Problem Set 8 Solutions

Problem Set 8 Solutions - C HAPTER 1 6 REDOX T ITRATIONS 16...

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Unformatted text preview: C HAPTER 1 6 REDOX T ITRATIONS 16 - 1 . Ce4++ e - * Ce3+ Fe3++ e - = : Fe2+ Ce4++ F e2+ = : C e3++ F e3+ y: 1 1 gn8t0.0596 : V E": 1.70 t r: 0 . 7 6 7 V : V tr : 1 .70 0 .767 0 .93r 16 : 1 9(l)(0.933)/0.059 1 915;7: 6 x 1 015 it Because herea re o nly 2 s ignificantd igits i n t he e xponent,15.77, w ould b e t justified t o w rite t he a nswera sj ust 1 016. 16-2. ( a) C e4+ + F e2+ - -- C e3+ + F e3+ (b) F e3+ + e - + F e2+ E : 0367 V E " : 1 .70V Ce4+ + e - + C e3+ (c)n : { o.ta7-0.05e16 - { o.z+r} r ogffit 1 6 os+:gl} t r" E : { r.zo-0.05e[U e+ -1 r - { o.z+r} ' (d) 1 0.0m L: 25.0mL: 49.0mL: 50.0m L: 51.0m L: 60.0mL: 100.0 L: m 16-3. (A) ( B) = b ecause U seE q.( A) w ith [ Fe2+]/[ne3+1 4 0.0110.0, E:0.490Y V ":50.0m L = = 0.526Y = [ Fe2+]/[F e 3 + ] : 2 5 . 0 1 2 5 . 0E 1 0 [ Fe2+]/[F e 3 + l: . 0 1 4 9 .= E : 0 . 6 2 6 v a T his i s V s,whereCe:*1 = [ Fe3+] nd[ Cea+]: [ Fez*r. [ V E E q. 1 6-ll g iv e s * : 1 . 2 3 a n dE : 0 9 9 V . : 5 0.0/l 0 = E : 1 .36 V . U seE q.( B) w ith [ Ce3+1/1Ce++] : 1.42v : [ ce3+1/JCe + +5 0 . 0 / 1 0 . 0 E ] : : .0 v [ ce3+]/[ce4+]5 0.0/50 = E 1 .46 ( a) C e4++ C u+ - -' C e3++ C u2+ (b) C e4++ e - i E " : 1 '70V C e3+ E":0.161V Cu2++ e - + C u+ - r oz} (c)E : { |. 700 .05e "s 16 r f *#l} { 0. ( A) r: { o 16 r-0.0 se 16r ogf \#t - { 10. r oz } ( B) \ - [ Luz-1' ' 139 1 44 l Chapter6 The f irst 2 5.0 m L o f F e3+w ere c onvenedt o F e2+,s o ( 25.0m r- 1 rr = ffiiffL) ( 0.100M ) : [Fez*, : 4 .e0'l 0-2 M : E+ 0 .732- l 6logltri 0 .05e : E+ 0 .732- r ogffi:#+ : o .64sv o .ose16 E : E **E _ : 0 .6490.241: 0 .408V rnL try) -0.143 -0.102 0. 5 0. 4 mL 24.0 25.0 t ff) - 0.061 0 .096 mL 26.0 30.0 E ( V) 0 .408 0.450 1.0 t2.5 ,-} ul O u; 0. 3 nl z0 uJ nl -0 .2 -0 .3 V o l u me o f F e 3 *( m L ) 16-7. (a) 2 Fe3+ + a scorbica cid + H 2O - -- 2 Fe2+ + d ehydroascorbic cid + 2 H+ a (b) T he e quivalence olume i s 1 0.0m L. v is At 5 .0 m L, h alf o f t he F e3+i s t itrateda nd t he r atio [ Fe2+]/[Ee3+1 5 .0/5.0: Fe3+ + e - = : F e2+ E ":0.767V L'I r 6r E : E * E -:{ o.tot-0.0seogli#t - { 0.roz} : : { o . t a t - 0 .0 5 e r 6 # t - { o .r e z} 0 .5 7 0 rog p oint. W e m ultiplyt hea scorbic cidN ernst a m 10.0 L i s t hee quivalence T f b equation y 2 a nda ddi t t o t he i ron N ernste quation. he r easonor i of t multiplying y 2 i s t o c ancelhe2 i n t hed enominator ( 0.0591 6)12n f ront b i of t he l og t erm. W hent he f actors n f ront o f t he l og t ermsa ree qualt o e ach w other, e c ana ddt hel og t erms. R edox itrations T 145 - o.o5e E-: 0 .767 r 6 ogltr+i r 2E+:z(0.:eo-rjtr"gls!e@Ltd.hyd,"r'., : - 0.059 3E+ 1 .547 l Ut "rffi p At t hee quivalenceoint, hes toichiometryf t het itration eactionellsu s t o r t : 2[dehydroascorbic a nd[ Fe:+,: 2[ascorbica cid]. that[ Fe2+] a cid] g Insertinghese qualities t he l og t erma bove ives t e i nto 3E +: 1 . 