Basis in Redox titration

1. Mr. Hemant U. Chikhale
Department of Pharmaceutical Chemistry
F. Y. B. PHARMACY…
SEM-II
PHARMACEUTICAL ANALYSIS-I

3. Half reaction:

4. NERNST EQUATION

5. REDOX EQUIVALENT WEIGHT:
Equivalent weight of a substance (oxidant or reductant) is equal to molecular weight
divided by number of electrons lost or gained by one molecule of the substance in a redox
reaction
Methods to calculate oxidation no.
Oxidation number method
Ion-electron method
REW- depends on oxidation number

6. Redox Indicator:
Visual indicator
mostly dye (high m.w.)
•Classify as:
Self indicator…. KMnO44
External indicator…. Starch
Redox indicator…Ferroin, methylene blue
Self indicator:
•Highly color
•KMnO4- pink, Mn2+
colourless
• End poin t- at fraction of drop
External indicator:
• In iodine titration- blue color complex
formed.
• Solution remain colorless upto
equivalence point- fraction of drop turn
solution blue
Redox indicator:
 Weak reducing or oxidizing agent,
 End point depend on-potential at given point
 Nernst equation-use to calculate potential

7. Titration involving:
1.Potassium permanganate
2.Ceriometry
3.Potassium dichromate
4.Iodine
5.Periodic acid
6.KBrO3
7.NaNO2
8.Titanious chloride:

8. Permanganate type of titration:
Direct titration: oxalic acid, hydrogen
peroxide.
Indirect titration: Assay of cherry juice.
Residual titration: Discussion below
Titrant:- KMnO4 (xM)
Titer:- Solution of drug/ sample+ vehicle
Indicator:- Self- KMnO4
End point:- Pink
Precaution while weighing KMnO4 :
• Must weigh on watch glass.
•Always filter solution with glass wool
and not with cotton wool

9. Ceriometry:
Ammonium ceric sulphate- Strong oxidizing agent (Acid medium)
Solution (yellow) on reduction cerous salt obtained (colorless)
Ceric sulphate has advantage over KMnO4 and Dichromate:
Solution remain stable if boiled
Cerous ion-colorless hence no interference with end point
Cerous ion result from cerric ion but, Mno4 ion can reduced to several oxidation
state
Arsenic trioxide / sodium oxalate- primary standard.
Indicator:
Ferrous phenanthrolone ion (Ferroin)

10. Sodium nitrite titration
 Aromatic primary amines react with sodium nitrite in acidic
solutions to form diazonium salts.
 C6H5NH2 + NaNO2+HCl C6H5N2Cl+ NaCl + 2H2O
 End point is indicated by the presence of small amounts of nitrous acid.
 End point detection by two methods,
 Visual end point
 Amperometrically
 Visual end point is indicated using starch iodide paper according to
the formula
 KI + HCl HI + KCl
 2HI + 2HNO2 I2 + 2NO + 2H2O
Application:
Used in the determination of primary aromatic amines.
May be used for the analysis of drugs such as benzocaine,
dapsone, primaquine etc.

11. Periodic Acid titration
Polyhydroxy compound determine- By acylation.
Procedure:- glycol added to periodic acid-oxidation completed
Then potassium iodide added – liberated iodine titrated with thiosulphate
2H+
+ HIO4 + 2I-
HIO3 + I2 + H2O
The iodic acid produced is itself capable of oxidizing iodide.
5H+
+ HIO3 + 5I-
3I2 + 3H2O
The overall result is- each mole of periodic acid yields 4moles of iodine.
Ex. Glycol oxidation. (Ethylene glycol)
Solution + excess periodic acid each HIO4 leads to 4I2 and
each HIO3 leads to 3I2
Note: if n no. of hydroxy group n-1 mole of periodic acid will be consume
and its equivalent weight is equal to 1/2(n-1) times its molecular weight.
Ex. Ethylene glycol n=2 ; MW/2 like wise.

13. iodine titration
Iodimetric Iodometric
Direct titration Direct titration (I2 liberates in
reaction KIO3 + KI)
Iodine used as titrant KIO3 used as titrant which react with
KI
Carried at neutral or alkaline solution
because it form hypoiodate ion from
I2 which is strong oxidizing agent
Carried at highly acidic condition.
Starch indicator added earlier in
titration
Starch added near end point because
it get decompose in highly acidic
condition
End point blue to colorless End point is brown to pale yellow to
colorless
Ex. Titration of iodine with Na2S2O3 Ex. Titration of Na2S2O3
with KIO3 /KBrO3 /K2 Cr2O7