In redox titration both the oxidation and reduction reaction take place. Titration is based on the oxidation and the reduction mechanism.

1. REDOX TITRATION
ASWINI SASIDHARAN
Assistant Professor
Nirmala College Of Pharmacy

2. REDOX TITRATION
 In redox titration both the oxidation and reduction
reaction takes place.
 Titration is based on the oxidation and the reduction
mechanism

3. OXIDATION
 Old concept - combination of the substances with oxygen is
termed as oxidation
C + O2 CO2
 Advanced concept - loss of electron is known as oxidation

4. REDUCTION
 Old concept - removal of oxygen from the substance
 Advanced concept - gain of electron is known as reduction

5. Oxidizing agent
 Substance which oxidizes others and itself get reduced.
 Substance which gain electrons are called as oxidizing agent.
 Eg- Potassium permanganate (KMnO4)
Hydrogen peroxide (H2O2)
Potassium iodate (KIO3)
Potassium bromate (KBrO3)
Potassium dichromate. (K2Cr2O7)

6. Reducing agents
 Substance which reduce others and itself get oxidized
 Substance which loss electrons are called as reducing
agents
 Eg- Iodide Ion
Hydrogen peroxide
Metal salts

8. Theory of redox titration
OXIDATION REDUCTION
In terms of electrons,
loss of electron by an atom, molecule or
ion is known as oxidation
In terms of electron, gain of electron by
an atom molecule or ion is known as
reduction
In terms of hydrogen,
Removal or loss of hydrogen from a
substance
In terms of hydrogen, gain or addition of
hydrogen to a substance
In terms of oxygen,
addition of oxygen to a substance
In terms of oxygen,
removal or loss of oxygen from a
substance

9.  Combination of oxidizing and reducing agents form a
chemical reaction which is used for the determination of
one of the reactant.
 Eg- Assay of ferrous sulphate

10. Redox potential
Tendency of a species to either reduced by
accepting electron or oxidized by donating
electrons

11. Nernst Equation
 The potential E (half cell potential) of any electron is given by equation
where;
 E= electrode potential of half cell
 Eo= standard electrode potential
 R= universal gas constant
 T= temperature
 F= Faradey's constant
 n =number of electron transferred into the half reaction
 [oxidation] = concentration of oxidized species
 [reduction] = concentration of reduced species

12.  By combining numerical constants [R, T, F] and
converting to logarithm

13. Redox indicators
 Indicators used in redox titration.
 Produce sudden change in oxidation-reduction potential
near end point.
 Most are dyes
 Used in low concentration
 Exhibit different colour in oxidized and reduced form

14. REDOX INDICATORS
internal indicator self indicator external indicator
potassium
ferricyanide
KMnO4
iodine
Ferroin
starch iodide
instrumental indicator

15. Internal indicator
 Compounds which have characteristic colour in
oxidized and reduced state
 [O] & [R] is reversible
 Eg- ferroin sulphate – used in cerimetry

16. External indicators
 Used in the titration of Fe Vs Potassium dichromate
 Fe2+ in the solution ----------- blue colour
 Fe3+ in the solution after end point does not produce colour

17. Self indicator
 Titrant itself acts as indicator
 Colorant titrant-------------------sharp colour change
 Eg- KMnO4, PURPLE COLOUR OF MnO4- ions
disappears on reduction.
 KMnO4 solution is coloured.
 Reduced form is colourless
 After the end point, single drop will produce pink colour.
R
-

18. TYPES OF REDOX TITRATION
 CERIMETRY
 IODIMETRY
 IODOMETRY
 BROMATOMETRY
 DICHROMETRY
 TITRATION WITH POTASSIUM IODATE

19. CERIMETRY/CERIOMETRIC
TITRATION

20. CERIMETRY/CERIOMETRIC TITRATION
PRINCIPLE
 Ceric ammonium sulphate acts as oxidizing agent.
 It can exist in +4 and +3 oxidation state
 Cerium atom in +4 oxidation state acts as better oxidant than +3
oxidation state
 Intense yellow colored solution is formed
 It is a self indicator
 Ceric ammonium sulphate is a powerful oxidant reduce yellow colored
Ce4+ ions into Ce3+ ion.

21. PRINCIPLE
 Ceric ammonium sulphate acts as self indicator only in strong
solutions
 In dilute solution, additional indicator is added.
Ce4+ + e Ce3+
 It cannot be used as an oxidizing agent in either basic/neutral
solution due to precipitation of ceric hydroxide
 Ceric ammonium solution act as oxidant in only acidic solution
 It is a better oxidizing agent.

