ELECTROCHEMISTRY - I 4.1 - Metallic and Electrolytic Conductors-Faraday’s Laws-Electro plating Specific conductance and Equivalent conductance - Measurement of equivalent conductance - Variation of Equivalent Conductance and Specific Conductance with Dilution Kohlrausch Law and its applications - Ostwald’s Dilution Law and its Limitations.

1. Dr.A.DINESHKARTHIK
ASSOCIATE PROFESSOR& HEAD,
P G & RESEARCHDEPT. OF CHEMISTRY
SHANMUGAINDUSTRIES ARTS& SCIENCECOLLEGE,
TIRUVANNAMALAI-606603.
dineshkarthik2008@gmail.com.
PART A (UNIT IV - 4.1)

2. UNIT-IV: ELECTROCHEMISTRY – I
PART A
2017 -2018 / 2020 – 2021 REGULATIONS
UCH 53 / BCh 53 / CCH 53

3. UNIT - IV
ELECTROCHEMISTRY - I
4.1 - Metallic and Electrolytic Conductors-
Faraday’s Laws-Electro plating Specific
conductance and Equivalent conductance -
Measurement of equivalent conductance -
Variation of Equivalent Conductance and
Specific Conductance with Dilution
Kohlrausch Law and its applications -
Ostwald’s Dilution Law and its Limitations.
Dr.A.DINESH KARTHIK

4. What is electrochemistry
• Electrochemistry is the science that unites
electricity and chemistry. It is the study of the
transfer of electrons. If a chemical reaction is
driven by an external applied voltage, as in
electrolysis, or if a voltage is created by a
chemical reaction, as in a battery, it is an
electrochemical reaction.
Dr.A.DINESH KARTHIK

5. In electrochemical reactions, electrons are
transferred from one species to another.
Electrochemistry
Dr.A.DINESH KARTHIK
Electrochemistry is the study of chemical
processes that cause electrons to move. This
movement of electrons is called electricity, which
can be generated by movements of electrons from
one element to another in a reaction known as an
oxidation-reduction ("redox") reaction.

6. Terminology in Electrochemistry:
• Electrodes are conductors by which electrons flow through to
generate a current. Electrodes are commonly made of metals such
as platinum and zinc.
• Anode: Electrode in an electrochemical cell on which the oxidation
reaction occurs.
• Cathode: Electrode in an electrochemical cell on which the
reduction reaction occurs.
• Oxidation: Lose of electrons, can occur only in combination with
reduction.
• Reduction: Gain of electrons, can occur only in combination with
oxidation.
• Oxidation number: Charge on an atom if shared electrons where
assigned to the more electronegative atom.
…continues
Dr.A.DINESH KARTHIK

7. Electricity: Flow of electrons over a wire that
is affected by the presence and flow of electric
charge.
Electrolysis: The decomposition of a substance
by means of electric current. This method
pushes a redox reaction toward the non-
spontaneous side.
Electrolytic cell: Electrochemical cell that is
being pushed toward the non-spontaneous
direction by electrolysis.
Dr.A.DINESH KARTHIK

8. Electromotive force, EMF (or cell potential): Difference of
potential energy of electrons between the two electrodes.
Redox reaction: Shorthand for reduction-oxidation reaction.
Voltaic cell or galvanic cell: An electrochemical cell that uses
redox reaction to produce electricity spontaneously.
Electrolytes are electrovalent substances that form ions in
solution which conduct an electric current. Sodium chloride,
copper (II) sulphate and potassium nitrate are examples of
electrolytes.

9. Electrical Units:
• Coulomb: A coulomb is a unit quantity of
electricity. It is the amount of electricity
which will deposit 0.001118 gram of silver
from a 15 per cent solution of silver nitrate
in a coulometer.
• Ampere: An ampere is a unit rate of flow of
electricity. It is that current which will
deposit 0.001118 gram of silver in one
second. In other words, an ampere is a
current of one coulomb per second.
Dr.A.DINESH KARTHIK

10. Ohm: An ohm is a unit of electrical resistance. It is the
resistance offered at 0ºC to a current by a column of
mercury 106.3 cm long of about 1 sq mm cross-
sectional area and weighing 14.4521 grams.
Volt: A volt is a unit of electromotive force. It is the
difference in electrical potential required to send a
current of one ampere through a resistance of one
ohm.
Faraday: Used in the study of electrochemical
reactions and equal to the amount of electric charge
that liberates one gram equivalent of any ion from an
electrolytic solution.

