Skip to main content
Pearson+ LogoPearson+ Logo
Ch.17 - Applications of Aqueous Equilibria
All textbooksMcMurry 8th EditionCh.17 - Applications of Aqueous EquilibriaProblem 117c
Chapter 17, Problem 117c

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.) (c) NaCN

Verified step by step guidance
1
Identify the solubility equilibrium of Zn(OH)_2: Zn(OH)_2(s) \rightleftharpoons Zn^{2+}(aq) + 2OH^{-}(aq).
Recognize that NaCN dissociates in water to form Na^+ and CN^- ions.
Consider the potential reaction between Zn^{2+} and CN^- to form a complex ion, such as Zn(CN)_4^{2-}.
Write the balanced net ionic equation for the formation of the complex ion: Zn^{2+}(aq) + 4CN^{-}(aq) \rightarrow Zn(CN)_4^{2-}(aq).
Conclude that the formation of the complex ion reduces the concentration of Zn^{2+} ions, shifting the equilibrium to dissolve more Zn(OH)_2, thus increasing its solubility.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
6m
Was this helpful?

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 a numerical value that represents the extent to which a sparingly soluble ionic compound can dissolve in water. 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, and changes in these concentrations can affect solubility.
Recommended video:
Guided course
01:47
Solubility Product Constant

Common Ion Effect

The common ion effect refers to the decrease in solubility of a salt when a common ion is added to the solution. In the case of Zn(OH)2, if NaCN is added, it introduces CN⁻ ions, which can affect the equilibrium of the dissolution reaction. Understanding this effect is crucial for predicting how the addition of certain ions influences the solubility of sparingly soluble compounds.
Recommended video:
Guided course
02:53
Common Ion Effect

Complex Ion Formation

Complex ion formation occurs when metal ions bind with ligands to form a larger, charged species. In this scenario, the addition of NaCN can lead to the formation of the complex ion [Zn(CN)4]²⁻, which effectively removes Zn²⁺ ions from the solution. This shift in equilibrium can increase the solubility of Zn(OH)2, as the dissolution reaction will shift to produce more Zn²⁺ ions to counteract the decrease caused by complexation.
Recommended video:
Guided course
02:20
Complex Ions and Formation Constant
Related Practice
Textbook Question

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

Textbook Question

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.) (b) KOH

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)
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+?