This document discusses potentiometry, which is a method of measuring electrical potential or electromotive force (emf) of a solution using indicator and reference electrodes. It describes the components of a potentiometric cell including the reference electrode, salt bridge, analyte solution, and indicator electrode. Various types of reference electrodes like standard hydrogen, saturated calomel, and silver/silver chloride electrodes are explained. The document also covers different types of indicator electrodes like metallic electrodes, membrane electrodes, and gas sensing probes. Direct potentiometry and potentiometric titration techniques are briefly mentioned.
Polarographic technique is applied for the qualitative or quantitative analysis of electroreducible or oxidisable elements or groups.
It is an electromechanical technique of analyzing solutions that measures the current flowing between two electrodes in the solution as well as the gradually increasing applied voltage to determine respectively the concentration of a solute and its nature.
The principle in polarography is that a gradually increasing negative potential (voltage) is applied between a polarisable and non-polarisable electrode and the corresponding current is recorded.
Polarisable electrode: Dropping Mercury electrode
Non-polarisable electrode: Saturated Calomel electrode
From the current-voltage curve (Sigmoid shape), qualitative and quantitative analysis can be performed. This technique is called as polarography, the instrument used is called as polarograph and the current-voltage curve recorded is called as polarogram
ESTIMATION OF THE RATE OF REACTION WILL BE DONE BASED ON THE POTENTIAL DIFFERENCE BETWEEN REFERENCE AND INDICATOR ELECTRODE. THE POTENTIAL OF THE REFERENCE ELECTRODE IS STABLE WHERE AS THE POTENTIAL OF THE INDICATOR ELECTRODE VARIES WITH THE POTENTIAL OF THE SOLUTION IN WHICH IT IS PLACED
It is an electrochemical method of analysis used for the determination or measurement of the electrical conductance of an electrolyte solution by means of a conductometer.
Electric conductivity of an electrolyte solution depends on :
Type of ions (cations, anions, singly or doubly charged
Concentration of ions
Temperature
Mobility of ions
The main principle involved in this method is that the movement of the ions creates the electrical conductivity. The movement of the ions is mainly depended on the concentration of the ions.
The electric conductance in accordance with ohms law which states that the strength of current (i) passing through conductor is directly proportional to potential difference & inversely to resistance.
i =V/R
Polarographic technique is applied for the qualitative or quantitative analysis of electroreducible or oxidisable elements or groups.
It is an electromechanical technique of analyzing solutions that measures the current flowing between two electrodes in the solution as well as the gradually increasing applied voltage to determine respectively the concentration of a solute and its nature.
The principle in polarography is that a gradually increasing negative potential (voltage) is applied between a polarisable and non-polarisable electrode and the corresponding current is recorded.
Polarisable electrode: Dropping Mercury electrode
Non-polarisable electrode: Saturated Calomel electrode
From the current-voltage curve (Sigmoid shape), qualitative and quantitative analysis can be performed. This technique is called as polarography, the instrument used is called as polarograph and the current-voltage curve recorded is called as polarogram
ESTIMATION OF THE RATE OF REACTION WILL BE DONE BASED ON THE POTENTIAL DIFFERENCE BETWEEN REFERENCE AND INDICATOR ELECTRODE. THE POTENTIAL OF THE REFERENCE ELECTRODE IS STABLE WHERE AS THE POTENTIAL OF THE INDICATOR ELECTRODE VARIES WITH THE POTENTIAL OF THE SOLUTION IN WHICH IT IS PLACED
It is an electrochemical method of analysis used for the determination or measurement of the electrical conductance of an electrolyte solution by means of a conductometer.
Electric conductivity of an electrolyte solution depends on :
Type of ions (cations, anions, singly or doubly charged
Concentration of ions
Temperature
Mobility of ions
The main principle involved in this method is that the movement of the ions creates the electrical conductivity. The movement of the ions is mainly depended on the concentration of the ions.
