26772095 matriculation chemistry electrochemistry
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Chapter 10
ElectrochemistElectrochemist
ryry
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Electrochemistry
Is the study of the relationship between electricity
and chemical reaction
Chemical reactions involved in electrochemistry are :Chemical reactions involved in electrochemistry are :
Oxidation
ReductionREDOX REACTION
One type of reaction cannot occur withoutOne type of reaction cannot occur without
the other.the other.
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REDUCTION
gain of electron
Oxidation no. decrease
Reaction at cathode
Remember…RED CATRED CAT
= REDREDuction at CAT CAT hode
Example:
Cu2+ + 2e- Cu
Oxidation no. ↓
OXIDATION
loss of electron
Oxidation no. increase
Reaction at anode
Example:
Mg Mg2+ + 2e-
Oxidation no.
REDOX Reaction
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Reduction :
Oxidation :
Cu2+(aq) + 2e- → Cu(s)
n(s) → n2+(aq) + 2e- Half-cellreaction
Cu2+(aq) + n(s) → Cu(s) + n2+
(aq)
Example
Overall cell
reaction :
Electrochemical reaction consists of reduction
and oxidation.These two reactions are called ‘half-cell
reactions’
The combination of 2 half reactions are called
‘cell reaction’
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CellsThere are 2 type of cells
ElectrochemicalCells
ElectrolyticCells
where chemical reaction
produces electricity
Uses electricity to
produce chemical
reaction
ChemicalEnerg
ElectricalEnerg
ElectricalEnerg
ChemicalEnerg
Also called;
alvanic cell or !oltaic cell
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Component and Operationof al!anic cell
Consists of :
"# $n metal in an a%ueous solution of $n2&
2# Cu metal in an a%ueous solution of Cu2&
- !he 2 metals are connected "# a $ire- !he 2 containers are connected "# a salt "ridge.- % &oltmeter is used to detect &oltage generated.
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nelectrode
Cuelectrode
'alt
"ridge
Zn2+ Cu2+
oltmeter
Galvanic cell
n'O(aq)solution
Cu'O(aq)solution
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"hat happens at the #incelectrode $
inc is more electropositi&e than copper.
!endenc# to release electrons: n * Cu.
n (s) → n2+ (aq) + 2e-
inc dissol&es. Oxidation occurs at the n electrode. n2+ ions enter n'O
) solution.
n is the &e electrode since it is a source of
electrons anode.
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Cu2+ (aq) + 2e- → Cu (s)
Copper is deposited. Reduction occurs at the Cu electrode.
Cu is the +&e electrode cathode
"hat happens at the copperelectrode $
!he electron from the n metal mo&es out through the $ire enter the Cu metal
Cu2+ ions from the solution accept electrons.
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Reactions ,n&ol&ed:
%node :Cathode :
n (s) → n2+
(aq) + 2e-
Cu2+ (aq) + 2e- → Cu (s)
n (s) + Cu2+ (aq)→ n2+ (aq) + Cu (s)O&erall cellreaction :
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%&nctions
'alt "ridge helps to maintain electrical neutralit#
Completes the circuit "# allo$ing ions carr#ing chargeto mo&e from one half-cell to the other.
'alt brid(e
%n in&erted tu"e containing a gel%n in&erted tu"e containing a gelpermeated $ith solution of anpermeated $ith solution of an inert electrol#te such as Cl/ 0aelectrol#te such as Cl/ 0a22'O'O/ 01/ 010O0O..
