THE TITRIMETRIC METHOD OF ANALYSIS IN THE LABORATORY
TABLE OF CONTENTS
TITLE PAGE – – – – – – – – i
CERTIFICATION – – – – – – – ii
DEDICATION – – – – – – – – iii
ACKNOWLEDGEMENTS – – – – – – iv
TABLE OF CONTENTS – – – – – – v-vii
CHAPTER ONE
1.0 INTRODUCTION – – – – – – 1-3
CHAPTER TWO
2.0 HISTORY AND ETYMOLOGY OF TITRATION – 4-5
2.1 General Procedure of Titration – – – – 5-6
2.1.1 Preparation of Techniques – – – – – 6-7
2.2 Titration Curves – – – – – – – 7-9
2.3 Types of Titrations – – – – – – 9
2.3.1 Acid-Base Titrations – – – – – – 9-12
2.3.2 Gas Phase Titration – – – – – – 12-13
2.3.3 Complexometric Titration – – – – – 13
2.3.4 Zeta Potential Titration – – – – – – 14
CHAPTER THREE
3.0 MEASURING THE ENDPOINT OF TITRATION – 15-18
3.1 Overview of Titration Method of Analysis – – – 18-19
3.1.1 Modes of Titration – – – – – – 19-23
3.1.2 Pretitration – – – – – – – – 23-24
3.1.3 Manual Volumetric Titration – – – – – 24
3.1.4 Automatic Volumetric Titration – – – – 25-26
3.2 Application of Different Types of Titration – – – 26
3.2.1 Acid-Base Titrations – – – – – – 26-28
3.2.2 Redox Titration – – – – – – – 28-29
3.3 Determination of Glucose Using Titration – – – 29-32
CHAPTER FOUR
4.0 SUMMARY AND CONCLUSION
4.1 Summary – – – – – – – – 33
4.2 Conclusion – – – – – – – – 33
References
CHAPTER ONE
1.0 INTRODUCTION
Titration (also known as titrimetry and volumetric analysis) is a common laboratory method of quantitative chemical analysis to determine the concentration of an identified analyte (a substance to be analyzed) (Whitney and Smith, 1911). A reagent, termed the titrant or titrator, is prepared as a standard solution of known concentration and volume. The titrant reacts with a solution of analyte (which may also be termed the titrand) to determine the analyte’s concentration (Mc Graw-Hill, 2011). The volume of titrant that reacted with the analyte is termed the titration volume.
Fehling’s test for reducing sugars has been used since the 1800’s to determine the amount of glucose and other reducing sugars (lactose in milk, for example). It has had many applications including use in agriculture (glucose determination in corn for use in corn syrup) and in medicine (glucose determination in urine for diabetes tests). The test works by taking advantage of the ability of aldehydecontaining sugars to reduce blue Cu2+ ions to Cu+ ions. A disadvantage of this reaction is that it must take place under basic conditions where Cu2+ tends to form an insoluble precipitate with hydroxide ions. In order to prevent this precipitation, tartrate ions are added to the solution in order to form a soluble complex with the Cu2+ (shown on the right), isolating it from the hydroxide.
The oxidation-reduction reaction between Cu2+ and the aldehyde portion of glucose is shown below.
RCHO (aq) + 2 Cu2+ (aq) + 5 OH– (aq) qe RCOO– (aq) + Cu2O (s) + 3 H2O (l)
Blue rust red
The reaction is self-indicating as the disappearance of the deep blue copper(II)-tartrate complex and appearance of Cu+ (in the form of a red Cu2O precipitate) signals the equivalence point of the reaction. As the amount of Cu2+ in solution decreases, however, it becomes difficult to see the actual equivalence point accurately. This leads to only a poorly reproducible, qualitative determination of the amount of sugar present in the titrant. To compensate for this, after most of the blue from the Cu2+ complex is gone, the indicator methylene blue is added to the solution. Methylene blue is a commonly used indicator for oxidation-reduction reactions. It is a deep blue color in its oxidized form but colorless when exposed to reducing agents. After the glucose titrant has completely reduced all of the Cu2+ to Cu+, the methylene blue will be reduced by the glucose, completely removing the blue color from the solution. This total disappearance of color indicates the end point of the titration.