The electric conductance in accordance with ohms law which states that the strength of current (i) passing through conductor is directly proportional to potential difference & inversely to resistance.
i =V/R
content- Principle
Ilkovic equation
Construction and working of dropping mercury electrode and rotating platinum electrode
Applications
Polarography is a voltammetric technique in which chemical species (ions or molecules) undergo oxidation (lose electrons) or reduction (gain electrons) at the surface of a dropping mercury electrode (DME) at an applied potential. Polarography only applies to the DME.
Objective of polarography
Polarography is an electroanalytical technique that measures the current flowing between two electrodes in the solution (in the presence of gradually increasing applied voltage) to determine the concentration of solute and its nature respectively
Polarography is based upon the principle that gradually increasing voltage is applied between two electrodes, one of which is polarisable (dropping mercury electrode) and other is non-polarisable and current flowing between the two electrodes is recorded.
A sigmoid shape current-voltage curve is obtained from which half wave potential as well as diffusion current is calculated.
Diffusion current is used for determination of concentration of substance.
Half wave potential is characteristic of every element.
Ilkovic equation is a relation used in polarography relating the diffusion current (id) and the concentration of the non-polarisable electrode, i.e., the substance reduced or oxidised at the dropping mercury electrode (polarisable electrode).
Definitions of types of currents
1. Residual current (ir), 2. Migration current (im): , 3. Diffusion current (id) 4.Half wave potential 5. Limiting current (il)
Dropping mercury electrode- Dropping mercury electrode (DME) is a polarisable electrode and can act as both anode and cathode.
The pool of mercury acts as counter electrode,
i.e., anode if DME is cathode or
cathode if DME is anode.
The counter electrode is a non-polarisable electrode.
To the analyte solution, electrolyte like KCl is added i.e., 50-100 times of sample concentration.
Pure nitrogen or hydrogen gas is bubbled through the solution, to expel (remove) out oxygen.
Eg: If the analyte solution contains cadmium ions, then cadmium ions are discharged at cathode (-)
Cd2+ + 2e- → Cd
Then, gradually increasing voltage is applied to the polarographic cell and current is recorded.
Graph is plotted between voltage applied and current. This graph is called Polarograph and the apparatus is known as Polarogram.
The diffusion current produced is directly proportional to concentration of analyte and this is used in quantitative analysis.
The half wave potential is characteristic of every compound and this is used in qualitative analysis.
Graph is plotted between voltage applied and current. This graph is called Polarograph and the apparatus is known as Polarogram.
The diffusion current produced is directly proportional to concentration of analyte and this is used in quantitative analysis.
The half wave potential is characteristic of every compound
The earliest voltammetric technique
Heyrovsky invented the original polarographic method in 1922, conventional direct current polarography (DCP).
It employs a dropping mercury electrode (DME) to continuously renew the electrode surface.
Diffusion is the mechanism of mass transport.
When an external potential is applied to a cell
containing a reducing substance such as CdCl2,
The following reaction will occur:
Cd2+ + 2e + Hg = Cd(Hg)
The technique depends on increasing the applied
voltage at a steady rate and simultaneously
record photographically the current-voltage
curve (polarogram)
The apparatus used is called a polarograph .
When an external potential is applied to a cell
containing a reducing substance such as CdCl2,
The following reaction will occur:
Cd2+ + 2e + Hg = Cd(Hg)
The technique depends on increasing the applied
voltage at a steady rate and simultaneously
record photographically the current-voltage
curve (polarogram)
The apparatus used is called a polarograph .
Capillary tube about 10-15cm
Int. diameter of 0.05mm
A vertical distance being maintained betwwen DME and the solution
Drop time of 1-5 seconds
Drop diameter 0.5mm
The supporting electrolyte
is a solution of (KNO3, NaCl, Na3PO4) in which the sample (which must be electroactive) is dissolved.
Function of the supporting electrolyte
It raises the conductivity of the solution.
It carries the bulk of the current so prevent the
migration of electroactive materials to working
electrode.
It may control pH
It may associate with the electroactive solute as
in the complexing of the metal ions by ligands.
