Changing of Electrical Conductivity, Acidity Function Voltage of Potential Difference for Salicylic Acid and Substituted to Study Adsorption Mechanism on Alumina Surface and the Factors Affecting it


In this study and for the first time there are the use of the specific electrical conductivity, acidity function, difference potential for salicylic and acetyl salicylic acids (Aspirin) solution before and after adsorption to describe and elicit adsorption mechanism as followed :-MO¯ + H2O → MOH (first step)MOH + H+ → MOH2+ MOH2+ + Anion L¯ → MOH2+ -------- ¯ L (second step)Mo¯ ( alumina surface ) , ¯ L ( anione )The adsorption mechanism is represented by two steps the first is to change the charge of the alumina surface from the negative polarized charge to the positive polarized charge by adsorption of hydrogen ions and water molecules from the acid solution to the surface of the alumina by adsorption and the second step represented by the adsorption of the negative anion of the acid to the surface. Salicylic acid give (H+) and salicylate ions (anione) and the presence of hydroxyl group on ortho position helps in the stabilization of anion and increase acidity compared with acetyl group. The adsorption process leads to an increase of acidity function by means of the decrease of (H+) ions in the solution by transition from solution to surface of alumina. This is the first step of adsorption and the second step represented by the transition of salicylate ions. This in turn causes decrease of difference potential between the acidic solution and alumina surface. Decrease of (H+) ions in solution causes decrease in electrical conductivity of solution. All these changes clarify mechanism of ions transition and their type from the solution to surface.