QUANTI TATI VEDETERMI MI NATI ON OF DI SSOLVED OXYGEN CON ONTENTBYWI WI NKLER REDOXTI TRATI ON W.YBAÑE ÑEZ NATI ONALI NSTI TUTEOFMO MOLECULARBI OLOGYANDBI OTECHNOLOGY, COLLEGEOFSCI ENCE UNI VERSI TYOFTHEPHI HI LI PPI NES,DI LI MAN,QUEZONCI TY1101,PHI HI LI PPI NES DATESUBMI MI TTED:23FEBRUAR ARY2016 DATEPERFORME MED:18FEBRUAR ARY20 16
ABSTRACT
I NTRODUCTI ON The di s s ol ved oxyge n( DO)cont enti n wat e ri s an i mpor t ant i nde xi n t he consi der at i on of wat er s ui t abi l i t y. S uffic i e ntc o nc e n t r a t i o no fDO DO i sc r i t i c a l f o rt hes ur vi v a lofmo mo s ta qua t i cl i f e ,a s we l la si n wa s t ewa t e rt r e a t me nt .I ti sa k e y pa r a me me t e rf o rc h a r a c t e r i z i ng na t ur a l and was t ewat er s and f or as s es s i ng t he [ 1] s t a t eoft hee nvi r onme nti ng ene r a l . The Wi nkl e rme me t hod i s a pr e mi e rand c l a s s i c a lme t ho df o rt hede t e r mi na t i o n of DO c ont enti nwat ers amp mpl e.A s amp mpl eof wa t e ri sc ol l e c t e di ns uc hawa yt ha ti t s exposuret ot heat mospher ei smi mi ni mi zed. Thi si sbe c a us ee x po s ur emi g hta l t e rt he l e ve lofdi s s ol veO2.Tofixt heDO DO c ont ent o ft hewa t e rs a mpl mp e ,i ti st r e a t e d wi t ha s ol ut i onofMnSO4,and t henaddedwi t h andt henwi wi t has ol ut i onofNaOH andKI ( he r e a f t e rr e f e r r e dt oa sa l ka l i ne i odi de [ 2] a zi de ) . The ba s i s of t hi s me t hod i s t he 2+ 3+ qua nt i t a t i v eo xi da t i o nofMn t oMn Mn by
di s s ol v e d O2 i nt hewat ers amp mpl e.Then, t he t r i val entMn oxi di zes I t oI na 2 i s ubsequentr edoxr eac t i on;t heamo mountof I ge ne r a t e di sde t e r mi mi ne db yt het i t r a t i on 2 2wi t h as t andar d S2O3 s o l ut i o n. The endpoi nt i s det er mi ned by t he c ol or c hange br oughtby t he f or mat i on ofa [ 3] s t a r c ht r i i odi dec ompl e x. Theobj ec t i vesoft heexper i mentwa wast o pe r f or m t he wa t e r s ampl i ng a nd pr e t r e a t me nt t e c h ni que sa c c ur a t e l y ,t o c al c ul at et he DO c ont entof t he wat er s amp mpl e,and t o di s c us st he c hemi mi s t r y be hi ndt heWi nkl e rme t hodf ordi s s ol ve d [ 4] o x yg e nde t e r mi na t i o n.
