JEE MAINS - VOL - VI ELECTRO CHEMISTRY
ELECTROCHEMISTRY
SYNOPSIS
SL. ELECTRONIC ELECTROLYTIC
Electro Chemistry: NO CONDUCTORS CONDUCTORS
Conducts electricity by Conducts Electricity by
It deals with 1
the flow of Electrons the movement of ions
I. The use of electrical energy for the dissociation Electrons flow from Charged species (ions)
negative end to positive move towardsthe
of chemical compounds (electrolysis) 2
end oppositely charged
II. The use of chemical reactions for the electrodes
No transfer of matter Transfer of matter takes
production of electrical energy (Electro- chemical 3 takes place place
cells) No chemical change Chemical change takes
4
takes place place at the electrodes
III. The use of electrical energy in the study and
It decreases with rise of It increases with
preparation of chemical substances. 5
temperature increase of temperature
IV. The commercial power generating cells, Metals, alloys, graphite, Liquids of molten salts,
solid salts such as CdS, aqueous solution of
namely secondary cells (batteries & fuel cells) CuS, etc., are all salts, acids ( Eg ;HCl,
The Basis of electro chemistry is thus a process 6 electronic conductors HNO3,H2SO 4) and
in which electrons are transferred from one bases ( NaOH, KOH)
are examples
system to another ofelectrolyticconductors
Electric current is considered as flow of electrons
or flow of electrical charges through a conducting
system. Note : CdS and CuS exhibits electronic conduction
The Substance which allows the electric current due to crystal defect.
to pass through it, is called Electrical Conductor. Electronic conduction depends on
(i) the nature and structure of the metal
The electrical conductors are of two types. (ii) the number of valence electrons per atom
(a) Electronic Conductors(Metals), (iii) temperature (it decreases with increase of
temperature)
(b) Electrolytic conductors
Electrolytic conduction depends on
Distinction between electronic conductors and (i) the nature of the electrolyte added
electrolytic conductors: (ii) size of the ions produced and their solvation
(iii) the nature of the solvent and its viscosity
(iv) concentration of the electrolyte
(v) temperature (it increases with the increase of
temperature)
Non-metals which are electronically conducting
Ex : Carbon-black, graphite, organic polymers
like polyaniline, polypyrrole, polythiophene,
polyacetylene when exposed to vapours of
iodine.
Metals and their alloys, at very low temperatures
(0 to 15 K) were known to behave as
superconductors.
Bapuji SPSS PU College, Tolahunse 75
,ELECTRO CHEMISTRY JEE MAINS - VOL - VI
Ceramic materials and mixed oxides also show It measures the ease with which the current flows
superconductivity at temperatures as high as 150 through a conductor
K. 1 1 1 1
The flow of current in the case of electrolytic
C C k
R l/a l/a
conductors (Eg.Solutions of salts in water ) is
due to the movement of ions in the solution under l
k C
the influence of an applied voltage. a
The movement of ions under applied voltage is Where C = Conductance
called electrical migration or mobility or ionic k Specific conductance (Conductivity)
conductivity of ions.
l
Electrolytic solution resistance and = Constant known as cell constant .
conductance: a
Aqueous electrolytic solutions also offer Its units are cm-1 (or) m-1
resistance like metallic wires to the flow of current S.I unit of conductance = Siemens (S)
and obey Ohm’s law. 1S = 1 ohm 1 ( or mho )
Ohm’s Law: It states that the current (I) flowing Specific Resistance (OR) Resistivity
through a conductor at a given temperature is ( )
proportional to the potential difference (V) and
inversely proportional to resistance (R). l l
We know that R R
Mathematically it can be expressed as a a
(or) R = x cell constant
V IR Where
= Resistivity
Resistance (R) : It is the opposition to the flow
l = Length and a = area of cross section of the
of current offered by the electrolytic solution. Its
conductor
units are ohm
l
= cell constant
S.I base units of ohm = kg m / S
2 3 2
A a
The resistance ‘R’ offered by the electrolytic The resistance in ohm of a conductor having
solution, taken in a conductivity cell, is directly length of 1cm and area of cross - section 1cm2 is
proportional to distance of separation ‘ l ’ called resistivity (or) “The resistance offered by
between the two parallel electrodes of the cell 1 cm3 solution of an electrolytic solution” is called
and inversely proportional to the area of cross- resistivity ( ).
section (a) of electrode i.e, Its units are ohm – cm
l l S.I unit : ohm - metre
R or R .
a a 1 m 100 cm
1 cm 0.01 m
where = specific resistance (Resistivity).
It can be measured with the help of wheatstone Measurement of conductivity of Ionic
bridge. solutions:
Conductance (C) : Unknown resistance can be calculated using
It is the reciprocal of the electrical resistance Wheatstone bridge. Resistance of ionic solution
(R) is measured by using an alternating current(AC)
source of power and specially designed vessel
1 called conductivity cell.
