USING POTENTIOMETRIC ACID-BASE TITRATION TO DETERMINE PKA FROM MANGOSTEEN PERICARPS EXTRACT

One of the uses of acid-base indicators is to show the end point of the titration, so the accurate determination of acidity constant and pH range of indicators needs to be done. This study aims to determine the acidity constant (pKa) of mangosteen pericarp extract and its accuracy as an indicator of acid-base titration. Determination of pKa was done by a simple potentiometric titration method. The titration data were plotted in three graphs, i.e., pH, ΔpH/ΔV (the (the first derivative), and Δ2pH/ΔV2 (the second derivative) versus titrant volume to determine the equivalence point of the titration. The accuracy test was carried out by comparing the volume of oxalic acid used to titrate NaOH solution using the indicator of mangosteen pericarp extract and phenolphthalein indicator. The result showed that the equivalence point was found on the titrant volume of 8.6 mL and a measured pH of 9.84. so the pKa value of mangosteen pericarp extract was 7.20, and the pH range was 6.20 to 8.20. the average volume of oxalic acid used to titrate 5 mL of NaOH using phenolphthalein as the indicator was 5.2 mL while the titration used mangosteen pericarp extract was 5.23 mL. The accuracy of mangosteen pericarp extract was 99.42%. By the result, it can be concluded that potentiometric titration can be used as a simple way to determine the acidity constant of mangosteen pericarp extract. Moreover, the mangosteen pericarp extract can be used as an alternative acid-base titration indicator to substitute the common acid-base titration in the laboratory.