Electra-chemistry

8/13/2019 Electra-chemistry

1/20

ELECTROCHEMISTRY by Giorgio Carboni, January 1998

Translate by G!L! Stuart

CO"TE"TS

I"TRO#$CTIO" CO"#$CTORS %&TTERIES THE LEMO" %&TTERY #&"IELL'S CELL THE CO"CE"TR&TIO" CELL (OLT&'S )ILE ME&S$RI"G )OTE"TI&LS O* RE#$CTIO" G&L(&"IC #E)OSITIO" CO"CL$SIO"

I"TRO#$CTIO"In 1+91 Luigi Gal ani is-o ere ele-tri-al a-ti ity in t.e ner es o/ t.e /rogs t.at .e0as isse-ting! He t.oug.t t.at ele-tri-ity 0as o/ ani al origin an -oul be /ounonly in li ing tissues! & /e0 years later, in 1822 &lessan ro (olta is-o ere t.atele-tri-ity -oul be 3ro u-e t.roug. inorgani- eans! In /a-t, by using s all s.eetso/ -o33er an 4in- an -lot. s3a-ers soa5e in an a-i solution, .e built a battery 6 t.e/irst a33aratus -a3able o/ 3ro u-ing ele-tri-ity! "aysayers 0ere 7ui-5 to 3re i-t t.atele-tri-ity 0oul ne er ser e a use/ul 3ur3ose! Ob iously t.ey 0ere ery 0rong!Ele-tri-ity .as a -entral role in our li es an to t.is ay Ele-tro-.e istry is a stan ar-ourse o/ stu y!

.ile listening to lessons on Ele-tro-.e istry, any stu ents ay 0on er 0.y it0as e er in ente , i/ it 0as really e er ne-essary to in ent it an i/ t.e 0orl 0oul

be better o// 0it.out it! it. t.e s all e 3eri ents t.at /ollo0, 0e .o3e to a5e 3ea-e bet0een t.ese stu ents an t.e stu y o/ Ele-tro-.e istry! T.ese /un an si 3lee 3eri ents -an tea-. t.e /un a ental -on-e3ts o/ Ele-tro-.e istry 0it.out as5ing

u-. o/ t.e stu ent! &s you 0ill see, any o/ t.ese e onstrations are easily a a3teto arious -on/igurations an ea-. -an be one in e3en ently or as 3art o/ t.e /ull-urri-ulu !

POROUS VASE 6 &n a-tual 3orous ase a e /or t.e 3ur3ose ay be i//i-ult toa-7uire! It is use to 3re ent t.e 7ui-5 i ing o/ arious solutions, 0.ile 3er itting
http://www.funsci.com/fun3_en/electro/electro.htm#0%230http://www.funsci.com/fun3_en/electro/electro.htm#1%231http://www.funsci.com/fun3_en/electro/electro.htm#2%232http://www.funsci.com/fun3_en/electro/electro.htm#2%232http://www.funsci.com/fun3_en/electro/electro.htm#3%233http://www.funsci.com/fun3_en/electro/electro.htm#4%234http://www.funsci.com/fun3_en/electro/electro.htm#5%235http://www.funsci.com/fun3_en/electro/electro.htm#6%236http://www.funsci.com/fun3_en/electro/electro.htm#7%237http://www.funsci.com/fun3_en/electro/electro.htm#8%238http://www.funsci.com/fun3_en/electro/electro.htm#contents%23contentshttp://www.funsci.com/fun3_en/electro/electro.htm#1%231http://www.funsci.com/fun3_en/electro/electro.htm#2%232http://www.funsci.com/fun3_en/electro/electro.htm#2%232http://www.funsci.com/fun3_en/electro/electro.htm#3%233http://www.funsci.com/fun3_en/electro/electro.htm#4%234http://www.funsci.com/fun3_en/electro/electro.htm#5%235http://www.funsci.com/fun3_en/electro/electro.htm#6%236http://www.funsci.com/fun3_en/electro/electro.htm#7%237http://www.funsci.com/fun3_en/electro/electro.htm#8%238http://www.funsci.com/fun3_en/electro/electro.htm#0%230


2/20

t.e e -.ange o/ ions! *or our 3ur3oses you -an a a3t a terra-otta 3ot o/ t.e ty3e usein gar ening si 3ly by 3lugging t.e .ole in t.e botto 0it. olten 0a an allo0ingit to -ool! &not.er e en ore e-ono i-al ans0er lies in -onstru-ting a barrier o/

3a3er! &s s.o0n in /igure :, roll t.e 3a3er to /or a -ylin er an glue it in 3la-e ont.e botto o/ t.e ain -ontainer using a sili-one a .esi e su-. t.at li7ui s -annot

3ass bet0een t.e t0o areas e/ine by t.e 3a3er! & barrier o/ ;ust one s.eet 0oul betoo 3er eable, t.ere/ore use at least t.ree layers o/ 3a3er 0.en buil ing t.is e i-e!