11. The power of electrolytes to conduct electric currents is termed conductivity or
conductance. According to this law, the current I flowing through a metallic
conductor is given by the relation.
I = E/R
where E is the potential difference at two ends (in volts); and R is the resistance
measured in ohms
Specific resistance: The resistance R of a conductor is directly proportional to its
length, l, and inversely proportional to the area of its cross-section, A. That is,
R ∝ l/A or R = ρ × l/A
where ρ “rho” is a constant of proportionality and is called resistivity or specific
resistance. Its value depends upon the material of the conductor.
Specific Conductance:The reciprocal of specific resistance is termed Specific
conductance or Specific conductivity. It is defined as : the conductance of one
centimetre cube (cc) of a solution of an electrolyte. The specific conductance is
denoted by the symbol κ (kappa).
CONDUCTANCE OF ELECTROLYTES
Dr.A.DINESH KARTHIK

12. Equivalent Conductance: It is defined as
the conductance of an electrolyte obtained
by dissolving one gram-equivalent of it in
Vcc of water.
The equivalent conductance is denoted
by Λ . It is equal to the product of the
specific conductance, κ and the volume V in
cc containing one gram-equivalent of the
electrolyte at the dilution V.
Thus, Λ = κ × V
Dr.A.DINESH KARTHIK

13. Molar Conductance: It is defined as : the conductance of all
ions produced by one mole (one gram-molecular weight) of
an electrolyte when dissolved in a certain volume V cc.
Molar conductance is denoted by μ. Its value is obtained by
multiplying the specific conductance, κ, by the volume in cc
containing one mole of the electrolyte.
Thus, Molar conductance, μ = k × V where V is the volume of
the solution in cc containing one mole of the electrolyte.
Calculating the emf of a cell: The emf of a cell can be
calculated from the half-cell potentials of the two cells (anode
and cathode) by using the following formula
Ecell = Ecathode – Eanode
= ER – EL

14. Single electrode potential: The potential of a single electrode in a half-cell is
called the Single electrode potential. In a Daniel cell - the electrodes are not
connected externally, the anode Zn/Zn2+ develops a negative charge and the
cathode Cu/Cu2+, a positive charge. The amount of the charge produced on
individual electrode determines its single electrode potential.
Standard emf of a cell: (E°)When the emf of a cell is determined under
standard conditions, it is called the standard emf. It may be defined as : the emf
of a cell with 1 M solutions of reactants and products in solution measured at
25°C.
The emf of the standard hydrogen electrode is arbitrarily assigned the
value of zero volts. So, SHE can be used as a standard for other electrodes.
Determining the emf of a given half-cell:The standard hydrogen electrode
can be placed on the left-hand side in the electrochemical cell (IUPAC). The
electrons flow from left-to-right and the given half-cell electrode gains
electrons (reduction). The observed emf of the combined electrochemical cell
is then the emf of the half-cell on the right-hand. Such emf values of half-cells,
or half reactions, are known as the Standard reduction potentials or
Standard potentials.
Dr.A.DINESH KARTHIK

15. Electrochemical Series:The standard reduction potentials (E°) are arranged in
the order of increasing potentials. The relative position of electrodes (M/M+) in
the table can be used to predict the reducing or oxidising ability of an
electrode.
Predicting Feasibility of Reaction:
The feasibility of a redox reaction can be predicted with the help of the
electrochemical series.
The net emf of the reaction, E°cell, can be calculated from the expression
E°cell = E°cathode – E°anode
In general, if E°cell = + ve, the reaction is feasible
E°cell = – ve, the reaction is not feasible
Dr.A.DINESH KARTHIK

