Permanganate titration by krishna baokar

OXIDATION-REDUCTION�(Permanganate Titration)

1. 1
OXIDATION-REDUCTION
(Permanganate Titration)
Mr. SHRIKRISHNA BAOKAR



Delonix Society’s
BARAMATI COLLEGE OF PHARMACY, BARHANPUR, BARAMATI
Email: [email protected]
Website: krishnabaokar.wordpress.com
Contact No. 9960225455
delonixsociety.org.in

2. Strictly for reference 2
The learner will be able to:
•Introduce permanganometry.
•Knows why Potassium Permanganate is not
used as primary standard.
•Learn why Permanganate solution must be
kept in a dark place or in dark glass bottles
•Preparation and standardization of
Potassium Permanganate .


Learning Outcomes

3. Strictly for reference 3
1.Why Potassium Permanganate acting as a
self indicator?
2.Why does permanganate behave
differently in acidic, neutral and basic
conditions





Reflection Spot

4. •Potassium permanganate is a very powerful
oxidizing agent.
•It was first introduced in volumetric analysis
by F. Marguerette in 1840 for the titration of
ferrous iron.
•It is readily available at moderate cost and
acts as a self indicator in most titrations.
•It is widely used volumetric oxidizing agent
Strictly for reference 4
PERMANGANATE TITRATIONS: Introduction

5. Why does permanganate behave differently in
acidic, neutral and basic conditions……?
Look at this ionic reaction….
Mno
2 + 4H
+
+2e -> Mn
++
+2H
2o ……(1)
•This is a two way reaction….
•Mno
2 gets reduced in presence of H
+
conditions
to Mn
++
.
•Absence of H
+
reverses the reaction,

•But we have to note that in reaction…….(1)
Mno
2 may also be formed but the amount of
acid taken to convert it into Mn
++
is negligible.
Strictly for reference 5
PERMANGANATE TITRATIONS: Introduction

6. •In acid solution the permanganate is most
widely used.
MnO
4- + 8H
+
+ 5e
-
 Mn
2+
+ 4H
2O
E
o = +1.51 V
•In Neutral or alkaline solution
2KMnO
4 + H
2O  2MnO
2 + 2KOH + 3[O]
E
o = + 0.59 V
•This shows (oxidation potential) that in acid
solution permanganate is a strong oxidizing
agent than in alkaline solution, and the
reducing agents which can be titrated with it in
acid solution are much more numerous.

Strictly for reference 6
PERMANGANATE TITRATIONS: Introduction

7. •Further almost colorless Mn
++
ions, which
remain in solution, are formed by titration in
acid solution.
•Titration in neutral or alkaline solution results
in formation of dark brown precipitate of
Manganous dioxide makes very difficult to
establish the equivalence point during the
titration.
• Therefore the oxidation with permanganate
in acid solution is generally used in
volumetric analysis.
Strictly for reference 7
PERMANGANATE TITRATIONS: Introduction

8. •Potassium permanganate is not a primary
standard because it is difficult to obtain a
substance perfectly pure and free from
manganese dioxide.
•Distilled water which is used to prepare the
solution is likely to contain reducing substances
like traces of organic matter etc. which will
react with potassium permanganate to form
manganese dioxide.
•The presence of manganese dioxide is highly
objectionable because it catalyses the auto
decomposition of the permanganate solution
on standing.
2MnO
4
-
+ 3Mn
+2
+ 2H
2O → 5MnO
2 + 4H
+

8
PERMANGANATE TITRATIONS: Disadvantages

9. •This reaction is slow in acid solution but is very
rapid in neutral solution.


•The decomposition is catalyzed by light, heat,
acids, bases, Mn
2+
ion and MnO
2 .

•It always contains some reduction products
such as MnO
2. Moreover it is easily
decomposed by reducing agents- ammonia,
organic substances entering the water in the
form of dust, etc. because of this the
concentration of a KMnO
4 solution falls
somewhat after preparation.
Strictly for reference 9
PERMANGANATE TITRATIONS: Disadvantages

10. •It must be remember that permanganate
oxidizes rubber, cork, paper etc these
substances must not be allowed to come in
contact with solution.
eg. Solution must filtered through the sintered
glass crucible but not through the paper.

