Date
Name
_
Class
Lab~
Redox: Oxidation-Reduction Reactions
Text reference: reference : Chapter 21, pp.
Pre-Lab Disc:ussion O x xid id ation is br oadly oadly defined as the los lo ss, or apparent loss loss,, of electrons by an ato tom m or ion. Sírnilarly, redu reducct ion ion is the gain ain,, or appar ent gain, of el elec ec trons by an at ato om or ion. ion. Nei Neitther oxida oxidation nor reduc redu ction can ever oc occ cur alone, Whe Whenev neveer el eleectrons ar e lost by one substa substance nce,, they mus must be gain gaineed by ano an oth theer . Rea Reacctions involving involving th thee exchang exchangee or tr t r ans ansfer of el elec ectron tronss from atomss or ions of on atom onee substan substancce to tho thosse of another substance substance ar e call calle ed oxidation--reduction oxidation reactions, or redox reactions, f or sh sho ort rt.. In su suc ch reactions,, the substanc reactions ubstancee tha thatt is oxidied !loses !loses el elec ectron tronss" is call calleed the r educ duciing aqent. #h #hee substan substance ce th thaat is reduc redu ced !gain gainss el elec ectron tronss" is call alle ed the o x xiid izing izing aqent . $ecau causse th theey are ma m ade up of t%o distinct proc proces esses-oxidati ses-oxidatio on and r edu duc ction-red tion-redox ox r eac acttion ionss ca can n be r e pr esent nteed by t%o ha haif if -r eac act t ions ons.. &or ex example, ample, the balanc balanced e'uation for the reaction of sodium %i %itth chlorine is (Naa ) *l2 (N
~
(Na (N a*l
In half -reactíon form, form , th thee e'u e'uaation for this reaction is (Na (Na + *l2 ) (e- +
(Na)) (e(Na)) (*l-(*l
!oxidation" !reductio !reducti on"
s th thee e'u e'uaation tionss for thes these half-r eactions eactions sho%, sho%, the t%o electr ons lost by thee sodiu th dium m atorns ar e gained by the chlorine chlorine ato tom ms. &or any r edo dox x re reac ac tio ti on, the numbe number of ele lecctrons gaine gained in the the reduction half half -reac -rea ction mu musst e'ual the numbe number of ele elecctron tronss lost in the oxidation half-reacti half-reactio on. In theo theor y, eve every ry half -rea reacction is r eversible eversible.. In one one dir ecti ctio on, it is an oxi xidation dation half-reaction. half-reaction . In the the revers reversee dir ection, it is a redu reducction half r eact actiion. #he #a #a ble of Sta St andard lec lectrode trode o otentials in ppendix of this la b manual li lists sts red ucti ction on half -r eactions. eactions. #hus, #hus, it is atable of of reducti reductio on po p otentials. /o%e /o%ever, each reaction reaction can b e rev reveersed and %r itten itten as an oxidation ha half -r eaction, in %hi %hicch case the si gn gn of the the el elec ectro tro de de p po otential (E") is reve reversed. &or example, exampl e, the reduction half-rea half-reacction Flg) ) (e- + (&- heads the Iist in this table. table. In this half -r eaction, &( is redu reducced and is thus the the oxidiing age agent nt.. #h #hee electrod lectrodee pot poteential for this half -reac reacttion is )(.01 volts. $y reve reversing this half -reaction, you get (&- + &2!g" ) ( e -, %hich is an an oxidation half-rea half-react ction ion.. &- is oxidi oxidieed and is thus the th e reducin reducing g agent. #he electrod lectrodee pot poteential for this half -reaction is is -( -(.0 .01 1 volts. #hee #a #h #able ble oí2 Standard lectr ode ote otential ntialss can be used to pr edi dic ct %hetheer or not a redox r eaction %ill occur spontane %heth spontaneously. &o &or a redo redox x r eaction eaction to to oc occcur, the reduc redu ction half -rea reacction must appear high higheer in thee tabl th tablee th thaan the ox oxidation idation half -reaction reaction.. *on onssider the poss possiible redo redox x r eaction3 Fp(~l
Ph(NO ) (aa) ~ b!s" F (NO ).,(aq)
_
613-61
!f
this r eaction does occur , the half -r eactíons %ill be3 F e( s )
b2
+
&e2 ) (e
(e- + b!s"
!oxidation" !reduction"
In the ta ble, the half-reaction for the reduction of b( does appear higher on the list than that for the oxidation of F e( s) !the r everse of the half -r eac tion for the r eduction of &e2". #hus, the redox r eaction %ill occur . s another chec4 , the alge braic sum of the EO values of t%o half-reactions must be positive f or the r eaction to occur . In this case, E O of the reduction r eaction is -5.67, %hile that of the oxidation r eaction is )5.88. #he alge braic sum is )5.7l. In this exper iment, you %il9 pr epare sever al dif f erent combinations of substances and observe %hether or not any visi ble r edox reactions occur. #his lab should help provide a better under standing of redox r eactions and the use of the #able of Standar d lectrode otentials.