DISTILLED WATER 6 #on't use e6ioni4e 0ater in 3la-e o/ a-tual istille 0ater!Many ti es 0ater sol /or use in .ouse.ol irons is e6ioni4e rat.er t.an istille0ater! ).ar a-ies sell a-tual istille 0ater! .at is t.e i//eren-e< Many substan-esare soluble in 0ater an a /e0 o/ t.ese substan-es se3arate into 3ositi e an negati eions in 0ater! Generally t.ese are a e u3 o/ ole-ules t.at .a e ioni- bon s, 0.ilenon6ioni- ole-ules re ain inta-t, ;ust in solution! *or e a 3le, sugar issol eseasily in 0ater an t.e sugar ole-ules re ain inta-t as sugar! #e6ioni4e 0ater -an.a e any nu ber o/ issol e substan-es t.at o not result in ions, yet are 3resentnonet.eless! &3art /ro t.is, a 3oor 7uality sa 3le o/ e6ioni4e 0ater -an -ontainsigni/i-ant a ounts o/ ions! On t.e ot.er .an , istille 0ater is usually ery 3ure 6-ontaining only a-tual 0ater ole-ules!

WHERE TO OBTAIN THE MATERIALS - You -an buy t.e -.e i-als in a storet.at sells -.e i-als an laboratory e7ui3 ent! O/ten, t.is ty3e o/ store is lo-ate nearuni ersities! So e gro-ery or .ar 0are store are able to get you t.e -.e i-als nee e/or t.ese e 3eri ents! You -an o/ten 3ur-.ase -o33er an 4in- stri3s at a .obbyretailer or .ar 0are store! You -an also as5 a /ir 0.i-. 0or5s 0it. s.eets o/ t.ese

etals /or so e 3ie-es, /or e a 3le a gutter63i3e /ir an a 4in- gal ani- treat ents/ir ! *or t.e /irst trials, you -an also use a 3ie-e o/ -o33er an a 4in-6gal ani4e nailor s-re0!

CATHODE AND ANODE - In t.e -ourse o/ t.ese e 3eri ents, o/ten I'll s3ea5 o/-at.o es an ano es! &s you ay noti-e, in so e -ases t.e -at.o e .as been assignea 3ositi e 3olarity an , in ot.er -ases, a negati e one! T.is is ue to t.e -at.o e beingt.e ele-tro e 0.ere t.e rea-tion o/ re u-tion o--urs! In t.e -ase o/ a battery, t.isre u-tion o--urs s3ontaneously an -onsu es ele-trons, so t.e -at.o e garners a

3ositi e -.arge! In t.e -ase o/ an ele-trolyti- -ell, t.e re u-tion is /or-e , 3ro u-ingele-trons, so t.e -at.o e -arries a negati e -.arge! T.e ano e 0ill .a e in ea-. -aset.e 3olarity o33osite t.e -at.o e's!

SOLUTIONS ( IMPORTANT ) - T.e ilution o/ a-i s is angerous! I/ 0ater is a eto a -on-entrate a-i , it -an e 3lo e iolently -ausing se ere in;uries! "e er 3our0ater into -on-entrate a-i ! &l0ays a t.e a-i to t.e 0ater! I/ you nee to

ilute an a-i , get .el3 /ro a C.e ist! .en a5ing a solution o/ -o33er sul/ate or4in- sul/ate, a t.ese -.e i-als to 0ater rat.er t.an a ing t.e 0ater to t.e-.e i-al!

OTHER PRECAUTIONS 6 #o not allo0 any o/ t.e -.e i-als is-usse in t.esee 3eri ents to get on your .an s or s5in! #o not 3ut t.e in your out. or eat t.e !#o not breat.e any a3ors /ro t.ese -.e i-als! #o not 5ee3 t.e in bottles or-ontainers t.at -oul be -on/use 0it. a /oo or rin5 -ontainer! #o not lea e t.ese-.e i-als in su-. a 3la-e t.at it ig.t be -on/use 0it. a /oo or rin5 =su-. as on a


3/20

5it-.en table or -ounter or in t.e re/rigerator>! Store t.e in a se3arate, -ontrolle 3la-e a0ay /ro /oo s an out o/ t.e rea-. o/ -.il ren! Label ea-. -ontainer -learly0it. t.e na e o/ t.e -ontents an as a non6/oo ite !

CO"#$CTORS

Materials?