METHOD ODOL OLOGY GY F i r s t l y ,t he s o l ut i o ns pr e pa r e df o rt he e xper i me ntwe r e25 . 0mL mLof4. 0M MnSO4, 2 5 . 0 mLo mL fa l ka l i nei o di dea z i de ,2 5 0 . 0 mL mL of0 . 12 5M s t oc k Na2S2O3,5 0. 0mL mL 0. 5M H2SO4, and f r es hl y pr epar ed s t ar c h s ol ut i on. Then, 250 . 0mL mL of 0. 012 5M
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s t andar d Na2S2O3 s ol ut i on waspr epar ed f r om t hes t ockNa2S2O3s o l ut i on. For t he s t andar di z at i on of t he Na O3s o l ut i o n, 0 . 1 5 0 0 g KI O3 powde r 2S 2 waswei ghedand s ubse quent l ydi s s ol ved i nt o a 50mL beake r .The c ont ent swer e t r ansf er r ed t o 100mL vol umet r i c flas k and bul ke d t o ma r k. Thr e e 10 . 00mL a l i quo t swe r et r a ns f e r r e de a c hi nt o25 0 mL Er l enmeye rflas ks,di l ut ed wi t h 20. 0mL di s t i l l ed wat erand added wi t h 1. 0g KI and10 . 0 mLof0 . 5M H2SO4.Thes o l ut i on wast hen t i t r at ed wi t hs t andar d Na2CO3 unt i lpa l eye l l o wc o l ouri sobs e r v ed.Unt i l t hen,1. 0mL oft he s t ar c hs ol ut i on was added t o t he anal yt e. Ti t r at i on was c o nt i nue d unt i lt hedi s a p pe a r a nc eo ft he bl uec ol our .Thepr oc e dur ewasr e pe a t e d f ort heo t he rt wofla s ks . Fort heanal ysi soft hewat ersampl e,a g l a s sb o t t l ec o v e r e d wi t ha l umi ni um f o i l wasfil l edt ot hebr i m wi t hpondwat er .I t wa sadde d wi t h 0. 5mL MnSO4 s ol ut i on a nd0 . 5 mLa l ka l i nei o di dea z i des o l ut i o n, t aki ng c ar et o avoi di ncl us i on of ai r bubbl e s .Thes ampl ewa st he nmi x e da nd t hef ormat i onofabr ownpr ec i pi t at ewas obs e r ve d.The s ampl e wasadded wi t h 2. 0mL c onc ent r at edH3PO4,agai nt aki ng c a r et oa v oi dt hei nc l us i onofa i rb ubbl e s . Thes ampl ewasmi xed,and l ef tt os t and f or 10 mi nut es . 50 mL al i quot of t he s ampl e was t r ans f er r ed i nt o a 25 0mL Er l e nme ye r flas k and t i t r at ed wi t h s t andar d Na2 CO3 s ol ut i on unt i l pal e yel l ow col ourwasobs er ved.1. 0mLoft he s t a r c hs o l ut i o n wa sa dde dt ot hea na l y t e and t i t r at i on was c ont i nued unt i lt he di s appear ance of t he bl ue c ol our .The a na l ys i swa spe r f or me di nt r i pl i c a t e .
RESULTSAND DI SCUSSI ON TheNa2S2O3 s o l ut i oni sno ts t a bl ea ndi s t he r e f o r es t a nda r di z e da ga i ns tapr i ma r y s t a nda r d, I O3- t o be c ome an e ffe c t i ve t i t r a nt .Dur i ng t he s t a nda r di z a t i on,t he c ompr opor t i onat i on r edox r ea c t i on [ 5] be t we e nI O3 andI oc c ur sa ss e e ni n( 1 ) .
−¿+ 3 H O ( 1 ) +¿ →3 I ¿ −¿+ 6 H ¿ −¿+ 8 I ¿ 2
3
¿ IO 3
Ther e a c t i oni n( 1 )y i e l dsI whi c hi st he n 3 2t i t r a t e dwi t hS2O3 ,a ss ee ni n( 2) .
−¿( 2 ) −¿+ S O¿ ¿ 2−¿ → 3 I −¿+ 2 S O¿ 2
4
2
6
3
¿
I 3
The r e f or e ,i nt e gr a t i ng r e a c t i ons ( 1 )a nd ( 2 ) ,wege tas t oi c hi ome t r i cr a t i oof1mol I O3- i st o6mol e so fS2O32- ( s eeAppendi xC f ort hedi me ns i ona la na l ys i s ) . Bef or e t he s t andar di za t i on of t he t hi os ul f a t es o l ut i on wi t hI O3,exc es sKI and H2SO4 was added t ot he s ol ut i on c o nt a i ni ngt hepr i ma r ys t a nda r d,i nt ha t s pec i fic or der . KI was added f or t he compr opor t i onat i on r eac t i on t o occ ur . H2SO4 i s added t o c r ea t e an ac i di c e nvi r o nme ntf ort her e a c t i on,e na bl i ngi t t ooc c ur .I ti si mpor t a ntt oa ddKIbe f or e s ul f ur i ca c i ds i nc et heH+ i o nsr e l e a s e d f r om H2SO4 wi l lr e a c twi t ht heI O3 i nt he s o l ut i ont of or mi odi ca c i d.HI O3 i saweak ac i d, and i t s f or ma t i on f r om i t s c ons t i t ue nt si ns o l ut i oni shi ghl ypr o ba bl e .