Purpose Study sorne simple redox reactions. :etermine the relative str engths of sorne oxidiing agents and r educing agents.
Equipment test tubes, 60x l;;-mm!0" test tube rac4 test tube holder graduated cylínder, 65-m< microspatula
dro pper pi pet burner safety goggles la b apr#n or coat
Materials 0.1 solutions 5=3
gN;3$ b! N57" >n! N57"( C u(N O:J)z
&e*l7 Sn*l
6M H Cl
silver foil iron fílings l-cm str ips of 3 inc lead cop per
Safety /andle the hydrochloric acid %ith extreme car eo void spills on your s4 in or clothing. &lush any spil9s %ith cool %ater and Na/*;?" solution and r eport them to your teacher. Note the caution alert sym bols he r e and %ith certain steps of the @r ocedure.@ R efer to page xi f or the pr ecautions associated %ith each symbol. l%ays %ear saf ety goggles and a lab coat or a pron %hen %or4ing in the lab. &
%
Pr oc ed ur e PA R A RE LA !"E A# !"! $ O% SO ME ME AL S 6.
dd A m< of 5.6 MAgN O;)
to a clean, dry
test tu be. dd a piece of coppe r metal to this soluti on. dd A m< of 5.6 M
&ame
-
'(
Redox: Oxidation-Reduction
Reactions
)continued*
the solution. llo% both test tubes to stand for several minutes. Record your observations. (. Stand t%o test tubes in a test tube rac4. dd A m< of 5.6 *B!N57"( to each tube. lace a strip of inc !>n" in one tube and a strip of lead !b" in the other. llo% the tubes to stand for a fe% minutes. Record your observations. 7. Bsing t%o clean, dry test tubes, repeat the procedure in step ( using 5.6 M b !N57"( and strips of copper !*u" and inc. Record your observations. 8. Repeat the procedure a third time, using 5.6 M >n!N5 7"( and strips of *u and b. fter you have recorded your observations, discard the materials in the test tubes as instructed. *lean and rinse the tubes. PAR + REA#!O&S O% !RO& MEAL A&O !RO& ,O&S
A. lace A m< of 5.6 M &e*I7 in a clean, dry test tube. Bsing a pipet, add Sn*l2 drop by drop until a change is observed. Record your observations. C. lace a heaping microspatulaful of iron filings !&e" into a clean, dry test tube. dd A m< of C /*9. *B#I;N3 !andl e thi s acid "er# carefull#. $t can cause painful burns. Bsing a test tube holder, %arm the contents of the test tube car e full# over a lo% bur ner flameo llo% the test tube to stand for several mi nutes. Record your observations.
Obserations and Data PAR A
;bservations
gN573
6. *u
2.
3.
4.
g
*B!N53D"(3
>n
*B!N57"(3
b
*B!N57"(3
*u
b!N57h3
>n
b!N57"(3
*u
>n! N;3Dh3
b
>n!N;37h3
PAR +
-
5.
&E)
6. &e
Sn()3 'el:
Equations
-
Write balanced chemical e'uations for each reaction that occurred in this experiment. $eneath each e'uation, %r ite e'uations for the half-r eactions, identifying each as an oxidation or r eduction half -reaction.
#onclusions and .uestions Where necessary, r ef er to the #able of Standar d lectrode otentials in ppendix to help you ans%er these 'uestions. 6. n as determined by your ex perimental results. :o these r esults agree %ith the positions of these metals in the tableF
(. Which metal listed in the #able of Standard lectrodo otcntials %ill r e place &e() but %ill not replace >n()F xplain, using the tableo
&ame
'(
Redox: Oxidation-Reduction
Reactions
7. :efine the f ollo%ing3 oxidation? r eduction? oxidiing agent? reducing agent.
