1) CONDUCTORS
10)
NERNEST EQUATION
11)CONCENTRATION CELL
12)
ELECTROLYSIS
13)
LAWS OF
ELECTROLYSIS
14) CORROSION
14) CORROSION
15
BATTERIES
CONDUCTORS
The
substances
that
allow
the
electric
current
to
pass
through
them
are
called
conductors
(i)
METALLIC
CONDUCTORS
The
substances
that
allow
electric
current
to
pass
through
them
without
undergoing
any
chemical
change
are
called
conductors.
E.g.
Cu,
Fe,
Ag,
Al
etc.In
metallic
conductors,
current
is
carried
by
the
electrons.
Hence,
they
are
also
known
as
electronic
conductors.
(ii)ELECTROLYTES
OR
ELECTROLYTIC
CONDUCTORS
The
substances
that
allow
electric
current
to
pass
through
them
in
their
molten
state
or
in
their
aqueous
solution
are
called
electrolytes.E.g.,
NaOH,NaCl,H2SO4
etc.In
electrolytes
current
is
carried
by
the
ions.
TYPES
OF
ELECTROLYTES
(I)
STRONG
ELECTROLYTES:-
The electrolytes which completely dissociate into ions and hence conduct electricity to a greater extent are called strong electrolytes.E.g .g. NaOH, NaCl, HCl, etc.
The electrolytes which completely dissociate into ions and hence conduct electricity to a greater extent are called strong electrolytes.E.g .g. NaOH, NaCl, HCl, etc.
NaCl(aq)
→ Na+(aq)
+ Cl-
(aq)
For
strong
electrolytes
degree
of
dissociation
is
always
=
1.
(II)
WEAK
ELECTROLYTES:-
The
electrolytes
which
do
not
completely dissociate
into
ions and
hence
conduct
electricity
to
a
smaller
extent
are
called
weak
electrolytes.E.g.CH3COOH,
NH4OH
etc.
CH3COOH
CH3COO- +
H+
For
weak
electrolytes,
the
degree
of
dissociation
is
<
1.
IMPORTANT
QUESTIONS
Q:
-
Conductivity
of
metallic
conductors
is
greater
than
electrolytic
conductors
.why?
Ans:
-
In
metallic
conductors
current
is
carried
by
the
electrons
having
negligible
mass
and
fast
speed
where
as
in
electrolytic
conductors
current
is
carried
by
the
bulky
ions
having
slow
speed
.Due
to
this
reason,
metallic
conductors
have
high
conductivity
as
compared
to
electrolytic
conductors.
Q
:
what
is
the
effect
of
temperature
on
the
conductivity
of
metallic
and
electrolytic
conductors?
Ans:
-
With
the
increase
in
temperature,
the
conductivity
of
metallic
conductors
decrease
whereas
that
of
electrolytes
increases.
Q
:
With
the
increase
in
temperature
the
conductivity
of
metallic
conductors
decrease
whereas
that
of
electrolytes
increases.
Why
?
Ans:
This
decrease
in
the
conductivity
of
metallic
conductors
with
the
increase
in
temperature
can
be
explained
on
the
basis
of
electron
sea
model.
with
the
increase
in
temperature
the
positively
charged
kernels
start
vibrating
and
create
hindrance
in
the
free
flow
of
electrons
whereas
in
case
of
electrolytic
conductors
the
ionic
mobility
increases
with
the
increase
in
temperature.
That
is
why
conductivity
of
metallic
conductors
decreases
and
that
of
electrolytic
conductors
increases
with
the
increase
in
temperature.
Q
:What
is
electrolytic
conduction?
Ans:
The
flow
of
electric
current
through
an
electrolytic
solution
is
known
as
electrolytic
conduction.
FACTORS
AFFECTING
THE
CONDUCTIVITY
OF
ELECTROLYTIC
SOLUTION
INTERIONIC
INTERACTION:
-
Greater
the
interionic
interactions
lesser
will
be
the
conductivity
of
the
solutions.