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'hat happened if there is no salt brid(e)
Zn Cu
eZn2+ Cu2+
V
e
e
e
ee
ZnSO4(aq !uSO4(aq
%s the 3inc rod dissol&es/ the concentration of n2+
in the left "ea4er increase. !he reaction stops "ecause the nett increase in
positi&e charge is not neutrali3ed.This excess char"e build#u$ can be reduced b% addin" a salt
brid"e
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Salt brid"e
(&!l
Zn2+
- +Zn
ZnSO4(aq !uSO4(aq
Cu
ee
n (s) → n2+ (aq) + 2e- Cu2+ (aq) + 2e- → Cu (s)
%0O5E (-) C%!1O5E (+)
Cu2+
E = +!.!" #
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*ow does the cell maintains its electrical neutrality)
$eft Cell Right Cell
Cl- ions from salt"ridge mo&e into n
half cell
+ ions from salt"ridge mo&e into Cu
half cell
Electrical neutralit# is maintained
n (s) → n2+ (aq) + 2e- Cu2+ (aq) + 2e- → Cu (s)
n2+ ions enter the solution.Causing an o&erall excess of
t&e charge.
Cu 2+ ions lea&e the solution.Causing an o&erall excess of
-&e charge.
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Electrochemical !ells
'.2
s$ontaneous
redox reaction
anodeoxidation
cathodereduction
half
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Zn (s ) !u2) (aq !u (s ) Zn2) (aq
Zn (s * Zn2) (aq ** !u2) (aq * !u (s
anode cathode
lso can !e represented as:
Cell notation
6hase "oundar#
'alt "ridge
Cell notation
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Exercise
7or the cell "elo$/ $rite the reaction at anodeand cathode and also the o&erall cell reaction.
n (s) 8 n2+ (aq) 88 Cr+ (aq) 8 Cr (s)
n(s) n→ 2+ (aq) + 2e-
Cr+ (aq) + e- Cr(s)→
n(s) + 2Cr+ (aq) + → n2+ (aq) +2Cr(s)
Cathode :
%node :
O&erall cellreaction:
9 2
9
Cell notation
2 2e
e-
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The difference in electrical $otential between the anode
and cathode is called:
+ cell voltage
+ electromotive force (emf)
+ cell potential
cts as ‘electrical pressure’ that
pushes electron throu"h the #ire$
measured "# a &oltmeter
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Electrode %otential
measure of the a!ilit& of a half-cell to attract electrons to#ards it$
Cu2+ 'a() + 2e * Cu's) Eored +,$. /
Zn2+ 'a() + 2e * Zn's) Eored -,$01 /
tandard reduction potential of copper half-cell is
more positive compared to 3inc$
tandard reduction
potential+4he more positive the half-cell’s electrode potential5 the
stron"er the attraction for electrons$
Tendenc% for reduction ,
(cathode
Zinc half-cell !ecomes anode$
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!ell -otential (Eocell Eo
catode / Eoanode
)0.14 (#0.3
)'.' 5
!u2) (aq ) 2e 6 !u(s Eored )0.14 5
Zn2) (aq ) 2e 6 Zn(s Eored #0.3 5
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n2+ (aq) + 2e- → n (s)
Cu2+ (aq) + 2e- → Cu (s)
E" = -".%&#
E" = +".'(#
E"cell = E"
cathode - E"anode
= +".'( ) *-".%&
= +!.!" #or E"cell = E"
red + E"ox
= +".'( + *+".%&
= +!.!" #
Change the sign
1alf-cell equation at:
%node :
Cathode :
n (s) → n2+ (aq) + 2e-
Cu2+
(aq) + 2e-
→
Cu (s)
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tandard Electrode %otentials 'Eo)
at 26oC5 the pressure is 7 atm 'for
"ases)5 and the concentration of
electrol&te is 78$
measure of the a!ilit& of half-cell
to attract electrons to#ards it
4he si"n of E, chan"es #hen the
reaction is reversed
+Chan"in" the stoichiometric
coefficients of a half-cell reaction
does not chan"e the value of E,
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7or example:
Cl2*g + 2e- 2Cl-*a, E" = +!.'& #
Cl2*g + e- Cl-*a, E" = +!.'& #
Cl-*a, Cl2*g + e- E" = -!.'& #
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tandard 9&dro"en Electrode '9E)
8ade up of a platinum electrode5 immersed in an
a(ueous solution of 9+ '7 8) and !u!!led #ithh&dro"en "as at 7 atm pressure5 and temperature at
26oC
telectrodeH+ *a,
! M
H2 ga/at ! atm
4he standard reduction of 9E is , /
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Standard Electrode -otentials
Zn (s * Zn2)
(' M ** 7)
(' M * 72 (' atm * -t (s
2e# ) 27) (aq8' M 72 ("8' atm
Zn (s Zn2) (' M ) 2e# 9node (oxidation:
!athode (reduction:
Zn (s ) 27) (aq8' M Zn2) (aq ) 72 ("8' atmCell reaction
0.3 5 0 - E Zn /Zn 0
2)
E Zn /Zn #0.3 50 2)
Zn2)
) 2e#
Zn E 0
#0.3 5
E 0 E H/H
- E Zn /Zn cell
0 0 ) 2)
2
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'tandard reduction potential of Copper half cell ismeasured "# setting up the electrochemical
cell as "elo$.
