Gen . B.
C Joshi APS
Half Yearly project
work
Submitted to: Mr. Rahul Parihar (PGT chem)
Submitted by : Nandani Nayak
Class : 12 C
ACKNOWLEGEMENT
I wish to express my deep gratitude and sincere thanks to the principal
Mr.Rahul Parihar for his encouragement and for all the facilities that
he provided for this project work and also guided me to the successful
completion of this project. I take this opportunity to express my deep
sense of gratitude for this invaluable guidance constant
encouragement, immense motivation, which has sustained my efforts
at all stages of this Project work.I can’t forget to offer my sincere
thanks to my parents and also to my classmates who helped me to
carry out this project successful and for their valuable advice and
support, which I received from then time to time.
INTRODUCTION
Electro Chemical Cell
Whenever a redox reaction is allowed to take place directly in a single beaker,
it is found that the solution becomes hot. For example, when zinc is placed in a
copper solution, the solution is found to be warmer as the reaction proceeds
according to the equation.Zn(s) +Cu (aq) ZnSo4 (aq) +Cu(s)Similar results are
observed when a rod of copper is placed in silver solution. The reaction taking
place as follows:Cu(s) +2AgNo3+2AgThus, we conclude that whenever a
redox takes place directly in a single in a single beaker, chemical energy in the
form of heat is produced. By suitable means it is possible to bring out the
redox reaction indirectly so as to convert the chemical energy into the
electrical energy.
Representation of an Electrochemical Cell
An electrochemical cell is represented in a manner an illustrated
below.Zn/Zn2+||Cu2+/CuI.e. by convention, the electrode on which
oxidation takes place is written on the left-hand side and the other
electrode on which reduction takes place is written on the right-hand
side. The electrode of the left-hand side is written by writing the symbol
of the metal first followed by the symbol of the ion with its concentration
in brackets. The electrode on the right-hand side is written by first
writing the ion along with its concentration in brackets followed by the
symbol of the metal.
Experimental Setup
A zinc rod is placed in the zinc sulphate solution taken in a
beaker. A copper rod is placed in the copper sulphate solution
taken in another beaker. The two rods are connected by a wire
and two solutions are connected by a salt bridge.
Salt bridge and Its FunctionA salt-bridge is a U-shaped tube
containing concentrated solution of an inert electrolyte like
KCL, KNO3 , K2SO4 etc. An inert electrolyte is one whose
ions do not take part in the redox reaction and also do not react
with electrolyte used. The function of the salt bridge is to allow
the movement of the ions from one solution to the other without
mixing of the two solutions. Thus, whereas the electrons flow in
the outer circuit in the wire, the inner circuit is completed by the
flow of ions from one solution to the other through the salt
bridge moreover, it helps to maintain the electrical neutrality of
the solution of the two half cells.
Thus, the main functions of the salt bridge are:
• To complete the electrical circuit by allowing the ions to flow from one
solution to the other without mixing of the two solutions
• To maintain the electrical neutrality of the solutions in the two half
cells.Let us see what would happen if the salt bridge were not used in
the cells show in the following diagram. Electrons are given out by the
zinc electrode wherethey will neutralize some of the Cu2+ions of the
solution. Thus So42-ions will not leave and the solution will acquire a
negative charge. At the same time, Zn2+ ions produced from zinc plate
will enter ZnSo4 solution. After some time, the flow of electrons will
stop and hence the current stops flowing.
Standard EMF of an Electrochemical Cell
An electrochemical cell is based on reaction which can be
split into the two half reactions:• Oxidation half reaction•
Reduction half reactionStandard EMF of the cell
Where,Ecell = Electrode Potential of the cells
cathode = Electrode Potential of the oxidation half
reaction
Eanode= Electrode Potential of the oxidation half reaction
According to Nernst Equation, the relation between
concentration of electrode and the standard electrode
potential can be given as
Ecell = Ecathode - EanodeE = Eo – 0.059/n Log [M]/
[Mn+]
Where,E= Electrode Potential at non-standard
conditionsEo=Electrode potential at standard conditionsn=
Number of electrons transferred in the
equation[M]=concentration of the
metal[Mn+]=concentration of metal ion
Some Important Features
• The electrode at which oxidation takes place is called the anode.
The electrode at which the reduction takes place is called the
cathode.
• Since electrons are produced at the zinc electrodes, this
electrode is rich in electrons, which pushes the electrons into the
external circuit and hence it is designated as the negative pole.
The other electrode, i.e. the copper electrode is in the need of
electrons for the reduction of Cu2+ ions into the Cu.
• The electrons flow from the negative pole to the positive pole in
the external circuit. However, conventionally, this current is set
to flow in the opposite direction.
• The oxidation of Zn into ions produces excess of Zn2+ ions in the
left beaker. This creates an unbalanced positive charge in the
solution. To maintain electrical neutrality of the solution in the two
beakers, the cations and anions move through the salt bridge.
• As copper from copper sulphate solution is deposited on the copper
electrode and sulphate ions migrate to the other side, the
concentration of the copper sulphate solution decreases. As the cell
operates consequently, the current falls.
• Evidently, the weight of the copper rod will increase while that of
zinc rod will decrease as the cell works.
Procedure
Take two clean beakers.
In one beaker take 0.5M copper sulphate solution and
in the other take 0.5M zinc sulphate solution.
Take a copper strip and clean it using a sandpaper.
Dip the copper strip into the beaker containing the
1M copper sulphate solution.
Similarly, take a zinc strip and clean it using a
sandpaper.
Then dip into the beaker containing 1M zinc sulphate
solution.
Take a salt bridge and connect the two solutions using the
salt bridge.
Take a voltmeter and connect the copper strip to the positive
terminal and the zinc strip to the negative terminal using
connecting wires.
Note the positive of the pointer in the voltmeter and record
the reading.
Repeat the experiment by taking different concentration of
zinc sulphate and the copper sulphate solutions.
Observations
S.no. MCuSo4 MZnSo4
EMF
1 0.5 0.5 0.98V
2 0.5 0.25 0.81V
3 0.25 0.25 0.90V
Conclusion
These observations, we conclude that EMF
of the cell increases with decreases in the
concentration of the electrolyte around the
anode and the increase in the concentration
of the electrolyte around the cathode.