16. Electrolytic Cell
 The phenomenon of decomposition of an electrolyte by passing electric
current through its solution is termed Electrolysis.
 The process of electrolysis is carried in an apparatus called the
Electrolytic cell.
 The cell contains water-solution of an electrolyte in which two metallic
rods (electrodes) are dipped.
 These rods are connected to the two terminals of a battery (source of
electricity).
 The electrode connected to the positive terminal of the battery attracts the
negative ions (anions) and is called anode.
 The other electrode connected to the negative end of the battery attracts
the positive ions (cations) and is called cathode.
Dr.A.DINESH KARTHIK

17. MECHANISM OF ELECTROLYSIS
• The cations migrate to the cathode and form a neutral atom by accepting
electrons from it. The anions migrate to the anode and yield a neutral
particle by transfer of electrons to it. As a result of the loss of electrons by
anions and gain of electrons by cations at their respective electrodes
chemical reaction takes place.
Let us consider the electrolysis of hydrochloric acid as an example.
In solution, HCl is ionised,
HCl ⎯⎯→ H+ + Cl-
• In the electrolytic cell Cl– ions will move toward the anode and H+ ions will
move toward the cathode. At the electrodes, the following reactions will
take place.
At cathode :
H+ + e– ⎯⎯→ H (Reduction)
• As you see, each hydrogen ion picks up an electron from the cathode to
become a hydrogen atom. Pairs of hydrogen atoms then unite to form
molecules of hydrogen gas, H2.
Dr.A.DINESH KARTHIK

18. What is voltage/charge/current
• An electric potential difference is called
as voltage. The SI unit of voltage is volts.
Dr.A.DINESH KARTHIK

19. Electrolytic Cells
Dr.A.DINESH KARTHIK

20. • Electric charge is that which causes
electrons and ions to attract each other,
and repel the particles of the same kind.
Coulomb is the unit used to measure
electric charge.
Dr.A.DINESH KARTHIK

21. Electrolytic Cells
• An electrolytic cell is an
electrochemical cell that drives a
non-spontaneous redox reaction
through an electric current
supplied by an external source.
• They are often used to
decompose chemical
compounds, in a process
called electrolysis—the Greek
word lysis means to break up.
Dr.A.DINESH KARTHIK

22. • Electrolysis of water is the
decomposition of water into
oxygen and hydrogen gas due to
the passage of an electric current.
• The reaction has a standard
potential of −1.23 V, meaning it
ideally requires a potential
difference of 1.23 volts to
split water.
• In a non-spontaneous reaction the
E0
net is always less than zero.
Dr.A.DINESH KARTHIK

23. Electroplating
Electroplating is a procedure that uses
electrolysis to apply a thin layer of a metal over
the surface of another metal.
Dr.A.DINESH KARTHIK

24. • In electroplating, the anode is made up of the metal
you want to use to coat the surface of another
metal.
• A salt solution containing the metal that makes up
the anode is used. During electrolysis, the anode
metal is oxidized and goes into solution as positive
ions.
• These positive ions are then reduced on the surface
of the cathode (the metal you are coating)
Dr.A.DINESH KARTHIK

25. Equivalent Conductance and Molar
Conductance
𝑪
λ = 𝟏𝟎𝟎𝟎 𝑳
(Equivalent conductance) (S.cm2.eq-1) ……….(3)
λ = 𝟏𝟎𝟎𝟎 𝑳
𝑵
where N = normality
λ = 𝟏𝟎𝟎𝟎𝑳
𝑪
(Molar conductance) (S.cm2.mole-1) ……… (4)
Equivalent conductance = (Molar conductance)/n
n = (M.Wt)/(Eq.Wt)
Dr.A.DINESH KARTHIK

26. Electrical conductance
The measurement of the conductivity in
solution is carried out in vessels provided
with electrodes that surface area (A) and
distance (l) between two electrodes must
be known.
In general, electrolytes, that conductivity is
well known are used to calibrate the cell.
Dr.A.DINESH KARTHIK