SOLVATION
OF
IONS:
-
Greater
the
salvation
of
ions
of
an
electrolyte
lesser
will
be
the
electrical
conductivity
of
the
solution
VISCOSITY
OF
THE
SOLVENT:
-
Greater
the
viscosity
of
the
solvent lesser
will
be
the
conductivity
of
the
solution.
TEMPERATURE:
-
Conductivity
of
an
electrolytic
solution
increases
with
the
increase
in
temperature.
This
is
due
to
increase
in
ionic
mobility.
CONCENTRATION:
-
With
the
increase
in
concentration,
the
conductivity
of
the
solution
decreases.
Q:
-
With
the
increase
in
dilution,
specific
conductivity
decreases
whereas
molar
conductivity
of
the
solution
increases.
Why?
Ans:
-
The
electrical
conductivity
of
an
electrolytic
solution
depends
upon
the
number
of
ions.
Now
with
the
increase
in
dilution
the
number
of
ions
per
unit
volume
decreases
hence
specific
conductivity
decreases.
On
the
other
hand
molar
conductivity
increases
with
dilution
because
it
is
the
product
of
specific
conductivity
and
volume.
Λm =
K
×
V
This
is
due
to
the
reason
that
increase
in
volume
is
much
more
than
decrease
in
specific
conductivity.
Moreover,
with
dilution
interionic
interactions
decrease,
this
further
enhances
molar
conductivity.
Q:
-
Explain
the
variation
of
molar
conductivity
with
dilution
both
for
strong
as
well
as
weak
electrolytes.
Ans:
-
The
variation
of
molar
conductivity
of
strong
electrolytes
with
dilution
Can
be
calculated
from
the
following
equation:
This
equation
is
called
Debye
Huckel
Onsager
equation.
Here
and
are
the
molar
conductances
at
a
given
concentration
and
at
infinite
dilution
(respectively).
b
is
a
constant
depending
on
the
viscosity
of
the
solvent. √C
is
the
square
root
of
the
concentration.
When
we
plot
a
graph
between
Λm
and
√C
we
observe
a
small
increase
in
the
molar
conductivity
of
strong
electrolytes
with
dilution.
This
is
due
to
the
reason
that
with
dilution
interionic
interactions
decreases.
In
case
of
strong
electrolytes,
the
value
of
molar
conductivity
at
infinite
dilution
(that
is
when
concentration
approaches
zero)
can
be
extrapolated
from
the
graph.
The
intercept
of
the
graph
gives
.
Graph
for
strong
electrolyte.
WEAK
ELECTROLYTES:-
Similarly
when
we
plot
a
graph
between
Λm
and
√C for
weak
electrolytes
,
we
observe
that
with
dilution
the
molar
conductivity
of
weak
electrolytes
increases
steeply
when
concentration
approaches
zero
and
becomes
parallel
to
molar
conductivity
axis.
Hence
the
value
of
molar
conductivity
at
infinite
dilution
(
) for
weak
electrolytes
cannot
be
extrapolated
from
the
graph.
Graph
for
weak
electrolytes
The
steep
increase
in
the
molar
conductivity
of
weak
electrolytes
can
be
attributed
to
the
reason
that
with
dilution
the
degree
of
dissociation
increases
which
results
in
the
increase
in
number
of
ions. α
for
weak
electrolytes
can
be
calculated
from
the
following
formula:
Q:
-
Explain
Kohlrausch’s
law.
Ans:
-
This
law
states
that at
infinite
dilution
each
ion
makes
a
definite
contribution
to
the
total
molar
conductance
irrespective
of
the
nature
of
the
other
ion.e.g
Λ∞(NaCl)
=
Λ∞Na+ +
Λ∞Cl-
Λ∞(MgCl2
)
=
Λ∞
Mg2+
+ Λ∞ 2Cl-
Λ∞ (CH3COOH)
= Λ∞CH3COO- +
Λ∞H+
REDOX
REACTIONS
The
reactions
that
involve
transfer
of
electrons
from
one
substance
to
another
are
called
redox
reactions.