C
R
76 Bapuji SPSS PU College, Tolahunse
, JEE MAINS - VOL - VI ELECTRO CHEMISTRY
Conductivity cell consists of two platinum It is the reciprocal of specific resistance ( )
electrodes coated with platinum black, whose 1
area of cross section equal to ‘a’ and are k
separated by distance ‘ l ’
Resistance of solution is determined by the l 1 1 l
R . ; .
equation. a C k a
R l
a ka k C
a
The quantity l / a is called cell constant denoted
Where
by the symbol, G*. It depends on
C = conductance
a) Distance between the electrodes
b) Area of cross sections l
= cell constant
The cell constant is determined by measuring the a
resistance of the cell containing a solution whose
l
conductivity is already known. Since : k C , if l = 1cm ; a 1cm2 then
a
k C thus the conductance of 1cm3 of
(u n k n o w n
re s is ta n c e ) electrolytic solution is called specific conductance
R2 R 1 (k)
D e te c to r (or)
P
Similarly, the conductance of the electrolyte in
the solution of volume of 1m3 is known as
R 4 R 3
specific conductance (k)
(or)
O s c illa to r The conductance of the solution enclosed
between two parallel electrodes of unit area of
1 4 RR cross-section separated by a unit distance is called
Unknown resistance R 2 R specific conductance (k)
3
Instead of AC if DC is used it leads to Its units are :
a) Electrolysis resulting in the change of ohm-1 ×cm-1 (in CGS system)
concentration. (or) ohm-1m-1 (or)S×m-1 (in SI system)
b) polarisation at the electrodes resulting in the
change of resistance. 1 Scm 1 100 Sm 1
Specific, Molar and equivalent conductance Note: - If l / a ( Cell constant ) = 1 then k = C
The conductance (or) the current conducting The conductivity of solutions of different
capacity of an electrolytic solution can be electrolytes in the same solvent and at a given
expressed in terms of temperature differs due to
a) Specific conductance (k), ( i ) Charge and size of the ions in which they
b) Molar conductance ( m ), dissociate.
( ii ) The concentrations of ions (or) ease with
c) Equivalent conductance which the ions move under a potential gradient.
Specific conductance (k): Molar Conductance ( m ): It is the conducting
power of all the ions produced by dissolving 1
gram mole of an electrolyte
(or)
Bapuji SPSS PU College, Tolahunse 77
ELECTROCHEMISTRY
SYNOPSIS
SL. ELECTRONIC ELECTROLYTIC
Electro Chemistry: NO CONDUCTORS CONDUCTORS
Conducts electricity by Conducts Electricity by
It deals with 1
the flow of Electrons the movement of ions
I. The use of electrical energy for the dissociation Electrons flow from Charged species (ions)
negative end to positive move towardsthe
of chemical compounds (electrolysis) 2
end oppositely charged
II. The use of chemical reactions for the electrodes
No transfer of matter Transfer of matter takes
production of electrical energy (Electro- chemical 3 takes place place
cells) No chemical change Chemical change takes
4
takes place place at the electrodes
III. The use of electrical energy in the study and
It decreases with rise of It increases with
preparation of chemical substances. 5
temperature increase of temperature
IV. The commercial power generating cells, Metals, alloys, graphite, Liquids of molten salts,
solid salts such as CdS, aqueous solution of
namely secondary cells (batteries & fuel cells) CuS, etc., are all salts, acids ( Eg ;HCl,
The Basis of electro chemistry is thus a process 6 electronic conductors HNO3,H2SO 4) and
in which electrons are transferred from one bases ( NaOH, KOH)
are examples
system to another ofelectrolyticconductors
Electric current is considered as flow of electrons
or flow of electrical charges through a conducting
system. Note : CdS and CuS exhibits electronic conduction
The Substance which allows the electric current due to crystal defect.
to pass through it, is called Electrical Conductor. Electronic conduction depends on
(i) the nature and structure of the metal
The electrical conductors are of two types. (ii) the number of valence electrons per atom
(a) Electronic Conductors(Metals), (iii) temperature (it decreases with increase of
temperature)
(b) Electrolytic conductors
Electrolytic conduction depends on
Distinction between electronic conductors and (i) the nature of the electrolyte added
electrolytic conductors: (ii) size of the ions produced and their solvation
(iii) the nature of the solvent and its viscosity
(iv) concentration of the electrolyte
(v) temperature (it increases with the increase of
temperature)
Non-metals which are electronically conducting
Ex : Carbon-black, graphite, organic polymers
like polyaniline, polypyrrole, polythiophene,
polyacetylene when exposed to vapours of
iodine.
Metals and their alloys, at very low temperatures
(0 to 15 K) were known to behave as
superconductors.
