ATQ #8

ATQ: Q:Exper i ment#8

1 . Gi v et hepe r t i ne ntc he mi mi c ale qua t i onsands t oi c hi ome t r yi nt hes t a nda r di z a t i onof Na2S2O3. Na2S2O3  wasfir s ts t andar di z edus i ngt hepr i mar ys t andar dKI O3  wi t hs t ar c hast hei ndi c at or . Thef ol l owi ngr eac t i ont ak espl ac e: I O3-+5I -+6H+ 3I H2O 2+3 ↔

Si nc ei odi nei sahal ogen,i tr eac t edwi t ht hewat erpr oduc edi nt hefi r s tr eac t i on: I H+  +I -+HI O 2+H2O ↔

Apal ey el l ows ol ut i onwoul dt henbeobt ai nedaf t ert hefi r s tt i t r at i on.Af t er war ds ,t he pr es enc eofi odi newast heni mpl i c at edb yt headdi t i onofs t ar c h.Anot hert i t r at i onwasmadeaf t er t headdi t i onofs t ar c h,ands l owl yt hebl uec ol orf aded: 2I S2O3 3I +S4O623 +2 ↔

St oi c hi omet r i cr at i oof1mmol ofI O3-i st o6mmol ofS2O32-. 2.E . Expl ai nt hepur poseoft headdi t i onofH2SO4  andexcessKIdur i ngt he st andar di zat i onandwhyt heaci dwasaddedbef or eKI . Topr oducem mo or eI t heappl i c at i onoft hepr i nc i pl eoft hec ommoni oneffec twasobs er v ed. 2, Theaddi t i onofH2SO4  bef or et het i t r at i onoc cur r edwoul dc aus et heequi l i br i um t os hi f tpr oduc i ng mo r ei od i n e.Th eH2SO4  l i ber at est hef r eei odi nef r om t hei odat ei nt hes ampl e.Thee x ces sKIt hat i saddedhel psma mak et hef r eei odi nes ol ubl et heandwoul dy i el das har pert i t r at i onendpoi nt . 3.G . Gi vet heper t i nentchemi mi calequat i onsandst oi chi omet r yi nt hesamp mpl eanal ysi s. Fo rt h es a mp mp l ean al y s i st h es a mec me on c ep t swe r eu s edt ode t e r mi n et h ea mo mo un to f di s s ol v edo xy gen. Mn2+  +2 OH-  —>Mn( —> OH) 2 4Mn( OH) Mn( OH) H2O 2+O2—>4 3+2 6H+  +2MnO( OH)+2I   —>2Mn2+ +I —> H2O 2+4

St oi c hi ome t r i cr at i oof1m mm mol O2i st o4m mm mol S2O32-

4.E . Expl ai nst epwi sehow I waspr oducedf r om t hedi ssol vedO2  i nt hewa wa t e rs a mp mpl e . 3  Expl ai nbr i eflywh whyt her eagent sar eaddedi nadefini t esequence.