6 a battery6 an ele-tri- lig.t bulban so-5et6 t.ree 0ires 0it.alligator -li3s6 a glass rin5ing -u3or a bea5er

6 istille 0ater 6 t0o ele-tro es o/ t.esa e aterial =/or e a 3le -o33er>6 table salt6 an a eter

$sing t.e ariousite s liste abo e,-onstru-t t.e e i-es.o0n in /igure 1=0.i-. is 5no0n as a-ontinuity tester>! &syou -an see, t.ere is a

brea5 in t.e ele-tri-al 3at. bet0een t.e battery an t.e la 3!$sing arious.ouse.ol ite s =su-.as a 3lasti- 3en, aneraser, a -era i- 3late,et-!> try to -o 3letet.e -ir-uit an see i/t.e la 3 lig.ts!

You 0ill noti-e t.at etalli- ite s -ause t.e la 3 to lig.t 0.ile ost ot.ers o not!Try using t.e gra3.ite =also 5no0n as t.e 'lea '> /ro a 3en-il! You 0ill noti-e t.att.is aterial allo0s t.e bulb to lig.t alt.oug. 3er.a3s not as brig.tly, e3en ing on.o0 long or s.ort t.e gra3.ite is! T.is is be-ause t.e gra3.ite, alt.oug. a -on u-tor

3resents a -ertain a ount o/ resistan-e to t.e /lo0 o/ ele-tri-ity! $sing t.is e i-e, 0e-an -.ara-teri4e soli aterials as eit.er -on u-tors or non6-on u-tors! "on-on u-tors are also 5no0n as insulators! T.ere are any soli aterials t.at .a e

inter e iate 3ro3erties bet0een -on u-tors an insulators, li5e gra3.ite!
http://www.funsci.com/fun3_en/electro/electro.htm#contents%23contents


4/20

.at about 0ater< Let's o i/yt.e -ir-uit 0e use earlier tono0 easure t.e -on u-ti ity o/0ater =see /igure @>! Instea o/ alig.t bulb to in i-ate t.e /lo0 o/

ele-tri-ity, no0 0e 0ill use ana eter set to t.e i-roa 3s-ale! T.is setu3 0ill be u-.

ore sensiti e an 0ill allo0 usto a-tually easure t.e ele-tri-al/lo0! *ill t.e -ontainer 0it.distilled water an 3la-e t.eele-tro es in t.e 0ater as s.o0n!%e -are/ul not to tou-. t.eele-tro es to ea-. ot.er! I/ t.ereis any in i-ation o/ -urrent /lo0on t.e eter, it s.oul be erys all! T.is s all -urrent is ueto t.e 3resen-e o/ H A an OH 6 ions 3ro u-e 0.en a /e0 o/ t.e0ater ole-ules isso-iate anre-o 3ose s3ontaneously! T.enu ber o/ ole-ules oing t.isin any gi en o ent is erys all an t.is is 0.y istille0ater is a ery 3oor -on u-tor!

it.out isturbing t.e e i-e, 3la-e a ery s all a ount o/ saltin t.e 0ater an 0it. a 3lasti- orglass utensil stir t.e 0ater to it.e solution! &s t.e salt -rystals

issol e, t.e nee le on t.ea eter 0ill o e noti-eably,in i-ating an in-rease-on u-ti ity o/ t.e 0aterBsaltsolution! e use t.e sa esetu3 as be/ore to .el3 illustrate

t.e si ilarity in t.e t0o e i-es, but you -an also -on u-t t.esa e e 3eri ent 0it.out t.e

battery, but 0it. an o. eterset to rea resistan-e, as t.eo. eter .as an internal batteryan a5es t.e setu3 less-o 3li-ate !

.at .a33ene < .y i t.e salt a5e t.e 0ater ore -on u-ti e to ele-tri-ity areattra-te to t.e-.arge -o33erele-tro e 0.eret.ey re-ei e t0oele-trons an

be-o e neutralan e3osit on

t.e ele-tro e inetalli- /or !T.e 3ositi e 4in-ions = n AA> o eto t.e 3orous

ase! *or ea-.-o33er ato t.atis e3osite ont.e -o33erele-tro e, a 4in-ato goes into

solution, gi ingu3 t0o ele-trons


10/20

to t.e 4in-ele-tro e!

T.e rea-tions at t.e ele-tro es -an be re3resente by t.is /or ula?

n n AA A @e6Cu AA A @e6 Cu

T.ese rea-tions result in t.e issolution o/ 4in- ato s in t.eir ioni- /or , 0.i-.-orres3on s to t.e e3osition o/ -o33er ions in t.eir etalli- /or ?

n A Cu AA n AA A Cu

T.e ele-trons a e a ailable by t.e 4in- ato s 3ass t.roug. t.e la 3 /ila ent, 3ro u-e lig.t t.roug. t.e ;oule e//e-t an e entually rea-. t.e -o33er ele-tro e!T.ese ele-trons a--ount /or t.e -urrent t.at is 3ro u-e by t.e battery an is use byt.e la 3! I/ 0e i n't .a e t.e 3orous ase, t.e Cu AA ions 0oul go ire-tly to t.e 4in-ele-tro e an 3i-5 u3 /ree ele-trons, t.ereby by3assing t.e e ternal -ir-uit ansto33ing t.e -urrent /lo0 t.roug. t.e 0ires an la 3! T.e battery 0oul no longer0or5! %e-ause t.e -o33er ele-tro e attra-ts ele-trons /ro t.e e ternal -ir-uit, it is-onsi ere t.e 3ositi e 3ole o/ t.e battery!

