Synthesis of Salicylic Acid and Potentiometric...

Synthesis of Salicylic Acid and Potentiometric Determination of its Purity and Dissociation Constant ------------------------------------------------- Abstract The purpose of the study is to synthesize salicylic acid from the ester, methyl salicylate, and determine the acid’s dissociation constant and purity. The ester was converted to salicylic acid by base hydrolysis. The products were refluxed and recrystallized, to ensure maximum purity, and filtered, dried, and weighed. The melting point of the product was determined using a Fischer-Johns melting point apparatus. The acid then dissolved in separate beakers with 95% ethanol and water and titrated with 0.050 M NaOH, previously standardized with potassium hydrogen phthalate, through†¦show more content†¦In the case where a weak monoprotic acid is being titrated with a strong base, subsequent addition of the titrant will cause a reaction to occur between the acid and the base. HA + OH– → H2O + A– (4) The presence of the acid and its conjugate base in solution will cause the formation of a buffer solution, which are solutions that resist a drastic change in pH, should a strong acid or base be added to the system. At these points, the slope of a constructed titration curve is at its minimum. This is the pre-equivalence point. There is a point during the pre-equivalence point region wherein both the acid and its conjugate base are present in equal amounts. This occurs when half of the acid has been neutralized, or when the titration is at the half-equivalence point. At this point, the buffering capacity of the system is at its maximum. Aside from that, simplifying Eq. 3 at this point by inspection, the [H+] is equal to that of the Ka. Taking the negative of the logarithm of both sides, one will be able to get the relation