5 4 7 0 . 0 5 9 lU' o , 3E , : 1 . 5 4 7 0 . 0 5 91 6 lo g ; 5 lfr l- g Using H*]:19-0 . 3 0 iv e s E l: 0 . 5 0 4V a n dE : 0 . 5 0 4 -0 . 1 9 7 : 0 . 3 0 7 V [ At 1 5.0 L, t her atio[ dehydro]/fascorbic i s 1 0.0/5.0: m a cid] dehydroascorbic + 2 H++ 2 e- € a scorbic cid+ H 2O a cid a E " : 0 .390V - r oz} E: E r-E-: { 0.:oo-tq+r! ' "*ffiffiffi} { o u #o'"r : { o.roo r ofi'&r,r} - t o r l7}: 0.184 v l6-8. -v F ort hes olidt itration urve, iphenylbenzidine c d s ulfonic cid( colorless--) iolet) a ( red or t ris(2,2'-bipyridine)iron - ' p aleb lue)w ouldb e s uitable. ort hed ashed F -+ curve, iphenylamine d s ulfonic cid( colorless r edv iolet)o r d iphenylbenzidine a - -+ sulfonic cid( colorless v iolet)w ouldb e s uitable. he f irsth int o f c olorw ould a T bet aken st hee ndp oint. a 16-9. p T her eduction otentialsre a Sn4++ 2 e- + .} S n2+ Mn(EDTA)-+ e - + M n(EDTA;z- E " : 0 . l3 9 V in lMHCl t " : 0 .825V Thee ndp ointw ill b eb etween.139 nd0 .825 . T ris(2,2'-bipyridine) h as V i ron 0 a ( p too h igha r eduction otentialI . 1 20V ) t o b e u seful or t hist itration. f f 6 -10. I - r eacts ith 1 2t o g iveI 3,w hichi ncreases s olubility f I 2 a ndd ecreases w i ts t he o volatility. R edoxT itrations 147 left o verf rom t he r eaction ith s ulfite. T hereforehe 1 3t hatr eacted ith w t w sulfite as( 0.563 6 - 0 .3098 ) : 0 .254 m mol1 3.O nem oleo f I 3 r eacrs w 7 0 with o nem oleo f s ulfite, ot here usth aveb een .2540 m mors o3- i n 5 0.0 s m 0 mL o f w ine. I SO3-]: 0 .254 m mot/50.0 L: 5 .079 x l 0-3M . W itha 0 m formula ass f 8 0.06 or s ulfite,hes ulfite ontents 4 06.6m s.lL. mo f t c i (d) s oooted:f / #:2.15 l c a l c u l a te d 3+3-2 V - 2 7 3 . 2 1Ih"i tz - l -' tt". t - ' " ' -t 2.ts ^ @ - : /table: 2 .776for95%oconfidencend 3 + 3 - 2 :4 d egrees f f reedom a o < lcalculatedl table, o t he d ifferencei s n ot s ignificanta t95%o onfidence evel. s c l \ 3+3 2 .56 16-14. ( a) l z@d + 2 e-= 2 l-t; + 2e- = 3 tt2@Q + I--I; 0.535 V : E :0.620- 0.535 0.085 V E" E" : 0 .620V : 7x K : 11nE1 0.05916: 102(0.085)/0.05916 1 02 (b) I 2(.r)+ 2 e-=2 tE" : 0.535 V -l; E" : 0.535 V + 2 e- = 3 tI2(s)+ I - .: K: (c) I: : E" : 0 .535 0 .535 0 .000 v 16: 19 2(-0.000)/0.059 1. 0 L Iz(s) + 2e- = 2 lI2@g + 2e- = . 2 lI2(s)= t z@q) 0.535 V 0.620 v L E" = 0 .5350.620:- 0.085 v : 16 : x K : [ r2@fl1 1 92(-0.085)/0.059 1.3 l 0- 3 : 0 .34 oft 2tL M g 1 6 -15. ( a) n : P' ' K1 *: 2 0 0 x l 0 -e b a r. l L = 8 n mo lO : .3 x 8.314 l 0-2L .barl(mol.K) 00K (b) o ne m ole o f 0 3 g enerates m ole o f 1 3,r equiring2 m oleso f t hiosulfatef or I titration. 