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AP Chemistry Practice Quiz: pH and Solubility

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Test your understanding with short quizzes. This quiz has 7 questions to check your progress.

Question 1 of 7

According to the provided text, the solubility of a salt is expected to be sensitive to changes in pH if one of its ions is which of the following?

All Questions (7)

According to the provided text, the solubility of a salt is expected to be sensitive to changes in pH if one of its ions is which of the following?

A) The cation of a strong base

B) The anion of a strong acid

C) A hydroxide ion

D) A noble gas ion

Correct Answer: C

The provided content explicitly states that the solubility of a salt is pH-sensitive if one of its constituent ions is a weak acid, weak base, or hydroxide. A hydroxide ion (OH-) is one of these conditions.

Consider a salt with the general formula MX, where X⁻ is the conjugate base of a weak acid. How will the solubility of MX be affected by a decrease in the pH of the solution, and which principle explains this effect?

A) Solubility will increase, as explained by Le Châtelier’s principle.

B) Solubility will decrease, as explained by Le Châtelier’s principle.

C) Solubility will remain unchanged, because the common ion effect does not apply.

D) Solubility will increase, because the temperature of the solution increases.

Correct Answer: A

A decrease in pH means an increase in H⁺ concentration. The H⁺ ions will react with the weak base anion X⁻, removing it from the solution. According to Le Châtelier’s principle, the removal of a product (X⁻) from the dissolution equilibrium MX(s) ⇌ M⁺(aq) + X⁻(aq) will cause the equilibrium to shift to the right, increasing the solubility of the salt.

The solubility of which of the following hypothetical salts would be LEAST affected by the addition of a strong acid?

A) A salt containing a hydroxide anion (OH⁻)

B) A salt containing the conjugate base of a weak acid

C) A salt containing the conjugate acid of a weak base

D) A salt composed of the cation of a strong base and the anion of a strong acid

Correct Answer: D

The solubility of a salt is pH-sensitive if its ions are weak acids, weak bases, or hydroxide. The ions from a strong acid and a strong base (e.g., Cl⁻ from HCl and Na⁺ from NaOH) do not react significantly with added H⁺ or OH⁻. Therefore, the dissolution equilibrium is not disturbed by changes in pH, and the solubility remains relatively constant.

A student observes that the solubility of a sparingly soluble salt, M(OH)₂, increases significantly when the pH is lowered. This observation is best explained by which of the following?

A) The added H⁺ ions react with OH⁻ ions, shifting the dissolution equilibrium to the right.

B) The added H⁺ ions increase the concentration of M²⁺ ions through a side reaction.

C) Lowering the pH decreases the kinetic energy of the solvent molecules, enhancing dissolution.

D) The salt M(OH)₂ is amphoteric and reacts with both acids and bases.

Correct Answer: A

According to Le Châtelier’s principle, the dissolution of M(OH)₂ is an equilibrium: M(OH)₂(s) ⇌ M²⁺(aq) + 2OH⁻(aq). Lowering the pH introduces H⁺ ions, which react with the OH⁻ product ions to form water. This removal of a product causes the equilibrium to shift to the right to produce more ions, thereby increasing the salt's solubility.

The qualitative effect of pH on salt solubility can be understood using Le Châtelier’s principle. This principle is applicable because the dissolution of a sparingly soluble salt is what type of process?

A) A non-spontaneous reaction

B) An irreversible chemical change

C) A reversible equilibrium process

D) An acid-base neutralization

Correct Answer: C

Le Châtelier’s principle applies to systems at equilibrium. The dissolution of a salt in a saturated solution is a reversible process where the rate of dissolving equals the rate of precipitation, establishing a dynamic equilibrium. Changes in conditions, like pH, can shift this equilibrium.

Consider a salt whose cation is the conjugate acid of a weak base (e.g., NH₄⁺). How would adding a strong base (increasing the pH) affect the solubility of this salt?

A) Solubility would decrease because of the common ion effect.

B) Solubility would increase because the added OH⁻ reacts with the cation.

C) Solubility would remain unchanged because the anion is from a strong acid.

D) Solubility would decrease because the added OH⁻ causes precipitation of the cation.

Correct Answer: B

The cation is a weak acid. Adding a strong base (OH⁻) will cause an acid-base reaction, removing the cation from the solution (e.g., NH₄⁺ + OH⁻ → NH₃ + H₂O). Based on Le Châtelier’s principle, the removal of a product ion from the dissolution equilibrium will cause the equilibrium to shift to the right, leading to an increase in the salt's solubility.

A salt's solubility is found to be pH-sensitive. Based on the provided information, what can be inferred about at least one of the ions that make up the salt?

A) The ion must be a metal.

B) The ion must be a nonmetal.

C) The ion acts as a weak acid or a weak base.

D) The ion must be polyatomic.

Correct Answer: C

The provided text states that pH sensitivity in salt solubility occurs if one of the constituent ions is a weak acid, weak base, or hydroxide. Hydroxide is a weak base. Therefore, the common characteristic is that at least one ion must be capable of acting as a weak acid or weak base, allowing it to react with added H⁺ or OH⁻.