Determination of the pKa Value of Phenolphthalein by Means of Absorbance Measurements

Manuel Alonso, Sebastián P. Chapela, María L. Cristaldo, Inés Nievas, Hilda I. Burgos Oliver Gamondi, Carlos A. Stella

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DOI: 10.4236/ce.2010.12020                

Abstract

We here report a laboratory protocol for the determination of the pKa value of an acid by means of determinations obtained with a spectrophotometer. Students determine the acidity constant (Ka) and the pKa associated with phenolphthalein from the absorbance values obtained from phenolphthalein solutions at different pHs. The present protocol for the determination of the pKa takes a very short time and is useful when teaching in conditions with limited equipment.

Keywords

Medical Science Teaching

Conflicts of Interest

The authors declare no conflicts of interest.

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