The common ion effect is a phenomenon that occurs when the presence of one ion in a solution affects the equilibrium constant of a chemical reaction involvi...
The common ion effect is a phenomenon that occurs when the presence of one ion in a solution affects the equilibrium constant of a chemical reaction involving another ion.
The common ion effect arises because the equilibrium constant for a reaction involving two ions is dependent on the concentrations of both ions in the solution. When the concentration of one ion is increased, the equilibrium constant decreases, which means that the forward reaction becomes less likely to occur.
The common ion effect can be used to qualitatively analyze a solution by identifying the ions present. By measuring the pH of the solution, we can determine the relative concentrations of hydrogen ions and hydroxide ions present. This information can then be used to identify the metal ions present in the solution through complexation reactions.
For example, if we add sodium ions (Na+) to a solution of hydrogen ions (H+), the equilibrium constant for the reaction between sodium and hydrogen ions is affected. This results in a decrease in the equilibrium constant, indicating that the forward reaction becomes less likely to occur. This means that the concentration of hydroxide ions (OH-) will increase, indicating that the solution is basic.
Similarly, if we add chloride ions (Cl-) to a solution of phosphate ions (PO4^3-), the equilibrium constant for the reaction between chloride and phosphate ions is affected. This results in an increase in the equilibrium constant, indicating that the forward reaction becomes more likely to occur. This means that the concentration of phosphate ions (PO4^3-) will decrease, indicating that the solution is acidic