22. Applications
 Assay of ferrous Ammonium Sulphate
 Determination of Titanium, chromium, uranium, vanadium,
oxides of Manganese, copper, formic acid, Tartaric acid, etc

23. Assay of ferrous Sulphate

24. Preparation of 0.1M Ceric ammonium sulphate
Weigh 65g of ceric ammonium sulphate and heat in a mixture of
30ml of H2SO4
Add 500ml of water
Cool and filter the solution (if turbid)
Dilute to 1000ml with water

25. Standardization of 0.1M Ceric ammonium sulphate
Weigh 3.92g of ferrous ammonium sulphate
Dissolve in a mixture of 4ml of 1M H2SO4
Add 20ml of water and makeup to 100ml with water in a standard flask
Pipette out 10ml solution from it
Add 2 drops of ferroin indicator
Titrate the contents in flask with 0.1 M ceric ammonium sulphate
Endpoint [ORANGE-----------GREEN]

26. Assay of ferrous sulphate
Weigh 0.5g ferrous sulphate
Dissolve in a mixture of 30ml of water and 20ml of 1M
H2SO4
Titrate with 0.1M ceric ammonium sulphate using ferroin
as indicator
Endpoint [orange--------green]

27. IODINE TITRATIONS
 Titration that involves iodine.
 Iodine acts as mild or weak oxidizing agent
2 TYPES:-
IODIMETRY
IODOMETRY

28. IODIMETRY

29. IODIMETRY
 Direct titration
 Type of redox titration
 Free iodine is used
 Iodine acts as mild or weak oxidizing agent
 Titration involves iodine is referred as iodine titration
 Based on the reaction in which iodine is converted into iodide

30. First iodine is mixed with potassium iodide because
it is not easily soluble in water

31.  Starch solution is used as indicator
 Iodine will react with starch
 It forms IODINE-STARCH COMPLEX

32. Preparation & Standardization of 0.05M Iodine
Preparation
14g of Iodine + 36g of KI
Add 3drops of HCl
Dilute to 1000ml with water

33. Standardization
0.15g of Arsenic trioxide [As2O3]
Add 2ml of NaOH Solution
Add 40ml water & dil. HCl
2g of NaHCO3 [Sodium bicarbonate]
Dilute with 50ml of water & add 3ml starch solution until
permanent blue color is produced

34. REACTION

35. Eg- Assay of ascorbic acid
Oxidation of ascorbic acid to dehydroascorbic acid with iodine in
acidic solution

36. PROCEDURE
Weigh 0.1g sample & dissolve in 100ml of freshly boiled
and cooled water
Add 25ml of 1M H2SO4
Titrate with 0.05M Iodine
Starch-----indicator

37. Applications
 Determination of ascorbic acid
 To determine the percentage purity of antimony
trichloride

38. IODOMETRY

39. IODOMETRY
Indirect titration
Type of redox titration
In this titration liberated iodine is used
Standard solution of sodium thiosulphate is used
for the determination of liberated iodine
Starch -indicator

40. Preparation Of 0.1M Sodium
Thiosulphate
Weigh 25g of sodium thiosulphate
add 0.2g of Na2CO3
Dilute to 1000ml with water

41. Standardization of sodium thiosulphate
Weigh 0.2g KBr
Makeup to 250ml with water
Pipette out 25ml from it
Add 1g KI and 1.5ml 2M HCl
Titrate with sodium thiosulphate
Indicator---starch [endpoint- blue to colorless]

42. Eg- Assay of copper sulphate
Weigh 1g sample
Dissolve in 100ml water
Pipette out 20ml from it
Add 3g KI
Titrate the liberated iodine with 0.1M sodium thiosulphate
Indicator- starch

43. Reactions

44. APPLICATIONS
Assay of copper sulphate
Assay of chlorinated lime
Assay of chloramine
Assay of benzyl benzelene

45. IODOMETRY IODIMETRY
Titration of liberated iodine
using primary std solution
Titration of substances using std
iodine solution
Indirect titration Direct titration
Analyzing several
compounds(most compounds
have the ability to oxidize iodide
to iodine)
Only few compounds are
analyzed (using iodine solution)
Applications Applications
• Assay of copper sulphate
• Assay of chlorinated lime
• Assay of chloramine
• Assay of benzyl benzelene
• Determination of ascorbic
acid
• To determine the percentage
purity of antimony trichloride