Solubility Equilibria (College Board AP® Chemistry): Exam Questions

A student is studying the properties of CaSO₄ and PbSO₄ . The student has samples of both compounds, which are white powders.

The student tests the electrical conductivity of each solid and observes that neither solid conducts electricity. Describe the structures of the solids that account for their inability to conduct electricity.

The student places excess CaSO₄ (s) in a beaker containing 100 mL of water and places excess PbSO₄ (s) in another beaker containing 100 mL of water. The student stirs the contents of the beakers and then measures the electrical conductivity of the solution in each beaker. The student observes that the conductivity of the solution in the beaker containing the CaSO₄ (s) is higher than the conductivity of the solution in the beaker containing the PbSO₄ (s).

Which compound is more soluble in water, CaSO₄ (s) or PbSO₄ (s) ? Justify your answer based on the results of the conductivity test.

The left side of the diagram below shows a particulate representation of the contents of the beaker containing the CaSO₄(s) from the solution conductivity experiment.

Draw a particulate representation of PbSO₄ (s) and the ions dissolved in the solution in the beaker on the right in the diagram. Draw the particles to look like those shown to the right of the beaker. Draw an appropriate number of dissolved ions relative to the number of dissolved ions in the beaker on the left.

The student attempts to increase the solubility of CaSO₄ (s) by adding 10.0 mL of 2 M H₂SO₄ (aq) to the beaker, and observes that additional precipitate forms in the beaker. Explain this observation.

Barium sulfate (BaSO₄​) is a sparingly soluble salt used in medical imaging. The solubility-product constant (K_sp​) for BaSO₄​ at 25 ^oC is 1.1×10⁻¹⁰.

A student prepares a saturated solution of BaSO₄ in water at 25 ^oC and wants to determine the molar solubility of the salt.

Write the dissolution equation and the K_sp​ expression for BaSO₄​.

Calculate the molar solubility of BaSO₄​ in pure water at 25 ^oC.

A saturated solution of BaSO₄ is instead prepared in a 0.10 M solution of Na₂SO₄​. Predict whether the solubility of BaSO₄​ will increase, decrease, or remain the same. Justify your answer based on equilibrium principles.

A student investigates whether a precipitate will form when mixing solutions of calcium chloride (CaCl₂) and sodium sulfate (Na₂SO₄​). The solubility-product constant (K_sp​) for calcium sulfate (CaSO₄​) at 25°C is 2.4 × 10⁻⁵.

The student mixes 50.0 mL of 0.0500 M CaCl₂ and 50.0 mL of 0.0300 M Na₂SO₄​ in a beaker and observes the solution.

Write the dissolution equation and the K_sp​ expression for CaSO₄​.

Determine the concentrations of Ca²⁺ and SO₄²⁻​ immediately after mixing.

i) Calculate the reaction quotient Q for CaSO₄​ in the mixed solution.

ii) Compare Q to K_sp​ and predict whether a precipitate will form. Justify your answer.

The solubilty of three fluoride salts, LiF, CaF₂ and MgF₂, in water at 25 ^oC is investigated. The following data is collected:

Write a balanced equation for the dissolution of CaF₂ (s) in water.

State the mathematical expression that relates the solubility (S) of CaF₂ to its K_sp.

Determine which of the three salts has the highest molar solubility.
Justify your answer.

An acidic solution is added to a saturated solution of CaF₂. Explain how this affects the solubility of CaF₂, considering that HF is a weak acid.

The dissolution of CaF₂ is endothermic (ΔH^o_soln = +16.6 kJ mol^-1).
Explain how increasing the temperature would affect the solubility of CaF₂.

A saturated solution of CaF₂ is mixed with a saturated solution of MgF₂.

Predict whether a precipitate will form when the two solutions are combined. Justify your answer.

Answer the following questions about the solubility of Ca(OH)₂  (K_sp = 1.3 × 10 ⁻⁶).

Write a balanced chemical equation for the dissolution of Ca(OH)₂ (s) in pure water.

Calculate the molar solubility of Ca(OH)₂ in 0.10 M Ca(NO₃)₂ .

In the box below, complete a particle representation diagram that includes four water molecules with proper orientation around the Ca²⁺ ion.

Represent water molecules as

Answer the following questions about Mg(OH)₂. At 25°C, the value of the solubility product constant, K_sp for Mg(OH)₂ (s) is  1.8 x 10⁻¹¹ .

Calculate the number of grams of Mg(OH)₂ (molar mass 58.32 g/mol) that is dissolved in 100 mL of a saturated solution of Mg(OH)₂ at 25°C.

The energy required to separate the ions in the Mg(OH)₂ crystal lattice into individual  Mg²⁺ (g) and OH ⁻(g) ions, as represented in the table below, is known as the lattice energy of Mg(OH)₂(s) . As shown in the table, the lattice energy of Sr(OH)₂ (s) is less than the lattice energy of Mg(OH)₂ (s) . Explain why in terms of periodic properties  and Coulomb's law.

A Lewis electron-dot diagram of the oxalate ion, C₂O₄²⁻, is shown.

Identify the hybridization of the valence orbitals of either carbon atom in the oxalate ion.

Silver oxalate, Ag₂C₂O₄ (s), is slightly soluble in water. The value of K_sp for Ag₂C₂O₄ is 5.40 × 10⁻¹².

i) Write the expression for the solubility-product constant, K_sp, for Ag₂C₂O₄.

ii) Calculate the molar solubility of Ag₂C₂O₄ in neutral distilled water.

iii) The molar solubility of Ag₂C₂O₄ increases when it is dissolved in 0.5 M  HClO₄ (aq) instead of neutral distilled water. Write a balanced, net-ionic equation for the process that occurs between species in solution that contributes to the increased solubility of Ag₂C₂O₄ (aq) in HClO₄ (aq).

A student is investigating the solubility of silver chromate, Ag₂CrO₄, which forms a red precipitate in aqueous solution. The student prepares a saturated solution of Ag₂CrO₄ and uses it in a series of solubility tests at 25 ^oC.

Write a balanced equation, including state symbols, for the dissolution of Ag₂CrO₄ (s) in water at 25 ^oC.

The K_sp for Ag₂CrO₄ at 25 ^oC is 1.1 × 10^-12.

Calculate the molar solubility of Ag₂CrO₄ in pure water at 25 ^oC.

A solution of 0.10 mol L^-1 AgNO₃ is added to a beaker containing the saturated Ag₂CrO₄ solution. Explain whether additional Ag₂CrO₄ will precipitate.

Another beaker contains a saturated solution of Ag₂CrO₄. Potassium chloride (KCl) is slowly added. Justify whether a precipitate will form.

A student claims that the solubility of Ag₂CrO₄ must be greater than that of BaSO₄ because Ag⁺ and CrO₄^2- are soluble ions according to the solubility rules.

Evaluate the validity of this claim using chemical reasoning.