Free Solubility Product MCQs with Answers

1. The solubility product Ksp of a sparingly soluble salt is

• A. the total mass of the salt dissolved
• B. the product of the concentrations of its ions in a saturated solution, each raised to the power of its coefficient
• C. the concentration of the undissolved solid
• D. the ratio of dissolved to undissolved salt

Explanation: For a saturated solution in contact with excess solid, an equilibrium exists between the solid and its ions, and Ksp is the equilibrium constant for that dissolving process. The concentration of the solid itself is constant and so is not included in the expression. If the ionic product exceeds Ksp a precipitate forms, which is the basis of qualitative analysis.

2. For the sparingly soluble salt AgCl, the solubility product expression is

• A. Ksp = [Ag+] + [Cl-]
• B. Ksp = [AgCl] divided by [Ag+][Cl-]
• C. Ksp = [Ag+][Cl-] divided by [AgCl]
• D. Ksp = [Ag+][Cl-]

Explanation: Silver chloride dissociates into one silver ion and one chloride ion, so Ksp is simply the product of the two concentrations, and the solid does not appear because its concentration does not vary. If the solubility is s moles per cubic decimetre then both ion concentrations equal s and Ksp equals s squared. Concentrations are always multiplied in such expressions, never added.

3. A saturated solution of a sparingly soluble salt is one in which

• A. no more solid can be added to the container
• B. the dissolved ions are in equilibrium with the undissolved solid
• C. the salt has completely dissolved
• D. the solubility product has been exceeded

Explanation: In a saturated solution ions leave the solid surface and return to it at the same rate, so the concentration of dissolved ions stays constant and equals the value fixed by Ksp. If the ionic product were pushed beyond Ksp the excess would precipitate until equilibrium was restored. Undissolved solid must be present for the equilibrium to exist at all.