Is the solubility of Zn(OH)₂ increased, decreased, or unchanged on addition of each of the following substances? Write a balanced net ionic equation for each dissolution reaction. (See Appendix C.6 for formulas of complex ions.) (a) HCl

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Identify the solubility equilibrium of Zn(OH)_2: Zn(OH)_2(s) \(\rightleftharpoons\) Zn^{2+}(aq) + 2OH^{-}(aq).

Recognize that adding HCl introduces H^+ ions into the solution, which can react with OH^- ions.

Write the reaction between H^+ and OH^-: H^+(aq) + OH^-(aq) \(\rightarrow\) H_2O(l).

Understand that the removal of OH^- ions shifts the equilibrium to the right, according to Le Chatelier's principle, increasing the solubility of Zn(OH)_2.

Write the net ionic equation for the dissolution of Zn(OH)_2 in the presence of HCl: Zn(OH)_2(s) + 2H^+(aq) \(\rightarrow\) Zn^{2+}(aq) + 2H_2O(l).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Solubility Product Constant (Ksp)

The solubility product constant (Ksp) is an equilibrium constant that quantifies the solubility of a sparingly soluble ionic compound. It is defined as the product of the molar concentrations of the ions, each raised to the power of their coefficients in the balanced dissolution equation. For Zn(OH)2, the Ksp expression would involve the concentrations of Zn²⁺ and OH⁻ ions. Changes in the concentration of these ions can shift the equilibrium, affecting solubility.

Common Ion Effect

The common ion effect refers to the decrease in solubility of an ionic compound when a common ion is added to the solution. In the case of Zn(OH)2, adding HCl introduces Cl⁻ ions, but more importantly, it increases the concentration of H⁺ ions, which can react with OH⁻ ions to form water. This reduction in OH⁻ concentration shifts the equilibrium, leading to decreased solubility of Zn(OH)2 due to the common ion effect.

Net Ionic Equations

A net ionic equation represents the chemical species that are involved in a reaction, excluding spectator ions that do not participate in the reaction. For the dissolution of Zn(OH)2 in the presence of HCl, the net ionic equation would show the dissociation of Zn(OH)2 into Zn²⁺ and OH⁻ ions, and the reaction of OH⁻ with H⁺ to form water. This helps in understanding the actual chemical changes occurring in the solution.

Related Practice

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Which of the following compounds are more soluble in acidic solution than in pure water? Write a balanced net ionic equation for each dissolution reaction. (b) Fe(OH)₃

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Textbook Question

Dissolution of 5.0 x 10^-3 mol of Cr(OH)3 in 1.0 L of 1.0 M NaOH gives a solution of the complex ion [Cr(OH)4]- (Kf = 8 x10^29). What fraction of the chromium in such a solution is present as uncomplexed Cr3+?

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Textbook Question

Is the solubility of Fe(OH)3 increased, decreased, or unchanged on addition of each of the following substances? Write a balanced net ionic equation for each dissolution reaction. (See Appendix C.6 for formulas of complex ions.) (b) NaOH(aq)

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