A
redox
reaction
involves
reduction
and
oxidation
processes.
E.g.
Na
+
Cl
→ Na+
Cl-
OXIDATION:-
The
process
that
involves
loss
of
electrons
is
called
oxidation.
Na
→ Na+
+
e-
REDUCTION:
-
The
process
that
involves
gain
of
electrons
is
called
reduction.
Cl + e-
→ Cl-
OXIDIZING
AGENT:
-
It
is
an
electron
acceptor.
Na
+
Cl
→ Na+
Cl-
Here
chlorine
accepts
an
electron
hence
it
is
an
oxidizing
agent.
REDUCING
AGENT:
-
It
is
an
electron
donor.
Na
+
Cl
→ Na+
Cl-
Here
sodium
donates
an
electron
hence
it
is
a
reducing
agent.
OXIDATON
AND
REDUCTION
ARE
COMPLEMENTARY
TO
EACH
OTHER
This
is
because
both
the
processes
occur
simultaneously.
In
other
words,
oxidation
cannot
take
place
without
reduction
and
reduction
cannot
take
place
without
oxidation.
Hence,
both
are
complementary
to
each
other.
REDOX
REACTIONS
(I)DIRECT
REDOX
REACTIONS:
-
The
redox
reactions
in
which
oxidation
and
reduction
take
place
in
the
same
vessel
are
called
direct
redox
reactions.E.g.
When
Zn
rod
is
dipped
in
the
aqueous
solution
of
CuSO4,
Zn
is
oxidized
to
Zn2+
ions
and
Cu2+
ions
are
reduced
to
Cu
metal
in
the
same
vessel.
(II)INDIRECT
REDOX
REACTIONS:-The
redox
reactions
in
which
oxidation
and
reduction
take
place
in
the
separate
vessels
are
called
indirect
redox
reactions.
E.g.
Electrochemical
cell.
ELECTROCHEMICAL
CELL
It
is
a
device
used
to
convert
chemical
energy
into
electrical
energy.
CONSTRUCTION:-It
consists
of
two
vessels.
Left
vessel
contains
zinc
electrode
dipped
in
one
molar
aqueous
solution
of
zinc
sulphate
.
Right
vessel
contains
copper
electrode
dipped
in
one
molar
aqueous
solution
of
copper
sulphate.
Both
the
vessels
are
connected
with
the
help
of
a
copper
wire
and
a
salt
bridge
.
Left
vessel
is
called
oxidation
half-cell
and
right
vessel
is
known
as
reduction
half-cell
An
electrochemical
cell
is
represented
as
follow:
WORKING
OF
ELECTROCHEMICAL
CELL
OXIDATION
HALF
CELL:
-
Here
oxidation
takes
place
and
each
zinc
atom
loses
two
electrons
to
form
Zn2+
ions.These
electrons
move
through
the
wire
and
reach
the
copper
electrode.
Zn
(s)
→ Zn2+
(aq)
+ 2e- (oxidation)
SALT
BRIDGE
AND
ITS
FUNCTIONS
It
is
a
U-shaped
inverted
tube
contains
solution
of
inert
electrolyte
in
agar-
agar.
It
is
plugged
with
cotton
on
both
the
ends.
(i)It
helps
to
complete
electrical
circuit
of
the
cell.
(ii)It
helps
to
maintain
electrical
neutrality
of
the
cell.
ELECTRODE
POTENTIAL
It
is
the
tendency
of
an
electrode
to
lose
or
gain
electrons.
It
is
of
two
types.
(1)REDUCTION
POTENTIAL:
-
It
is
the
tendency
of
an
electrode
to
gain
electrons.
It
is
expressed
in
volts.
E.g.
in
electrochemical
cell
copper
electrode
has
reduction
potential.
(2)OXIDATION
POTENTIAL:
-
It
is
the
tendency
of
an
electrode
to
lose
electrons
.It
is
expressed
in
volts.
E.g.
in
electrochemical
cell
zinc
electrode
has
oxidation
potential
.
