Potentiometry involves measuring electrode potentials across electrochemical cells to perform electrochemical analysis. An electrochemical cell consists of two half-cells connected by a salt bridge. In one half-cell, oxidation occurs, generating electrons that travel through the salt bridge to the other half-cell, where reduction occurs. The potential difference between the indicator and reference electrodes relates to the analyte concentration based on the Nernst equation and can be used to determine concentration. Common applications of potentiometry include clinical analysis, environmental analysis, and potentiometric titrations for accurate endpoint detection.

1. Mehrab Tahir
19S- 0324
Potentiometry
Lecture Summary
Potentiometry: Electro-chemical analysis by studying Electrode potentials across Electro-chemical cells.
Electro-Chemical cell: A circuit of 2 half cells connected by salt bridge(junction). Here Electrons
generated in one half cell are used up in the other through Redox (chemical ) reactions. The movement
of electrons from the Oxidation half cell (anode, Reference electrode=maintained fixed potential Eref
)
towards the Reduction half cell (cathode, Indicator electrode=varied potential Eind
directly propotional
to analyte ion concentration) plus the movement of current through the salt bridge(junction potential Ej
)
acount for the net electrical activity through this apparatus.
Hence Ecell
= Eind
- Eref
+ Ej
Theory: Through the use of Nernst Equation, concentration c of analyte solution can be calculated :
Ecell
= Eref
+(0.592/n) log c where n=valency of analyte ions
Left Side:
Anode
Reference Electrode
Oxidation Reaction
M(s) Mn(+)
(aq) + ne_
Right Side:
Cathode
Indicator Electrode
Reduction Reaction
*Mn(+)
(aq) + ne_
*M(s)
M(s) M(s)
ne_
e_
e_
e_
e_
ne_
Mn(+)
(aq) *Mn(+)
(aq)
Types of
Ref. Electrodes:
1. Primary Standard
Electrode
e.g. SHE
2. Secondary
Standard
Electrode
e.g. Saturated Calomel
Electrode
Types of
Ind. Electrodes:
1. Metal indicator
Electrode
2. Ion-Selective
Electrode
What is potentiometry?
Potentiometer
Salt Bridge
Analyte Solution
Reference Solution

2. Applications of potentiometry
How do we perform potentiometric titrations?
Clinical Chemistry: Clinical sample analysis (analyte conc. detected)
Environmental Chemistry: Analysis of samples of air, water etc
Potentiometric Titrations: pH change, end point detection with much accuracy
Agriculture: Analysis of soil, fertilizers, plant materials.
Food Processing: Analysis of food samples for nutrients/toxins
Apparatus Setup:
Precipitation Titration:
M(s)
ne_
*Mn(+)
(aq)
Potentiometer
Titrate in burette
2H+
(aq)
e_
e_
Titrand/ Analyte Solution
H2
ne_
Ag(s)
ne_
Ag+
(aq)
Potentiometer
halides e.g. Iodide, Chloride, Bromide etc
2H+
(aq)
e_
e_
AgNO3
H2
ne_ AgNO3
+ NaCl (limited as per titrand conc.)
AgCl + NaNO3
At End Point:
When all NaCl is used up,
AgNO3 drop next added
Ag+
conc. increases
EMF spikes up
EMF
AgNO3 (ml)
End Point
Sharp EMF Rise
observed at End Point
SHE
SHE

3. Acid-Base Titration:
NaOH + HCl (limited as per titrand conc.)
NaCl +H-OH
At End Point:
When all HCl is used up,
NaOH drop next added
OH-
conc. increases
pH spikes up
pH
NaOH (ml)
pH Acidic
pH Basic
Sharp pH Rise
observed at End Point
End Point
1-Strong Acid- Strong Base Titration
NH4
OH + HCl (limited as per titrand conc.)
NH4
Cl + H-OH
At End Point:
When all HCl is used up,
NH4
OH drop next added
OH-
conc. increase
pH increases slightly
2-Strong Acid-Weak Base Titration
pH Acidic
pH Basic
pH
NH4
OH (ml)
Slight pH Rise
observed at End Point
End Point
pH Basic
End Point
pH Acidic
NH4OH + Acetic Acid (limited as per titrand conc.)
NH4-acetate + H-OH
At End Point:
When all acetic acid is used up,
NH4
OH drop next added
OH-
conc. increase
pH increases slightly
pH
NH4
OH (ml)
Slight pH Rise
observed at End Point
4-Weak Acid-Weak Base Titration
pH Acidic
pH Basic
NaOH + Acetic Acid (limited as per titrand conc.)
Na-acetate + H-OH
At End Point:
When all acetic acid is used up,
NaOH drop next added
OH-
conc. increase
pH increases
pH
NaOH (ml)
pH Rise
observed at End Point
End Point
3-Weak Acid- Strong Base Titration

4. Much like the conventional Redox Potentiometry.
Involves the transfer of electrons from the substance being oxidized to the substance being reduced.
Oxidation/Reduction Titration:
Complex Formation Titration:
Cu(s)
ne_
Cu+2
(aq)
Potentiometer
EDTA
2H+
(aq)
e_
e_
CuSO4
H2
ne_
CuSO4
+ EDTA (limited as per titrand conc.)
Cu-EDTA Complex
At End Point:
When all EDTA is used up,
CuSO4
drop next added
Cu+2
conc. increases
abrupt EMF changes
SHE