Predicting Precipitation
The use of the ionic product and solubility product to decide whether a solid will form on mixing two solutions.
Formula / equation
Q_sp > Ksp → precipitate
Unit
Dimensionless
In depth
After allowing for the dilution that mixing causes, the ionic product is calculated and compared with Ksp. Precipitation continues until the ionic product falls back to Ksp, at which point the remaining solution is exactly saturated.
Examples in the real world
Mixing equal volumes of 0.02 M Pb(NO₃)₂ and 0.02 M KI gives Q_sp far above the Ksp of PbI₂, so yellow solid appears.