fællesioneffekten

The fællesioneffekten, often translated as the common ion effect, is a chemical principle describing the decrease in solubility of a sparingly soluble salt when a soluble salt containing a common ion is added to the solution. This phenomenon is a direct consequence of Le Chatelier's principle.

When a sparingly soluble salt, such as silver chloride (AgCl), is dissolved in water, it establishes an equilibrium: AgCl(s) <=> Ag+(aq) + Cl-(aq). If a soluble salt containing either silver ions (e.g., silver nitrate, AgNO3) or chloride ions (e.g., sodium chloride, NaCl) is added to this saturated solution, the concentration of that specific ion increases. According to Le Chatelier's principle, the equilibrium will shift to counteract this change. In this case, the increased concentration of the common ion (either Ag+ or Cl-) drives the equilibrium to the left, favoring the formation of solid AgCl.

Consequently, more of the sparingly soluble salt precipitates out of the solution, leading to a decrease in its overall solubility. This effect is significant in various chemical processes, including precipitation reactions, buffer solutions, and analytical chemistry techniques like gravimetric analysis. Understanding the common ion effect is crucial for controlling solubility and predicting the outcome of reactions involving ionic compounds.