Multiple Choice
A solution contains 2.2 × 10^-3 M in Cu2+ and 0.33 M in LiCN. If the formation constant (Kf) for the complex ion Cu(CN)4^2- is 1.0 × 10^25, how much copper ion (Cu2+) remains at equilibrium?
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18. Aqueous Equilibrium
Complex Ions: Formation Constant
Multiple Choice
A solution is composed of 3.20 × 10−4 M Co(NO3)3 mixed with 0.200 M NH3. Determine the [Co3+] that remains once the solution reaches equilibrium in the formation of Co(NH3)63+.
A
2.30 × 10−33 M
B
7.03 × 10−37 M
C
2.76 × 10−38 M
D
8.40 × 10−42 M
Verified step by step guidance1
Identify the chemical reaction involved: Co(NO3)3 dissociates to form Co3+ ions, and NH3 acts as a ligand to form the complex ion Co(NH3)6^3+.
Write the equilibrium expression for the formation of the complex ion Co(NH3)6^3+. The equilibrium constant expression (Kf) is given by:
Determine the initial concentrations of the reactants: [Co3+] = 3.20 × 10−4 M and [NH3] = 0.200 M. Assume that initially, the concentration of Co(NH3)6^3+ is 0 M.
Set up an ICE table (Initial, Change, Equilibrium) to track the changes in concentration as the reaction proceeds to equilibrium. Use the stoichiometry of the reaction to express the changes in terms of x, where x is the change in concentration of Co3+ that forms the complex.
Substitute the equilibrium concentrations from the ICE table into the equilibrium expression and solve for x, which represents the concentration of Co3+ remaining at equilibrium. This involves solving a polynomial equation derived from the equilibrium expression.
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