Solubility Constants: Ksp

Ionic Compounds that are water soluble break apart into their ions and create a solubility constant (Ksp).

Ksp is the amount that can be dissolved in a given amount of water – it tells when the solution is saturated

The smaller the Ksp, the less soluble the substance

Ksp is written exactly like Keq!

Write the solubility constant for Mg(OH)2

Solubility constants for several compounds are on page 578 in the chemistry

book!

Solving for the concentration

The mole to mole ratio of Ag+ and I- are the same, so algebra can be used to solve for the concentration

Calculate the solubility of CuCO3

Write the solubility expression for Mg(OH)2

Solve for OH- and Mg2+

What is [OH-]?

When the concentrations of ions are given, you can solve for the solubility.

The number you solve for is called Qsp

You can compare your number to the Ksp or the maximum amount that can be disolved

Predicting Precipitates

Qsp < Ksp : the solution is unsaturated and no precipitate will occur

Qsp = Ksp : the solution is saturated and no precipitate will occur

Qsp > Ksp : the solution is saturated and a precipitate will occur

Comparing Qsp and Ksp

Predict if a precipitate will form if a PbCl2 solution has a Ksp of 1.7 x 10-4. The concentration of Cl- is 0.005M and the concentration of Pb2+ is 0.01M.

Answer