Question 1

What is the solubility product Ksp?

Accepted Answer

For a sparingly soluble salt at a specified temperature, Ksp is the equilibrium product of dissolved-ion concentrations, each raised to its stoichiometric coefficient. Its numerical value is valid at the stated temperature, such as 298 K.

Question 2

How is the ionic product Q different from Ksp?

Accepted Answer

Q is calculated from the current solution concentrations, whereas Ksp is the equilibrium value at a fixed temperature. Q < Ksp means the solution is unsaturated, Q = Ksp means saturated equilibrium, and Q > Ksp causes precipitation.

Question 3

Why does a common ion decrease the solubility of AgCl?

Accepted Answer

Adding extra Cl- or Ag+ raises the product of the two ion concentrations, so more AgCl must precipitate to restore equilibrium. The molar solubility therefore falls, while Ksp stays constant at the same temperature.

Question 4

Why does AgBr precipitate before AgCl in an equimolar halide mixture?

Accepted Answer

At equal initial Br- and Cl- concentrations, AgBr reaches its precipitation threshold at 5.0×10^-10 M free Ag+, while AgCl needs 1.8×10^-7 M free Ag+. AgBr therefore forms first; Ksp alone does not determine the order when the competing-ion concentrations are unequal.

Question 5

How does lowering pH increase the solubility of Mg(OH)2?

Accepted Answer

Added H+ reacts with OH- to form water, lowering the hydroxide-ion concentration. Because Ksp = [Mg2+][OH-]^2, the Mg2+ concentration at equilibrium can rise, and more Mg(OH)2 dissolves.

Solubility Product Lab — Ion Clouds, Crystals & Order of Precipitation

About this lab

Practice