In a battery, t.ere isal0ays a /lo0 o/ele-trons in t.ee ternal -ir-uit =t.e

ele-tri-al -ir-uit ore i-e> an a-orres3on ing /lo0in t.e internal -ir-uit=t.e ele-trolyti--ir-uit>! Li5e any

battery, t.e #aniellCell oes not last/ore er, but only aslong as t.ere are Cu AA ions a ailable an

t.e 4in- ele-tro e isnot -onsu e ! Inreality, t.e

3ro u-tion o/-urrent i inis.esas t.e -on-entrationo/ t.e ele-trolyte

bat.ing t.e 4in-ele-tro e in-reasesan t.at bat.ing t.e-o33er ele-tro e

e-reases! In /a-t,t.e 3ositi e ions


11/20

3ro u-e by t.e 4in-ele-tro e nee SO : ions to balan-e t.e-.arges! T.e e a-to33osite o--urs in

t.e -o33er solution,0.i-. be-o ess-ar-e o/ 3ositi eions!

Sin-e t.e ele-tro oti e /or-e o/ a battery is e3en ant not only u3on t.e nature it's-o 3onents, but also u3on t.e -on-entration o/ it's ele-trolytes, t.e gra ient o/-on-entrations t.at results /ro t.e 3ro u-tion o/ ele-tri-ity -auses t.e battery togenerate lo0er an lo0er oltages an -urrents until /inally it is -onsi ere ea ! &tt.e en , n AA ions /inally rea-. t.e -o33er ele-tro e, surroun ing it an blo-5ing any/urt.er o e ent o/ Cu AA ions by 3olari4ing t.e ele-tro e!

You -an also buila #aniell Cell0it.out a 3orous

ase by using 0.atis 5no0n as aSaline %ri ge =/ig!

an +>! T.ise i-e is a e by

using a $ s.a3e

tube /ille 0it.saline solution!You -an a5e one0it. t.e 3lasti-tube -alle out int.e aterials listearlier! *ill t.etube 0it. a)otassiu "itrate= "O D> or Salt="aCl> issol e

in istille 0ater=about 12 gra s o/-.e i-al 3er 122-- o/ 0ater>! )lugt.e en s 0it. t.e-otton so t.at t.esaline solution 0illre ain in t.e

bri ge an not i0it. t.eele-trolytes! T.e

bri ge ser es t.esa e 3ur3ose as


12/20

t.e 3orous ase,a-ting as a barrier

bet0een t.e t0oi//erent

ele-trolytes 0.ile

allo0ing t.e /lo0o/ -.arges!

I/ you 0ant .ig.er oltages, you -an -onne-t ulti3le #aniell Cells in series as s.o0nin /igure 8! "ote t.at bet0een one -ell an anot.er, t.e -onne-tion is a etalli- 0irerat.er t.an a saline bri ge!

THE CO"CE"TR&TIO" CELL

Materials?6 t0o stri3s o/ -o33er 6 a large bea5er, bo0lor ot.er suitable-ontainer 6 a 3orous ase =as

is-usse in t.eIntro u-tion>

6 a 3lasti- tube =asuse in 3re iouse 3eri ent>6 -otton6 F2g o/ Co33erSul/ate =CuSO : >6 1B@ liter o/ istille0ater 6 a olt eter 6 t0o -ables 0it.alligator -li3s
http://www.funsci.com/fun3_en/electro/electro.htm#contents%23contentshttp://www.funsci.com/fun3_en/electro/electro.htm#contents%23contents


13/20

T.e setu3 o/ t.is e 3eri ent =/ig! 9> is ery si ilar to t.e #aniell Cell's setu3 =/ig! :an F>! T.is battery ta5es a antage o/ t.e ten en-y o/ t0o solutions .a ing i//erent-on-entrations to rea-. t.e sa e -on-entration le el! In -ontrast to t.e #aniell's Cell,0e use only one aterial /or t.e ele-tro es, in t.is -ase -o33er! &s ele-trolyte, use-o33er sul/ate in t0o -on-entrations, one using D2 gra s o/ -.e i-al in 122-- o/

0ater, t.e ot.er using t0o gra s o/ -.e i-al in 122 -- o/ 0ater! &s you 3la-e t.eolt eter in t.e -ir-uit, it s.oul in i-ate t.e oltage generate by t.e -ell!