Thei odi nehasal ows ol ubi l i t yi nwat ermak i ngi tfi r s tt obec on ver t edt oac ompl e x c ons i s t i ngofI odi ne.Thi si sdonebydi s sol v i ngt heI i naKIs ol ut i on. 2  I +I -—>I 2  3TheI 2pr oduc edi nt her eac t i oni st hent i t r at edwi t hNa2S2O3  whi c hy i el dst her eac t i on: 22I S2O3   —>2I -+S4O6 2+2 Th ewa t e rs a mp l ewa sfi l l e dt ot h eb r i ma ndwh ent h eb o t t l ewa sop en edMn SO4,NaOH wi t hKIa ndNa N3  we r ea dd edt ot hes amp l e.Upo ns hak i n gt h es amp l ef or msb r o wnpr e ci pi t a t ei n t hef or m ofMn( OH) a ndt heo xy genc ont enti sfi x ed.H3PO4  i saddedandt hebo t t l ei sshak ent o 3  di s sol v et hepr ec i pi t at e.Onc et hepr ec i pi t at edi s sol v est hes ol ut i oni st i t r at edandf ol l owst hes ame pr oc edur east hes t andar di z at i on. 5.Gi vet her easonwhyst ar chwasusedasani ndi cat ori nt heanal ysi sandwhyi t wa sa dde dt owa r dst hee ndoft het i t r a t i on. St ar c hi sus edasani ndi c at orf orr edoxt i t r at i onswher et r i i odi dei spr es ent .St ar c hf or msa v er ydar kbl uebl ac kc ompl e xwi t ht r i i odi dewhi c hc anbemadeb ymi x i ngi odi newi t hi odi dewhi c h i sof t enf r om pot as si um i odi de.Theaddi t i onofs t ar c hi sdel ay edatt hepoi ntwher edi l ut ei odi ne i mpar t sapal ey el l owc ol ort ot hes ol ut i on.Addi ngt hes t ar c hi ndi c at oratt hebegi nni ngoft he t i t r at i onwhi l et hei odi nec onc ent r at i oni shi ghai odi nes t ar c hc ompl exwi l l f or m andpr oduc ea r eddi s hbr ownc ol orendpoi nt .Thes t ar c hma yh ydr ol y zeandi nt er f er ewi t ht her eac t i oni nac i di c s ol ut i ons . 6 . How i st hi sa na l y s i s( a ni odome t r i cpr oc es s)di ffe r e ntf r om a ni odi me t r i cone ? Forani odomet r i cpr oc es shet i t r antus edi ssodi um t hi os ul f at eandt heanal y t ei si odi ne. Ont heo t herhandani odome t r i cpr oc es sus esi odi neasat i t r antands odi um t hi os ul f at eas ananal y t e. 7.Fr om t hecal cul at edppm O2,i dent i f yt hedegr eeofwat erpol l ut i onandabi l i t yof t hewa t e rs a mpl esour c et os us t a i na qua t i cl i f e . Af t e rc o mp ut i n gt h ep pm o fd i s s o l v e do x y g eni nt h ewa t e rs a mp l et h ev a l u ec o mp ut e dwa s 1. 7638ppm.Ther es ul t sobt ai nedi ndi c at est hatt hepondwat eri nt hemat hbui l di ngi shi ghl y pol l ut edandi snotagoods our c et os us t ai nl i f e. 8 . Pr e di c tt heeffe ct ,i fa ny ,ofe ac hoft hef ol l owi ngont heDO c ont e ntobt a i ne d: a.Thewat ersampl ei smadet ost andover ni ghtbef or eanal ysi s. Theeffec tofl ea vi ngt hes ampl eo ver ni ghtt ot hec ont entofdi s s ol v edo xy geni s i nde t er mi nat e.Thewat ers ampl ema yha v ehe t er o t r ophi corpho t os y nt he t i cor gani s mst hatc oul d per f or mc el l ul arr es pi r at i onandpho t os y nt hes i s .Theeff ec tont heo xy genc anno tbede t er mi ned.

b.MnSO4  i saddedandt hesol ut i onmadet ost andf oranhourbef or et he al kal i neKIsol ut i oni sadded. Theamountofdi s s ol v e do x ygenwi l l dec r eas e.Manganes ei ss ens i t i v et ol i ghtand under goesr educ t i on.Thi swi l l c aus et hev ol umeoft het i t r antus edt odec r eas eandt hec al c ul at ed di s sol v edo xy genc onc ent r at i onwi l l dec r eas e. 9.Whatar et hepossi bl esour cesofer r or sandt hei reffectont hecal cul at ed pa r a me t e r s ?Ra t i ona l i s e. Apar t i al l yfil l edbot t l emayr es ul ti nani nc r eas edc al c ul at edDO c onc ent r at i onduet ot he addi t i onal ox ygenc omi ngf r om t heai rs pac es .I ft hebot t l ei snots hak enwel l t hec al c ul at edDO wi l l dec r eas ebec aus eno tal l oft heDO i sac count edf or .Notus i ngboi l eddi s t i l l edwat ert hec al c ul at ed mol ar i t yofs odi um t hi os ul f at ewi l l dec r eas ebec aus eoft hepos si bl ec ar boni cac i der r or .I ft he s ampl ei sl ef ti nt hel oc k ert hecal c ul at edDO c ont entwi l l dec r eas ebec aus et heo x y genma ybe c on su me db yhe t e r o t r o phi co r g an i s ms .