Electrochemistry form 4

8/18/2019 Electrochemistry form 4

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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

Electrochemistry form 4

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