.at is .a33ening in t.is battery< T.e ele-tro es areun ergoing a si ilarre u-tion rea-tion, but int0o i//erent-on-entrations! #ue to t.is

i//eren-e, t.ere is ai//eren-e in 3otential

= oltage> bet0een t.eele-tro es! &t t.e ano e,-o33er ato s issol e intosolution an gi e u3ele-trons, 0.ile at t.e-at.o e, -o33er ions

e3osit on t.e ele-tro ean a-7uire ele-trons!

Cu Cu AA A @e6

CuAA

A @e6

CuYou -an buil a s aller,si 3ler ersion o/ t.is

battery by substituting a$ s.a3e tube in 3la-e

o/ t.e 3orous ase! In t.e-enter o/ t.e lengt. o/tubing, tig.tly 3ress a7uantity o/ -otton in or erto /or a barrier bet0een

t.e i//erent-on-entrations o/ solutionsan 3re ent 3re ature

i ing! & t.e solutionsan t.e ele-tro es! In t.is

o el t.e battery 0ill notlast ery long, ;ust until t.esolutions e7uali4e a-rosst.e -otton barrier!

THE (OLT&'S )ILE


14/20

Materials?6 si stri3s or

is-s o/-o33er 6 si stri3s or

is-s o/ 4in-6 /ilter 3a3er 6 one o/ t.e/ollo0ingele-trolytes? 6 le on

;ui-e 6 inegar 6 a solutiono/ so iu-.lori e =salt0ater> 6 a solutiono/ -o33ersul/ate6 a olt eter 6 at.er o eteror -lo-5 0it.an LC#

is3lay6 t0o -ables0it.alligator-li3s

In .is /a ous e 3eri ent in t.e year 1822, &lessan ro (olta use a solution o/sul/uri- a-i as t.e ele-trolyte! In .ig. -on-entrations, t.is a-i -an be ery

angerous! I/ it gets on t.e s5in or in t.e eyes, it -an -ause ery serious burns an -an 3er anently blin ! Sin-e 0e -an buil a /un-tioning ersion 0it. ot.er ty3es o/ele-trolytes, in t.is e 3eri ent 0e 0ill use a ore benign substan-e, li5e t.oses3e-i/ie in t.e aterials list 6 -o33er sul/ate, /or e a 3le! #es3ite t.is s all

o i/i-ation in (olta's )ile, our inten e result 6 t.e 3ro u-tion o/ ele-tri-ity by-.e i-al eans, -an be e//e-ti ely e onstrate using our ersion o/ t.e 3ile! I/ youe-i e to try t.e e 3eri ent using sul/uri- a-i , use a 2!1 nor al or less solution!ear 3rote-ti e gear 6 es3e-ially eye 3rote-tion an .a e a -ontainer o/ so iu

bi-arbonate saturate solution at .an to 7ui-5ly neutrali4e any s3ills! I/ you use t.ea-i , an a ult ust be 3resent! =see t.e note on solutions in t.e intro u-tion>!

)la-e ea-. 4in- is- on a -o33er is-! You s.oul .a e si sets o/ Cu6 n is- 3airs!&s s.o0n in /ig! 11, buil a sta-5 or 3ile o/ t.ese 3airs o/ is-s, 0it. a is- o/ele-trolyte soa5e /ilter 3a3er se3arating ea-. 3air /ro its neig.bors! %e -are/ul t.att.e solution oes not ribble o0n t.e si e o/ t.e sta-5 as t.is -an -ause a s.ort-ir-uit bet0een t.e ele ents o/ t.e 3ile! "ote t.at t.e se7uen-e o/ t.e ele ents is as/ollo0s? Cu, n, ele-trolyte, Cu, n, ele-trolyte, et-! .en t.e e i-e is all arrange


15/20

as s3e-i/ie , easure t.e oltage bet0een t.e t.e botto ele ent o/ Cu an t.e to3ele ent o/ n! You s.oul see ! olts or 1!1 olt 3er 3air o/ ele ents! T.e oltagegenerate is also e3en ent u3on t.e ele-trolyte use an it's -on-entration! &s you

ay .a e one 0it. t.e le on battery, try to 3o0er a s all LC# ele-troni- e i-esu-. as a -lo-5, t.er o eter or e en a -al-ulator!

T.is in ention in 1822 s3urre intense resear-. in t.e /iel o/ ele-tri-ity! &bout a-entury later, t.is resear-. 0ill .a e -ul inate in ele-tri- lig.ts, t.e tele3.one anra io re-ei ers in illions o/ .o es! To ay, ele-tri-ity is an i 3ortant 3art in e ery

o ent o/ our li es!

ME&S$RI"G )OTE"TI&LS O* RE#$CTIO"

&not.er et.o o/ e 3laining t.e /un-tion o/ a battery lies in t.e o i ation re u-tionrea-tions at t.e ele-tro es! O i ation re u-tion rea-tions in ol e t.e trans/er o/

ele-trons /ro one -.e i-al ele ent to anot.er! T.e ten en-y o/ an ele ent toa-7uire or gi e u3 ele-trons is easure as ele-tri-al 3otential -o 3are to t.at o/ as3e-ial .y rogen ele-tro e, 0.i-. is -onsi ere by -on ention to .a e 4ero ele-tri-al

3otential at @FKC! &t t.is ele-tro e, t.e /ollo0ing rea-tion o--urs?