8 n mol 0 3 g enerates n mol 1 3,r equiring l 6 n mol S 2O2r-. f t 8 t nmol 1 3w ere g eneratedn, s ay l 0 m L o f s olution,t he c oncentration ould i w be 8 ' 1 0-e ol/(0.01 ): 8 > < 0-7 . T hetext s aysthatthe olorof m L 1 M c 1 32 Chapter5 l l5-7. R elative obilities: m K+ - -- 7 .62 5.19 * - N a+ NO; - --' 7 .40 7.91 * - C l- K+ d iffuses aster hanN a+,l eading o e xcess ositive harge n t her ight. c lf t p t c o diffuses aster hanN o3, l eading o e xcess egative harge n t he l eft. B oth t he f t t n c o cation nda niond iffusion ause egative hargeo b uildu p o n t hel eft. a c n c t 15-8. R elative obilities: m H+ - -+ 3 6.30 7.62 < - K + Cl- - -. 7 .91 7.91 < - C lFor 0 .1M H CI | 0 .1M K Cl, t hec oncentration C l- i s t hes ame n b oths ides, o of o s Cl- c ontributesothing o t hej unctionp otential. hem obilityo f H + i s m uch n t T greaterhant hato f K +, s o H + d iffuses o t her ight f aster hanK + d iffuses o t he t t t t left. T her ights ideo f t hej unctionb ecomesositive. p For 0 .1M H CI | 3 .5M K Cl, t hep ositive igno f t hej unctionp otentialellsu st hat s t ther ights ideo f t hej unction ecomesositive.A lthough + h asa bout5 t imesa s p b H great m obilitya sK +,t hec oncentration K + i s 3 5 t imesg reaterhant hato f H + a of t on t he l eft. T heh igher oncentration K + o utweighs l owerm obility. I f a ll c of i ts elsew eree qual, here ouldb e a n etd iffusion f p ositive hargeo t hel eft. t w o c t However, hec oncentrationf C l- o n t he r ight s idei s 3 5 t imesg reaterhant hat t o t on t he l eft. T hereforeherew ill b e a n etd iffusiono f C l- f rom r ight t o l eft, t leaving xcess ositive harge n t her ight. T hen etr esult f t het wo c ompeting e p c o o effectss a s mallp ositive harge n t her ight. i c o 15-9. T hee rrors howni n t heg raph s - 0.33 p H u nits. hee lectrode ill i ndicate i T w : 1 0.67. r r .00- 0 .33 15-10. ( a) T hej unctionp otential hanges c f rom- 6.4 m v t o - 0.2 m v. A c hange f o 6.4- 0 .2 : 6 .2m Y w ill a ppear b ea p H c hange f ( 6.2m V)/(59.16 to o mV/pHu nit; : + 0.10 H u nits. p (b) A t p H 6 .54, H*] : l 0 -6 . 5 4 : 2 . 8 8 l 0 -7M . x [ = At p H 6 .60, H+]: 1 9-6'602 .51x l 0-7M . [ ( 2'88 2'51) x l o-z x f ig : Percentage c hangen [ H+] : i 2 . 