8. Study the chemical combinations listed belo%. Bsing the table, predict %hich combinations %ill produce a s pontaneous redox reaction. &or those r edox reactions that %ill occur3 !6" complete the balanced e'uation f or the reaction? !(" %rite the half -reactíons for each r eaction and identify them as oxi dation or r eduction? !7" name the oxidiing and reducing agents in each r eaction? and !8" calculate the net EO for each reaction at standard conditions !6 molar ion concentration, 2() *, 1+1.3 4a". a. &e *u*l b. g /,S58 Na' *. l d. /( *a*l(
)continued*
_l0,-1-)2 Name _
0s4
5~0:h#&
Date
_
Class
_
Redox: Oxidation-Reduction Reactions Text reference: *hapter (6, pp. C67-C6
Pre-Lab Discussion Oxid at ion is broadly defined as the loss, or a pparent loss, of electrons by an atom or ion. Sirnilarly, red uction is the gain, or appar ent gain, of elec
7 r
tr ons by an ato m or ion. Neither oxidation nor r eduction can ever occur alone. Whenever electrons ar e lost by one substance, they must be gained by another , Reactíons ínvolvíng the exchange or transfer of electrons from atoms or ions of one substance to those of another substance ar e called oxidatíon-reduction reactions, or redox reactions, for short. In such r eactions, the substance that is oxidied !loses electrons" is called the r educing agent. #he substance that is reduced !gains electrons" is called the o xidi zing aqent . $ecause they ar e made up of t%o distinct processes-oxidation and r eduction-redox r eactions can be r e presented by t%o half-reactions. &or example, the balanced e'uation for the r eaction of sodium %ith chlor ine is (Na ) *I2
--4
(Na*I
In half-reaction form, the e'uation for this r eaction is (Na *l (e-
--4 --4
( Na)) (e(*I-
!oxidation" !reduction"
s the e'uations for theGsehalf -r eactions sho%, the t%o electr ons lost by the sodium atoms are gained by the chlorine atoms. &or any r edox reac tion, the number of electrons gained in the reduction half -reaction must e'ual the number of electrons lost in the oxidation half-r eaction. In theory, every half -reaction is reversible. In one direction, it is an oxidation half-r eaction. In the r everse dir ection, it is a reduction half r eaction. #he #able of Standard lectrode otentials in ppendix of this la b manual lists red uction half -r eactions. #hus, it is atable of reduction potentials. /o%ever, each r eaction can be reversed and %ritten as an oxidation half -r eaction, in %hich case the sig n of the electrode potential ( E" ) is reversed. &or example, the reduction half-reaction & (!g" ) (e - --4 (&- heads the list in this table. In this half -reaction, &( is reduced and is thus the oxidiing agent. #he electrode potential for this half-reaction is )(.01 volts. $y reversíng this half-reaction, you get (&- --4 &(!g" ) ( e @, %hích is an oxídation half -reaction. &- is oxidied and is thus the reducing agent. #he electrode potential for this half -r eaction is -(.01 volts. #he #a ble of Standard lectrode otentials can be used to pr edict %hether or not a r edox r eaction %ill occur spontaneously. &or a r edox r eaction to occur, the reduction half -reaction must appear higher in the table than the oxidation half-r eaction. *onsider the pos sible r edox r eaction3
T h t 0D e t h
t a n # 8 # 8 L
!f
this reaction does occur , the half -reactions %ill be3 F e( s)
b(
(e-
!oxidation" !r eduction"
In the table, the half -r eaction f or the reduction of b( does appear higher on the list than that f or the oxidation of &e! s) !the reverse of the half-reac tion for the reduction of &e2". #hus, the r edox reaction %ill occur. s another chec4, the algebraic sum of the E O values of t%o half-reactions must be positive for the reaction to occur . In this case, EO of the r eduction r eaction is -5.67, %hile that of the oxidation reaction is )5.88. #he alge braic surn is )5.76. In this experiment, you %ill pr e par e several dif ferent combinations of substances and observe %hether or not any visible redox r eactions occur . #his lab should help provide a better understanding of r edox reactions and the use of the #able of Standard lectrode otentials.