@HA A @e6 H @To a5e t.ese easure ents, use is a e o/ a -ell 0it. one ele-tro e o/ .y rogen

an t.e ot.er o/ t.e aterial to be easure ! T.e oltage 3ro u-e in i-ates t.e 3otential o/ re u-tion o/ t.e ne0 aterial in ter s o/ 3ositi e or negati e olts in

res3e-t to t.e .y rogen ele-tro e! C.e i-al ele ents t.at .a e a 3ositi e 3otential o/re u-tion ten to be re u-e , t.at is to a-7uire ele-trons, 0.ile ele ents t.at .a e a

negati e 3otential ten to o i i4e, t.at is to gi e u3 ele-trons!

&t t.is 3oint, t.e oltage 3ro u-e by a battery -an be -al-ulate by /in ing t.ei//eren-e bet0een t.e 3otentials o/ re u-tion o/ t.e t0o .al/ -ells? E E 1 6 E@ as

s.o0n belo0!

rea"ti !+ te!tial ' red&"ti !

(V)

E , Cu AA A @e6 Cu A 2!D:@

E n AA A @e6 n 6 2!+ @

In t.is -ase, t.e oltage generate 0oul be?

E A2,D:@ 6 =62!+ @>E A1!12: (!

You -an a5e a battery /ro any i//erent aterials! It is 3ossible to -al-ulate ina an-e t.e oltage to e 3e-t /ro arious aterials by using t.e stan ar 3otential

o/ re u-tion /or t.e aterials in 7uestion! T.is in/or ation -an be /oun in any-.e istry te tboo5!

Let's get starte 0it. t.e e 3eri ent!


16/20

Materials?6 a stri3 o/ -o33er 6 arious aterials totry as ele-tro es6 t0o bea5ers or

a33ro3riate-ontainers6 3lasti- tubing6 -otton6 F2 g! o/ -o33ersul/ate =CuSO : >6 F2 g! o/ a sul/ate o/t.e sa e ele ent ast.e ele-tro e you0ant to try6 F g! 3otassiunitrate = "O D>6 Fg! so iu-.lori e ="aCl> asan alternati e to t.e

3otassiu nitrate6 1B@ liter o/ istille0ater 6 a olt eter =it is

best to use a igitalo el be-ause t.e

.ig. in3uti 3e an-e 0ill nota//e-t t.e oltage as

u-. as a lo0i 3e an-e analog

o el>6 a -able 0it.alligator -li3s6 san 3a3er

Constru-t a setu3 su-. as t.at s.o0n in /ig! 1@, ery si ilar to t.e #aniell's Cell 0it.

t.e saline bri ge! *ill t.e -ontainer .a ing t.e -o33er -on u-tor 0it. -o33er sul/atesolution in t.e -on-entration o/ 1M! *ill t.e ot.er -ontainer 0it. t.e a33ro3riatesolution also in t.e -on-entration o/ 1M! Conne-t t.e negati e si e o/ t.e olt eter tot.e -o33er ele-tro e an t.e 3ositi e si e to t.e ele-tro e o/ test aterial an easuret.e oltage!In or er to get ali test easure ents, it is ne-essary to .a e -lean ele-tro es! $set.e san 3a3er to -lean o// any o i es or any ot.er -oatings or -onta ination so t.att.e sur/a-es o/ t.e ele-tro es are -lean an brig.t! So e etals o i i4e ery easily,su-. as alu inu , titaniu , an agnesiu ! In t.e -ase t.at you are using a etalt.at o i i4es 7ui-5ly, -lean t.e ele-tro e 0it. san 3a3er ;ust be/ore 3la-ing it in t.eele-trolyte an t.en, uring t.e e 3eri ent, 0ait a /e0 o ents /or t.e -.e i-al

rea-tion to re o e t.e slig.t a ount o/ o i e t.at /or e 0.ile you 0ere -leaning it!You 0ill see t.e oltage slo0ly rise to a a i u alue! "ote t.is rea ing as it


17/20

re3resents t.e 3otential o/ re u-tion o/ t.e aterial un er test 0it. res3e-t to -o33er!I/ t.e oltage starts i e iately to ro3, use t.e .ig.est obser e rea ing as t.e

a i u alue!

