Problem Set 8 Solutions

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

This preview shows page 1. Sign up to view the full content.

This is the end of the preview. Sign up to access the rest of the document.

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"[email protected],"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 [email protected] + 2 e-= 2 l-t; + 2e- = 3 [email protected] + 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 [email protected] + 2e- = . 2 lI2(s)= t [email protected]) 0.535 V 0.620 v L E" = 0 .5350.620:- 0.085 v : 16 : x K : [ [email protected] 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 ...
View Full Document

This note was uploaded on 04/06/2011 for the course CHEM 2011 taught by Professor Buhlman during the Spring '10 term at Minnesota.

Ask a homework question - tutors are online