STANDARD
REDUCTION
POTENTIAL
If
an
electrode
undergoes
reduction
with
respect
to
standard
hydrogen
electrode
then
the
electrode
potential
is
called
standard
reduction
potential
.It
is
expressed
in
volts
with positive
sign
.
On
the
other
hand,
if
an
electrode
undergoes
oxidation
with
respect
to
the
SHE
then
standard
reduction
potential
is
expressed
in
volts
with
negative
sign.
E.g.,
the
standard
reduction
potential
of
Cu
electrode
is+0.34
volts
and
that
of
Zinc
electrode
is
-0.76
volts.
ELECTROMOTIVE
FORCE
(EMF)
OR
STANDARD
CELL
POTENTIAL
It
is
the
maximum
potential
difference
between
the
two
electrodes
of
a
cell
when
no
current
flows
through
the
circuit.
It
is
expressed
in
volts.
It
is
calculated
as
follow
:
STANDARD
HYDROGEN
ELECTRODE
It
is
used
to
find
out
electrode
potential
of
the
electrodes
of
various
elements.
The
standard
reduction
potential
of
NHE
is
taken
as
zero.
It
is
a
reversible
electrode.
It
is
a
reversible
electrode.
It
consists
of
a
platinum
wire
sealed
in
a
glass
tube
and
has
a
platinum
foil
attached
to
it.
The
foil
is
coated
with
finely
divided
platinum.
It
is
dipped
in
one
molar
HCl
solution.
Hydrogen
gas
is
constantly
bubbled
through
the
solution
at
one
atmospheric
pressure
and
298
K.
ELECTROCHEMICAL
SERIES
The
arrangement
of
elements
in
the
decreasing
order
of
their
standard
reduction
potential
values
is
called
electrochemical
series.
APPLICATIONS
OF
ELECTROCHEMICAL
SERIES
(1)
DETERMINATION
OF
EMF
OF
THE
CELL:-
Electrochemical
series
is
very
helpful
in
the
calculation
of
emf
of
an
electrochemical
cell.
It
is
calculated
as
follow
:
(2)
COMPARISON
OF
STRENGTH
OF
OXIDIZING
AGENTS
AND
REDUCING
AGENTS
As
we
move
down
the
series
the
strength
oxidizing
agents
decreases
and
that
of
reducing
agents
increases.
Hence
the
strongest
oxidizing
agent
is
present
at
the
top of
the
series
(F-)
and
strongest
reducing
agent
is
present
at
the
bottom
of
the
series
(Li+).
(3)
PREDICTION
OF
LIBERATION
OF
HYDROGEN
BY
METALS
FROM
PROTIC
ACIDS
Metals
with
negative
value
of
standard
reduction
potential
liberate
hydrogen
from
protic
acids.
E.g.
Zn
(s)
+ H2SO4
(aq)
→ ZnSO4
(aq)
+
H2
(g)
Fe
(s)
+ H2SO4
(aq)
→ FeSO4
(aq)
+
H2
(g)
(4)
COMPARISON
OF
REACTIVITY
OF
METALS
Metals
with
negative
value
of
standard
reduction
potential
like
Na,
K,
Zn,
Fe
etc
are
called
active
metals
whereas
metals
with
positive
value
of
standard
reduction
potential
like
Cu,
Ag,
Hg
etc
are
called
inactive
metals.
(5)
PREDICTING
THE
FEASIBILITY
OF
A
REDOX
REACTION
A
redox
reaction
takes
place
if
an
element
with
lower
value
of
standard
reduction
potential
loses
electrons
and
the
element
with
higher
value
of
standard
reduction
potential
gains
electrons.
E.g.
following
rxn
is
not
feasible.
Cu
(s) + Zn2+ (aq)
→ Cu2+ (aq)
+
Zn (s)
Whereas
reverse
reaction
is
feasible,
that
can
take
place.
Zn
(s)
+
Cu2+ (aq)
→
Zn
2+
(aq) +
Cu (s)
(6)
DISPLACEMENT
OF
A
METAL
FROM
ITS
SALT
SOLUTION
BY
OTHER
METAL
A
metal
can
replace
other
metal
from
its
salt
solution
if
that
metal
has
low
reduction
potential
value
than
the
metal
present
in
the
salt
solution.
