Nem o PbCl2 nem o PbF2 são apreciavelmente solúveis em água....

Nem o $\mathrm{PbCl}_2$ nem o $\mathrm{PbF}_2$ são apreciavelmente solúveis em água. Se colocarmos $\mathrm{PbCl}_2$ sollido e $\mathrm{PbF}_2$ sólido, cada qual num bécher com a mesma quantidade de água, em qual deles a concentraçio do $\mathrm{Pb}^{2+}$ será mais elevada? As constantes de equilibrio destes solidos, na dissolução $\mathrm{em}$ água, são $$ \begin{aligned} & \mathrm{PbCl}_2(\mathrm{~s}) \rightleftarrows \mathrm{Pb}^{2+}(\mathrm{aq})+2 \mathrm{Cl}^{-}(\mathrm{aq}) \quad K=1,7 \times 10^{-3} \\ & \mathrm{PbF}_2(\mathrm{~s}) \rightleftarrows \mathrm{Pb}^{2+}(\mathrm{aq})+2 \mathrm{~F}^{-}(\mathrm{aq}) \quad K=3,7 \times 10^{-8} \\ & \end{aligned} $$

Nem o $\mathrm{PbCl}_2$ nem o $\mathrm{PbF}_2$ são apreciavelmente solúveis em água. Se colocarmos $\mathrm{PbCl}_2$ sollido e $\mathrm{PbF}_2$ sólido, cada qual num bécher com a mesma quantidade de água, em qual deles a concentraçio do $\mathrm{Pb}^{2+}$ será mais elevada? As constantes de equilibrio destes solidos, na dissolução $\mathrm{em}$ água, são
$$
\begin{aligned}
& \mathrm{PbCl}_2(\mathrm{~s}) \rightleftarrows \mathrm{Pb}^{2+}(\mathrm{aq})+2 \mathrm{Cl}^{-}(\mathrm{aq}) \quad K=1,7 \times 10^{-3} \\
& \mathrm{PbF}_2(\mathrm{~s}) \rightleftarrows \mathrm{Pb}^{2+}(\mathrm{aq})+2 \mathrm{~F}^{-}(\mathrm{aq}) \quad K=3,7 \times 10^{-8} \\
&
\end{aligned}
$$

Key Concepts

Solubility Equilibrium

This concept describes the state in which a sparingly soluble solid dissolves in a solvent and establishes a dynamic balance between the undissolved solid and its dissolved ions. The equilibrium is characterized by the fact that the rate at which the solid dissolves equals the rate at which the ions recombine to form the solid, resulting in constant ion concentrations at equilibrium.

Solubility Product (Ksp)

The solubility product, often denoted as Ksp, is the equilibrium constant for the dissolution of a sparingly soluble salt. It is defined by the product of the concentrations of the ions each raised to the power of their stoichiometric coefficients. Ksp values provide a quantitative measure of a salt’s solubility, indicating how much of the salt can dissolve before the solution becomes saturated.

Chemical Equilibrium

Chemical equilibrium refers to the state in a reversible reaction when the forward and reverse reaction rates are equal, leading to constant concentrations of reactants and products. In the context of sparingly soluble salts, this equilibrium is represented by the dissolution reaction where the solid forms a saturated solution with its constituent ions.

Stoichiometry in Dissolution Reactions

Stoichiometry in dissolution reactions relates the molar amounts of the constituent ions produced when a solid dissolves. Understanding the stoichiometric coefficients is crucial because they determine the relationship between the concentration of one ion and another, which is a key factor in using the Ksp expression to calculate ion concentrations in a saturated solution.

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