Solubility Equilibria and Solubility Product (Ksp) – Step-by-Step Study Guidance

L Q1. Which of the following has the greatest molar solubility?

• A. PbF2 Ksp = 4.1x10-8

• B. Ag2SO4 Ksp = 1.4x10-5

• C. CaF2 Ksp = 4.0x10-11

• D. BaF2 Ksp = 1.7x10-6

Background

Topic: Solubility Product Constant (Ksp) and Molar Solubility

This question tests your understanding of how to relate the Ksp value of a salt to its molar solubility, taking into account the stoichiometry of the dissolution reaction.

Key Terms and Formulas

• Ksp (Solubility Product Constant): The equilibrium constant for the dissolution of a sparingly soluble salt.

• Molar Solubility (s): The number of moles of solute that dissolve per liter of solution to reach saturation.

For a salt dissolving as $\mathrm{MX_2} \rightarrow M^{2+} + 2X^-$, $K_{sp} = [M^{2+}][X^-]^2$.

For a salt dissolving as $\mathrm{M_2X} \rightarrow 2M^+ + X^{2-}$, $K_{sp} = [M^+]^2[X^{2-}]$.

Step-by-Step Guidance

1. Write the dissolution equation for each salt and express Ksp in terms of molar solubility $s$.

2. For each salt, set up the Ksp expression using the stoichiometry of the ions produced.

3. Express the ion concentrations in terms of $s$ (e.g., for $\mathrm{MX_2}$, $[M^{2+}] = s$, $[X^-] = 2s$).

4. Substitute these expressions into the Ksp formula to get an equation in terms of $s$.

5. Solve for $s$ (molar solubility) in terms of Ksp for each salt, but do not calculate the final value yet.

Try solving on your own before revealing the answer!

Final Answer: Ag2SO4 (B)

Ag2SO4 has the highest molar solubility when you solve for $s$ using the Ksp expressions for each salt.

Q2. Which of the following salts has the greatest solubility in water?

• A. CaSO4

• B. BaSO4

• C. CaCO3

• D. MgCO3

• E. BaCO3

Background

Topic: Solubility of Ionic Compounds

This question tests your ability to compare the solubility of different salts, likely based on their Ksp values (which may be provided in a table).

Key Terms and Formulas

• Solubility: The amount of a substance that dissolves in a given quantity of solvent at a specific temperature.

• Ksp: The solubility product constant, which can be used to compare the solubility of different salts with similar stoichiometry.

Step-by-Step Guidance

1. Recall that for salts with the same stoichiometry, a higher Ksp generally means higher solubility.

2. If Ksp values are not given, consider periodic trends and the general solubility rules for sulfates and carbonates.

3. Think about which cations and anions tend to form more soluble or less soluble salts (e.g., BaSO4 is known to be very insoluble).

4. Use your knowledge of common ion effects and solubility rules to eliminate unlikely options.

Try solving on your own before revealing the answer!

Final Answer: CaSO4 (A)

CaSO4 is more soluble than the other listed salts based on typical Ksp values and solubility rules.

Q3. Consider the molar solubility (s) of silver sulfate (Ag2SO4). Which one of the following relationships is correct?

• A. 2[Ag+] = s

• B. [Ag+] = s

• C. [2Ag+] = s

• D. 2[SO42-] = s

• E. [SO42-] = s

Background

Topic: Relating Molar Solubility to Ion Concentrations

This question tests your understanding of how the dissolution of a salt relates the molar solubility to the concentrations of ions in solution.

Key Terms and Formulas

• Molar Solubility (s): The number of moles of solute that dissolve per liter of solution.

• Dissolution Equation: $\mathrm{Ag_2SO_4 (s) \rightarrow 2Ag^+ (aq) + SO_4^{2-} (aq)}$

Step-by-Step Guidance

1. Write the balanced dissolution equation for Ag2SO4.

2. Define $s$ as the number of moles of Ag2SO4 that dissolve per liter.

3. Relate the change in concentration of each ion to $s$ (e.g., for every $s$ mol of Ag2SO4 that dissolves, how many moles of Ag+ and SO42- are produced?).

4. Express $[Ag^+]$ and $[SO_4^{2-}]$ in terms of $s$.

Try solving on your own before revealing the answer!

Final Answer: [SO42-] = s (E)

For every $s$ mol of Ag2SO4 that dissolves, $[SO_4^{2-}] = s$ and $[Ag^+] = 2s$.