27. The equation below which gives the resistance
𝒍
R α 𝑨
𝒍
R = 𝝆 𝑨
……….……………….…(1)
𝝆 = 𝑹 𝒙 𝑨
𝒍
………………………… (2)
Where
R is the resistance (Ω, ohm)
𝝆 is the specific resistance (Ω.cm)
𝑨 is the electrode's area (cm2)
𝒍 is the distance between two electrods (cm)
Dr.A.DINESH KARTHIK

28. 𝟏
G = 𝑹
……………………………….(3)
G is the conductance (Ω-1or S or mho)
𝟏
L = 𝝆
…………………………..(4)
L = Specific conductance(conductivity)
(Ω-1. cm-1 ) or (S. cm-1 )or(mho. cm-1)
𝟏 𝟏 𝒍
L = 𝝆
= 𝑹
x 𝑨
…………………(5)
Dr.A.DINESH KARTHIK

29. So
𝒍
L = G x 𝑨
…………………….(6)
𝑬
R = 𝑰
(from ohm law) …………..(7)
Where
𝑰 𝒍 𝑰 𝒍
E = potential
I= Current
After Instead of equation 7 in equation 5
L = 𝑬
x 𝑨
→ L = 𝑨
x 𝑬
………(8)
Dr.A.DINESH KARTHIK

30. 𝑰/𝑨
L = 𝑬/𝒍
As
𝑰 𝑬
i = 𝑨
and Ei = 𝒍
So
𝒊
L = 𝑬𝒊
………………………..(9)
where 𝒊 is the current density
𝑬𝒊 is the potential energy.
Dr.A.DINESH KARTHIK

31. Cell constant
𝒍
(K= cell constant)
L= G. 𝑨
…………(1)
𝒍
K = 𝑨
So
L = G.K…………(2)
Dr.A.DINESH KARTHIK

32. Q/ Why use KCl solution when the measured
conductivity?
KCl solution has physical properties are
1. It is easily dissolve
2. It is stable at high temperature
3. It has high molecular weight
4. It is non-hygroscopic
Dr.A.DINESH KARTHIK

33. Chapter 1. Electrolyte
Solid
e-
h+
+ -
Conductivity:
A
L
R


Solid - liquid
+
-
+ -
Ion
Ionic Conductor
Aqueous electrolytes, polymer, and solid electrolytes
Electrolytes = Ionic conductor
Dr.A.DINESH KARTHIK

34. 1.1 Liquid Electrolyte Solution
Salt
A+Z B-Z
E.g.





 O
H
O
H
2 2
2
Cl
Na
O
)H
(
NaCl n
m
n
m
Ion-dipole interaction
Ions: free mobility
Dr.A.DINESH KARTHIK

35. Alternating current polarization effect
Known conductivity solution  cell constant 

 R
Z
Solution with unknown conductivity:
Measure R and with cell constant (Z)  unknown
 = -1; (: specific conductivity; : specific resistivity)
cm
-1cm-1 = S  cm-1
Siemens per centimeter
molar conductivity:
c
m


Λ concentrations of salt
in a solution; molcm-3
S  cm-2mol-1
Dr.A.DINESH KARTHIK

36. H+
MnO4
- Fe+2
Connected this way the reaction starts
Stops immediately because charge builds up.
Dr.A.DINESH KARTHIK

37. H+
MnO4
- Fe+2
e-
l Electricity travels in a complete circuit
Dr.A.DINESH KARTHIK

38. FARADAY’S LAWS OF ELECTROLYSIS
First Law
The amount of a given product liberated at an electrode during electrolysis is
directly proportional to the quantity of electricity which passes through the
electrolyte solution.
If m is the mass of substance (in grams) deposited on electrode by passing Q
coulombs of electricity, then
m ∝ Q
or m = Z × I × t
where Z is the constant known as the Electrochemical equivalent of the substance
(electrolyte). If I = 1 ampere and t = 1 second, then, m = Z
Thus, the electrochemical equivalent is the amount of a substance deposited by 1
ampere current passing for 1 second (i.e., one coulomb).
Second Law
This law states that ” the mass of a substance deposited or liberated at any
electrode on passing a certain amount of charge is directly proportional to its
equivalent weight of the substance”.
That is w ∝ E
where w is the mass of the substance in grams while E is its chemical equivalent
Dr.A.DINESH KARTHIK

