Question

how do i find ksp

Answer 1

The solubility product constant, Ksp​, is the equilibrium constant for a solid substance dissolving in an aqueous solution. It represents the level at which a solute dissolves in solution. The more soluble a substance is, the higher the Ksp value it has.

The solubility product for a general binary compound AaBb is given by

AaBb ⇌ a A^b+ + b B^a−

K_sp = [A]^a[B]^b

For example let us find K_sp for 0.5M Pb(NO₃)₂

Pb(NO₃)₂⇌Pb²⁺ + 2NO₃^-

1.0M Pb(NO₃)₂ solution contains;

1.0M Pb²⁺ and 2.0M of NO₃^- and 0.5M solution contains 0.5M Pb²⁺ and 1.0M NO₃^-

So K_sp= [0.5][1.0]²

K_sp = 0.5

Also note below points:

• For highly soluble ionic compounds the ionic activities must be found instead of the concentrations that are found in slightly soluble solutions.
• Common Ion Effect: The solubility of the reaction is reduced by the common ion. For a given equilibrium, a reaction with a common ion present has a lower  Ksp​, and the reaction without the ion has a greater Ksp.
• Salt Effect (diverse ion effect): Having an opposing effect on the Ksp value compared to the common ion effect, uncommon ions increase the Ksp value. Uncommon ions are ions other than those involved in equilibrium.