Write the expression for the solubility-product constant for each of the following ionic compounds: Fe(OH)2.

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Identify the dissociation equation for the compound Fe(OH)_2 in water: Fe(OH)_2(s) \rightleftharpoons Fe^{2+}(aq) + 2OH^{-}(aq).

Understand that the solubility-product constant (K_{sp}) is an equilibrium constant that applies to the dissolution of a sparingly soluble compound.

Write the expression for the solubility-product constant (K_{sp}) using the concentrations of the ions in the dissociation equation: K_{sp} = [Fe^{2+}][OH^{-}]^2.

Note that the concentration of the solid Fe(OH)_2 is not included in the K_{sp} expression because it is a pure solid and its activity is considered to be 1.

Remember that the K_{sp} expression is used to determine the solubility of the compound in water and to predict whether a precipitate will form under certain conditions.

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 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 a compound like Fe(OH)2, Ksp helps predict how much of the compound can dissolve in water at a given temperature.

Dissociation of Ionic Compounds

Ionic compounds dissociate into their constituent ions when they dissolve in water. For Fe(OH)2, the dissociation can be represented as Fe(OH)2(s) ⇌ Fe²⁺(aq) + 2OH⁻(aq). Understanding this dissociation is crucial for writing the Ksp expression, as it determines the concentrations of the ions involved in the equilibrium.

Equilibrium Expressions

Equilibrium expressions are mathematical representations of the relationship between the concentrations of reactants and products at equilibrium. For Ksp, the expression is derived from the dissociation of the ionic compound and includes the concentrations of the ions raised to their respective stoichiometric coefficients. This concept is essential for formulating the correct Ksp expression for Fe(OH)2.

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