39. Faraday's Laws
Any electrochemical reaction involves passage
a current through the electrode solution
interface.
The current is carried by electrons, therefore,
at the electrode/ solution interface electrons
are transferred from the electrode to the
solution ions (at the cathode) or conversely,
from the ions to the electrodes (at the anode)
Dr.A.DINESH KARTHIK

40. Dr.A.DINESH KARTHIK

41. Reduction Processes
The processes which involve the transfer
of electron from the electrode to the
solution
Oxidation Processes
The processes which involve the transfer
of electron from the solution to the
electrode
Dr.A.DINESH KARTHIK

42. Faraday's First Law
The amount of substance which reacted at the
electrodes is directly proportional to the quantity
of electricity which has passed through the
solution.
Q α W
Q = It
W α It
W = EeIt
where W is weight of chemical change at an
electrode (g)
Q is the amount of electricity (C)
I is the intensity of current (Ampere)
t is the time (s)
Ee is electrochemical equivalent
Dr.A.DINESH KARTHIK

43. Dr.A.DINESH KARTHIK

44. Faraday's Second Law
When the same quantity of electricity is passed through different
electrolytes, the mass of various substances which reacted or
deposited at the electrodes is directly proportional to the chemical
equivalent or equivalent weight of these substance.
Dr.A.DINESH KARTHIK

45. 𝑴
W α e
Chemical Equivalent (e) = Atomic Weight / valence
e = 𝒛
Q/ Calculate the chemical equivalent of Cu+2,
Ag+1, H+. If you know the atomics weights of
the cations respectively are 63.6, 107.9, and
1.008
Dr.A.DINESH KARTHIK

46. Link between first and second lows of Faraday's
Dr.A.DINESH KARTHIK

47. Q1/ How many coulombs are required for the following reduction
1- 1 mole of Al+3 to Al
2- 1 mole of Cu+2 to Cu
Q2/ How many coulombs are required to 50gm of Al from molten
Al2O3? If you know the Atomic Weight of Al = 27.
Q3/ Ni(NO3)2 solution is electrolyzed between pt electrodes using a
current of 5.0 Ampere for 30 minutes. What is the Weight of Ni will
be produced at the cathode? If you know the atomic Weight of Ni
=58.69.
Dr.A.DINESH KARTHIK

48. Q4/ The current passage was 15A through silver nitrate
solution for 10 sec that required to precipitate 9.9gm silver.
What is the current efficiency? If you know the atomic
Weight of Ag= 108.
Q5/ The current passage was 0.1A through CuSO4 solution
for 10 min at 25Co, if used pt electrode as cathode. If you
know the atomic Weight of Cu= 63.5.
 Calculate copper weight at cathode?
 Calculate Oxygen volume is evolved at anode at 740
mmHg?
Dr.A.DINESH KARTHIK

49. Applacations of Faraday's Laws
Coulometer is an instrument of chemical analysis that
determines the amount of a substance released in electrolysis by
measurement of the quantity of electricity used.
There are three types of coulometers:-
1-Weight coulometer
The quantity of electricity is determined by the amount of metal
deposited cathodically silver and copper coulometer.
The copper coulometer is essentially on glass vessels electrolytic
copper plates attached to its opposite walls.
The cathode is placed between these plates and the aqueous
solution consists of:
Dr.A.DINESH KARTHIK

50. CuSO4.5H2O (125-150)gm, H2SO4 (50 gm) as factor assist, and ethanol (50gm) in order to
prevent oxidation of the copper deposited at the cathode.
The current density at the cathode should be within (20 to 200) A/cm2. After the
electrolysis has been completed, the cathode is quickly washed with distilled water and
then ethanol to avoid oxidation of cathode electrode. Then, it's dried and weighted.
The accuracy of copper coulometer is (0.1- 0.05%)
The purpose of using two electrodes of an anode in order to increase the
efficiency Dr.A.DINESH KARTHIK

