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CHAPTER 6: ELECTROCHEMISTRY
TERMS MEANING
ELECTROLYSIS a process whereby a compou! "s!ecompose! "#o "#s cos#"#ue# e$eme#
we e$ec#r"c curre# passes #hrou%h ae$ec#ro!e
ELECTROLYTE Subs#ace !a# ca co!uc# e$ec#r"c"#ye"#her " mo$#e or a&ueous so$u#"o
u!er%o chem"ca$ cha%es a# e$ec#ro!e
'Cos"s# (ree mo)"% "o co* "# "s " mo$#eor a&ueous s#a#eProcess o( e$ec#ro$ys"s ")o$)es + s#a%es,-
mo)eme# o( "os . e$ec#ro!e a! !"schar%e o( "os
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E$ec#ro$ys"s " Mo$#e Compou!• Consist only 1 type of cation and 1 type of anion
• EXAMPLE: molten lead (II) bromide
ca#ho!e ao!e
obser)a#"o A sh"y %$obu$e (ou! a# bo##omo( cruc"b$e
A brow %as w"#h pu%e# sme$$"s re$ease!
pro!uc#s $ea! /rom"e %as
0 e&ua#"o
O)era$$ "o"c
e&ua#"oobser)a#"o
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E$ec#ro$ys"s " A&ueous So$u#"o
FACTORS DAT INFLUENCE THECHOICE OF IONS TO BE
DISCHARGED
• Position of ions in ECS
• Concentration of ions in electrolytes
• ypes of electrode !sed in electrolysis
"# P$SII$% & C$%CE%'AI$% & ELEC'$E "
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12 Pos"#"o o( Io " ECSConditions: dil!te sol!tion & inert electrode
* electropositi+e cations , * electone-ati+e anions in ECS .ill b disc/ar-ed
Ions presents
CA0$E A%$E
Ions attracted
Ion disc/ar-es
e2!ation
Prod!ct$bser+ation
E3planation 444 are attracted tocat/ode b!t only 4 isdisc/ar-ed as it is lo.ert/an4 in ECS
4455 are attracted toanode b!t only 4 isdisc/ar-ed as it is lo.ert/an4 in ECS
EXAMPLE: THE ELECTROLYSIS OF O.1 MOL DM3 OF CUSO4 SOLUTION USING
CARON ELECTRODE
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+2 Coce#ra#"o o( Ios " E$ec#ro$y#es• Conditions : inert electrodes & concentrated sol!tion
• $nly tr!e for /allide ions 6%a7 Cl7 8r 9
• is factor only affected at anode cat/ode !se factor position in ECS
• concentration of ion ; .ill be disc/ar-ed
EXAMPLE: ELE'$L5? M$L M"@ %ACI SI%B CA'8$% ELEC'$E
Ions presents
CA0$E A%$E
Ions attracted
Ion disc/ar-es
e2!ation
Prod!ct$bser+ation
E3planation 444 are attracted tocat/ode b!t only 4 isdisc/ar-ed as it is lo.ert/an4 in ECS
4455 are attracted toanode b!t only 4 isdisc/ar-ed as it is /asconcentration t/an 45
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32 Types o( E$ec#ro!e 4se!I( use me#a$ e$ec#ro!e 5Cu A% N"7' No "os !"schar%e a# ao!e howe)er me#a$ a#om o( ao!e re$ease e$ec#ro #o (orm
me#a$ "o-8me#a$ ao!e !"sso$)e
' Reac#"o a# ca#ho!e use me#a$ e$ec#ro!e9 use (ac#or pos"#"o o( "o " ECS
Ions presents
CA0$E A%$E
Ions attractedIon disc/ar-es
e2!ation
Prod!ct
$bser+ationE3planation 444 r attracted " cat/ode
b!t only 4 is disc/ar-ed as itis lo.er t/an4 in ECS
Alt/o!-/ 4444 r attracted"anode7 bot/ r not disc/ar-e5Instead7 455 dissol+e
The intensity of blue CuSO4 unchange co* #he concentration unchanged
co* no Cu atoms form CuSO4 at anode = the no of CuSO4 ions form Cu
Eamp$e: e$ec#ro$ys"s o( 12; mo$ !m-3 CuSO< so$u#"o us"% Cu e$ec#ro!e
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E!t"#$tion o% M&t#'s
Ions presents
CA0$E A%$E
Ions attracted
Ion disc/ar-ed
e2!ation
Prod!ct
$+erall e2!ation
'Reac#")e me#a$ ca be e#rac#e! (rom "#s ore by e$ec#ro$ys"s
'Me#a$ (orme! #hrou%h #he reac#"o a# ca#ho!e
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P("i%i$#tion o% M&t#'s ' Impure me#a$s ca be pur"("e! us"% e$ec#ro$ys"s' me#a$ "s #ras(erre! (rom ao!e -8 ao!e
' A(#er process: mass o( ao!e re!uce! wh"$e ca#ho!e "crease
Ions presents
CA0$E A%$E
Ions attracted
Ion disc/ar-es
e2!ation
Prod!ct
$bser+ation
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E'&$t"o)'#tin*" process !sed to coat 1
metal .if a layer of anot/er metal
• Rsons %o" &'&$t"o)'#tin*:
Pre+ent corrosion" electroplated obDect more resistant tocorrosion
Loos more attracti+e" /a+e s/iny appearance
• Condition 4 *ood &'&$t"o)'#tin*
$bDect c!rrent"small
$bDect be plated t!rned steadily
Concentration ion platin- metal lo.
