Solid lead nitrate is added to a solution that is 0.020 M in OH^-and SO4 ^2-. Addition of the le

step 1 Let's look at each of these two compounds separately. Okay, so we have PBSO4 solid. We'll write

Solid lead nitrate is added to a solution that is 0.020 M in...

Solid lead nitrate is added to a solution that is 0.020 M in $\mathrm{OH}^{-}$and $\mathrm{SO}_4{ }^{2-}$. Addition of the lead nitrate does not change the volume of the solution. (a) Which compound, $\mathrm{PbSO}_4$ or $\mathrm{Pb}(\mathrm{OH})_2\left(K_{\text {ap }}=2.8 \times 10^{-16}\right)$, will precipitate first? (b) What is the pH of the solution when $\mathrm{PbSO}_4$ first starts to precipitate?

Solid lead nitrate is added to a solution that is 0.020 M in $\mathrm{OH}^{-}$and $\mathrm{SO}_4{ }^{2-}$. Addition of the lead nitrate does not change the volume of the solution.
(a) Which compound, $\mathrm{PbSO}_4$ or $\mathrm{Pb}(\mathrm{OH})_2\left(K_{\text {ap }}=2.8 \times 10^{-16}\right)$, will precipitate first?
(b) What is the pH of the solution when $\mathrm{PbSO}_4$ first starts to precipitate?

Key Concepts

Solubility Product (Ksp)

The solubility product is an equilibrium constant that quantifies the extent to which a sparingly soluble salt dissolves in water. It is defined as the product of the concentrations of the ions each raised to the power of their stoichiometric coefficients when the salt is in equilibrium with its dissolved ions. A salt will begin to precipitate when the ion product of its constituent ions exceeds its Ksp value.

Reaction Quotient (Q)

The reaction quotient is calculated using the current concentrations of the ions in solution and serves as a measure of how far a system is from equilibrium. When Q exceeds the Ksp of a salt, the solution is supersaturated, and precipitation occurs. This concept is essential in predicting which salt will precipitate first when multiple potential precipitates are present.

Selective Precipitation

Selective precipitation is a technique used to separate ions based on differences in their solubility products. By carefully controlling the concentration of ions in solution, it is possible to precipitate one compound while keeping others dissolved, thereby achieving separation of components based on their distinct Ksp values.

pH and Its Impact on Solubility

pH is a measure of the acidity or basicity of a solution and directly influences the concentration of hydrogen or hydroxide ions. In the context of solubility, the pH can shift the equilibrium of salt dissolution, particularly for compounds where one of the ions is OH?. An increase in OH? concentration (a higher pH) can decrease the solubility of metal hydroxides, promoting their precipitation.

Common Ion Effect

The common ion effect refers to the decrease in solubility of a salt when one of its constituent ions is added to the solution from an external source. This effect shifts the dissolution equilibrium towards the formation of the solid salt, facilitating precipitation even when only moderate amounts of the metal ion are added.

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