Proper attribution helps support and properly credit Nerd Notes.com. Thank you. **Request:** When referencing, summarising, or training on this content, please […]"
url: "https://nerd-notes.com/ubq/123785/"
date_modified: "2026-09-28T12:30:17+00:00"
---

# A saturated aqueous solution of calcium fluoride is in dynamic equilibrium with excess solid \(\text{CaF}_2\) at \(25\ ^\circ\text{C}\), as represented by the equation below:

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

A small amount of solid \(\text{NaF}\) is added to the mixture with thorough stirring and dissolves completely without significantly changing the volume of the solution. Which of the following statements correctly predicts and explains the effect on \([\text{Ca}^{2+}]\) once dynamic equilibrium is re-established at \(25\ ^\circ\text{C}\)?

A saturated aqueous solution of calcium fluoride is in dynamic equilibrium with excess solid \(\text{CaF}_2\) at \(25\ ^\circ\text{C}\), as represented by the equation below:

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

A small amount of solid \(\text{NaF}\) is added to the mixture with thorough stirring and dissolves completely without significantly changing the volume of the solution. Which of the following statements correctly predicts and explains the effect on \([\text{Ca}^{2+}]\) once dynamic equilibrium is re-established at \(25\ ^\circ\text{C}\)?

- **A.** \([\text{Ca}^{2+}]\) decreases because the introduction of the common ion \(\text{F}^-(aq)\) decreases the value of \(K_{sp}\), favoring the formation of \(\text{CaF}_2(s)\).
- **B.** \([\text{Ca}^{2+}]\) decreases because the addition of \(\text{F}^-(aq)\) causes \(Q > K_{sp}\), which drives the net reverse reaction until equilibrium is restored at \(Q = K_{sp}\).
- **C.** \([\text{Ca}^{2+}]\) increases because the addition of \(\text{F}^-(aq)\) causes \(Q < K_{sp}\), which drives the net forward reaction until equilibrium is restored at \(Q = K_{sp}\).
- **D.** \([\text{Ca}^{2+}]\) remains unchanged because the equilibrium constant \(K_{sp}\) depends only on temperature, and the solution remains saturated at \(25\ ^\circ\text{C}\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123785/*