T.e oltages t.at you re-or are relati e to -o33er! In or er to obtain t.e alue

relati e to .y rogen, t.at is t.e stan ar alue, you 0oul /a-tor out t.e stan aralue o/ -o33er =CuBCu AA>! *or e a 3le, i/ you easure t.e oltage bet0een 4in- an

-o33er 0it. t.is setu3, you s.oul see 61!1 olts out3ut! %y a ing 61!1 an A!D: =t.estan ar alue /or -o33er> you get 6!+ olts 0.i-. is e a-tly t.e 3otential o/re u-tion /or 4in- = nB n AA> relati e to .y rogen!

Co 3are t.e alues you easure 0it. your a33aratus to t.e tables o/ stan ar 3otentials o/ re u-tion t.at you /in in a -.e istry te t! You 0ill 3robably /in t.att.e alues you get using your setu3 0ill be -lose, but not e a-t at-.es to t.estan ar alues, an -ertainly -lose enoug. to a5e interesting obser ations about

arious aterials!

Try any i//erent aterials 6 arious etals, i//erent alloys, an e en -on u-ti e 3lasti-s, rubber, -era i-s! So e resear-.ers are 0or5ing on batteries t.at .a eele-tro es a e o/ 3lasti-! & battery a e o/ 3lasti-s 0oul .a e t.e a antage o/

being ery lig.t! Lig.t0eig.t batteries 0oul be ne-essary to reali4e lig.t0eig.tele-tri- e.i-les!

G&L(&"IC #E)OSITIO"

Materials?6 t0o -o33er stri3s6 one 4in- stri36 one iron stri36 one stainless steel stri36 a -ontainer 6 F2 g! -o33er sul/ate =CuSO : >6 1B@ liter o/ istille 0ater 6 a battery

6 an a eter 6 t0o -ables 0it. alligator -li3s6 an analyti- balan-e6 san 3a3er

O ire u-tion rea-tions in ol e t.e e -.ange o/ ele-trons bet0een one -.e i-al ananot.er, al0ays o ing to0ar lo0er energy le els! In an ele-trolyti- -ell, t.e-.e i-al 3ro-esses in ol e -an be re erse si 3ly by su33lying ele-tri-al energy tot.e -ell instea o/ ra0ing it /ro t.e -ell! "o0 0e 0ill use t.is 3rin-i3le to e3osit

etalli- -o33er on an ele-tro e!


18/20

E )ERIME"T 1? CuSO : in solution an -o33er ele-tro es!Constru-t a setu3 su-. as t.at s.o0n in /igure 1D! $se a solution o/ -o33er sul/ate ast.e ele-trolyte =D2g! o/ CuSO : 3er 122 -- o/ 0ater> an stri3s o/ -o33er as t.eele-tro es! In t.is -ell, t.e sul/ate ions re ain in solution, 0.ile -o33er ions are

e3osite on t.e -at.o e an issol e /ro t.e ano e! &s t.e -o33er is -onstantly

being re3lenis.e into solution /ro t.e ano e, e entually it 0ill be -onsu eentirely an re e3osite ato by ato on t.e -at.o e! &ny i 3urities 3resent in t.eano e 0ill settle out o/ solution at t.e botto o/ t.e -ontainer! T.e -o33er e3ositeat t.e -at.o e is ery 3ure! In /a-t, t.is et.o is use in in ustrial en iron ents to

3uri/y etals, t.e resultant being -alle ele-trolyti-ally 3ure ! You -an easily eri/yan onitor t.e 3rogress o/ t.is trans/er o/ etal /ro ano e to -at.o e by 0eig.ingt.e ele-tro es be/ore starting an at arious ti es uring t.e e 3eri ent! %y -.angingt.e oltage a-ross t.e -ell, you -an -ontrol t.e -urrent /lo0! Ma5e a -.art o/ t.e rateo/ e3osition on t.e -at.o e as -o 3are to t.e -urrent /lo0 o er /i e 3erio s o/ti e!

E )ERIME"T @? CuSO : solution an stri3s o/ 4in- an iron!

)er.a3s you are 0on ering 0.y 0e.a en't been using a -at.o e o/ 4in-0.i-. 0oul a5e t.e e3osition o/-o33er easily isible! %y irtue o/ it's

bol -olor, -o33er 0oul be easilyisible on 4in- 0.i-. is a ull gray -olor!

T.is 0ay, 0e 0oul n't nee to use t.es-ale to eri/y t.e e3osition o/ -o33er!

T.e 3roble is t.at t.e -o33er 0oul begin e3ositing on t.e 4in- be/ore t.e-urrent is e en turne on! Co33er ions/ro t.e -o33er sul/ate 0ouls3ontaneously e3osit on t.e 4in- stri3!&s you re-all /ro earlier e 3eri ents,t.e -o33er ato s .a e a u-. strongerattra-tion /or ele-trons t.an t.e 4in-ato s! &s t.e 4in- stri3 is sub erge int.e solution -ontaining -o33er ions, so e4in- ato s are issol e in solution as

nAA

ions an t.e sa e nu ber o/ CuAA

ions are e3osite on t.e 4in- 0.ere t.ey 3i-5 u3 t.e ele-trons lost by t.e 4in-ato s an be-o e ele-tri-ally neutral!T.e 4in- stri3 gets -o ere in a isiblelayer o/ -o33er! "or ally 4in- gets a

e3osit t.at a33ears ar5 in -olor, is o/ a 3o0 ery te ture an .as a en riti-,-rystalline /or ! I/ you use an iron stri3instea o/ 4in-, you get a u-. ore-o 3a-t, etalli- e3osit o/ -o33er =/ig!

