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title: "A student compares the molar solubility of excess solid \\(\\text{Mg(OH)}_2\\) in pure water with its molar solubility in a pH-controlled acidic solution at the same temperature. The acidic solution does not initially contain \\(\\text{Mg}^{2+}\\). The relevant equilibria are  \\(\\text{Mg(OH)}_2\\text{(s)} \\rightleftharpoons \\text{Mg}^{2+}\\text{(aq)} + 2\\text{OH}^{-}\\text{(aq)}\\)  \\(\\text{H}_3\\text{O}^{+}\\text{(aq)} + \\text{OH}^{-}\\text{(aq)} \\rightleftharpoons 2\\text{H}_2\\text{O(l)}\\), which is strongly product-favored.  Which of the following correctly predicts and explains how the molar solubility of \\(\\text{Mg(OH)}_2\\) in the acidic solution compares with its molar solubility in pure water?"
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url: "https://nerd-notes.com/ubq/119459/"
date_modified: "2026-08-19T12:40:31+00:00"
---

# A student compares the molar solubility of excess solid \(\text{Mg(OH)}_2\) in pure water with its molar solubility in a pH-controlled acidic solution at the same temperature. The acidic solution does not initially contain \(\text{Mg}^{2+}\). The relevant equilibria are

\(\text{Mg(OH)}_2\text{(s)} \rightleftharpoons \text{Mg}^{2+}\text{(aq)} + 2\text{OH}^{-}\text{(aq)}\)

\(\text{H}_3\text{O}^{+}\text{(aq)} + \text{OH}^{-}\text{(aq)} \rightleftharpoons 2\text{H}_2\text{O(l)}\), which is strongly product-favored.

Which of the following correctly predicts and explains how the molar solubility of \(\text{Mg(OH)}_2\) in the acidic solution compares with its molar solubility in pure water?

A student compares the molar solubility of excess solid \(\text{Mg(OH)}_2\) in pure water with its molar solubility in a pH-controlled acidic solution at the same temperature. The acidic solution does not initially contain \(\text{Mg}^{2+}\). The relevant equilibria are

\(\text{Mg(OH)}_2\text{(s)} \rightleftharpoons \text{Mg}^{2+}\text{(aq)} + 2\text{OH}^{-}\text{(aq)}\)

\(\text{H}_3\text{O}^{+}\text{(aq)} + \text{OH}^{-}\text{(aq)} \rightleftharpoons 2\text{H}_2\text{O(l)}\), which is strongly product-favored.

Which of the following correctly predicts and explains how the molar solubility of \(\text{Mg(OH)}_2\) in the acidic solution compares with its molar solubility in pure water?

- **A.** It is lower because \(\text{H}_3\text{O}^{+}\) is a common ion in the dissolution equilibrium and shifts the equilibrium toward the solid.
- **B.** It is lower because neutralization removes \(\text{OH}^{-}\), causing the dissolution equilibrium to shift toward the solid.
- **C.** It is higher because decreasing the pH increases the value of \(K_{sp}\) for \(\text{Mg(OH)}_2\).
- **D.** It is higher because \(\text{H}_3\text{O}^{+}\) consumes \(\text{OH}^{-}\), causing the dissolution equilibrium to shift toward the dissolved ions.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119459/*