The document discusses amperometry, an electrochemical method for quantitative analysis involving the measurement of current under constant voltage, with applications in various titrations. It explains the principle, instrumentation, advantages, disadvantages, and types of titration curves associated with the technique. Key components include the dropping mercury electrode and rotating platinum micro-electrode, which are used to quantify analyte concentrations based on diffusion current changes.

1. AMPEROMETRY
Presented By:
K. Muthu Kannan,
II M.Sc.,Chemistry,
S.B.K.College,
Aruppukottai – 626 101.

2. 2
CONTENTS
Introduction
Principle
Instrumentation
Titration curves
Advantages
Disadvantages
Applications

3.  It is one of the electrochemical method.
 It is form of quantitative analysis.
 Derived form ampere, the unit of current.
 It refers to the measurement of current under a constant applied voltage.
 Concentration of the analyte which determine magnitude of the current.
 Diffusion current (or limiting current – residual current) is proportional to the
concentration of the electroactive material present in the solution.
 Electroactive material is removed by interaction with titrating reagent, the
diffusion current will decrease.
INTRODUCTION
3

4. PRINCIPLE
 Potential applied between the indicator electrode (Dropping mercury
electrode) and reference electrode (Saturated calomel electrode) is kept
constant and the current through the electrolytic cell is then measured on
the addition of each increment of titrating solution.
 The diffusion current at an appropriate applied voltage is measured as a
function of the volume of the titrating solution.
 The end point is the intersection of two lines giving the change of current
before and after the equivalence point.
4

5. PRINCIPLE
Id = 607 n C D1/2 m2/3 t1/6
Where,
Id = Diffusion current.
n = Number of electrons involved in the reaction.
C = Concentration of analyte in mmol/lit.
D = Diffusion co-efficient (cm2/sec).
m = Weight of mercury flowing through capillary (mg/sec).
t = Drop time in seconds.
If some of the electroactive material in the analyte is removed by interaction with
some other reagent the diffusion current will decrease proportionally.
Ilkovic Equation
5

6. INSTRUMENTATION
Apparatus
 Pyrex glass, that is three necked, flat
bottomed flask.
 A micro burette.
 Dropping mercury electrode (indicator
electrode) (Cathode).
 Gas outlet for N2, with an additional inlet N2
provision.
 Connected to a reference electrode (Anode).
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7. 7
INSTRUMENTATION
Dropping Mercury Electrode
 Capillary tube about 10 – 15 cm.
 Internal diameter of capillary 20 – 50 µm.
 Drop time 1 – 5 seconds.
 Drop diameter 0.5 mm.
 A vertical distance maintained between
DME and the solution.

8. 8
INSTRUMENTATION
Rotating Platinum Micro-Electrode
 It consist of a glass rod with bent platinum wire
at about 600 rpm.
 Glass tube about 15 – 20 cm length and 6 mm in
diameter.
 A short length of platinum wire extends 5 – 10
mm from the fall of the glass tube.
 Removal of oxygen is done by bubbling purified
nitrogen before the titration.

9.  It is simple to construct.
 Mercury cannot be used as electrode at positive potential
because of its oxidation, RPME is used.
 Diffusion current is 20 times larger than DME which allows to
measure the small concentration of ion.
 The rotating platinum electrode can be used at positive
potential up to +0.9 volt where as DME can be used only +0.4
volt to -2.0 volt.
Advantages of RPME
INSTRUMENTATION
9

10. AMPEROMETRIC TITRATION
10
 The diffusion current at an appropriate applied voltage is measured
as a function of the volume of the titrating solution.
 Intersection of two lines providing the change of current before and
after the equivalence point.
 Depending on the selection of the applied voltage among DME and
reference electrode various kinds of titration curves are obtained.
Titrating Curves

11. 11
AMPEROMETRIC TITRATION CURVES
Titration of reducible ions Vs non reducible ions
(Pb2+) Vs (SO4
2-)
 Reducible ion – Pb2+
 Non-reducible ion – SO4
2-
Pb2+ + SO4
2- → PbSO4
Pb2+ + 2e- → Pb0

12. 12
AMPEROMETRIC TITRATION CURVES
Titration of non reducible ions Vs reducible ions
(Cl-) Vs (Ag+)
 Reducible ion – Ag+
 Non-reducible ion – Cl-
Ag+ + Cl- → AgCl
Ag+ + e- → Ag0