1:>! E 3eri ent /reely 0it. t.is 3.eno enon!


19/20

E 3eri ent D? CuSO : solution an -at.o e o/ stainless steel!Stainless steel is 0ell a a3te /or use as a e onstrator o/ t.e e3osition o/ -o33er onan ele-tro e! It .as a gray -olor t.at a5es -o33er e3osits easy to see an it 0ill nots3ontaneously 3i-5 u3 -o33er e3osits /ro -o33er sul/ate solution! It is ne-essary torun a -urrent t.roug. t.e solution in or er to ri e t.e -o33er e3osits onto t.e

stainless steel ele-tro e! T.is is ue to t.e /a-t t.at t.e stainless steel .as a 3otential o/re u-tion greater t.an t.at o/ -o33er! &s s.o0n in /igure 1D, use your stri3 o/stainless steel as t.e -at.o e an a33ly ele-tri- -urrent to t.e -ir-uit! You 0ill see t.att.e 3ortion o/ t.e -at.o e sub erge in t.e ele-trolyte a-7uires a lig.t -oating o/-o33er, as s.o0n by t.e -.ange in -olor!

In t.e -ourse o/ t.ese e 3eri ents, you -an eri/y *ara ay's la0, 0.i-. states t.at t.e7uantity o/ ele-trons /urnis.e is e7ual to t.e ioni- -.arge trans/erre ! T.e 0eig.t o/t.e aterials trans/or e is ire-tly 3ro3ortional to t.e a ount o/ -urrent su33liean t.e ole-ular 0eig.t o/ t.e ions an in ersely 3ro3ortional to t.e nu ber o/-.arges t.e aterial 3ossesses in t.e ioni- state! %y 0ay o/ e a 3le? a -ertain7uantity o/ -urrent 0ill e3osit a -ertain nu ber o/ ions 0it. a -.arge o/ 1, an .al/as any ions t.at .a e a -.arge o/ @!

Ele-trolyti- e3osition is 0i ely use in in ustry as a sur/a-e treat ent on etals!T.ese treat ents -an 3rote-t t.e un erlying stru-ture /ro o i ation, or -an ser e a

e-orati e /un-tion! Je0elry a5ers e3osit ery t.in layers o/ gol on base etals toa-.ie e a 3ro u-t 0.i-. is /ar less -ostly, yet .as all t.e a33earan-e o/ soli gol ! Inele-troni-s, gol is 0i ely use to -oat ele-tri-al -onta-ts an is alue /or itsresistan-e to o i ation an it's long6ter stability! Gal ani- te-.ni7ues -an also beuse /or ot.er sur/a-e treat ents o/ etals /or e-orati e an 3rote-ti e 3ur3oses!&lu inu is o/ten ano i4e 0.i-. eans t.at it is use as t.e ano e in a 3ro-esst.at o i i4es t.e sur/a-e, 3rote-ting it /ro -orrosion an a-.ie ing arious-olorations all t.e 0ay to bla-5!

CO"CL$SIO"In t.e -ourse o/ t.esee 3eri ents, you .a e be-o e/a iliar 0it. arious -on-e3tssu-. as t.e -on u-ti ity o/solutions by 0ay o/ issol eions! you .a e seen re orea-tions at 0or5, an t.at t.ey-an be re erse by running-urrent t.roug. t.e -ir-uit! You.a e learne to easure

3otentials o/ re u-tion o/arious aterials an to 3re i-t

t.e oltage generate by a battery 0.en you 5no0 it's

aterial -o 3onents! You -an buil a 0or5ing battery /ro

arious aterials, in-lu ingle ons, to atoes, 3otatoes,


20/20

al ost any /ruit or egetable!$3 until no0, batteries ay.a e see e ysterious, butno0 0e are a ong t.e /e0 t.at.a e a 0or5ing 5no0le ge o/

.o0 an 0.y t.ey 0or5! You-an a a4e your /rien s by

buil ing a battery out o/ al ostanyt.ing, but ore i 3ortantt.an t.is, no0 t.e stu y an

astery o/ t.is sub;e-t 0ill beeasier an ore eaning/ul!

666 oOo 666

T.an5s go to #r! )atri4ia %uttol /or re ie0ing t.is te t an /or .er aluablesuggestions

Electra-chemistry

Documents

Transcript of Electra-chemistry