WHAT IS OXIDATION?
During a chemical reaction, loss of electron is non as oxidation
or
During a chemical reaction removal of oxygen and the addition of hydrogen is called oxidation.
WHAT IS REDUCTION?
During a chemical reaction gain of electrons is non as reduction.
or
During a chemical reaction addition of oxygen and removal of hydrogen is called reduction.
Similar to acid-base titration, redox titration is also carried out potentiometrically. In this titration, the electrode is placed in a solution containing both the species’ oxidized and reduced forms, and the electrode, reversible concerning H+ ions, is replaced by inert metal. Here, the electrode act as an oxidation and reduction electrode.
Consider the redox reaction,
This reaction involving the oxidation of Fe+2 and ions by Ce+4 ions is transported potentiometrically.
Titration starts with adding Ce+4 ions, in that solution contains only Fe+2 ions, and Fe+2 ions oxidized to Fe+3 ions by adding a small amount of Ce+4 ions in the solution.
Presence of Fe+2 and Fe+3 ions in the solution, the electrode behaves as an oxidation-reduction electrode in the potential; according to the Nernst equation is,
At 25˚c
Starting an electrode potential is controlled by the ratio of [Fe+3]/[Fe+2]. If the ratio is equal to 0.01, then the electrode potential would be,
With the further addition of Ce+4 ions, the ratio of [Fe+3]/[Fe+2] changes, therefore changing the value of Eel.
For the ten-fold change in the ratio of [Fe+3]/[Fe+2], the electrode’s potential also changes by 0.1182V.
At equivalence point, [Fe+2]= [Ce+4] and [Fe+3]=[Ce+3] that the electrode potential at equivalence point equation Eeq is,
The above equation (3) is also written as,
And,
Adding and simplifying the equivalent point,
The equation we get,
The value of reduction potential of Fe+3 and Ce+4 is 0.77v and 1.61v, respectively.
Above the equivalence point [Fe+3] ≈ 0 as s result, the electrode potential is controlled only by the ratio of [Ce+4]/[Ce+3]
For potentiometric measurement, oxidation-reduction electrode (Pt electrode) is combined with a reference electrode, e.g. calomel electrode to form galvanic cell is denoted as,
Before the equivalent point, the Emf of the cell is given by,
After the equivalence point, the Emf of a cell is given by,
At the equivalence point, Emf of a cell is,
Emf data obtained are processed for the equivalence point, and Emf of the cell is measured at each stage of titration potentiometrically. Redox titration curve same as Acid-Base titration curve shown Acid-Base Titration Figure (a) and (b).