92 '") 26o
C7 atm$
Cu
Cu2
CuO.'a()
78
9+
'a()78
/
-t
E, , + -
+
-
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-t (s * 72 (' atm * 7) (' M ** !u2) (' M * !u (s
2e# ) !u2) (' M !u (s
72 (' atm 27) ) 2e# 9node (oxidation:
!athode (reduction:
72 ) !u2) !u (s ) 27)
E 0 E cathode - E anodecell 0 0
E cell E Cu /Cu E H /H 2) )
2
0 0 0
0.14 E Cu /Cu # 00 2)
E Cu /Cu 0.14 52)0
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!he direction of half-reaction of '1E depends on theother
half-cell connected on it.!he cell notation for '1E is either:
t*/ 0 H2*g 0 H+ *a, 1hen it i/ anode
H+*a, 0 H2*g 0 t*/ 1hen it i/ cathode
,n either case/ E; of '1E remains ;
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n2+ (aq) + 2e- → n (s)
Cu2+ (aq) + 2e- → Cu (s)
E" = -".%&#
E" = +".'(#
E"cell = E"
cathode - E"anode
= +".'( ) *-".%&
= +!.!" #or E"cell = E"
red + E"ox
= +".'( + *+".%&
= +!.!" #
Change the sign
1alf-cell equation at:
%node :
Cathode :
n (s) → n2+ (aq) + 2e-
Cu2+
(aq) + 2e-
→
Cu (s)
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%t standard-state condition
E 0cell = E 0red + E 0ox
E 0cell = E 0cathode - E 0anode
or
E i
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ExerciseCalculate the standard cell potential of the follo$ing electrochemical cell.
Co(s) 8 Co2+ (aq) 88 %g+(aq) 8 %g(s)
AnswerCathode (Red) :
%node (Ox) : Co(s) → Co2+ (aq) + 2e-
%g+(aq) + e- → %g(aq) E; < +;.=;
E;ox < +;.2=
E"cell = E"
cathode - E"anode
= +"." ) *-".2
= +!." #
%g+(aq) + e- → %g(aq)
Co2+
(aq) + 2e-→ !o(s E
;
< -;.2=
E; < +;.=;
Refer to the list of 'tandard Reduction 6otential:
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Oxidation agent left of the half cell e,uation)
Reduction agent right of the half cell e,uation)
Example :
Oxidationagent
Reducingagent
Refer to the list of 'tandard Reduction 6otential:
%g+ (aq) + e- %g (s)→ E; < +;.=;
Cu2+ (aq) + 2e- Cu (s)→ E; < +;. 0i2+ (aq) + 2e- 0i (s)→ E; < -;.2> ,ncrease
strength asreducing
agent
The more +ve the value of E0 the stronger→ the oxidizing agent
The more -ve the value of E0 the stronger→ the reducing agent
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%rrange the elements in order of increasingstrength of reducing agents
3'+ + 'e- 3 E" = -!.&& #
42+
+ 2e-
4 E"
= -2.% #
$2+ + 2e- $ E" = +".5 #
Answer :$ 6 3 6 4
Exercise
Exam$le
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!alculate the E0 cell for the reaction ::
"($ * "2)(a; ** Sn4)
(a; 8Sn2)(a; * -t($
<iven :
"2)(a; ) 2e6 "($ E= #2.1> 5
Sn4)(a; ) 2e 6 Sn2)
(a; E= )0.'? 5
Oxidation : "($ 6 "2)(a; ) 2e Eo
ox )2.1> 5
@eduction : Sn4)(a; ) 2e 6 Sn2)
(a; Eo )0.'? 5
"($ ) Sn
4)
(a; 6 "
2)
(a; ) Sn
2)
(a; Ecell )2.?1 5
Exam$le
E cell E o red + E o ox
E 0 cell E cathode - E anode
+,$76- '-2$;)
+2$6/
)2.1> ) 0.'?