13. 13
AMPEROMETRIC TITRATION CURVES
Titration of reducible ions Vs reducible ions
(Pb2+) Vs (Cr2O7
2-)
 Reducible ion – Pb2+
 Reducible ion – Cr2O7
2-
Pb+2 + Cr2O7
-2 → PbCr2O7
Pb+2 + 2e- → Pb0
Cr6+ + 3e- → Cr3+

14. 14
AMPEROMETRIC TITRATION CURVES
Redox titration (oxidant and reductant)
(I-) Vs (Hg2+)
 Non-reducible ion – I-
 Non-reducible ion – Hg2+

15. ADVANTAGES
15
 Rapid, simple apparatus.
 The reaction carried out can be reversible or irreversible.
 These titration can be carried rapidly because the end point is found
graphically.
 Determining traces 0.001M (0.00001M) with ease and good precision.
 Accuracy is higher in amperometric titration than polarography.
 Amperometric titration can be performed in those cases where both the
titrant and titrated ion do not undergo electrolytic reaction.

16. DISADVANTAGES
16
 If the foreign substances are present in higher concentration than the
substance to be titrated then relative changes of the current becomes
smaller and unreliable results are obtained.
 In accurate results are sometimes obtained because of co-
precipitation.

17. APPLICATIONS
17
 Wider range of applications than polarography because even electro-
inactive substances can be determined using electro-active titrant.
 Determination of moisture by Karl Fischer reagent
(bioamperometry).
 Qualification of ions or mixture of ions.
 Amperometric titrations are used for redox, precipitation and
complexometric titrations of reducible inorganic or organic ions.

18. EXCRCISE PROBLEMS
EXERCISE: 1 The concentration of electroactive substance is measured by -----
---------- in Amperometric titrations.
A. Potential
B. pH
C. Resistance
D. Current
EXERCISE: 2 The -------------- current is proportional to the concentration of
the electroactive species in solution in amperometric methods.
A. Residual
B. Migration
C. Diffusion
D. All of the above
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19. EXCRCISE PROBLEMS
EXERCISE: 3 The indicator electrode mainly used in Amperometric titration is
----------------.
A. SCE
B. DME
C. Cu
D. Pt
EXERCISE: 4 Amperometric titrations can be carried out up to concentration
of -------------.
A. 10-2M
B. 10-4M
C. 10-6M
D. 10-8M
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20. EXCRCISE PROBLEMS
EXERCISE: 5 The shape of the titration curve in Amperometry titration of Ca2+
by sulphate is------------------- .
A. Flat first then rising
B. Falling first then flat
C. Falling first then raising
D. Flat throughout
EXERCISE: 6 Rotating Pt electrode is used as indicator electrode above --------
------- potential with respect to SCE.
A. -0.4 V
B. +0.4 V
C. 0 V
D. 1.1 V
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21. EXCRCISE PROBLEMS
EXERCISE: 8 The shape of the titration curve obtained in the titration of Ni2+
Vs DMG is ------------------ shape.
A. L
B. S
C. V
D. A
EXERCISE: 7 Supporting electrode used in Amperometric titration is -----------.
A. AgCl
B. KCl
C. NaF
D. CaSO4
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22. EXCRCISE PROBLEMS
EXERCISE: 9 ------------- electrode can only be reference electrode from the
below list.
A. DME
B. Rotating Pt
C. SCE
D. Pt
EXERCISE: 10 What is the diameter of DEM ?
A. 10 – 30 µm
B. 20 – 50 µm
C. 0 – 5 µm
D. 20 – 30 µm
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23. EXERCISE: 11 Which sentence is false about DEM ?
A. Potential range -0.4 to +0.18 v
B. 5 – 30 drops per minute is possible
C. Capillary diameter is 20 – 50 µm
D. Potential range +0.4 to -0.18 v
EXCRCISE PROBLEMS
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24. REFERENCES
 https://www.brainkart.com/article/Amperometric-Methods_30873/
 https://www.brainkart.com/article/Amperometric-Methods--Theory_30874/
 https://www.brainkart.com/article/Amperometric-Methods--Instrumentation_30875/
 https://www.brainkart.com/article/Applications-of-Amperometric-Titrations-in-Pharmaceutical-
Substances_30876/
 https://www.slideshare.net/AkshayAkotkar/amperometry
 https://www.slideshare.net/ISFCPISFCollegeofPha/amperometric-titrations
 https://www.slideshare.net/ArpitSuralkar/amperometry-249854286
 https://youtu.be/5mRoyvSOYVA
 https://gpatindia.com/amperometry-titration-principleinstrumentation-and-multiple-choice-questions/
 http://www.expertsmind.com/topic/polarography-and-amperometric-titrations/amperometric-
titrations-911514.aspx