Potentiometry, Electrochemical cell, construction and working of indicator an...Vandana Devesh Sharma
Potentiometry - Electrochemical cell -Construction and working of reference (Standard hydrogen, silver chloride electrode and calomel electrode)
Indicator electrodes (metal electrodes and glass electrode)
Methods to determine end point of potentiometric titration
and applications
Potentiometry is the method to find the concentration of solute in
A given solution by measuring the potential between two Electrodes
(reference and Indicator electrode) . Potentiometric titration involves
the measurement of the potential of the indicator electrode and
reference electrode.
In potentiometric titration reference and indicator electrodes are
immersed in the solution of particular analyte (titrand) and
potential of indicator electrode is measured with relation to
reference electrode.
Titrant is added in analyte (Titrand) and change in potential is noted
down.
At the end point there is sharp change in potential on indicator
electrode.
Graph is plotted between the indicator electrode potential and
volume of titrant added.
This method is used for determination of sharp end point.
Types of Potentiometric Titration
1. Acid-base titration 2. Redox Titration 3.Complexometric titration 4. Precipitation Titration
This presentation includes the most important cell used in polarography Dropping Mercury Electrode. Its structure, uses/Advantages and limitations are explain here
Amperometry refers to the measurement of current under a constant applied voltage and under these conditions it is the concentration of analyte which determine the magnitude of current.
In Amperometric titrations, the potential applied between the indicator electrode (dropping mercury electrode) and the appropriate depolarizing reference electrode (saturated calomel electrode) is kept constant and current through the electrolytic cell is then measured on the addition of each increment of titrating solution. It is a form of quantitative analysis.
Otherwise called as Polarographic or polarometric titrations.
Potentiometry is the field of electro-analytical chemistry in which potential is measured without current flow.
It is a method of analysis in which we determine the concentration of solute in solution and the potential difference between two electrodes.
content- Principle
Ilkovic equation
Construction and working of dropping mercury electrode and rotating platinum electrode
Applications
Polarography is a voltammetric technique in which chemical species (ions or molecules) undergo oxidation (lose electrons) or reduction (gain electrons) at the surface of a dropping mercury electrode (DME) at an applied potential. Polarography only applies to the DME.
Objective of polarography
Polarography is an electroanalytical technique that measures the current flowing between two electrodes in the solution (in the presence of gradually increasing applied voltage) to determine the concentration of solute and its nature respectively
Polarography is based upon the principle that gradually increasing voltage is applied between two electrodes, one of which is polarisable (dropping mercury electrode) and other is non-polarisable and current flowing between the two electrodes is recorded.
A sigmoid shape current-voltage curve is obtained from which half wave potential as well as diffusion current is calculated.
Diffusion current is used for determination of concentration of substance.
Half wave potential is characteristic of every element.
Ilkovic equation is a relation used in polarography relating the diffusion current (id) and the concentration of the non-polarisable electrode, i.e., the substance reduced or oxidised at the dropping mercury electrode (polarisable electrode).
Definitions of types of currents
1. Residual current (ir), 2. Migration current (im): , 3. Diffusion current (id) 4.Half wave potential 5. Limiting current (il)
Dropping mercury electrode- Dropping mercury electrode (DME) is a polarisable electrode and can act as both anode and cathode.
The pool of mercury acts as counter electrode,
i.e., anode if DME is cathode or
cathode if DME is anode.
The counter electrode is a non-polarisable electrode.
To the analyte solution, electrolyte like KCl is added i.e., 50-100 times of sample concentration.
Pure nitrogen or hydrogen gas is bubbled through the solution, to expel (remove) out oxygen.
Eg: If the analyte solution contains cadmium ions, then cadmium ions are discharged at cathode (-)
Cd2+ + 2e- → Cd
Then, gradually increasing voltage is applied to the polarographic cell and current is recorded.
Graph is plotted between voltage applied and current. This graph is called Polarograph and the apparatus is known as Polarogram.
The diffusion current produced is directly proportional to concentration of analyte and this is used in quantitative analysis.
