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Title of Thesis

Zahida Tasneem Maqsood
Institute/University/Department Details
University of Karachi/ Department of Chemistry
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
tea, gallic acid, iron, ascorbic acid, cyclic voltammetry

Stability constants have been measured spectrophotometricallyas well as potentiometrically for iron (III) gallic acid complex. B values determined by both the methods were compared and found to be in good agreement with each other. For spectrophotometric study molar absorptivity of the complex at each pH was measured and used for further calculations.

In potentiometric titrations experimental results were treated in two different ways. Classical Bjerrum method was applied and these data were further used by well known computer program “Best” and compared. The results were also refined by this program.

The stoichiometric rations of different species formed during this complex formation were determined. Concentrations of the species present in aqueous solution at different pH were also studied by these methods.

For thermodynamic study the changes in B values at different temperature were examined and enthalpy and entropy values were determined.

Iron (III) complex with gallic acid methyl ester was also prepared.

The above results were compared with this new complex and the role of carboxylate group on the complex was studied.

The redox potential of these complexes were found to be less positive than the redox potential of Fe(III)/Fe(II) in form of aquo complex which is 0.77v vs NHE. The Eo value of iron (III) gallic acid methyl ester was found to be lower than that of Fe(III)-galilic acid complex at corresponding pH,s.

The rate constants for this redox reaction were studied at pH 4, 4.2, 4.4, 4.6, 4.8, 5.0, 5.3 and 5.4. These values were found to be greater in case of iron gallic acid when compared with the rate constants of iron gallic acid methyl ester. It was also observed that these values had inverse relation with pH. When pH was increased these values became smaller.

Activation parameters were studied for the redox reactions of both the complexes. These values were obtained for gallic acid at pH 4 and 5 and for gallic acid methyl ester at pH 4 only. In both the cases G were found to be positive.

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908.27 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
132.91 KB
2 1 Introduction 1
198.44 KB
  1.1 Tea and Iron 3
  1.2 Tea and gallic acid 3
  1.3 Iron and Gallic acid 5
  1.4 Iron and Ascorbic acid 7
3 2 Theoretical aspects 12
124.89 KB
  2.1 Formation of the complex 12
  2.2 Potentiometric study of the 15
  2.3 Computation of stability 17
  2.4 Interaction of 23
  2.5 Reduction of the complex by ascotbate 25
  2.6 Redox potential 28
4 3 Experimental 34
100.14 KB
  3.1 Materials 34
  3.2 Preparation of iron (III0 stock solution 35
  3.3 Preparation of Gallic aicd stock solution 35
  3.4 Preparation of Ascorbic acid stock solution 36
  3.5 Preparation of Buffers 36
  3.6 Methods 38
  3.7 Recording of Spectra of the complex 38
  3.8 Treatment of Solution for job’s method 39
  3.9 Treatment of Solution for mole ratio method 39
  3.10 Determination of molar absorptivities 40
  3.11 Procedure for potentiometric titrations 41
  3.12 Kinetic measurement and data analysis 44
  3.13 Measurement of redox potential of complex 46
5 4 Formation Equilibria 49
307.57 KB
  4.1 Stoichiometry and mode of coordination 49
  4.2 Job’s method 50
  4.3 Molar ratio method 50
  4.4 Study of the equilibrium constants 51
  4.5 Potentiometric study 51
  4.6 Spectrophotometric study 55
6 5 Results and Discussion 95
201.26 KB
  5.1 Redox reactions 95
  5.2 Study of the rate of reduction 95
  5.3 Redox potential of the complex 102
7 6 Conclusion 132
35.21 KB
8 7 Further attempts 137
104.47 KB
  7.1 Reduction by V (II ) 137
  7.2 Cyclic voltammetry 139
  7.3 References 142