Variation of Cell Potential with
Concentration
CHEMISTRY PROJECT
ACKNOWLEDGEMENT
I, [Your Name], would like to thank our school Principal,
Chemistry teachers, laboratory in-charge and support staff for
extending their support that enabled me to successfully
complete my Chemistry Project on “Variation of Cell Potential
with Concentration” in the school laboratory for the academic
year _______.
INDEX
TOPIC
S.No
Pg. No
1
Introduction
1
2
Theory
3
3
Aim of Experiment
5
4
Apparatus and Chemicals used
6
5
Procedure
7
5
Observations
7
6
Inference
8
7
Precautions
9
8
Applications
9
9
Proof of Expermient
9
10
Bibliography
10
Georges Leclanché
Luigi Galvani
Alessandro Volta
Walther Nernst
INTRODUCTION
The variation of cell potential with concentration is a fundamental
concept in electrochemistry that explores how the electrochemical
potential of a cell, which is essentially the cell's ability to generate
electrical energy, changes with alterations in the concentration of the
chemical species involved in the electrochemical reactions. This concept
is crucial in understanding and optimizing the performance of
electrochemical cells, including galvanic cells and Leclanché cells.
Galvanic cells, also known as voltaic cells, are electrochemical devices
that convert chemical energy into electrical energy. They consist of two
half-cells connected by an electrolyte bridge. The chemical reactions
occurring in these half-cells result in a flow of electrons through an
external circuit, generating an electric current. The concentration of the
reactants and products in each half-cell plays a critical role in
determining the cell potential.
Leclanché cells, invented by Georges Leclanché in 1866, are early
examples of a primary battery that operate based on the variation of cell
potential with concentration. They consist of a zinc anode and a
manganese dioxide cathode immersed in an ammonium chloride
solution. The chemical reactions taking place in the Leclanché cell are
driven by the variations in the concentrations of these reactants within
the cell, leading to the production of electric current. This was a
significant advancement in the field of electrochemistry and a precursor
to the modern dry cell battery.
The history of understanding the variation of cell potential with
concentration can be traced back to the work of Luigi Galvani,
Alessandro Volta, and others in the late 18th century. Luigi Galvani's
experiments with frog muscles and metals laid the foundation for the
study of bioelectricity and electrochemical reactions. Alessandro Volta's
invention of the voltaic pile in 1800, a predecessor to the modern
battery, demonstrated the principles of generating electricity through
chemical reactions. These early developments ultimately led to the
formalization of electrochemical concepts and the development of the
field of electrochemistry.
Over time, researchers like Michael Faraday and Nernst made
significant contributions to our understanding of how concentration
affects cell potential. Their work helped establish the Nernst equation,
which quantitatively describes the relationship between concentration
and cell potential in electrochemical cells. This equation is a critical tool
for predicting and controlling the behavior of electrochemical systems
and remains a cornerstone of modern electrochemistry.
In summary, the variation of cell potential with concentration is a vital
concept in electrochemistry that has a rich historical background, with
roots in the experiments of Galvani and Volta, leading to the
development of galvanic cells and ultimately contributing to the
foundational knowledge of electrochemical principles. This topic
continues to be of great importance in various fields, including battery
technology, corrosion science, and electrochemical sensor development.
Variation of Cell Potential of Zn-Cu Cell
THEORY
The potential difference between two electrodes of a galvanic cell is called
Cell Potential and is measured in volts. It is the difference between the
reduction potentials (or oxidation potentials) of the cathode and anode.
Nernst showed that electrode potential of a cell with respect to standard
hydrogen electrode can be measured at any concentration. For the
electrode reaction of the type:
The electrode potential at any concentration measured with respect to
standard hydrogen electrode can be represented by:
The concentration of solid M is taken as unity and we have
The Daniel cell is based on the reaction between zinc metal and a copper
sulfate solution. If this reaction is performed in a test tube, no electricity
is produced. However, if the same reaction is performed in a Daniel cell,
electricity is produced.
In a Daniel cell, the current flows from the copper electrode to the zinc
electrode. Under standard conditions, it generates an emf of 1.1V.