The half wave potential is characteristic of every compound and this is used in qualitative analysis.
Graph is plotted between voltage applied and current. This graph is called Polarograph and the apparatus is known as Polarogram.
The diffusion current produced is directly proportional to concentration of analyte and this is used in quantitative analysis.
The half wave potential is characteristic of every compound
The earliest voltammetric technique
Heyrovsky invented the original polarographic method in 1922, conventional direct current polarography (DCP).
It employs a dropping mercury electrode (DME) to continuously renew the electrode surface.
Diffusion is the mechanism of mass transport.
When an external potential is applied to a cell
containing a reducing substance such as CdCl2,
The following reaction will occur:
Cd2+ + 2e + Hg = Cd(Hg)
The technique depends on increasing the applied
voltage at a steady rate and simultaneously
record photographically the current-voltage
curve (polarogram)
The apparatus used is called a polarograph .
When an external potential is applied to a cell
containing a reducing substance such as CdCl2,
The following reaction will occur:
Cd2+ + 2e + Hg = Cd(Hg)
The technique depends on increasing the applied
voltage at a steady rate and simultaneously
record photographically the current-voltage
curve (polarogram)
The apparatus used is called a polarograph .
Capillary tube about 10-15cm
Int. diameter of 0.05mm
A vertical distance being maintained betwwen DME and the solution
Drop time of 1-5 seconds
Drop diameter 0.5mm
The supporting electrolyte
is a solution of (KNO3, NaCl, Na3PO4) in which the sample (which must be electroactive) is dissolved.
Function of the supporting electrolyte
It raises the conductivity of the solution.
It carries the bulk of the current so prevent the
migration of electroactive materials to working
electrode.
It may control pH
It may associate with the electroactive solute as
in the complexing of the metal ions by ligands.
Potentiometry, Electrochemical cell, construction and working of indicator an...Vandana Devesh Sharma
Potentiometry - Electrochemical cell -Construction and working of reference (Standard hydrogen, silver chloride electrode and calomel electrode)
Indicator electrodes (metal electrodes and glass electrode)
Methods to determine end point of potentiometric titration
and applications
Potentiometry is the method to find the concentration of solute in
A given solution by measuring the potential between two Electrodes
(reference and Indicator electrode) . Potentiometric titration involves
the measurement of the potential of the indicator electrode and
reference electrode.
In potentiometric titration reference and indicator electrodes are
immersed in the solution of particular analyte (titrand) and
potential of indicator electrode is measured with relation to
reference electrode.
Titrant is added in analyte (Titrand) and change in potential is noted
down.
At the end point there is sharp change in potential on indicator
electrode.
Graph is plotted between the indicator electrode potential and
volume of titrant added.
This method is used for determination of sharp end point.
Types of Potentiometric Titration
1. Acid-base titration 2. Redox Titration 3.Complexometric titration 4. Precipitation Titration
This presentation includes the most important cell used in polarography Dropping Mercury Electrode. Its structure, uses/Advantages and limitations are explain here
Amperometry refers to the measurement of current under a constant applied voltage and under these conditions it is the concentration of analyte which determine the magnitude of current.
In Amperometric titrations, the potential applied between the indicator electrode (dropping mercury electrode) and the appropriate depolarizing reference electrode (saturated calomel electrode) is kept constant and current through the electrolytic cell is then measured on the addition of each increment of titrating solution. It is a form of quantitative analysis.
Otherwise called as Polarographic or polarometric titrations.
Potentiometry is the field of electro-analytical chemistry in which potential is measured without current flow.
It is a method of analysis in which we determine the concentration of solute in solution and the potential difference between two electrodes.
Potentiometry: Electrical potential, electrochemical cell, reference electrodes, indicator
electrodes, measurement of potential and Ph, construction and working of electrodes,
Potentiometric titrations, methods of detecting end point, Karl Fischer titration.
An ideal I.S.E. consists of a thin membrane across which only the
intended ion can be transported.
