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title: "A student investigates the solubility of two metal sulfide salts, \\(\\text{ZnS}\\) and \\(\\text{CuS}\\), by adding \\(10.0\\text{ mL}\\) of \\(1.0\\text{ M }\\text{HCl(aq)}\\) to separate test tubes each containing \\(0.10\\text{ g}\\) of the solid salt. The relevant equilibrium equations and constants at \\(298\\text{ K}\\) are shown below.  \\[\\text{ZnS}(s) \\rightleftharpoons \\text{Zn}^{2+}(aq) + \\text{S}^{2-}(aq) \\quad K_{sp} = 2.0 \\times 10^{-24}\\] \\[\\text{CuS}(s) \\rightleftharpoons \\text{Cu}^{2+}(aq) + \\text{S}^{2-}(aq) \\quad K_{sp} = 6.0 \\times 10^{-36}\\] \\[\\text{H}_2\\text{S}(aq) \\rightleftharpoons 2\\text{H}^+(aq) + \\text{S}^{2-}(aq) \\quad K = 1.0 \\times 10^{-20}\\]  Which of the following best predicts and explains the outcome of adding \\(1.0\\text{ M }\\text{HCl(aq)}\\) to each test tube?"
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date_modified: "2026-08-21T08:16:23+00:00"
---

# A student investigates the solubility of two metal sulfide salts, \(\text{ZnS}\) and \(\text{CuS}\), by adding \(10.0\text{ mL}\) of \(1.0\text{ M }\text{HCl(aq)}\) to separate test tubes each containing \(0.10\text{ g}\) of the solid salt. The relevant equilibrium equations and constants at \(298\text{ K}\) are shown below.

\[\text{ZnS}(s) \rightleftharpoons \text{Zn}^{2+}(aq) + \text{S}^{2-}(aq) \quad K_{sp} = 2.0 \times 10^{-24}\]
\[\text{CuS}(s) \rightleftharpoons \text{Cu}^{2+}(aq) + \text{S}^{2-}(aq) \quad K_{sp} = 6.0 \times 10^{-36}\]
\[\text{H}_2\text{S}(aq) \rightleftharpoons 2\text{H}^+(aq) + \text{S}^{2-}(aq) \quad K = 1.0 \times 10^{-20}\]

Which of the following best predicts and explains the outcome of adding \(1.0\text{ M }\text{HCl(aq)}\) to each test tube?

A student investigates the solubility of two metal sulfide salts, \(\text{ZnS}\) and \(\text{CuS}\), by adding \(10.0\text{ mL}\) of \(1.0\text{ M }\text{HCl(aq)}\) to separate test tubes each containing \(0.10\text{ g}\) of the solid salt. The relevant equilibrium equations and constants at \(298\text{ K}\) are shown below.

\[\text{ZnS}(s) \rightleftharpoons \text{Zn}^{2+}(aq) + \text{S}^{2-}(aq) \quad K_{sp} = 2.0 \times 10^{-24}\]
\[\text{CuS}(s) \rightleftharpoons \text{Cu}^{2+}(aq) + \text{S}^{2-}(aq) \quad K_{sp} = 6.0 \times 10^{-36}\]
\[\text{H}_2\text{S}(aq) \rightleftharpoons 2\text{H}^+(aq) + \text{S}^{2-}(aq) \quad K = 1.0 \times 10^{-20}\]

Which of the following best predicts and explains the outcome of adding \(1.0\text{ M }\text{HCl(aq)}\) to each test tube?

- **A.** Both \(\text{ZnS}(s)\) and \(\text{CuS}(s)\) will dissolve completely because \(\text{H}^+(aq)\) reacts with \(\text{S}^{2-}(aq)\) to form \(\text{H}_2\text{S}(aq)\), shifting the dissolution equilibria of all salts containing basic anions completely to the right regardless of \(K_{sp}\).
- **B.** Neither \(\text{ZnS}(s)\) nor \(\text{CuS}(s)\) will dissolve because the \(K_{sp}\) values of both salts are significantly smaller than the equilibrium constant \(K\) for the ionization of \(\text{H}_2\text{S}(aq)\).
- **C.** Only \(\text{ZnS}(s)\) will dissolve appreciably because protonation of \(\text{S}^{2-}(aq)\) creates a net equilibrium constant large enough to support dissolution for the salt with the larger \(K_{sp}\), whereas the extremely low \(K_{sp}\) of \(\text{CuS}(s)\) leaves its net dissolution reaction heavily reactant-favored.
- **D.** Only \(\text{CuS}(s)\) will dissolve appreciably because \(\text{CuS}(s)\) has a smaller \(K_{sp}\), requiring fewer \(\text{S}^{2-}(aq)\) ions to be protonated to achieve a reaction quotient where \(Q < K_{sp}\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119856/*