The reactions occurring in a Daniel cell are as follows:
→
2+
→
Zinc electrode: Zn(s)
Zn (aq) + 2e2+
Copper electrode: Cu (aq) + 2e Cu(s)
———————————————————————————————
2+
2+
Net reaction: Zn(s) + Cu (aq)
Zn (aq) + Cu(s)
———————————————————————————————
→
The cell under investigation in this experiment is represented as
follows:
Here x M denotes varying concentrations of
ions. In other
words, to study the variation in cell potential with concentration, the
concentration of
is varied while that of
is kept
constant. The measured cell potential enables us to calculate the
electrode potential of
electrode for each concentration of
copper (II) ions. This variation is theoretically depicted according to the
equation:
(1)
The variation in the electrode potential of
electrode
consequently brings variation in the cell potential according to the
relation:
(2)
Equation (2) clearly suggests that even if
is kept constant, the
variation in would bring corresponding variation in . .
Similarly, keeping the concentration of
ions constant, one can
study the variations in the cell potential with the variation in
concentration of
ions.
AIM OF THE EXPERIMENT
To study the variation in cell potential of the cell Zn/Zn2+||Cu2+/Cu with
change in concentration of electrolytes (CuSO4 /ZnSO4 ) at room
temperature.
APPARATUS AND CHEMICALS
REQUIRED
Zinc plate
Copper plate
Beakers
Voltmeter (Potentiometer)
Salt bridge
1.0M Zinc sulphate solution
0.25 M, 0.5M, and 1M Copper
sulphate solutions
PROCEDURE
1. Set up the cell using 1.0 M ZnSO4 and 0.25 M CuSO4 solution.
2. Measure the potential difference of the cell using a voltmeter.
3. Replace the beaker of 0.25 M CuSO4 with 0.5 M CuSO4 solution in
the beaker and note the cell potential.
4. Repeat this procedure for other solutions of copper sulphate in
increasing order of concentrations of copper sulphate solution.
5. Calculate log [Cu2+(aq)] and then
for each variation in the
concentration of copper (II) in the solution.
6. Record electrode potential values of Cu2+(aq)/Cu(s) electrode for
different concentrations of Cu 2+ ions in the given table.
OBSERVATION
S.No
[Cu2+(aq)]/mol L-1
log[Cu2+(aq)]/mol L-1
Ecell/V
E(Cu2+/Cu)
Experimental value
1
0.25
-0.60
1.08
1.05
2
0.5
-0.30
1.09
1.07
3
1
0
1.1
1.1
INFERENCE
The experiment demonstrated that changing the concentration of the
copper sulfate (CuSO4) solution in the anode compartment and the
zinc sulfate (ZnSO4) solution in the cathode compartment
significantly influenced the cell potential.
Increasing the concentration of CuSO4 in the anode compartment
led to a higher cell potential, indicating that higher concentrations of
the copper ions (Cu2+) promote a more positive electrode potential.
These results align with the Nernst equation and demonstrate the
dependence of cell potential on ion concentrations
PRECAUTIONS
1. Clean copper and zinc strips and connecting wires with sand paper
before use.
2. Place the salt bridge immediately in distilled water after its use.
3. Carry out dilution of the solution to another concentration very
carefully.
4. Choose appropriate scales for plotting the graph.
APPLICATIONS
1. Battery Research and Development: Understanding how varying
the concentration of electrolytes affects the Daniell cell's
performance is essential in designing and improving batteries,
including exploring new energy storage technologies.
2. Electrochemical Engineering: Engineers use these principles to
optimize electrochemical processes and devices, such as fuel cells,
supercapacitors, and sensors.
3. Environmental Monitoring: Electrochemical sensors that rely on
concentration variations, similar to those observed in the Daniell cell
experiment, are used for environmental monitoring, such as
measuring pollutant levels in air and water.
4. Corrosion Mitigation: Insights from the experiment can be applied
to control corrosion rates by modifying the concentrations of
specific ions, which is important in preserving infrastructure and
equipment.
5. Chemical Analysis: The principles can be used in analytical
chemistry to determine the concentration of specific ions in
solutions, which is valuable in fields like water quality testing and
pharmaceutical analysis.
BIBLIOGRAPHY
https://nationalmaglab.org/magnet-academy/history-of-electricitymagnetism/museum/leclanche-cell-1866/
https://ncert.nic.in/pdf/publication/sciencelaboratorymanuals/classXII/chem
istry/lelm104.pdf
https://testbook.com/chemistry/variation-of-cell-potential-in-zn-cu-cell