The transport of ions from a high conc. to a low one through a selective binding with some sites within the membrane creates a
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2. pH is a Potentiometric Measurement
The Measuring System consists of a pH Measuring
Electrode (indicating electrode) and Reference Electrode
The Potential Difference Between the Two Electrodes is a
Function of the pH Value of the Measured Solution.
The Analyte Solution Must Be Conductive and is Part of
the Electrical Circuit.
3. POTENTIOMETRIC ANALYSIS
Based on potential measurement of
electrochemical cells without any appreciable
current
The use of electrodes to measure voltages from
chemical reactions
5. The potential(E)of a metal elctrode at25 C,immersed into a
solution of its own ions is given by
E=E0 + 0.0592 × logc
n
Where, E0 = standard potential of the electrode
n = valency of ions
c = concentration of ions
Nernest equation
6. COMPONENTS OF A
POTENTIOMETRIC CELL
1. Reference electrode
2. Salt bridge
3. Analyte
4. Indicator electrode
RE SB A IE
– Eref + Ej + Eind
7. REFERENCE ELECTRODE
• Half-cell with known potential (Eref)
• Left hand electrode (by convention)
• Easily assembled
• Rugged
• Insensitive to analyte concentration
▫ Reversible and obeys Nernst equation
▫ Constant potential
▫ Returns to original potential
8. INDICATOR ELECTRODE
Generates a potential (Eind) that depends on
analyte concentration
Selective
Rapid and reproducible response
9. SALT BRIDGE
Prevents mixing up of analyte components
Generates potential (Ej) = negligible
12. HYDROGEN ELECTRODE
o It can be used as Indicator as well
as Reference eletrode.
o It can be consist of platinum foil
coated with platinum balck and has
a wire contacts through a mercury.
o This assembly is enclosed in a glass
covering.
o Hydrogen gas is passed at
1atmospheric pressure
continuously.
o (Pt (H2 (1 atm), H+ (1M)
13. o Then eletrode is dipped into the standard acid /unknown
solution.
o All the times surface of the electrode and the solution
should be saturated with the gas.
o potential ,
o E=E0H+0.0592log[H+]
=E0H-0.0592pH(pH=-log [H+]
E=-0.0592 pH.
E0=std Eof H2 electrode ,taken as 0
14. Advantages and Disadvantages of H2Electrode:
Advantages:
It can be used over the entire pH.
Itcan be used as a reference electrode when dipped with
standard acid solution and as a indicator electrode when
dipped into a sample solution.
It is the primary reference standard against which the
potentials of other electrodes are measured.
Disadvantages
It is effected by the presence of oxidizing agent and reducing
agent.
It is rather difficult to regulate the pressure of H2 gas to be
exactly 1 atm throughout the experiment.
Platinum foil gets easily poisoned by the impurities present in
the H2 gas and Hcl solution.
15. Saturated calomel elctrode
• It consist of inner jacket and outer
sleeve
• Inner tube has a wire contact with
mercury(Hg) and plugged with a
mixture of calomel(Hg2cl2)and KCL.
• This is surrounded by an outer sleeve
• Tip is filled with Crystals of KCL and
porous plug of asbestos.
• The space between inner jacket and
outer sleeve is filled with saturated
KCL/1N KCL/0.1 N KCL.
• Potential of the electrode depends on
• The Concentration of the KCL
Solution. And Temperature.
16. • Merits:
Easy of construction
Stability of Potential.
• Demerits:
Dependent on temp
Toxic
• Applications:
Used in pH Measurement
Equation: Hg2Cl2(s)+2e-2Hg(l)+2Cl-(aq)
• 0.2444 V at 25C
17. Silver –Silver Chloride electrode
It is also widely used reference
electrode,
Because,It is simple
In expensive
Very stable
Non –toxic.
It is mainly used with Saturated KCL
Electrode (kcl electrolyte) but canbe
used with low concentration such as
1MKCL and even directly in sea water.
“Ag-wire coated
electrolytically with AgCl2 and dipped
into KCL
18. Potential depends on the concentration of the KCL and
temperature.