Metal obDect be plated clean , free from -rease
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=o$#a"c>Ga$)a"c Ce$$' A ce$$ !a# pro!uces e$ec#r"ca$ eer%y we chem"ca$ reac#"o occur " "#
Further distance of metals b/w ECS, voltage of chemical cell
' e$ec#ropos"#")eme#a$
'Me#a$ a#om RELEASEe$ec#ro !a# w"$$ ($ow
#hrou%h e#era$c"rcu"#
'Me#a$ a#om becomesme#a$ "o 5corro!es7
' *e$ec#ropos"#")eme#a$
'Me#a$ a#om ACCEPTe$ec#ro !a# ($ow (rom
e#era$ c"rcu"#'Pos"#")e "os becomesa#om>mo$ecu$e
" E'MI%AL &E'MI%AL e2!ation
$bser+ation
E3planation Fn electropositi+e t/an C!5
Fn release more electron t/anC! to form Fn ion
C! ions from C!S$
recei+e electron ti formcopper metal
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?a"e$ ce$$ 5eamp$e o( )o$#a"cce$$7
' + so$u#"o are coec#e! #hrou%h sa$# br"!%e orporous po#
' @uc#"o o( sa$# br"!%e:
. Pre)e# #he + so$u#"os (rom m""%. A$$ow #he ($ow o( "os so !a# #he c"rcu"# "scomp$e#e!
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Dislacement !eaction' Me#a$ p$ace h"%her up " ECS are ab$e #o !"sp$ace
me#a$s p$ace be$ow #hem (rom "#s sa$# so$u#"oReac#"o b>w $ea! a! M%SO<'Reac#"o o# occur co* $ea! e$ec#ropos"#")e #ha ma%es"um
'Lea! !"sp$ace M% (rom M%SO<
'Io"c e&ua#"o:
Reac#"o b>w *"c a! CuSO<'Reac#"o occur co* *"c e$ec#ropos"#")e #ha copper
'*"c !"sp$ace copper (rom CuSO
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E$ec#roChem"ca$ Ser"es 5ECS7• Arran-ement of metals based on t/e
tendency of eac/ metal atom to releaseelectrons to form positi+e ions
• Importance:
To d&t&"+in& t,& t&"+in#' o% -o't#i$ $&''s position; "terminal77 * position ; &terminal
To d&t&"+in& t,& st#nd#"d $&'' -o't#*&
/e f!rt/er apart t/e metals are in series7 t/ebi--er t/e +olta-e
To d&t&"+in& t,& #i'it/ o% # +&t#' todis)'#$& #not,&" +&t#' %"o+ its s#'tso'(tion
More electropositi+e able to displace less
electropositi+e metal from its salt sol!tion
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COMPARISON
Property Electrolytic cell Goltaic cell
Ener-y
c/an-e
Electrical H c/emical C/emical H Electrical
Polarity Cat/ode ; " terminal
Anode ; & terminal
Cat/ode ; &terminal
Anode ; " terminal
=lo. ofelectron & terminalH "terminal "terminal H &terminal
Electrode Anode , cat/odemay be same or
different
Anode , cat/odem!st be different
metals
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