The electrokinetic potential of a positively charged colloidal particle in an aqueous solution is significantly affected by the pH of the solution. To understand this effect, we need to consider the theory of double layer formation.When a positively charged colloidal particle is dispersed in an aqueous solution, it attracts negatively charged ions anions from the solution, forming a layer of these ions around the particle. This layer of tightly bound ions is called the Stern layer. Beyond the Stern layer, there is a second layer of loosely associated ions, called the diffuse layer, which consists of both anions and cations positively charged ions . The combination of the Stern layer and the diffuse layer is known as the electrical double layer.The electrokinetic potential, also known as the zeta potential, is the potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed particle. It is an important parameter that influences the stability of colloidal dispersions, as it determines the degree of repulsion between adjacent, similarly charged particles.Now, let's consider the effect of pH on the electrokinetic potential of a positively charged colloidal particle. When the pH of the solution is increased i.e., the solution becomes more alkaline , the concentration of hydroxide ions OH- increases. These hydroxide ions can adsorb onto the surface of the positively charged colloidal particle, neutralizing some of the positive charges. As a result, the magnitude of the positive charge on the particle decreases, which in turn reduces the electrokinetic potential.Conversely, when the pH of the solution is decreased i.e., the solution becomes more acidic , the concentration of hydronium ions H3O+ increases. These hydronium ions can interact with the negatively charged ions in the double layer, effectively compressing the double layer and increasing the electrokinetic potential.In summary, the electrokinetic potential of a positively charged colloidal particle in an aqueous solution is influenced by the pH of the solution. An increase in pH leads to a decrease in the electrokinetic potential, while a decrease in pH leads to an increase in the electrokinetic potential. This effect can be explained by the changes in the electrical double layer surrounding the colloidal particle due to the adsorption of hydroxide ions or the interaction of hydronium ions with the double layer.