AgAgCl (satd),KCl (satd)
AgCl(s) + e-Ag(s)+Cl-(aq)
E = 0.199 V
Advantage:
Easy to use
Dis advantage:
Difficult to prepare.
19. LIQUID JUNCTION POTENTIAL
Liquid junction - interface between two solutions containing
different electrolytes or different concentrations of the same
electrolyte
A junction potential occurs at every liquid junction.
Caused by unequal mobilities of the + and - ions.
20. INDICATOR ELECTRODES
I. Metallic IE
A. Electrodes of the First Kind
B. Electrodes of the Second Kind
C. Inert Metallic Electrodes (for Redox Systems)
II. Membrane IE/Ion –Selective Electrodes.
A. Glass pH IE
B. Glass IE for other cations
C. Liquid Membrane IE
D. Crystalline-Membrane IE
III.Gas Sensing Probes/Gas Sensing Electrode.
22. ELECTRODES OF THE FIRST KIND
Pure metal electrode in direct equilibrium with its cation
Metal is in contact with a solution containing its cation.
M+n(aq) + ne- M(s)
23. DISADVANTAGES OF FIRST KIND ELECTRODES
Not very selective
Ag+ interferes with Cu+2
May be pH dependent
Zn and Cd dissolve in acidic solutions
Easily oxidized (deaeration required)
Non-reproducible response
24. ELECTRODES OF THE SECOND KIND
Respond to anions by forming precipitates or stable complex
Examples:
1. Ag electrode for Cl- determination
2. Hg electrode for EDTA determination
25. INERT METALLIC (REDOX) ELECTRODES
Inert conductors that respond to redox systems
Electron source or sink
An inert metal in contact with a solution containing the soluble
oxidized and reduced forms of the redox half-reaction.
May not be reversible
Examples:
Pt, Au, Pd, C
26. ION SELECTIVE ELECTRODES
Other synonym:Membrane electrodes
Definition:
“ ISE are known as specific ion electrode, it is a membrane
that Converts the activity of a specific ion dissolved in a
solution into an electrode
Potential”.
The voltage is theoritically dependent on the negative
logerithem of the ionic activity, according to the Nernest
equation.
27. Uses:
ISE are used in analytical chrmistry,bio-chemical/
biophysical research.
whwre, measurements of ionic concentration in
aqueous solutions are required.
TYPES OF ISE:
1.Glass Membrane electrode
2.Liquid-Liquid electrode/Liquid membrane
electrode.
3.Crystal Membrane electrode.
4.Gas sensing electrode.
31. STYLE OF GLASS ELECTRODE
• The glass membrane itself
is not limited to any
configuration or shape; its
only requirement is contact
with solution.
• Therefore, different styles
of glass electrodes have
evolved to maximize pH
sensing ability and extend
longevity in some of the
more difficult applications.
32. PROPERTIES OF GLASS PH ELECTRODE
Potential not affected by the presence of oxidizing or reducing
agents
Operates over a wide pH range
Fast response
Functions well in physiological systems
Very selective
Long lifespan
33. Theory of the glass membrane potential
For the electrode to become operative, it must be soaked in water.
During this process, the outer surface of the membrane becomes
hydrated.
When it is so, the sodium ions are exchanged for protons in the
solution:
The protons are free to move and exchange with other ions.
Charge is slowly carried
by migration of Na+
across glass membrane
Potential is determined
by external [H+]
34. ALKALINE ERROR
Exhibited at pH > 9
Electrodes respond to H+ and
alkali cations
C,D,E and F: measured
value is < true value
Electrode also responds to
other cations
Higher pH at lower [Na+]
35. ACID ERROR
Exhibited at pH < 0.5
pH readings are higher
(curves A and B)
Saturation effect with
respect to H+
36. 2.LIQUID MEMBRANE ELECTRODES
• Potential develops across the interface between the analyte
solution and a liquid ion exchanger (that bonds with analyte)
• Similar to a pH electrode except that the membrane is an organic
polymer saturated with a liquid ion exchanger
• Used for polyvalent ions as well as some anions
• Example:
• Calcium dialkyl phosphate insoluble in water, but binds Ca2+
strongly
41. 3.CRYSTALLINE-MEMBRANE ELECTRODES
Solid state electrodes
Usually ionic compound
Crushed powder, melted and formed
Sometimes doped to increase conductivity
Operation similar to glass membrane
43. EX:F- SELECTIVE ELECTRODE
A LaF3 is doped with EuF2.