)2.?1 5
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Exercis
e% cell is set up "et$een a chlorine electrode and ah#drogen electrode
(a) 5ra$ a diagram to sho$ the apparatus and chemicals
used.(a) 5iscuss the chemical reactions occurring in theelectrochemical cell.
6t 8 12(g/ ? atm) 8 1+(aq/ ?@) 88 Cl2(g/ ?atm) 8 Cl-(aq/ ?@) 8 6t
E"cell
= +!.'& #
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Answer
92 '")5
7 atm$
%t
9+'a()5 78
%t
E,cell 7$1/
- +
/- + Cl2 '")5
7 atm$
Cl-'a()5 78
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7$ ho# the process occur at anode and
cathode
2$ Overall reaction
- 9alf-cell reaction
Answer
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Answer Reduction (cathode)
Cl2 *g + 2e- 2Cl- *a,
Oxidation(anode)
H2 *g 2H+
*a, + 2e-
E
o
cell <+?.
E, ,
Eocell < Eo
cathode - E;anode
+?. < Eocathode ;
E;cathode < +?. 'o the standard reduction potential forCl2 is:
Eo < +?.
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+ S$ontaneous A Bon#S$ontaneous
reactions # @edox reaction is s$ontaneous when
Ecell is )ve.
# Bon s$ontaneous is when Ecell is ve.
E= cell 0 The reaction is at equilibrium
%redict #hether the follo#in" reactions occur
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n.+ <n2+
%redict #hether the follo#in" reactions occur
spontaneousl& or non-spontaneousl& under standard
condition$
Zn + n.+ * n2+ + Zn2+
4he t#o half-cells involved are:-
nod : Zn * Zn2+ + 2e Eo
ox +,$01 /
Cathode: n.+ + 2e * n2+ Eo +,$76 /
Zn + n.+ ** Zn2+ + n2+
Eocell Eo
+,$=7 /
spontaneous
Zn<Zn2+* Eo
+,$76 > '-,$01 )
Eocell Eo
red + Eoox
'+,$76) + ',$01)
+,$=7 /Or
n.+ <n2+Eo +,$76/
Eo
Zn<Zn2+ - ,$01/$
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-b2)(aq ) 2!l#(aq 6 -b(s ) !l2("
-redict : S$ontaneous or non#
s$ontaneousC
Reduction
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%!2+ 'a() + 2Cl-'a() * %!'s) + Cl2'")%!2+ 'a() + 2Cl-'a() * %!'s) + Cl2'")
cathode: %!2+ 'a() + 2e * %!'s)
anode: 2Cl-'a() * Cl2'") + 2e
%!2+ 'a() + 2Cl-'a() * %!'s) + Cl2' ")
Eo -,$7 /
Eoox -7$1
Eocell Eo
red + Eo
ox
Oxidation
'-7$1) + '-,$7)
-7$.; /
?on-spontaneous
?o Reaction
Example :
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p
29"(s 29")(aq ) 2e E=
ox # 0.>0 5
Dr 2(aq ) 2e 2Dr #(aq E=
)'.03 5
29"(s ) Dr 2(aq 29")(aq ) 2Dr #(aq Esel
) 0.23 5
The reaction is spontaneous
Answer :
Predict whether the following reactions occurspontaneously :
29"(s ) Dr 2(aq 29")(aq ) 2Dr #(aq
E Ag /Ag )0.> 5)0
2E Br /Br )'.03 50
-
standard reduction
$otential
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Exercise
% cell consists of sil&er and tin in a solution of ? @sil&er ions and tin (,,) ions. 5etermine the spontaneit#of the reaction and calculate the cell &oltage of thisreaction.
