Academic class : Bachelor’s in Petroleum
& Natural Gas Engineering
Batch 12PG
By
Engr. Asadullah Memon
B.E (Petroleum and Natural Gas)
Electro Chemistry Electrolysis
 Electrochemistry is a branch of chemistry that studies
chemical reactions which take place in a solution at the interface of
an electron conductor (a metal or a semiconductor) and an ionic
conductor (the electrolyte), and which involve electron transfer
between the electrode and the electrolyte in solution.
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. In contrast, chemical
reactions where electrons are transferred between molecules are
called oxidation/reduction (redox) reactions.
 Electrochemistry concerns the effects of electricity on chemical
changes.
Electro Chemistry Electrolysis
Types of electro chemical cells
There are two kinds electrochemical cells.
1.
Electrochemical cells containing nonspontaneous chemical
reactions are called electrolytic cells.
2.
Electrochemical cells containing spontaneous chemical
reactions are called voltaic or galvanic cells.
Electro Chemistry Electrolysis
Electrical Conduction
 Metals conduct electric currents well in a process called
metallic conduction.
 In metallic conduction there is electron flow with no atomic
motion.
 In ionic or electrolytic conduction ionic motion transports the
electrons.
 Positively charged ions, cations, move toward the negative
electrode, cathode.
 Negatively charged ions, anions, move toward the positive
electrode, anode.
Electro Chemistry Electrolysis
Electrodes
 The following convention for electrodes is correct for either
electrolytic or voltaic cells:
 The cathode is the electrode at which reduction occurs.
The cathode is negative in electrolytic cells and positive in
voltaic cells.
 The anode is the electrode at which oxidation occurs.
The anode is positive in electrolytic cells and negative in
voltaic cells.
Electro Chemistry Electrolysis
In general, electrochemistry deals with situations where oxidation
and reduction reactions
Oxidation (Loss of Electron).
Reduction (Gain of Electron).
 Electrochemical reactions are oxidation-reduction reactions.
 The two parts of the reaction are physically separated.
 The oxidation reaction occurs in one cell.
 The reduction reaction occurs in the other cell.
Electrolyte & Electrolysis
 Electrolytes are electrovalent substances that
form ions (Cation & Anion) in solution which
conduct an electric current
 The Phenomenon of decomposition of an
electrolyte by passing electric current through its
solution is known as Electrolysis.
 Examples:
Electrolysis of Hydrochloric acid (HCL)
Electrolysis of Sodium Chloride (Nacl)
 Electrolytic Cell
Faraday’s Law of Electrolysis
In 1834, Studied the quantitative aspect of Electrolysis.
(Existence of Electrons)
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.
Second law: When the same quantity of electricity passes
through solutions of different electrolytes, the amount of
substances liberated at the electrodes are directly proportional
to their chemical equivalents (Z)
Importance of first law of electrolysis:
Estimate,
1. The value of electrochemical equivalents of different substances.
2. The masses of different substances produced by passing a known
quantity of electricity through their solution.
 Importance of Second law of electrolysis:
Estimate,
1. Equivalent weight of metal.
2. Unit of electric current.
3. Avogadro’s number
Electrolytic Conductance
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Conductance is the measure of the ease with which current can
flow in the material (i.e. wire).
Depends on the physical parameters of the material (length, area
of cross section) as well as the conductivity.
Conductivity, a measure of a material's ability to conduct an
electric current (Electrical).
Conductivity (electrolytic), a measurement of an electrolytic
solution, such as water, HCL etc…
The conductivity (or specific conductance) of an electrolyte
solution is a measure of its ability to conduct electricity. It is the
reciprocal of Resistivity.
The SI unit of conductivity is siemens per meter (S/m).
Conductivity Measurement
 The electrical conductivity of a solution
of an electrolyte is measured by
determining the resistance of the
solution between two flat or cylindrical
electrodes separated by a fixed distance.
 An alternating voltage is used in order
to avoid electrolysis.