Eu2+ has less charge than the La3+, so an anion vacancy occurs
for every Eu2+.
A neighboring F- can jump into the vacancy, thereby moving the
vacancy to another site.
Repetition of this process moves F- through the lattice.
45. 4.GAS SENSING ELECTRODE
A galvanic cell whose potential is related to the concentration of a
gas in solution
Consist of RE, ISE and electrolyte solution
A thin gas-permeable membrane (PTFE) serves as a barrier
between internal and analyte solutions
Allows small gas molecules to pass and dissolve into internal
solution
O2, NH3/NH4
+, and CO2/HCO3
-/CO3
2-
49. POTENTIOMETRIC TITRATION
Involves measurement of the potential of a suitable indicator
electrode as a function of titrant volume
Provides MORE RELIABLE data than the usual titration
method
Useful with colored/turbid solutions
May be automated
More time consuming
51. POTENTIOMETRIC TITRATIONS
Is a technique similar to direct titration of a redox
reaction.
No indicator is used, (instead the potential across the
analyte) typically an electrolyte solution is measured.
To do this, two electrodes are used, an indicator electrode
and a reference electrode.
The indicator electrode forms an electrochemical half
cell with the interested ions in the test solution.
The reference electrode forms the other half cell,
holding a consistent electrical potential.
52. WHEN POTENTIOMETRIC TITRATIONS IS
USED?
It is used when the endpoints are very difficult to
determine either when:
1- very diluted solution.
2-coloured and turbid solution.
3-absence of a suitable indicator.
53. INSTRUMENTS
PH meter
Reference electrode.
Indicator electrode.
Voltmeter which measures the potential difference.
Magnetic stirrer.
hot plate ( use the stirrer and make sure heat is off ).
magnet capsule .
•Glass (burrete and beaker)
54.
55. of 0.1 N NaOH
Potentiometric titration curve of (0.1 N) NaOH against
(?? N ) acetic acid :
56. Do not place the electrodes anywhere except attached to the
electrode holder.
At the end of the experiment rinse the electrodes and place
each one in its housing as required.
Never touch the glass part of the electrode with anything
except soft tissue paper. While in use, the bulb of the glass
electrode should be immersed in solution.
IMORTANT TO KNOW
57. o For short-term storage the combined glass electrode
should be immersed in solution of 2 M KCl.
o Buffer solutions of known pH are used for the pH
calibration.
o For high accuracy, calibration and measurements are to
be performed at the same temperature.
58. 1-the outside surface of the glass membrane is in contact with
the sample being measured.
2-and the inside surface contact the inner filling solution .
3-A complex mechanism at each glass liquid interface defines the
potential of the pH glass electrode.
4-While the pH inner glass /filling solution potential is constant ,
the outside potential varies based on the hydrogen ion
concentration in the sample.
59. Applications of Potentiometry:
1. Direct potentiometry:
A rapid and convinient method of detecting the
activity of cations and anions.
The technique used in this method is a comparison of
the potential developed by the indicator electrode when
it is immersed in the solution with that when it is
immersed in standard solution of the analyte.
2. The calibration curve method:
It is applied for determination of substance by direct
potentiometry.
In which we plot potential of the cell Vs a series of
standard solution of extragrade of the substance to be
determined.
60. Then measure the potential prodused when using the
unknown solution and from the calibration curve we can
obtain its concentrations.