Purpose Study sorne simple r edox reactions. :etermine the relative str engths of sorne oxidiing agents and reducing agents.
Equipment
afet9
:
Ca8t0#n st8dents t# handle the C M 'C! ;0th c#ns0derable car e# <#8 ma9 ;ant t# have st8dents ;ear r8bber l#=es ;hen the9 handle th0s ac0d. 5mphas0>e the se=er0t9 #f the 0n ?8r0es that c#8ld #cc8r 0f th0s ac0d ;ere t# splash #n the0r s@0n #r 0n the0r e9es.
d=ance 7reparat0#n et #8t extra test t 8 bes. C8t al8m0n8m f#0l 0nt# l-cm sA8ar es and c8t metal r0bb#n 0nt# l-cm lenths pr0#r t# class. 7repare the f#ll#;0n s#l8 t0#ns pr 0#r t# class. B!nstr 8c t0#ns f #r pr eparat0#n #f these s#l8t0#ns ar e 0=en 0n ppen d0x 7 #f th0s Teachers 5d0t0#n." 0.1 s#l8t0#ns #f: N+7 7bBN+7"( nBN+7h 6' (+ C8BN+7 "( 3',
test tubes, 60 x l;;-mm!0" test tube rac4 test tube holder graduated cylinder, 65-rn< microspatula
dropper pipet burner saf ety goggles la b apron or coat
Materials 0.1 solutions of3
gN5 7 b! N57"( >n!N5 7"( *B! N57"( &e*6 7 Sn*6(
% !&l silver foil iron Hlings l-cm strips of 3 inc lead copper
Safety /andle the hydrochloric acid %íth extreme careo void spills on your s4in or clothing. &lush any spills %ith cool %ater and Na/*57 solution and r e port them to your teacher. Note the caution alert symbols her e and %ith certain steps of the @rocedure.@ Refer to page xi f or the precautions associated %ith each syrnbol. l%ays %ear safety goggles and a lab coat or apron %hen %or4ing in the lab.
Procedure PAR A RELA!"E A#!"!$ O% SOME MEAlS
I
6D'C! n 6 J +oíl
K33?/Dl
6. dd A rn< of 5.6 M g N57 to a clean, dry test tube. dd a
Name
'(
Redox: Oxidation-Reduction
Reactions
Bc#nt0n8ed"
the solution. llo% both test tubes to stand for several minutes. R ecord your observations, (. Stand t%o test tubes in a test tube rac4. dd A m< of 5.6 *B!N5 7"( to each tube. lace a strip of inc !>n" in one tube and a strip of lead !b" in the other. llo% the tubes to stand for a f e% minutes. R ecord your observations. 3. EsFn t%o clean, dry test tubes, repeat the procedure in ste p ( usíng +.1 M b !N57"( and strips of copper !*u" and inc.
R ecord your observations. 8. Repeat the procedur e a third time, using 5.6 >n! N57"( and strips of *u and b. fter you have recorded your observations, discard the materials in the test tubes as instructed, *lean and rinse the tubes. PAR + REA#!O&S O% !RO& MEAL A&D !RO& !O&S
A. lace A m< of 5.6 &e*l7 in a clean, dry test tu be. Bsing a pipet, add Sn*l( drop by drop until a change is observed. R ecord your observations, C. lace a heaping microspatulaful of iron filings !&e" into a clean, dry test tube. dd A m< of C /*9. *B#I;N3 !andl e thi s acid "er# carefullu. $t can cause painful burns. Bsing a test tube holder, %arm the contents of the test tube car ef ull# over a lo% burner flameo llo% the test tube to stand for several mi nutes. Record your o bservations.
Obserations and Data PAR A
;bservations dar @ s#l0d f#rms and the s#l8t0#n
t8rns bG8e.
The sample #bser=at0#ns and data 0=en here are 0ntended t# be 8sed as a bas0s f#r c#m par0s#n ;0th st8dent re sp#nses. !n m#st cases, st8dent resp#nses ;0ll =arI s#me;hat fr#m these sample r esp#nses.
N# =0s0ble r eact0#n H8bbl0n
#cc8r s and a dar @ br #;n0sh
s#l0d f #r ms.
H8bbl0n
#cc8r s and a dar @ br #;n0sh
s#l0d f#r ms.