8 8x l 0 -7 l 3oh l5-11. M easuringH+] w ith a n i on-selective e lectrode s ubjecto t heu nceftain is t [ M Electrode easurements r33 m a junction p otentialthatp lagues lmosta ll d irect p otentiometric easurements' e xactly' o n u [ The u nknownj unction p otentialp revents s f rom m easuring H+] s mall c the o ther h and,t hej unction p otentialcannot hangev ery m uch d uring h ardly t additions o f t itrant b ecause he c ompositiono f t he t itration s olution p recisione ven w i changes.T hereforec hangesn [ H+] c an b e m easured ith h igh thoughtheabsoluteva|ueof[H+]isnotaccurate|yknown. c ontaining a c harged 15-12. T he l iquid-basedi on-selectivee lectrodeh as a m embrane i on, w hich w e b t o ion e xchanger r a n eutrali onophore hat s electively inds a nalyte s urfaceo f t he i supposes t he c ation,C +, f or t he s akeo f d iscussion.A t t he o uter C + i n t he ion-selectivem embrane,t here i s a n e quilibrium b etweenb ound F ree C + i s u a hydrophobicm embrane nd f ree C + i n a queous nknown s olution' A h ydrophobic hydrophilic,s o i t i s n ot s olublei n t he h ydrophobicm embrane' c + d iffuses i nto anion, R -, i s l eft b ehind i n t he m embranew hen t he h ydrophilic i s a s imilar t o s the a queous olution. O n t he i nsides urface f t he m embrane,here b ound C + i n f equilibriumb etweenC + i n t he i nternala queous illing s olutiona nd C + i n t he the m embrane. I f t here i s a d ifferenceb etweent he c oncentrationo f d ifference externals olutiona nd t he i nternals olution,t herew ill b e a n et c harge and t hereforea p otential d ifferencea crosst he m embrane. o m embrane utsidet he a c 15-13. A c ompounde lectrode Ontains s econdc hemicallya ctive a nd m m ion-selective embrane.T he s econdm embrane ay b e s emi-permeable s econd t o only a llows t he s pecies f i nterest o p asst hrough. A lternatively,t he w ith a nalyte ( membranem ay c ontain a s ubstance such a s a n e nzyme)t hat r eacts r m t t to g eneratehe s pecies o w hich t he i on-selective embrane esponds' l5-14. e lectrode o T he s electivityc oefficientg ivest he r elativer esponse f a n i on-selective t he m ore to t he i on o f i nteresta nd a n i nterfering i on. T he s maller t he c oefficient, t ( i selective s t he e lectrode smallerr esponseo t he i nterferingi on)' l5-15. i oni w T he e lectrode orks t he s amew ay a s d escribedn F igure l 5-6' T he H * b y a ctinga s ( n selective, eutrall igand L i s t ridodecylamineRsN),w hich b inds a b ase: R :N + H * + p a R 3NH*. T he h ydrophobic nion i s t etraphenylborate' Ka = y ou w ould for a minesi s n ormally s o h igh ( e.g.,p Ku 1 0.72f or ( C:Hs)lN) t hat thinkthatR:NisfullyprotonatednearpHT'5insidealivingcell.However' t p rotonate han aminesd issolvedi n h ydrophobicl iquids a re m uch h ardert o n ot s tabilize t s aminesi n a queous olution,b ecausehe h ydrophobicl iquid d oes 1 34 l Chapter5 t ions a s w ell a s w ater d oes. T herefore, he a miner emainsm ostly u nprotonated p p until t he a queous hasei n c ontactw ith t he h ydrophobic hasei s v ery a cidic ( e.g., m a pH 3 ). T herefore, :N r emainsn eutrali n t he i on-selective embrane nd i s R availablet o s ervea s t he H *-binding l igand. 