3. Environmental chemistry:
Pollution monitoring: CN,F,S,Li,Na, etc…..in effluents
and natural water
4. Agriculture :
NO3,Cl,I,K,Ca,CN, in Soil, plant material, Fertilizers,
Feedstuffs.
61.
62. 5 . Food processing:
No3,No2 in Meat, and preservatives.
6. Florin in drinking water and other drinkers.
7. Salt content of Meat,Fish,Dairy
products,Fruits,Juices,Brewing Solutions.
8. Potentiometric titrations:
Acid-Basetitrations (aqueous and non aqueous)
Redox titrations
Diazotisation titrations
Precipitation titrations
Complexometric titrations
Dead stop end point technique.
63. 1.Acid –base titrations:
Titrations can be done in aqueous and non-aqueous
medium.
E+k-0.0592pH.
Ex:-Aqueous medium:any strength-0.01N,0.1N,1N.
o Acid-base combinations:
Weak acid - Weak base Weak acid-Strong base
(CH3COOH Vs NH4OH) (CH3COOH-NAOH)
Strong acid-Strong base Strong acid-Weak base
(HCL-NAOH) (HCL-NH4OH)
oMixture of acids Vs bases: (CH3COOH+HCL)Vs NAOH
oMixture of bases Vs acids: (NH4OH+NAOH) Vs HCL.
oPoly basis acids Vs bases: Citric acid Vs NAOH
Tartaric acid Vs NAOH.
64. • Non aqueous medium:
Weak acidVs pottasium(KOME)/Lithium methoxide(Liome)
Ex:-Barbituric acid Vs LiOMe
Weak bases Vs perchloric acid
Ex:-Ephedrine Hydrochloride
/Q.sulphate/Metronidazole/Chloroquine phosphate Vs
0.1NHCLO4.
Indicator electrode:Glass electrode
Reference electrode:SCE
65. 2. Redox-titrations:
Reaction:Ce4+ + Fe2+ Ce3+ + Fe3+
Ce4+ is an oxydising agent which oxidises Fe2+
(ferrous) to Fe3+(ferric ion), in this process
Ce4+(cerric) gets redused to Ce3+ (cerrous ions).
E =E0 + 0.0592/n.log(ox)/(Red).
Where,E0= std potential.
n= no.of electrons involved in the reaction,
(ox)= conc. Of oxidant
(Red)= conc of reductant.
66. Reference electrode:SCE,Ag-Agcl2 electrode.
Indicator electrode:platinum wire or foil.
mv scale is used for end point detection.
Ex:-Ferrous ammonium sulphate in dilute
H2SO4VsKMNO4/K2Cr2O7.
3.Diazotisation titrations:
Drugs or substances containing aromatic amino group can
be titrated against sodium nitrate in acidic medium.
Result in the formation of diazonium salt this type of titration
is called as Diazotisation titration.
67. End point detecting:by
a)Starch iodide paper(externalindicator method)
Potentiometric method of detecting end point.
Reference electrode:SCE
Indicator electrode:Glass electrode.
Ex:Alkaloids,Amines,Sulpha drugs which contain
primary aromatic amino group can be titrated
against0.1N sodium Nitrate in HCl .
68. 4)Precipitation titrations:
For quantitative determination of several ions or elements
precipitating agents are used as titrants,
End point is determined by potentiometric method.
E=E0+0.0592/n.log[Mn+]
where, [Mn+]=conc of ions
n= electronic state.
Reference electrode:SCE,H2,Ag-AgCl2 electrode
Indicator electrode:Silver wire electrode.
69. Ex: Determination of Hg,Ag,Pb,Cu, and other
ions using precipitants to form insoluble salts.
5)Complexometric titrations:
Metalic ions (divalent)can be titrated against disodium
edetate solutions by potentiometric method
Measurements are made inmv scale.
70. • Reference electrode:SCE/ any other.
• Indicator electrode:Ag / Hg electrode.
• Ex:-Di and Trivalent ions.
(mix of Bi3+,Cd2+,Ca2+ by using EDTA).
Applications of Potentiometer
as (I.Pmethods )