Use solubility products and predict which of the following...

Use solubility products and predict which of the following salts is the most soluble, in terms of moles per liter, in pure water: $\mathrm{CaF}_{2}, \mathrm{Hg}_{2} \mathrm{Cl}_{2}, \mathrm{PbI}_{2},$ or $\mathrm{Sn}(\mathrm{OH})_{2}$ .

Key Concepts

Solubility Product Constant (Ksp)

The solubility product constant is an equilibrium constant that applies to the dissolution of sparingly soluble salts. It expresses the product of the molar concentrations of the ions produced by the salt, each raised to the power of their coefficients in the balanced dissolution reaction. Ksp provides a quantitative measure to compare how much of a salt can dissolve in water before the solution becomes saturated.

Dissolution Equilibrium

Dissolution equilibrium refers to the dynamic balance between the undissolved salt and its ions in solution once the salt is added to water. At this equilibrium, the rate of dissolution of the salt equals the rate of precipitation of the salt from the solution. This concept is foundational for understanding how solubility is limited by the product of ion concentrations reaching a specific constant value (Ksp).

Stoichiometry of Dissolution

In dissolution reactions, the stoichiometric coefficients determine how many moles of each ion are produced from one mole of salt. This stoichiometry is critical when applying the Ksp expression, as it affects the exponents on the concentrations of the ions in the equilibrium constant equation. Correct interpretation of these coefficients is key to accurately calculating the molar solubility of a salt.

Calculating Molar Solubility from Ksp

Calculating molar solubility involves expressing the concentrations of the ions in terms of the solubility variable and substituting these into the Ksp expression. The resulting equation, which often involves powers of the solubility variable due to stoichiometry, is then solved to yield the molar solubility—the number of moles of the salt that can dissolve per liter of water under equilibrium conditions.

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