15-16. E 1 : c onstant+ q $!log 1 .00 * l g-al + E2 = c onstant q S'9t - l og[ l.oo , , l o-3] = v LE: E z-Et t 51t'"*]*H-iH:+0.02e58 15-17. : : l F-]prouidenc. I . 00 m g F -/L 5 .26 x I 0 -5 M : Eprovidence c onstant- 0 .059161og 5.26 x 1 0-s1 [ : EFoxboro c onstant- 0 .059l 6 l og [ F-]no*uoro : AE : E p6xboro E providence 0 .0400 V : - o.o5el6logS-bffi 1. x = [ F-]poxuoro : 1 1 l 0 -5M : 0 . 2 1 1 mg lL : ( 1.00x l 0-3) > c onstant - 0.407 V 15-18. ( a) - 0.230 : c onstant ( 0.05916)log (b) - 0.300: - 0.407 (0 . 0 5 9 1 6 )lo x 9 x: l . 5 s " l 0 -2 M : -0.333V : c onstant ( 0.059 6) og [ 3.44x l 0-4] > c onstant - 0.128V + 1l Withs odium: : x + + V E = _ 0.128 ( 0.0596 ) t o g1 3 . 4 4 1 0 -4 ( 5 x l 0 -: )(0 . 1 0 0 )l _ 0 . 3 1 0 l t he w If w e d id n otk nowt hatN a+w erei nterfering, e w ouldc alculate f ollowing p o of concentration L i+ f romt heo bservedotential f - 0.3 l 0 V : : - 0.128 ( 0 . 0 5 9 6 ) o g [ L i+ ] 3 [ L i+ 1= 8 . 4 l 0 -4M + -0.310 1l V " 15-20. T hep otential ithoutM g2* i t w . E : c onstan, ( t?t) ' o, = m 1 t0 -41 c onstant I 1 8.3 V p Addition o f 1 m M M g2+ g ives a n e lectrode otentialo f E :constan,* l 6\ r0.0se l o g [ 2 J 1 0 )l [ 0 . 0 0 0 0 0+ (0 . 0 1 0 X 0 . 0 0 1 : c onstant-l7.l m V l is ; Thec hange - l l 7.l - ( -l 1 8 . 3= + l . 2m V . E lectrode easurements M 135 * We c ouldg ett hes ame l . 2 m Y ( : 0 .001 V ) i ncreasey increasing 2 b [ Ca2+]: Einitiur: onstant.( *, c : Ennatconstant . ( ng*) Efinat-Einitiur ) tog [ ca2+];n;1;61 l og [ ca2+]6nu1 l og [ Ca2+]6"",- ( ry, ) l og [ Ca2+];n1;u1 o.oor2 , "r(,ffiu-"*,J = m:r.ro We c ouldg ett he 1 .2m V i ncrease p otential y i ncreasing[Ca2+lby in b l 0%. 15-21. ( a) A g rapho f E (mV) v ersusog [ NH3 ( M)] g ivesa s traightine w hosee quation l l isE : 5 63.4+ 9 . 0 5 1 o[g 5 NH: ] . F o rE : 3 3 9 . 3 m V , [ NH: ] : 1 . 6 0 x l 0 -4 M (b) T he s ample nalyzedontains100.0 l-)(l.60 l 0-aM ) : 0 .0160m molo f ( a c m " j ust2.00%o ( 20.0m L/1.00 ) o f t hef ood nitrogen. ut t his s ampleepresents B r L = 0 .800 molof sample. herefore, f oodc ontains .016/0.0200 T t he 0 m : nitrogen l l . 2 m g o f N : 3 .59w tolo itrogen. n 15-22. K + h as t he l argests electivity c oefficient a nd i nterferest he m ost. 15-23. ( a) E : c onstant+p u?I'o*[Lu3*]outrid. (b) I f [ La3+1 i ncreasesy a f actoro f 1 0,t hep otentialncreasesy 0 .0591 613: b i b 19.7 Y . m (c) E 1 : c onstant+(1.00)q!:ry g(2.36 l O-a) b " q !#! + E2 : c onsrant( l.oo) b g(4.44 l o-3) ' : + 25.1 V m : LE E z-Et t q?t (d) t :constant. * fU ^ r#F* *# t og{ U-a:*1 t Fe:+11 g qru : : . 0.100 c onstant l og( 1.00 l 0-4) c onstant0 .178eV m ' q !