Potentiometry is an analytical technique that measures the potential of electrochemical cells without drawing current. It involves using a reference electrode with a known potential and an indicator electrode whose potential varies with analyte concentration. The cell potential is measured and related to concentration using the Nernst equation. Common reference electrodes include the standard hydrogen electrode and saturated calomel electrode. Glass membrane and ion-selective electrodes are often used as indicator electrodes to detect specific ions like hydrogen or fluoride ions. Potentiometry finds applications in clinical analysis, environmental monitoring, and titration experiments.

1. Potentiometry
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2. Potentiometry
• Potentiometric methods of analysis are based on measuring the
potential of electrochemical cells without drawing appreciable
current.
• The equipment required for potentiometric methods is simple and
inexpensive and includes:
1. An Indicator electrode
2. A Reference electrode
3. A Potential measuring device
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3. Principle
• The basic principle involved in the Potentiometry is when the pair of
electrodes is placed in sample solution, it shows the potential
difference by addition of the titrant or by the change in concentration
of the ions.
• The electromotive force of the complete cell is given by the following
equation:
E cell = E reference + E indicator + E junction
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4. REFERENCE ELECTRODE
A reference electrode is a half-cell having a known potential that remains constant at
constant temperature and independent of the composition of the analyte solution. The
reference electrode is always treated as the left-hand electrode in potentiometric
measurements.
INDICATOR ELECTRODE
An indicator electrode has a potential that varies with variations in the concentration of
an analyte. Most indicator electrodes used in potentiometry are selective in their
responses.
SALT BRIDGE
a salt bridge that prevents the components of the analyte solution from mixing with
those reference electrode. A potential develops across the liquid junctions at each end of
the salt bridge. The junctions potential across the salt bridge is small enough to be
neglected.
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5. Instrumentation of Potentiometry:
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6. Theory:
• The main theory involved in the potentiometry is, when the known
potential electrode immersed in the sample solution then the
potential is given by Nernst equation:
E= E₀ +(0.592/n) log c
• Where E is the potential of the solution; E₀ is the standard electrode
potential; n is the valency of the ions; c is the concentration of the
sample solution; 0.592 is the value obtained from the RT/F; where R is
the gas constant, T is the temperature in Kelvin, F is the faradays
constant.
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7. Electrodes:
• These are mainly used to measure the voltages. Mainly two
electrodes are used in the potentiometry .They are as follows:
 Reference electrode
 Indicator electrode
• Reference electrode: These are mainly used for the determination of
the analyte by maintaining the fixed potential. The reference
electrodes are classified into two main classes they are as follows:
 Primary standard electrodes ex: Standard hydrogen electrode
 Secondary standard electrodes ex: silver-silver chloride electrode, saturated
calomel electrode
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8. Reference electrode: Standard hydrogen
electrode
• It consists of a platinum wire in an inverted
glass tube.
• Hydrogen gas is passed through the tube at
1atm.
• A platinum foil is attached at the end of the
wire.
• The electrode is immersed in 1M H⁺ ion
solution at 25°C.
• The electrode potential of SHE is ZERO at all
temperatures.
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9. Reference electrode: Saturated Calomel
Electrode
• It is commonly used reference electrode.
• It consists of a glass tube that contains Hg at bottom
covered with solid Hg₂Cl₂ and above this, the tube is
filled with KCl solution.
• A platinum wire is in touch with Hg and it is used for
electrical contact.
• The KCl solution inside tube can have ionic contact
with solution outside and act as a salt bridge.
• The electrode potential of SCE is +0.2422V.
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10. Indicator electrode: It is used to measure the potential of the analyte
solution comparing with that of reference electrode . Its potential is directly
proportional to ion concentration.
Ex: Hydrogen electrode.
Glass electrode.
Antimony –antimony oxide electrode.
There are two classes of indicator electrodes:
 Metal indicator electrodes
 Ion-selective electrodes
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11. Metal Indicator Electrodes
These develop electric potential in response to redox reaction on the
metal surface. These are mainly classified into three types of
electrodes:
• First kind electrodes: They are composed of the metal rod immersed
in its metal solution. Ex: silver electrode dipped in the silver nitrate
solution.
• Second kind electrode: These are composed of the metal wires
coated with the salt precipitates. Ex: Ag/ AgCl/ KCl
• Third kind electrodes: These electrodes are also known as inert
electrodes and redox electrodes. Ex: Pt-H2 electrode
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12. Ion Selective Electrodes
An ion-selective electrode (ISE), also known as a specific ion
electrode (SIE) converts the activity of a specific ion dissolved in
a solution into an electrical potential.
Example:
 Glass membrane electrode
 Fluoride selective electrode
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13. Ion Selective Electrodes: Glass membrane
electrode
A glass electrode is a type of ion-selective
electrode made of a doped glass membrane that is
sensitive to a specific ion. The most common
application of ion-selective glass electrodes is for
the measurement of pH. The pH electrode is an
example of a glass electrode that is sensitive to
hydrogen ions. The voltage of the glass electrode,
relative to some reference value, is sensitive to
changes in the activity of certain type of ions.
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14. Ion Selective Electrodes: Fluoride selective
electrode
A fluoride selective electrode is a type of ion selective electrode sensitive to the
concentration of the fluoride ion. A common example is the lanthanum
fluoride electrode.
In the lanthanum fluoride electrode, the sensing element is a crystal
of lanthanum fluoride (LaF3 )
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15. Applications:
• Clinical chemistry: Ion selective electrodes are present sensors for
clinical samples because of their selectivity for analyte in complex
matrices. The most common analytes are electrolytes such as Na, K,
Ca, H and Cl and dissolved gases such as CO₂.
• Environmental chemistry: For analysis of CN- ,NH₃, NO₃, F in water
and waste water.
• Potentiometric titrations: For determining the equivalence point of
an acid base titration. Possible for redox, precipitation, acid-base,
complexation as well as for all titrations in aqueous and non-aqueous
solvents.
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16. References
• Skoog D A, West D M, Holler F J, Crouch S R, “Fundamentals of
Analytical Chemistry”, CENGAGE Learning, Eighth Edition, page n.
588-632.
• Dotson J D, “The Advantages of Potentiometric Titration”, Sciencing,
Updated May 2018, Page no. 1-3.
• Buck R P, “Ion Selective Electrodes, Potentiometry and
Potentiometric Titrations”, Analytical Chemistry, Volume 44, Issue 5,
April 1972, Page no. 270-295.
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