Oxidation and Reduction (Uses of Redox potential data) By Latish Barve.pdf

Here is the Presentation on the topic of Redox potential data.

2. 0
❖Oxidation :Loss of electrons / increase in oxidation number
❖Reduction : Gain of electron / decrease in oxidation number
❖Oxidizing agent (O.A.) :electron acceptor/oxidation number decreases
❖Reducing agent (R.A.) :electron donor / oxidation number increases.

4. Electrode potential (E):
Electrode potential is a measure of the tendency of an electrode in a half-cell reaction to gain or
lose electrons.
Standard electrode potential (E°):When potential measured at standard conditions ;
concentration is 1M, Pressure is 1 atmat 25°C temperature.
Types od Standard Electrode Potential
1) Oxidation electrode potential (E°
ox):It is measure of the tendency of the electrode in a half-
cell to get oxidized or to lose electrons.
Zn(s) →Zn
2+
(aq) + 2e–, E°
oxor E°
Zn/Zn2+= +0.76 V
2) Reduction electrode potential (E°
red):It is measure of the tendency of the electrode in a half-
cell to get reduced or to gain electrons.
e.g. –Cu
2+
(aq) + 2e-→ Cu(s), E°
redor E°
Cu2+/ Cu= +0.34 V

5. for standard electrode potentials
•An important convention
According to the present convention, the value of electrode potential is expressed as
reduction electrode potential. Thus, if we say that the value of standard electrode
potential of zinc electrode is –0.76 volt, this means that the given value is the value of
the standard reduction electrode potential of Zn electrode
i.e., E
Zn
2+
/ Zn = -0.76 volt
(E°
ox) = –(E°
red)
–(E°
ox) = (E°
red)

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Electrochemical Series
The values of standard reduction
potential of many electrodes have
been determinedAt 25°C
or (25 + 273) = 298K. These values
have been arranged in their
Increasingorder, in the form
of a series, which is called as
electrochemical series.

7. USE OF
ELECTRODE
POTENTIAL DATA

8. 1) To know the feasibility of a chemical reaction
With the help of potential data, we can determine the feasibility of a
redox reaction. The electric pressure that makes current flow in a circuit
is called aselectromotive force.
Electromotive force (E.M.F.) = E°
cathode–E°
anode
= E°
more–E°
less
= E°
right–E°
left
Suppose, we want to know feasibility of the following redox reaction:
Sn
2+
+ Cu→ Sn+ Cu
2+
(E°
Sn
2+
/Sn= –0.136 v and E°
Cu
2+
/Cu= 0.34)
As reduction potential of E°
Cu
2+
/Cuis higher as compared to E°
Sn
2+
/Sn
reduction will takes place at copper half cell.

9. 2e
–
+ Sn
2+
→ Sn (E°
Sn
2+
/Sn= –0.136 v) Cathode
Cu → Cu
2+
+ 2e
–
(E°
Cu/Cu
2+
= –0.34) Anode
E.M.F. = E
cathode–E
anode
= –0.136 –(+0.34)
= –0.476V
Due to negative value of E.M.F. of the cell, it is not a feasible cell.
Whereas if the cell reaction is
Cu
2+
+ Sn→ Sn
2+
+ Cu
Then, it will be feasibleto occur, because now E.M.F. will be positive.
E°
cell= E°
cathode–E°
anode
Note:-If we know E°
cathodeand E°
anodewe can easily calculate K. If K is very high, the
reaction will proceed towards forward direction.

10. 2) To calculate the redox potential and free energy change
There is the following relationship between standard Eletrode Potential (E°)and
free energy change(ΔG°):
ΔG°= –nFE°
If E°is positive, the value of ΔG°will be negative and a reaction is generally
thermodynamically feasibleif value of ΔG°is negative.

11. 3) To calculate the value of reduction electrode potential of a given
electrode in non-standard conditions
The value of (E
red)
elec.can be calculated by using the following Nernst Equation:

12. 4) To calculate the value of potential (e.m.f.) of a given cell in standardconditions
The value of E°
cellcan be calculated by using the equation.
E°
cell= (E°
red)
cathode
–
(E°
red)
anode
5) To calculate the value of Ecellby using Nernst equation

13. 6) To know oxidizing and reducing property of substances in aqueous solution
•The substance which has a (+)vevalue of E°
red, has a tendency to gain electrons
to undergo reduction and hence is capable of acting as an oxidizing agent in
aqueous solutionand hence higher the oxidizing power of the substance.
•The substance which has a (–)vevalue of E°
red, has a tendency to lose electrons
to undergo oxidation and hence is capable of acting as an reducing agent in
aqueous solutionand hence lower is the reducing power of the substance.
•Since, E°
redvalue increases down the electrochemical series (–→ O → +), the
oxidizing power of oxidizing agents also increases.
•Since, E°
redvalue increases down the electro-chemical series, the reducing
power of the reducing agents decreases in the series.

15. 7) To calculate redox potential and equilibrium constant
As redox reactions are reversible in nature, therefore, there is equilibrium between
oxidizing and reducing agent. If we know the redox potential, we cancalculate
equilibrium constant for the reaction which can further decide the directionof the
reaction forward / backward
Zn(s) + Cu
2+
(aq) ⇌Zn
2+
(aq) + Cu(s)
(Equilibrium constant) K = [Zn
2+
][Cu(s)] / [Zn(s)][Cu
2+
]
As concentration of solids remains constant, [Cu(s)]/[Zn(s)] =1 (constant)
So, K= [Zn
2+
] / [Cu
2+
]
K is related to E.M.F. of a cell by the following relation :
E°cell= 2.303RT/nFLog K
= 0.059/n log K (at 25°C )

16. Thank
You!