Which of the following compounds precipitates from a...

Which of the following compounds precipitates from a solution that has the concentrations indicated? (See Appendix J for $K_{\mathrm{sp}}$ values. $)$ (a) $\mathrm{KClO}_{4} :\left[\mathrm{K}^{+}\right]=0.01 M,\left[\mathrm{ClO}_{4}^{-}\right]=0.01 M$ (b) $\mathrm{K}_{2} \mathrm{PtCl}_{6} :\left[\mathrm{K}^{4}\right]=0.01 \mathrm{M},\left[\mathrm{PtCl}_{6}^{2-}\right]=0.01 \mathrm{M}$ (c) $\mathrm{PbI}_{2} :\left[\mathrm{Pb}^{2+}\right]=0.003 M,[\mathrm{I}]=1.3 \times 10^{-3} \mathrm{M}$ (d) $\mathrm{Ag}_{2} \mathrm{S} :\left[\mathrm{Ag}^{+}\right]=1 \times 10^{-10} M,\left[\mathrm{S}^{2-}\right]=1 \times 10^{-13} \mathrm{M}$

Which of the following compounds precipitates from a solution that has the concentrations indicated? (See Appendix J for $K_{\mathrm{sp}}$ values. $)$
(a) $\mathrm{KClO}_{4} :\left[\mathrm{K}^{+}\right]=0.01 M,\left[\mathrm{ClO}_{4}^{-}\right]=0.01 M$
(b) $\mathrm{K}_{2} \mathrm{PtCl}_{6} :\left[\mathrm{K}^{4}\right]=0.01 \mathrm{M},\left[\mathrm{PtCl}_{6}^{2-}\right]=0.01 \mathrm{M}$
(c) $\mathrm{PbI}_{2} :\left[\mathrm{Pb}^{2+}\right]=0.003 M,[\mathrm{I}]=1.3 \times 10^{-3} \mathrm{M}$
(d) $\mathrm{Ag}_{2} \mathrm{S} :\left[\mathrm{Ag}^{+}\right]=1 \times 10^{-10} M,\left[\mathrm{S}^{2-}\right]=1 \times 10^{-13} \mathrm{M}$

Key Concepts

Solubility Product Constant (Ksp)

The solubility product constant is an equilibrium constant that applies to the dissolution of a sparingly soluble compound. It expresses the product of the molar concentrations of the constituent ions, each raised to the power of its stoichiometric coefficient, at equilibrium. This concept is a fundamental tool in predicting the solubility of ionic compounds in solution.

Reaction Quotient (Q) Versus Ksp

The reaction quotient is calculated in the same way as the solubility product but uses the current ion concentrations in the solution rather than the equilibrium concentrations. By comparing Q with Ksp, one can predict whether precipitation will occur—if Q exceeds Ksp, the solution is supersaturated and precipitation is expected, while if Q is less than Ksp, the solution remains unsaturated.

Precipitation Conditions

Precipitation refers to the process by which a solid forms and separates out from a solution when the ion concentrations exceed the solubility product limit. Understanding the conditions under which precipitation occurs helps in predicting and controlling the formation of solid phases in chemical reactions, which is important in areas such as analytical chemistry, industrial processes, and environmental science.

Ionic Concentrations and Stoichiometry

Calculating the ion concentrations based on the stoichiometry of dissolution is crucial for determining both the reaction quotient Q and comparing it to Ksp. This involves understanding how each formula unit of the salt dissociates into its individual ions in solution, and how the concentrations of these ions combine according to the established stoichiometric coefficients to influence solubility behavior.

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