%g+ (aq) + e- %g (s)→
'n2+ (aq) + 2e- 'n (s)→
E; < +;.=; E; < -;.?
(cathode)
(anode)
E;
cell < E;
cathode - E;
anode
< +;.=; (-;.?)< +;.A
E;
cell < +&e ( reaction is spontaneous)
?ernst e(uation
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?ernst e(uation
ernst e!uation can "e used to calculate the E cell
for any chosen concentration :
Ecell Eocell @T ln $roduct Fx
nG reactantF%
9t 2> & and @ >.1'4 H &#' mol#' 8 ' G ?00 !
Ecell Eocell 0.02?3 $roduct Fx
n reactantF%
2.101 lo"
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Ecell Eocell 0.0?2 $roduct Fx
n reactantF%
lo"
Ecell Eocell 0.0?2
n
lo" Q
n # no of e- that are involvedQ # reaction !uotient
$ product %x
$ reactant%yQ
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E*ample1
&alculate the Ecell for the following cell
Zn(s I Zn2) (aq8 0.02 II !u2) (aq8 0.40 I !u(s
Answer
'n(s) + &u*+ (a!) 'n*+ (a!) + &u(s)
Eocell Eo
red ) Eoox J
)0.14 5 ) 0.3 5
)'.'0 5
Eocell Eo
cathode Eoanode
)0.14 5 # (# 0.3 5
)'.'0 5
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E # Eo 0,0.* log $ 'n*+ %
n $ &u*+ %
E # +/,/0 0,0.* log (0,0* )
* ( 0,10)
# +/,/0 (-0,023)
# +/,/2.
At e!uili"rium:
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At e!uili"rium:
4 o net reaction occur (Q#K )
4 Ecell # 0
Ecell Eocell 0.0?2
n
lo" K
0 Eocell 0.0?2
n
lo" K
E=cell 0.0?2
nlo" K
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E*ample+&alculate the e!uili"rium constant (K ) for the
following reaction,
&u(s) + *Ag+(a5) &u*+
(a5) + *Ag(s)
At e!uili"rium6 E cell # 0
E ocell # E o cathode - E o anode
# +0,30 ( +0,21)
# +0,17
Answer
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Ecell # Eocell 0,0.* log K
*
0 # 0,17 0,0.* log K
*
0,0.* log K # 0,17
*
log K # /,1
K # 2,178 x /0/
El l i
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ElectrolysisElectrol#sis is a chemical process that uses electricit#
for a non-spontaneous redox reaction to occur.'uch reactions ta4e place in electroltic cell/.
Electrolytic Cell ,t is made up of 2 electrodes immersed in an
electrol#te.
% direct current is passed through the electrol#tefrom an external source.
@olten salt and aqueous ionic solution are commonl#
used as electrol#tes.