•Permanganate solution must be kept in a dark
place or in dark glass bottles, because light
accelerates decomposition of KMnO
4 by the
reaction
4 KMnO
4­ + 2H
2O → 4MnO
2 + 4KOH + 3O
2↑
Strictly for reference 10
PERMANGANATE TITRATIONS: Disadvantages

11. •In the view of all these considerations
KMnO4 is prepared.

•Single drop of KMnO
4 solution, even at a
concentration of 0.01N, confers a distinct
pink colour to 50 ml solution at the end
point, there is no need to use 0.1N
permanganate solution. Generally 0.02N
solutions are used.
Strictly for reference 11
PERMANGANATE TITRATIONS: Preparation of KMnO4

12. •0.63g (0.02 x 31.61g) is dissolved in 1 liter water.
•KMnO
4 crystals dissolve slowly so heat a part of
water (1 liter) dissolve, decant again repeat
the procedure.
•The solution should be kept for 7-10 days or the
process accelerated by boiling for 1-2 hrs.
•All the precautions mentioned above should
be taken care( storing,stopper,filtering etc)

Strictly for reference 12
PERMANGANATE TITRATIONS: Preparation of KMnO4

13. •With oxalic acid
•With sodium oxalate,
•With ferrous ammonium sulphate,
•Arsenic trioxide,
•Potassium ferricyanide.
Strictly for reference 13
PERMANGANATE TITRATIONS: Standardization of KMnO4

14. •The most convenient of the above are sodium
oxalate and oxalic acid.
•Both must be chemically pure and must
correspond to there formulas.
•It is easy to purify Sodium Oxalate (Na
2c
2o
4)by re
crystallization from water and drying
at 240
0
– 250
0
c.
•Oxalic acid is more difficult to purify and is non
hygroscopic, however it contains water of
crystallization and it is efflorescent.

Strictly for reference 14
PERMANGANATE TITRATIONS: Standardization of KMnO4

15. Strictly for reference 15
PERMANGANATE TITRATIONS: Standardization of KMnO4

16. •For sodium oxalate: 0.02 x 67.00 x 0.25
For oxalic acid : 0.02 x 63.03 x 0.25,
•Transfer the substance without loss in a
250ml flask mix, make up to volume with
water.
•Calculate and record the normality of the
solution.

Strictly for reference 16
PERMANGANATE TITRATIONS: Standardization of KMnO4

17. •Pipette out 25ml of primary std solution.
•Add 2 N sulfuric acid solution
•Heat to 75
o
c-80
o
c( boiling will decompose the
oxalic acid) ,………………(Please refer whole
procedure at Alexeyev p no 348).
•3 concurrent readings to be taken and
calculations for normality is done.
Strictly for reference 17
PERMANGANATE TITRATIONS: Standardization of KMnO4

18. Determination of -
• Ferrous Ion,
• Nitrites
• H
2O
2 (Hydrogen peroxide),

Strictly for reference 18
PERMANGANATE TITRATIONS: Applications

19. •Proceed with the titration but in contrast to
titration of oxalic acid is performed with cold
solution as ferrous salts are oxidized by
atmospheric oxygen on heating.
Strictly for reference 19
PERMANGANATE TITRATIONS: Applications
Ferrous Ion

20. (H
2O
2)






•Since commercial hydrogen peroxide
contains about 30% H
2O
2 it must be diluted
to great extent with water,
•Rest of procedure……….Alexeyev p no 349


Strictly for reference 20
PERMANGANATE TITRATIONS: Applications

21. (Nitrites)
Strictly for reference 21
PERMANGANATE TITRATIONS: Applications
•As a result titration process must be reversed to
avoid losses
•Kmno
4 is taken in flask and nitric solution in
burette,
When the solution comes in contact with Kmno
4 it
is oxidized to nitrate instantly and nitrogen oxides
are not formed.
Procedure………………Alexeyev p no 350

22. •Determination of iron in ferric chloride
applications,
•Determination of chromium in potassium
dichromate solution,
•Determination of calcium in calcium carbonate,
•Determination of manganese steel( cast iron)
etc.

Strictly for reference 22
PERMANGANATE TITRATIONS: Applications

23. “When you live for others' opinions, you are dead.
I don't want to live thinking about how I'll be remembered."

-- Carlos Slim Helu

Strictly for reference 23
PERMANGANATE TITRATIONS: