Determination of Deprotonation Constant of Glycine in 10, 20 and 30% Dioxane in Dioxane-Water System and Related Thermodynamic Quantities at 308.15K by E.M.F. Measurement

Abstract

<p>The deprotonation constant (pK₁) of glycine in 10, 20 and 30% dioxane in dioxane-water system at 308.15K was determined by potentiometric method using calomel electrode with the help of modified Davies equation, the dissociation of glycine is given as:</p> <p>ZH⁺ Z^± + H⁺</p> <p>m₂(1-?) m₂? m₂?</p> <p>where ZH⁺= NH₃⁺-CH₂-COOH</p> <p>Z^± = NH₃⁺-CH₂-COO^- (Zwitter ion)</p> <p>and Z = NH₂-CH₂-COOH = glycine</p> <p>k₁ = acidic dissociation constant</p> <p>k₁ is given by:</p> <p>log k₁ = log k₁(A) - (2A¢√μ/(1+ √μ)) + ?₁μ</p> <p>where k₁ real dissociation constant </p> <p>k₁(A) = Apparent Dissociation Constant </p> <p>Rearrangingthe above equationwe have:</p> <p>log K₁- ?₁μ = logK₁(A) - (2A¹√μ) / (1 + √μ)</p> <p>= q where q = log K₁(A) - (2A¹√μ) / (1 + √μ) </p> <p>or q = log K₁- ?₁μ</p> <p>-q = pK₁ + ?₁μ</p> <p>The constant value of m_H⁺ was calculated by:</p> <p>log m_H⁺= (E⁰- E)/K - log m_Cl^_ + (2A¢√μ/(1+ √μ)) - ?₁μ</p> <p>The value of deprotonation constant was calculated by extrapolating graph at μ = 0 where is μ is ionic strength.The related thermodynamic quantities ΔG⁰, ΔH⁰ and ΔS⁰ and free energy transfer ΔG_t were calculated by the following least square method.The deprotonation constant was calculated by least square method:</p> <p>log K₁= -A^*/ T + D^*-C^*T </p> <p>The related thermodynamic quantities ΔG⁰, ΔH⁰ and ΔS⁰ and free energy transfer ΔG_t was calculated by the following least square method:</p> <p>ΔG⁰ = -19.1438(-A^* + D^*T - C^*T²)</p> <p>ΔH⁰ = -19.1438(-A^*- C^*T²)</p> <p>ΔS⁰ = -19.1438(D^* - 2C^*T)</p>