E.g.
Zn
can
displace
Cu
from
copper
sulphate
solution
but
Cu
cannot
displace
Zinc
from
zinc
sulphate
solution.
Zn (s)
+ CuSO4 (aq)
→ ZnSO4 (aq)
+
Cu (s)
Cu (s)
+ ZnSO4 (aq)
→ No
reaction
CONCENTRATION
CELL
That
cell
in
which
both
the
electrodes
are
of
the
same
element
but
the
solutions
in
which
they
are
dipped have
different
concentrations
is
called
concentration
cell.
The
electrode
with
lower
concentration
of
solution
acts
as
anode
and
that
of
higher
concentration
acts
as
cathode.
FIRST
LAW
OF
ELECTROLYSIS
This
law
states
that
mass
of
a
substance
deposited
is
directly
proportional
to
the
quantity
of
current
passed.
For
example
if
w
is
the
mass
and
Q
is
the
quantity
of
the
current
then
W
α
Q
W
=
Z
×
Q…………………………..
(1)
Here
Z
is
called
electrochemical
equivalent
Now
Q
=
I
×
t
Put
the
value
of
Q
in
eq
(1) W
=
Z
×
I
×
t
ELECTROCHEMICAL
EQUIVALENT:
-
It
is
defined
as
the
amount
of
the
substance
deposited
when
a
current
of
one
ampere
passes
through
the
electrolytic
solution
for
one
second.
W
=
Z
×
I
×
t
If I
=
1
ampere
And t
=
1
second
Then W
=
Z
Z
can
be
calculated:
SECOND
LAW
OF
ELECTROLYSIS
When
the
same
quantity
of
electricity
is
passed
through
different
electrolytes
connected
in
series
the
weight
of
substances
deposited
at
the
electrodes
is
directly
proportional
to
their
equivalent
weights.Example:
If
CuSO4
and
ZnSO4
solutions
are
connected
in
series.
ALTERNATE
STATEMENT
OF
THE
2ND
LAW
To
deposit
one
mole
of
a
substance
we
must
pass
an
integral
number
of
Faraday's.
For
example:-
For
one
mole
of
sodium
(at.
wt
23)
=
1F
For
one
mole
of
calcium
(at.
wt
40)
=
2F
For
one
mole
of
Aluminium
(at.
wt
23)
=
3F
Q
:-
What
is
Faraday
constant?
Ans:
-
it
is
defined
as
the
amount
of
charge
carried
by
one
mole
of
electrons
and
it
is
around
96500
coulombs.
It
is
denoted
by
the
symbol
F.
APPLICATIONS
OF
ELECTROLYSIS
(1) Production
of
hydrogen
gas
by
the
electrolysis
of
acidulated
water.
(2) Production
of
chlorine
gas
by
electrolysis
of
NaCl.
(3)
Electroplating
of
and
electro-
refining
of
metal.
(4)
Manufacturing
of
heavy
water.
CORROSION
The
process
of
deterioration
of
a
metal
when
it
is
exposed
to
atmospheric
conditions
is
called
corrosion.
For
example,
iron
metal
when
exposed
to
atmospheric
conditions
like
water
air
etc
.it
undergoes
corrosion.
The
corrosion
of
iron
is
called
rusting.
When
iron
undergoes
corrosion,
it
forms
a
brown
colored
compound
known
as
rust.
It
is
hydrated
ferric
oxide
and
its
formula
is
Fe2O3.XH2O.
The
process
of
rusting
can
be
explained
on
the
basis
of
electrochemical
theory.
According
to
this
theory
metal
has
uneven
surfaces
called
pits;
these
pits
contain
H2O,CO2 and
dissolved
oxygen.
During
the
reaction,
pure
metal
acts
as
anode
and
pits
act
as
cathode.
The
material
present
in
the
pit
behaves
like
electrolyte.
