Consider a beaker containing a saturated solution of CaF2 in equilibrium with undissolved CaF2(s). Solid CaCl2 is then added to the solution.
Will the concentration of Ca2+ ions in solution increase or decrease?
We’re being asked what would happen to the concentration of Ca2+ ions when solid CaCl2 is added to CaF2 solution upon reaching equilibrium.
The common ion effect states that the solubility of a salt is lower in the presence of a common ion.
For CaF2: The chloride ion, Cl–, has a charge of –1. Calcium is in Group 2A then has a charge of +2:
CaF2(s) ⇌ Ca2+(aq) + 2 Cl–(aq)