51. 2- Titration Coulometer
The quantity of electricity is determined by titration of the
substance formed in the solution during electrolysis.
3- Volume coulometer
The quantity of electricity is determined by the volume of gas that
evolved during (from anodic) electrolysis.
H2O ↔ H+ (at cathode) + OH- (at anode)→ O2↑ (at anode)
Dr.A.DINESH KARTHIK

52. Conductivity Measurement
is the
Conductance
Conductance can
reciprocal of resistance. Hence, the
be obtained by the measurement of the
resistance and latter can be found by Wheatstone bridge method
shown in Figure 1.
Figure1: Principle of Wheatsatone bridge method
Dr.A.DINESH KARTHIK

53. It consists of four resistances R1, R2, R3, R4 arranged in a manner
as shown in figure 1. R1 is the variable resistance and R2 is the
unknown resistance. When null point is obtained, i.e, there is
no deflection in the galvanometer G, we have
R1/ R2 = R3/R4
Knowing the values of R1, R3 and R4, R2 can be calculated.
In finding the resistance of the solution of an electrolyte, a
special type of cell has to use such that the solution is present
between the two electrolytes. The cell thus used is called
conductivity cell. It is made up of Pyrex glass and two platinum
electrodes at a fixed distance apart as shown in Figure 2.
Dr.A.DINESH KARTHIK

54. Figure 2: Apparatus for the measurement of electrolytic
conductance
Dr.A.DINESH KARTHIK

55. Various designs of conductivity cells are available. If direct
current is used, it causes electrolysis of the solution and
these results in the change in the resistance of the
solution. These effects are called polarization effects.
To overcome this problem, an alternating current of
frequency 50-200 cycles per second is used. Also we have
to use a head phone instead of a galvanometer to detect
the null point.
The complete assembly for the measurement of the
electrolytic conductance is shown in figure 2.
Dr.A.DINESH KARTHIK

56. A suitable value of the resistance R is introduced from the standard
resistance box such that when the sliding contact, i.e, the jockey J is
moved along the stretched wire, the sound in the earphone is
reduced to minimum at a point somewhere in the middle of the
wire AC, say at the point D. then, if X is resistance of the electrolyte
solution, by Wheatstone bridge principle,
So
𝑹𝒆𝒔𝒊𝒔𝒕𝒂𝒏𝒄𝒆 𝑹
= 𝑹𝒆𝒔𝒊𝒔𝒕𝒂𝒏𝒄𝒆 𝒐𝒇 𝒘𝒊𝒓𝒆 𝑨𝑫
= 𝑳𝒆𝒏𝒈𝒕𝒉 𝑨𝑫
𝑹𝒆𝒔𝒊𝒔𝒕𝒂𝒏𝒄𝒆 𝑿 𝑹𝒆𝒔𝒊𝒔𝒕𝒂𝒏𝒄𝒆 𝒐𝒇 𝒘𝒊𝒓𝒆 𝑪𝑫 𝑳𝒆𝒏𝒈𝒕𝒉 𝑪𝑫
𝑹𝒆𝒔𝒊𝒔𝒕𝒂𝒏𝒄𝒆 𝑿 = 𝑹𝒆𝒔𝒊𝒔𝒕𝒂𝒏𝒄𝒆 𝑹 .
𝑳𝒆𝒏𝒈𝒕𝒉 𝑪𝑫
𝑳𝒆𝒏𝒈𝒕𝒉 𝑨𝑫
Dr.A.DINESH KARTHIK

57. Q1/what is the purpose of using alternating current
instead of direct current?
sol/ using alternating current in order to avoid the
polarization effects which causes electrolysis of
the solution and these results will change the
resistance of the solution.
Q2/ The resistance of a conductivity cell when filled with 0.02M
KCl solution is 164 ohm at 298K. However, when filled with
0.05M AgNO3 solution, its resistance is found it be 78.5
ohm. If the specific conductivity of 0.02M KCl is 2.768 x10-3
ohm-1.cm-1. Calculate:
A- The specific conductivity (L) of 0.05M AgNO3
B- The molar conductivity of AgNO3 Solution
Dr.A.DINESH KARTHIK

58. Dr.A.DINESH KARTHIK