N# =0s0ble react0#n H8bbl0n
#cc8r s and a dar@ s#l0d f #rms.
N# =0s0ble r eact0#n N# =0s0ble react0#n
b >n!N57"3+3
The 9ell#;0sh-br #;n
s#l8t0#n
t8rns c#l#rless.
PAR +
C. &e /*l3
The 0r #n f 0l0ns
react and d0sappear
as a as 0s e=#l=ed,
pr#d8c0n
a cl#8d9 appearar8
-
Equations Write balaneed ehemieal e'uations for eaeh reaetion that oeeurr ed in this experimento $eneath eaeh e'uation, %rite e'uations for the half-reaetions, identifying eaeh as an oxidation or r eduetion half -reaetion.
a. C8 C8
2N+7
2 -
n
2 e-
n2
--L
C8(
CE2~
-L
2e-
-L
e %
c. 7b CEBN+7"( 7b
7b2 -
--L
C82-
d. n n
-L
7b2
-
n( -
/e
B#x0dat0#n" Bred8ct0#n" 7b -1- ,nBN+7"( B#x0dat0#n"
7b
-L
Bred8ct0#n" 2/eC1( nC!8
-1- 2e -
-
--4
2/e(
B#x0dat0#n" -
Br ed8ct0#n"
/eC!2 '2
. /e% - -- 2e -
2' - 2e -
C8 -- 7bBN+7h
-4
-L
n8
f . /e 'C! ~
Bred8ct0#n"
2e-
-
nC! (
2e
2/e7-
B#x0dat0#n"
C8
--4
2e -
---4
Bred8ct0#n"
2e -
7bBN+7"(
e. 2/eC!7
-L
.i,
2e-
n2
C8
--L
CEBN+7"(
B#x0dat0#n"
-1- 2e -
-
2
-L
--4
'2
B#x0dat0#n" Bred8ct0#n"
#onclusions and .uestions Where neeessary, refer to the #able of Standard leetrode otentials in ppendix to help you ans%er these 'uestions. 6. n as determined by your experimental r esults. :o these results agr ee %ith the positions of these metals in the tableF #st act0=e t# least act0=e: n, 7b, C8, . These res8lts aree ;0th the p#s0t0#ns #f these metals 0n the table.
(. Whieh metal listed in the #able of Standard leetrode otentials %ill r e plaee &e2) but %ill not re+lace >n2),F xplain, using the table. Chr#m08m
BCr" ;0ll replace /e . 0n a react0#n
bel#; /e 0n the table b8t 0s ab#=e n .
b8t ;0ll n#t r eplace n (
-.
Cr 0s
Name_
'(
Redox: Oxidation-Reduction Reactions
7. :efine the follo%ing3 oxidation? reduction? oxidiing agent? reducing agent. x0dat0#n
0s a l#ss #f electr#ns. Jed8ct0#n
aent 0s the s8bstance that
0s a a0n #f electr#ns. n #x0d0>0n
0s red8ced 0n a react0#n.
red8c0n
aent
0s the
s8bstance that 0s #x0d0>ed 0n a react0#n.
8. Study the chemical combinations listed belo%. Bsing the table, predict %hich combinations %ill produce a spontaneous redox reaction. &or those redox reactions that %ill occur3 !6" complete the balanced e'uation for the reaction? !(" %rite the half-reactions for each reaction and identify them as oxi dation or reduction? !7" name the oxidiing and reducing agents in each reaction? and !8" calculate the net EO for each reaction at standard conditions !6 molar ion concentration, (M0 , 656.74a"G a. &e *u*l2
' (2+8
c. l d. &(
Na;/ *a*l(
b.
Halanced eA8at0#n a. /e --C8C! 2
:
Net e
'alf-react0#ns /eC!2
-t-
C8
x0dat0#n: /e /e2 red8c0n
+.K) =#lt 2e
-
aent Jed8ct0#n: C82 - - 2e
--K
C8
#x0d0>0n aent
b. 1-12A52 ~ N# react0#n Na!-l ~ N# react0#n c. l d. /2..,.. CaC!2 ~ Ca/2 C!2 _?_
Jed8ct0#n:
&O ) 2e #x0d0>0n aent
Net 2/
x0dat0#n: 2C! C!(2ered8c0n aent
-
e
1.) =#lts
Bc#nt0n8ed"
