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Ch.18 - Aqueous Ionic Equilibrium
Tro - Chemistry: A Molecular Approach 6th Edition
Tro6th EditionChemistry: A Molecular ApproachISBN: 9780137832217Not the one you use?Change textbook
All textbooksTro 6th EditionCh.18 - Aqueous Ionic EquilibriumProblem 115
Chapter 18, Problem 115

A solution is made 1.1⨉10-3 M in Zn(NO3)2 and 0.150 M in NH3. After the solution reaches equilibrium, what concentration of Zn2+(aq) remains?

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Identify the relevant chemical equilibrium: The complexation reaction between Zn(NO_3)_2 and NH_3 forms a complex ion, typically Zn(NH_3)_4^{2+}. The equilibrium can be represented as: Zn^{2+} + 4NH_3 \(\rightleftharpoons\) Zn(NH_3)_4^{2+}.
Write the expression for the equilibrium constant (K_f) for the formation of the complex ion: K_f = \(\frac{[Zn(NH_3)_4^{2+}\)]}{[Zn^{2+}][NH_3]^4}.
Determine the initial concentrations: Initially, [Zn^{2+}] = 1.1 \(\times\) 10^{-3} M and [NH_3] = 0.150 M. Assume [Zn(NH_3)_4^{2+}] = 0 M initially.
Set up an ICE (Initial, Change, Equilibrium) table to track the changes in concentrations as the system reaches equilibrium. Define the change in concentration of Zn^{2+} as -x, NH_3 as -4x, and Zn(NH_3)_4^{2+} as +x.
Substitute the equilibrium concentrations into the K_f expression and solve for x, which represents the change in concentration of Zn^{2+}. The equilibrium concentration of Zn^{2+} will be the initial concentration minus x.

Key Concepts

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

Equilibrium in Chemical Reactions

Equilibrium in chemical reactions refers to the state where the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. In this context, understanding how the concentrations of Zn2+ and NH3 interact at equilibrium is crucial for determining the final concentration of Zn2+ in the solution.
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Complex Ion Formation

Complex ion formation occurs when metal ions, such as Zn2+, interact with ligands like NH3 to form a complex. This process can significantly affect the concentration of free metal ions in solution, as the formation of complexes reduces the amount of free Zn2+ available, which is essential for calculating the equilibrium concentration.
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Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is disturbed, the system will adjust to counteract the disturbance and restore a new equilibrium. In this scenario, changes in concentration of NH3 or Zn(NO3)2 will shift the equilibrium position, impacting the concentration of Zn2+ ions in the solution.
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