Bapuji SPSS PU College, Tolahunse 75
,ELECTRO CHEMISTRY JEE MAINS - VOL - VI
Ceramic materials and mixed oxides also show It measures the ease with which the current flows
superconductivity at temperatures as high as 150 through a conductor
K. 1 1 1 1
The flow of current in the case of electrolytic
C C k
R l/a l/a
conductors (Eg.Solutions of salts in water ) is
due to the movement of ions in the solution under l
k C
the influence of an applied voltage. a
The movement of ions under applied voltage is Where C = Conductance
called electrical migration or mobility or ionic k Specific conductance (Conductivity)
conductivity of ions.
l
Electrolytic solution resistance and = Constant known as cell constant .
conductance: a
Aqueous electrolytic solutions also offer Its units are cm-1 (or) m-1
resistance like metallic wires to the flow of current S.I unit of conductance = Siemens (S)
and obey Ohm’s law. 1S = 1 ohm 1 ( or mho )
Ohm’s Law: It states that the current (I) flowing Specific Resistance (OR) Resistivity
through a conductor at a given temperature is ( )
proportional to the potential difference (V) and
inversely proportional to resistance (R). l l
We know that R R
Mathematically it can be expressed as a a
(or) R = x cell constant
V IR Where
= Resistivity
Resistance (R) : It is the opposition to the flow
l = Length and a = area of cross section of the
of current offered by the electrolytic solution. Its
conductor
units are ohm
l
= cell constant
S.I base units of ohm = kg m / S
2 3 2
A a
The resistance ‘R’ offered by the electrolytic The resistance in ohm of a conductor having
solution, taken in a conductivity cell, is directly length of 1cm and area of cross - section 1cm2 is
proportional to distance of separation ‘ l ’ called resistivity (or) “The resistance offered by
between the two parallel electrodes of the cell 1 cm3 solution of an electrolytic solution” is called
and inversely proportional to the area of cross- resistivity ( ).
section (a) of electrode i.e, Its units are ohm – cm
l l S.I unit : ohm - metre
R or R .
a a 1 m 100 cm
1 cm 0.01 m
where = specific resistance (Resistivity).
It can be measured with the help of wheatstone Measurement of conductivity of Ionic
bridge. solutions:
Conductance (C) : Unknown resistance can be calculated using
It is the reciprocal of the electrical resistance Wheatstone bridge. Resistance of ionic solution
(R) is measured by using an alternating current(AC)
source of power and specially designed vessel
1 called conductivity cell.
C
R
76 Bapuji SPSS PU College, Tolahunse
, JEE MAINS - VOL - VI ELECTRO CHEMISTRY
Conductivity cell consists of two platinum It is the reciprocal of specific resistance ( )
electrodes coated with platinum black, whose 1
area of cross section equal to ‘a’ and are k
separated by distance ‘ l ’
Resistance of solution is determined by the l 1 1 l
R . ; .
equation. a C k a
R l
a ka k C
a
The quantity l / a is called cell constant denoted
Where
by the symbol, G*. It depends on
C = conductance
a) Distance between the electrodes
b) Area of cross sections l
= cell constant
The cell constant is determined by measuring the a
resistance of the cell containing a solution whose
l
conductivity is already known. Since : k C , if l = 1cm ; a 1cm2 then
a
k C thus the conductance of 1cm3 of
(u n k n o w n
re s is ta n c e ) electrolytic solution is called specific conductance
R2 R 1 (k)
D e te c to r (or)
P
Similarly, the conductance of the electrolyte in
the solution of volume of 1m3 is known as
R 4 R 3
specific conductance (k)
(or)
O s c illa to r The conductance of the solution enclosed
between two parallel electrodes of unit area of
1 4 RR cross-section separated by a unit distance is called
Unknown resistance R 2 R specific conductance (k)
3
Instead of AC if DC is used it leads to Its units are :
a) Electrolysis resulting in the change of ohm-1 ×cm-1 (in CGS system)
concentration. (or) ohm-1m-1 (or)S×m-1 (in SI system)
b) polarisation at the electrodes resulting in the
change of resistance. 1 Scm 1 100 Sm 1
Specific, Molar and equivalent conductance Note: - If l / a ( Cell constant ) = 1 then k = C
The conductance (or) the current conducting The conductivity of solutions of different
capacity of an electrolytic solution can be electrolytes in the same solvent and at a given
expressed in terms of temperature differs due to
a) Specific conductance (k), ( i ) Charge and size of the ions in which they
b) Molar conductance ( m ), dissociate.
( ii ) The concentrations of ions (or) ease with
c) Equivalent conductance which the ions move under a potential gradient.
Specific conductance (k): Molar Conductance ( m ): It is the conducting
power of all the ions produced by dissolving 1
gram mole of an electrolyte
(or)
Bapuji SPSS PU College, Tolahunse 77
