The addition of an electrolyte to a colloidal suspension can significantly affect its stability. Colloidal suspensions consist of small particles 1 nm to 1 m dispersed in a continuous medium, such as a liquid. These particles carry an electric charge, which creates a repulsive force between them, preventing them from aggregating and maintaining the stability of the suspension.When an electrolyte is added to the colloidal suspension, it dissociates into its constituent ions. These ions can interact with the charged colloidal particles and affect the stability of the suspension in two main ways:1. Charge neutralization: The ions from the electrolyte can neutralize the charge on the colloidal particles, reducing the repulsive forces between them. As a result, the particles can come closer together and aggregate, leading to coagulation and the eventual settling of the particles. This process is known as coagulation or flocculation.2. Compression of the electric double layer: The presence of electrolyte ions in the suspension can also compress the electric double layer surrounding the colloidal particles. This double layer is formed due to the distribution of ions in the medium around the charged particles. When the double layer is compressed, the repulsive forces between the particles decrease, allowing them to come closer together and aggregate.The mechanism behind coagulation in the presence of an electrolyte can be explained by the DLVO Derjaguin, Landau, Verwey, and Overbeek theory. According to this theory, the stability of a colloidal suspension is determined by the balance between attractive van der Waals forces and repulsive electrostatic forces between the particles. When an electrolyte is added, the electrostatic repulsion is reduced, and the attractive forces dominate, leading to coagulation.The effectiveness of an electrolyte in causing coagulation depends on its valency. The higher the valency of the ions, the more effective they are in destabilizing the colloidal suspension. This is known as the Schulze-Hardy rule. For example, trivalent ions e.g., Al3+ or Fe3+ are more effective in causing coagulation than divalent ions e.g., Ca2+ or Mg2+ , which are in turn more effective than monovalent ions e.g., Na+ or K+ .In summary, the addition of an electrolyte to a colloidal suspension affects its stability by neutralizing the charge on the colloidal particles and compressing the electric double layer, which reduces the repulsive forces between the particles and promotes coagulation. The effectiveness of an electrolyte in causing coagulation depends on its valency, with higher valency ions being more effective.