9. Predicting the Formation of a Precipitate

In the chapter “Chemical Equilibrium” we discussed how the value of the concentration quotient Q can be used to predict whether a reaction will proceed in the forward or backward direction. When two solutions containing ionic salts are mixed, we calculate Q by determining the concentrations of the appropriate ions immediately after mixing and comparing Q with the value of K_sp we can predict what will happen.

• Q = K_sp saturated solution, no precipitation
• Q < K_sp unsaturated solution; no precipitation
• Q > K_sp supersaturated solution; precipitation untill Q = K_sp

Summary