Effect of Ionic Strength on Deprotonation of Salicylic Acid and its Derivative

Document Type : Research Paper

Authors

• Mohammad Faraji Faraji ¹
• Ali Farajtabar ²

¹ Department of Chemistry, Babol Branch, Islamic Azad University, Babol, Iran

² bDepartment of Chemistry, Jouybar Branch, Islamic Azad University, Jouybar, Iran

Abstract

The protonation constant values of salicylic and 5-nitrosalicylic acid werestudied by a combination
of spectrophotometric and potentiometric methods at 25 °C in wide range of ionic strength. The ionic
strength of solutions was kept constant by sodium perchlorate as background electrolyte at 0.10 to 3.0 mol
dm-3. Potentiometer was calibrated according to Gran method at each of ionic strength. The pKa values
were calculated using STAR program by multivariate curve fitting of absorbance data. The dependence of
deprotonation constants on ionic strength were explained by means of Specific ion Interaction Theory (SIT).
Activity coefficients of species were calculated by a modified SIT approach. The specific ion interaction
parameters were extracted associated with the thermodynamic protonation constant.

Keywords

• pKa
• Salicylic acid
• Ionic Strength
• Specific ion Interaction Theory

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