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Anion Cation
Oxidation Reduction
Electrolytic Cell
Electrolyte
(M+
X-
)X-,OH- M+,H+
+ -
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An
ode
Cat
hod
e
6ositi&e electrode
!he electrode $hich is connected to the
positi&e terminal of the "atter# Oxidation ta4es place
0egati&e electrode
!he electrode $hich is connected to thenegati&e terminal of the "atter#
Reduction ta4es place
Electron/ flo1 from anode to cathode
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Electrode
as circuit connectors
as sites for the precipitation of insolu"leproducts
example: 6latinum / Braphite (inert electrode)
Electrolyte
a liquid that conducts electricit# due to the presence of +&e and &e ions must "e in molten state or in aqueous
solution so that the ions can mo&e freel#example: Cl(l)/ 1Cl(aq)/ C1COO1(aq)
parison bet,een an electrochemical
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parison bet,een an electrochemicaland an electrolytic cell
Cathode%node
- +e- e-
%node Cathode
+ -
e- e-
+ -
Electrolytic Cell Electrochemical Cell
El t l ti C ll El t h i l C ll
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Electrolytic Cell Electrochemical Cell
Cathode < negati&e
%node < positi&e
Cathode < positi&e
%node < negati&e
0on-spontaneous redoxreaction requires energ#
to dri&e it
'pontaneous redoxreaction releases energ#
Oxidation occurs at anode/ reduction occursat cathode
%nions mo&e to$ards anode/ cations mo&eto$ards cathode. Electrons flo$ from anode to cathode in anexternal circuit.
7imilaritie/8
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Electrolysis of molten salt
Electrol#sis of molten salt requires high temp. Electrol#sis of molten 0aCl
Cation : 0a+ %nion : Cl-
Anode 8
Cathode 8 +a& ,l# & e- +a ,s#→
Cl- ,l# Cl→ 2,(# & 2e-
O9erall 8 2+a& ,l# & 2Cl-,l# Cl→ 2,(# & 2+a,s#
2+a& ,l# & 2e- 2+a ,s#→
El t l sis f m lt 0 Cl i s s di m m t l
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Electrol#sis of molten 0aCl gi&es sodium metaldeposited at cathode and chlorine gas e&ol&ed atanode.
Electrol#sis of molten 0aCl is industriall# important.!he industrial cell is called 5o$ns CellD
El t l i f A ' lt
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Electrolysis of A-&eo&s 'alt Electrol#sis of aqueous salt is more complex
"ecause the presence of $ater. %queous salt solutions contains anion/ cation and $ater. ater is an electro-acti&e su"stance that ma# "e
oxidised or reduced in the process depending on
the condition of electrol#sis.
Reduction :
Oxidation :
2*2O ,l# & 2e- *2 ,(# & 2O*- ,a%#
2*2O ,l# *& ,a%# & O2 ,(# & e-
E; < -;.=
E; < -?.2
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%redictin" the products of electrol&sis
Factors influencing the products :
7$ Reduction<oxidation potential of the
species in electrol&te2$ Concentrations of ions
$ 4&pes of electrodes used > active or
inert
Electrolysis of A-&eo&s NaCl
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Electrolysis of A-&eo&s NaCl
!he electrol#sis of aqueous 0aCl depends on theconcentration of electrol#te.
0aCl aqueous solution contains 0a+ cation/ Cl- anion
and $ater molecules On electrol#sis/
the cathode attracts 0a+ ion and 12O molecules
the anode attracts Cl-
ion and 12O molecules
Electrolysis of dil&ted NaCl sol&tion
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Cathode
2*2O ,l# & 2e- *2 ,(# & 2O*- ,a%# E; < -;.= +a
&
,a%# & e-
+a ,s# E; < -2.F?
E; for $ater molecules is more positi&e.
12O easier to reduce.
Electrolysis of dil&ted NaCl sol&tion
Anode
Cl2 ,(# & 2e- 2Cl- ,a%# E; < +?.
O2 ,(# & *& ,a%# & e- 2*2O ,l# E; < +?.2
,n dilute solution/ $ater $ill "e selected foroxidation "ecause of its lo$er Eo.