 The resistance is measured by a
conductivity meter.
 Typical frequencies used are in the range
1-3 kHz.
Uses of Conductivity
 Conductivity measurements are used extensively in
many industries.
For example,
1. To monitor quality in public water supplies,
2. In hospitals
3. In boiler water
4. To determine the amount of total dissolved solids
(T.D.S.)
5. Petroleum
6. Iron and steel
7. Food Processing
FACTORS AFFECTING ON ELECTROLYTIC
CONDUCTANCE
(1) Nature of electrolyte :
The conductance of an electrolyte depends upon the number of ions present in
the solution. Therefore, the greater the number of ions in the solution the greater
is the conductance.
The number of ions produced by an electrolyte depends upon its nature. The
strong electrolytes dissociate almost completely into ions in solutions and,
therefore, their solutions have high conductance. On the other hand, weak
electrolytes, dissociate to only small extents and give lesser number of ions.
Therefore, the solutions of weak electrolytes have low conductance.
(2) Temperature : The conductivity of an electrolyte depends upon the
temperature. With increase in temperature, the conductivity of an electrolyte
increases.
(3) Concentration of the solution
Galvanic cell
A Galvanic cell, or Voltaic cell, is an electrochemical
cell that derives electrical energy from chemical
reactions taking place within the cell.
It generally consists of two different metals connected
by a salt bridge, or individual half-cells separated by a
porous membrane (As shown in Figure).
Transport numbers
 The fraction of the total current carried by the cation or
the anion is known as Transport number or
Transference number or Hittorf’s number.
 It may be denoted by sets symbols like
t+ and t– or tc and ta or nc and na”
Where,
ta = Current carried by an anion/Total current passed
through the solution
tc = Current carried by a cation/Total current passed
through the solution
evidently, ta + tc = 1
If v+ Represents the speed of migration of the cation
and v_ that of the anion,
the transport number of cation (t +)
the transport number of anion (t_ )
Or
The fraction of the total current carried by the ions are
directly proportional to their velocities (HITTORF’S Rule).
Hittorf’s Rule
It state that “The loss in concentration around any electrode is
proportional to the speed of the ion moving away from it
Or
Determination Methods of Transport
Number
The are two methods for determination of the
transport number of an ion:
1.
2.
HITTORF’S METHOD
MOVING BOUNDARY METHOD
1. HITTORF’S METHOD
Calcutions:
Case # 01: When electrodes are unattackable (Pt
Electrodes are used)
Case# 02: When electrodes are attackable (Ag Electrodes
are used)
2. MOVING BOUNDARY METHOD
Suppose the boundary moves a distant x from AA’ to
BB’ for the passage of Q coulombs. All the ions,
H+, passed through the boundary AA’.
The amount of substances transported is then Q/F,
of which t+Q/F are carried by the positive ion. If the
volume between the boundaries AA’ and BB’ is V,
and the concentration of HCl is c, then
tQ / F  Vc
FVc
t 
Q
Problems: Example no 1 (Page # 711), Example no 2 (Page
# 712) and Example no 3 (Page # 714) ( Do your self)
(Book referred Physical chemistry by B s Bahl)
Surface and interfacial tension
 In dealing with multiphase systems, it is necessary to
consider the effect of the force at the interface.
 When two immiscible fluid are in contact (Liquid and Gas),
the term surface tension is used to describe the forces
acting on the interface.
 When the interface is between liquid, the acting forces are
called interfacial tension.
 Surface tension is caused by the net inward pull on the
surface molecule.
 The inward forces on the surface molecules minimize the
surface area and form a drop.
 Unit is dyne/cm (CGS) and N/M (SI)
Factors Effecting on Surface Tension:
1.
2.
3.
Temperature
Pressure
Density
Calculation: Capillary Rise Method
Surface tension = h.r.d.g / 2
Where,
h = Height of liq: in cap:, cm
r = Radius of cap, cm
d = Density of liquid, g/cm
g = Accerated due to gravity, cm/sec2