From the value of Kf listed in Table 17.1, calculate the concentration of NH3 required to just dissolve 0.020 mol of NiC2O4 (Ksp = 4 * 10^-102) in 1.00 L of solution? (Hint: You can neglect the hydrolysis of C2O4^2- because the solution will be quite basic.)

Verified step by step guidance

Identify the relevant equilibrium reactions: The dissolution of NiC2O4 and the formation of the complex ion with NH3. Write the balanced chemical equations for these reactions.

Write the expression for the solubility product constant (K_{sp}) for NiC2O4. This will involve the concentrations of Ni^{2+} and C2O4^{2-} ions.

Write the expression for the formation constant (K_f) for the complex ion [Ni(NH3)_6]^{2+}. This involves the concentration of Ni^{2+} and NH3.

Set up the equilibrium expressions for both the dissolution and complex formation reactions. Use the stoichiometry of the reactions to relate the concentrations of the species involved.

Combine the expressions for K_{sp} and K_f to solve for the concentration of NH3 required to dissolve 0.020 mol of NiC2O4 in 1.00 L of solution.

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 applies to the solubility of sparingly soluble ionic compounds. It represents the maximum concentration of ions that can exist in a saturated solution at a given temperature. For a compound like NiC2O4, Ksp is calculated from the concentrations of its dissociated ions, and a low Ksp value indicates very low solubility.

Formation Constant (Kf)

The formation constant (Kf) quantifies the stability of a complex ion formed in solution. It is the equilibrium constant for the formation of a complex from its constituent ions. In this context, NH3 can form a complex with Ni^2+, which significantly affects the solubility of NiC2O4 by reducing the concentration of free Ni^2+ ions in solution, thus allowing more of the salt to dissolve.

Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the system will adjust to counteract that change and restore a new equilibrium. In this scenario, adding NH3 shifts the equilibrium towards dissolving more NiC2O4 by reducing the concentration of Ni^2+ ions, thereby allowing more of the salt to dissolve in the solution.