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ctrolysis of Concentrated NaCl sol&ti
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ctrolysis of Concentrated NaCl sol&ti
Cathode
2*2O ,l# & 2e- *2 ,(# & 2O*- ,a%# E; < -;.= +a
&
,a%# & e-
+a ,s# E; < -2.F?
E; for $ater molecules is more positi&e
12O easier to "e reduceAnode
Cl2 ,(# & 2e- 2Cl- ,a%# E; < +?.
O2 ,(# & *& ,a%# & e- 2*2O ,l# E; < +?.2
,n concentrated solution/ chloride ions $ill "eoxidised "ecause of its high concentration.
R i i l d
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Reactions involved
2*2O ,l# & 2e
-
*2 ,(# & 2O*
-
,a%# E;
< -;.= 2Cl- ,a%# Cl2
,(# & 2e- E; < -?.
Cellreaction: 2*2O,l# & 2Cl- Cl2,(# & *2,(# & 2O*-,a%#
E;cell < -2.?A
Cathode8
Anode8
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0a2'O aqueous solution contains 0a+ ion/ 'O2- ion
and $ater molecules
On electrol#sis/ the cathode attracts 0a+ ion and 12O molecules
the anode attracts 'O2- ion and 12O molecules
Exercise
6redict the electrol#sis reaction $hen0a2'O solution is electrol#sed using platinum electrodes.
Soltion
Cathode
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Anode
E; for $ater molecules is less positi&e
12O easier to oxidise
02O12- ,a%# & 2e- 20O
2- ,a%# E; < +2.;?
O2 ,(# & *& ,a%# & e- 2*2O ,l# E; < +?.2
Cathode
2*2O ,l# & 2e- *2 ,(# & 2O*- ,a%# E; < -;.=
+a& ,a%# & e- +a ,s# E; < -2.F?
E; for $ater molecules is more positi&e12O easier to reduce
E ti
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Cathode < 12 gas is produced and solution "ecome:a/ic at cathode "ecause O1- ions are formed
%node < O2 gas is produced and solution "ecomeacidic at anode "ecause 1+ ions are formed
E!ation
Cathode8
Anode8 E; < -?.2
2*2O ,l# & 2e- *2 ,(# & 2O*- ,a%# E; < -;.=
2*2O ,l# O2 ,(# & *& ,a%# & e-
Cell
Reaction:
E;cell < -2.; 2*2O,l# O2,(# & 2*2,(#
%araday.s /a, of
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%araday s /a, ofElectrolysis
5escri"es the relationship "et$een the amount ofelectricit# passed through an electrol#tic cell andthe amount of su"stances produced at electrode.
%araday.s %irst /a,
ates that the !antity o" s#stance "ormed at a
ectrode is directly $ro$ortional to the !antityelectric char%e s$$lied&
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%araday.s 1st /a,
m α Q
3 electric char(e in coulombs ,C#
m 3 mass of substance dischar(ed
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The End
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Q = It
3 electric char(e in coulombs ,C#
I 3 current in amperes ,A#
t 3 time in second ,s#
7arada# constant (7)is the charge on ? mole of electron
' ( ) *+ ,--C
Exam$l
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Exam$l
e%n aqueous solution of Cu'O is electrol#sed using acurrent of ;.?>; % for > hours. Calculate the mass
of copper deposited at the cathode.
Answer
Electric charge/ G < Current (,) x time (t)
G < (;.?>; %) x ( > x ; x ; )s
G < 2F;; C
? mole of electron H ? 7 H A >;; C
0o. of e- passed through <2F;;
A >;;
< ;.;2= mol
C 2+ ( ) 2 C ( )
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Cu2+ (aq) + 2e- → Cu (s)
7rom equation:
2 mol electrons → ? mol Cu
;.;2= mol electrons→ ;.;? mol Cu
@r for Cu < .>@ass of Copper deposited < ;.;? x .>
< ;.==A g