+l! : x + + E:0.178e t og{ 1r.00 l 0-4) *o f o.or0)} + 100.7 V m E lectrode easurements M t37 15-26. W e w ill u set hee ffective ormation onstantor P bY2-( whereY : E DTA: f c f pb2++ y 4- = p by2- K 1 : c r" a _ r: ( 1 . 5 l 0 -8 )(lg l8 . 0:; 1 . 5 , .l 0 r0 K " [ PbY2-l , whereE DTA , _ .,, Kf' : ( i s t he t otalc oncentrationf a ll s pecies f o o t p#+ltEDTA-i EDTA n ot b ound o P b2+) t If w e c anf ind t he c oncentrations [ PbY2-]a nd [ EDTA], t henw e c anc ompute of the c oncentrationf [ Pbz+1. o Therei s a l argee xcess f E DTA i n t heb uffer. W e e xpect ssentially ll l eadt o o e a be i n t he f orm P bY2-. : lM lpbvz-1 , "##(o.to M ) : 7 .3sxo-a ( o.o5o ) : o .o4e6 rotar DrA: # #* E M M : FTeeE DTA0.0496M -7 . 3 5 " l 0 -4 M : 0 . 0 4 8 e M EDTA b ound to P b2+ [ PbY2-] u, ri=tpffirffi=[Pb2+]_ - [ PbY2-l K f'[EDTA] 7 ' 35x 1 0-a : : l 'o l o-r2 M ' { ts; l o9-(0048t 15-27. ( a) W e s eef romt he f lat p ortions f t hec urves hatt heh ighert hec oncentration o t of n itrite, hel owert hee lectrodeotential. Kuf or H NO2i s 3 .15. B elow p p t pH = 4 , a s ignificantractiono f N O2 i s c onvertedo H NO2,s o t he e lectrode f t senses n itritea ndt hev oltage ises. l ess r (b) A t h ighp H, t herei s a h ighc oncentration O H-. T hem ostl ikely of explanation t hef allingc urvess t hatO H- i nterferes ith t hee lectrode: f or i w Thee lectrode r esponds O H- a si f i t w ereN O;. T heh igher hep H, t he to t greaterhec oncentration O H-,a ndt hem oret hep otentialalls. t of f (c) T het riangularegion hows here hep otentials i ndependent p H. T he r w s i t of p optimum H a ppears b en ear4 .5,w here hew idest ange f n itritec anb e to r t o measuredithoutd ependence p H. w on (d) F ormula ass f n itrite NOi) i s 4 6.006.I p pm= 1 p glmL:21.74 p M ( mo 138 Chapter1 5 I Herea ret hev alues measured. oursw ill b e Y slightlyd ifferent. E ppm 100 l0 | 0.1 t Noil (rM) 2174 2 t7.4 2 1.74 2 .174 mV 169.9 2 28.6 2 86.9 3 37.4 3 62.6 4 0.01 0 .217 Datap ointsd eviate rom l inearityn earl og [ NO)l = - 5.5 o r f NO; f = 3 p m. f l 15-28. l eft h alf-cell: A g+(aq, 1) e -+ r A g(s) E -: E " - 0 .05916og(1/c1) c+ l righth alf-cell: g+(aq, r) + e -+ A g(s) E +: E " - 0 .059 6 l og(l/c) A c : E + - E -: cellv oltage: E cel l t'- 0 .05 9 1 6o g (l/ c ' )* { 8 " - 0 . 0 5 9 1 6o g (l/ q )} l = 0 .059 6log(c/c) 1 p E With a mmonia resent, cel: - 0.289 V : 0 .0591 6log(crlc). : 0 .010 M , s ow e c ans olvef or c .: But c 1 0 -0.289 : 0 .0596 l og(c./0.0100) V l : c rl0.0100 q : 1 .3x l 0-7M 19-{.289/0.05916 A g * + 2 NH3 = A g (NH3 )t ( M):0.0100 0 .100 lnitialc oncentration ( M): x Finalc oncentration 0 .080 0 0 0 .010 B2 = ffi:ffi:12x1117 _ t neNHr)jl_ t o.oloot ...
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