Following
ions
are
present
in
the
pit:
At
anode:
2Fe
→
2Fe2+
+
4e-
These
electrons
are
taken
up
by
H+
ions
at
cathode
At
cathode:- 4H+
+ 4e-
→ 4H
The
hydrogen
atoms
react
with
dissolved
oxygen
to
form
water
4H
+
O2
→ 2H2O
Ferrous
ions
formed
at
anode
react
with
oxygen
and
water
to
form
rust.
|
|
rusting
of
iron |
FACTORS
THAT
PROMOTE
CORROSION:
-
1)
Reactivity
of
metal
2)
Presence
of
impurities
3)
Presence
of
air,
moisture,
gases
like
SO2
and
CO2
4)
Presence
of
electrolytes
PREVENTION
OF
RUSTING:-
(A)
Barrier
protection:-
The
metal
surface
is
not
allowed
to
come
in
contact
with
moisture,
O2
and
CO2.
It
is
done
as
follow:
i)
Coating
the
metal
surface
with
paint.
ii)
Applying
oil
or
grease.
iii)
Electroplating
with
non-corroding
metals
like
Ni,
Cr,
Al,
Sn,
Zn
iv)
Coating
with
alkaline
phosphate
(anti
rust)
solution
(B) Sacrificial
protection:-
Covering
the
surface
with
a
more
electro
positive
metal
than
Fe.
The
more
electro
positive
metal
loses
electrons
and
as
long
as
this
coating
is
present
Fe
is
protected.
FOR
EXAMPLE:
Galvanization
-
Covering
with
zinc.
(
C
) Electrical
protection
(Cathodic
protection)
:-
The
iron
object
is
connected
to
a
more
active
metal
either
directly
or
through
a
wire.
Fe
acts
as
the
cathode.
The
more
reactive
metal
is
the
anode.
It
loses
electrons
and
gradually
disappears.Example:
Fe
can
be
connected
to
Mg,
Zn
or
Al
which
are
called
the
sacrificial
anodes.
Used
for
protecting
underground
pipes
from
rusting.
|
|
Electrical
protection
of
underground
iron
pipesAdd
caption |
BATTERY
It
is
an
arrangement
of
cells
connected
in
series
to
produce
electrical
energy
TYPES
OF
CELLS
(1)
PRIMARY
CELLS:
-
Cells
which
can
be
used
only
once
and
cannot
be
recharged.
E.g.
dry
cell,
mercury
cell
etc.
(2)
SECONDARY
CELLS:
–
Cells which
can
be
used
again
and
again
by
recharging
are
called
secondary
cells.
E.g.
lead
storage
battery.
(3)
FUEL
CELLS:
-
The
cells
in
which
some
fuel
is
burnt
to
produce
electricity
are
called
fuel
cells.
E.g.
H2-O2
fuel
cell.
(4)
PHOTOVOLTAIC
CELLS:-
The
cells
in
which
solar
energy
is
converted
into
electrical
energy
are
called
photovoltaic
cells.
e.g.
solar
panels
of
Si
and
Ge.
ADVANTAGES
OF
THE
FUEL
CELLS
(1)
They
are
free
from
pollution.
(2)
They
are
75
%
efficient.
(3)
Water
formed
as
byproduct
can
be
used
for
drinking
purpose.
(4)
They
can
be
operated
at
higher
temperature.
NICKEL
CADMIUM
BATTERY
This
is
a
secondary
cell.
Cadmium
electrode
acts
as
anode
and
NiO2
electrode
acts
as
cathode.
KOH
is
used
as
an
electrolyte.
It
gives
a
potential
difference
of
1.14
v.
It
is
used
in
calculators,
watches
and
mobiles.
Working:
During
discharging
forward
reaction
takes
place
and
during
recharging
backward
reaction
occurs.
Manufacture
of
Chlorine
:-
The
industrial
production
of
chlorine
is
carried
out
by
electrolysis
of
natural
brines
or
concentrated
aqueous
solutions
of
NaCl.
Sodium
hydroxide
and
hydrogen
are
the
byproduct.
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