## Chemistry: The Molecular Science (5th Edition)

Some $Ca(OH)_2$ would precipitate, forming a white solid.
This is the equilibrium reaction: $Ca(OH)_2(s) \lt -- \gt Ca^{2+} (aq) + 2OH^-(aq)$ When we add $CaCl_2$, it has $Ca^{2+}$ ions, so, the common ion effect will act. And the reaction will be more reactant-favored. That follows the Le Chatelier's principle. Since we are raising the concentration of one of the products, the equilibrium will try to reduce this concentration, to reduce the change. Since the original solution of $Ca(OH)_2$ is saturated, if the equilibrium moves to the solid's side, the precipitation will occur.