2. Introduction
Electrochemistry is branch of chemistry
concern with the interaction of electrical and
chemical effects
A large part of this field deals with the study of
chemical changes caused by the passage of an
electrical current and the production of
electrical energy by chemical reaction.
3. It is named electrochemistry because its
originated from the study of the movement of
electrons in an oxidation–reduction reaction.
Electrochemical methods: are analytical
techniques that use a measurement of
potential, charge, or current to determine an
analyte’s concentration or to characterize an
analyte’s chemical reactivity.
4. It is a qualitative and quantitative methods of
analysis based on electrochemical phenomena
occurring within a medium or at the phase
boundary and related to changes in the structure,
chemical composition, or concentration of the
compound being analyzed.
These methods are divided into five major
groups: potentiometry, voltammetry, coulometry,
conductometry, and dielectrometry.
5. Applications
1. Obtaining thermodynamic data about a
reaction.
2. To generate an unstable intermediate such as
radical ion and study its rate of decay or it is
spectroscopic properties.
3. They use to analyze a solution for trace
amount of metal ions or organic species.
6. 4. The electrochemical properties of the
system themselves are of primary interest,
for example, in the design of a new power
source or for the electrochemical methods
have been developed.
7. Type of electrochemical techniques
1.Bulk techniques, in which we measure a
property of the solution in the
electrochemical cell. An example is the
measurement of a solution’s conductivity,
which is proportional to the total
concentration of dissolved ions,
8. 2. Interfacial techniques, in which the
potential, charge, or current depends on the
species present at the interface between an
electrode and the solution in which it sits.
An example is the determination of pH
using a pH electrode.
9. Despite the difference in instrumentation, all
electrochemical techniques share several
common features.
(1)The electrode’s potential determines the
analyte’s form at the electrode’s surface
(2)The concentration of analyte at the
electrode’s surface may not be the same as its
concentration in bulk solution;
10. (3) Current is a measure of the rate of the
analyte’s oxidation or reduction; and
(4) We cannot simultaneously control
current and potential.
11. Interfacial ElectrochemicalTechniques
The interfacial electrochemical techniques is
divided into Static techniques and dynamic
techniques
Static technique the current is not pass through
the analyte’s solution. Potentiometry, in which
we measure the potential of an electrochemical
cell under static conditions, is one of the most
important quantitative electrochemical methods
12. Dynamic techniques, in which we allow current
to flow through the analyte’s solution, it
comprise the largest group of interfacial
electrochemical techniques e.g. Coulometry, in
which we measure current as a function of time,
Amperometry and voltammetry, in which we
measure current as a function of a fixed or
variable potential
13.
14. Controlling and Measuring Current and
Potential
we cannot simultaneously control both
current and potential
if we choose to control the potential, then we
must accept the resulting current, and we
must accept the resulting potential if we
choose to control the current.
15. The second electrode, which we call the
counter electrode, completes the electrical
circuit and provides a reference potential
against which we measure the working
electrodes potential. Ideally the counter
electrode’s potential remains constant so that
we can assign to the working electrode any
change in the overall cell potential.
16. Electrochemical measurements are made in an
electrochemical cell consisting of two or more
electrodes and the electronic circuitry for controlling
and measuring the current and the potential.
The simplest electrochemical cell uses two
electrodes. The potential of one electrode is
sensitive to the analyst’s concentration, and is
called the working electrode or the indicator
electrode.
17. If the counter electrode’s potential is not
constant, we replace it with two electrodes: a
reference electrode whose potential remains
constant and an auxiliary electrode that
completes the electrical circuit.
Because we cannot simultaneously control the
current and the potential, there are only three
basic experimental designs
18. (1) Measure the potential when the current is zero,
(2) Measure the potential while controlling the current,
(3) Measure the current while controlling the potential
Each of these experimental designs relies on Ohm’s
law, which states that a current, i, passing through an
electrical circuit of resistance, R, generates a
potential, E. (E =iR)
Each of these experimental designs uses a different
type of instrument
19. Type of Electrochemical Methods
1. Potentiometry methods: it measures the
potential of a solution between two electrodes.
The potential is then related to the concentration
of one or more analytes. The cell structure used
is often referred to as an electrode even though it
actually contains two electrodes: an indicator
electrode and a reference electrode.
20. Potentiometry usually uses electrodes made
selectively sensitive to the ion of interest,
such as a fluoride-selective electrode. The
most common potentiometric electrode is the
glass-membrane electrode used in a pH meter.
21. 2. Voltammetry method: is based on the applies a
constant and/or varying potential at an
electrode's surface and measures the resulting
current with a three electrode system.
Voltammetry, with its variety of methods,
constitutes the largest group of electrochemical
methods of analysis and is commonly used for
the determination of compounds in solutions
(for example, polarography and amperometry).
22. 3. Coulometry methods: based on the
measurement of the amount of material
deposited on an electrode in the course of an
electrochemical reaction in accordance with
Faraday’s laws. A distinction is made between
coulometry at constant potential and
coulometry at constant current.
23. Coulometry uses applied current or potential to
completely convert an analyte from one
oxidation state to another. In these experiments,
the total current passed is measured directly or
indirectly to determine the number of electrons
passed. Knowing the number of electrons passed
can indicate the concentration of the analyte or,
when the concentration is known, the number of
electrons transferred in the redox reaction.
24. 4. Conductometry methods: in which
the electrical conductivity of electrolytes
(aqueous and non-aqueous solutions, colloid
systems and solids) is measured
It is based on the change in the concentration
of a compound or the chemical composition
of a medium in the interelectrode space;
