Synthesis of Salicylic Acid and Potentiometric Determination of Its Purity and Dissociation Constant
Synthesis of Salicylic Acid and Potentiometric Determination of its Purity and Dissociation Constant
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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 potentiometric titration. The pH after addition of base was measured and plotted against the volume of titrant added using three different plots. Results show a 61.0% yield and the melting point differed from the theoretical by a range of 3.11-6.83%. The pKa calculated was 2.865, differing from the literature value of 2.98, by 3.86%. The theoretical purity of the sample was 100.0%, which differed with the experimental one by 1.7%; the experimental purity is 101.7%. Potentiometric titration proves to be adequate in the determination of the acid dissociation constant and purity of a sample. Aside from that, the synthesis proved adequate given the high purity of the product.
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Keywords: acid dissociation constant purity melting point ester
INTRODUCTION
Potentiometric methods of analysis are based on measuring the potential of electrochemical cells without drawing much, appreciable current. For centuries, potentiometry has been used to locate the endpoint in most titration set-ups. (Skoog, et al., 2004). Potentiometric methods offer a myriad of advantages, its main advantage being its low operational costs. Voltmeters and electrodes are, generally, far
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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 potentiometric titration. The pH after addition of base was measured and plotted against the volume of titrant added using three different plots. Results show a 61.0% yield and the melting point differed from the theoretical by a range of 3.11-6.83%. The pKa calculated was 2.865, differing from the literature value of 2.98, by 3.86%. The theoretical purity of the sample was 100.0%, which differed with the experimental one by 1.7%; the experimental purity is 101.7%. Potentiometric titration proves to be adequate in the determination of the acid dissociation constant and purity of a sample. Aside from that, the synthesis proved adequate given the high purity of the product.
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Keywords: acid dissociation constant purity melting point ester
INTRODUCTION
Potentiometric methods of analysis are based on measuring the potential of electrochemical cells without drawing much, appreciable current. For centuries, potentiometry has been used to locate the endpoint in most titration set-ups. (Skoog, et al., 2004). Potentiometric methods offer a myriad of advantages, its main advantage being its low operational costs. Voltmeters and electrodes are, generally, far
References: [1] Day, R. A. and A. L. Underwood. (1991). Quantitative Analysis. Sixth Edition. Prentice Hall, Inc., USA. [3] McMurry, J. (2004). Organic Chemistry. Sixth Edition. Brooks/Cole – Thomson Learning, CA, USA. [5] Skoog, D.A., D.M. West, F.J. Holler, S.R. Crouch. (2004). Fundamentals of Analytical Chemistry. Eighth Edition. Brooks/Cole – Thomson Learning, CA, USA.