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+¿+ I + 4 H O +¿ → 2 Mn¿ −¿+ 6 H ¿ ¿ 2 MnO ( OH )+ 2 I 2
Thef or mat i onofHI O3 wi l lc a us eer r or si n t he ca l cul at ed mol ar i t y ofNa2SO3,and [ 3] s ubs e q ue nt l y , t heDO,t oi nc r e a s e . Thea na l ys i so ft hewa t e rs a mpl eoc c ur r e d a f t e rt hes t a nda r di z at i onoft het hi os ul f a t e s ol ut i on.I nt he wat ers ampl i ng,whi l e t aki ngwat erf r om t hes ampl es our ce ,t he bot t l ewasc appe dunde r wat e rt oa voi dt he i nc l us i o no fa i rbubbl e s .Thi si sb e c a us e t he i ncl usi on of ai r bubbl es woul d i ncr eas et heDO i nt hewat ers ampl ef r om whi c hdi s s o l v e df r o mt hea i r .Theb ot t l e wa s a l s o c ove r e d wi t h a l umi num be f or e hand
2
2
−¿ ¿ −¿ ↔ I 3 ¿
I 2 + I
−¿ −¿+ S O¿ ¿ 2−¿ → 3 I −¿+ 2 S O¿ 2
4
6
2
3
¿
I 3
−¿ −¿+ S O¿ −¿+ starch → 3 I ¿ 2
Thei mpor t a nc eo fa ddi ngt hes ul f ur i ca c i d be f or e KI c r ys t a l si s be c aus et he ac i d s e pa r a t e st hef r e ei o di nef r o mt hei o da t e . S ol ubi l i z i ng t he f r e ei odi ne c o me sa f t e r [ 6] t hea ddi t i onofe x c e s sKI .
4
6
¿
I 3
−¿ −¿+ S O¿ ¿ 2−¿ → 3 I −¿+ 2 S O¿ 2
4
6
2
3
¿
I 3
−¿ → Mn( OH ) ¿ 2 +¿+ 2 OH
2
¿ Mn
(
) + O + 2 H
(
) +O
4 Mn OH
2
2
2
O → 4 Mn ( OH )3
or 4 Mn OH
2
2
+¿+ I + 6 H O +¿ → 2 Mn¿ −¿+ 6 H ¿ ¿ 2 Mn ( OH ) + 2 I 2
2
(
)+ 2 H
→ 4 MnO OH
2
O
SUMMARYAND CONCLUSI ONS
2
3
REFERENCES [ 1 ]
He l m,I . ,J a l uks e ,L. ,a nd Le i t o ,I .( 2 0 1 2 ) . Re p o r to nme t h o df o ri mp r o v e d ,g r a v i me t r i c
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r i eve f r om [ 4] Wi nk l e r t i t r a t i o n . Ret ht t ps : //s i s u. ut . e e /s i t e s /de f a ul t /fil e s /me a s u r e me nt /fil e s /g _wi nkl e r _ r e po r t _ 2 8 0 6 1 3 . pdf ,o nMa r c h23 ,2 0 1 6
Anal yt i c a l Chemi s t r y Gr oup. ( 20 13 ) . Anal yt i c a l Che mi s t r y Lab Ma nual . Que z onCi t y :Uni v e r s i t yo ft hePhi l i ppi ne s I ns t i t ut eofChe mi s t r y
[ 2]
Ha r ve y , D. ( 20 00 ) . Moder n Anal yt i c al[ 5] Che mi s t r y .( 1st Edi t i on) .( pp.3 45 3 46 ) .The Mc Gr awHi l lCompani es .
[ 3]
t e r mi na t i o n Bel l ,S.& J ohns on,R.( 1997) .De o fDi s s o l v e d Ox y g e nb y Wi nk l e rTi t r a t i o n . Be r mudaBi o l o gi c a lS t a t i o nF orRe a s e a r c h , I nc . pp.2 93 0
University of Malaya. (n.d.). Department of Chemistry, Faculty of Science. Retrieved from http:!!!."imia.um.edu.myima#es "imiala$%&'manuallevel %&'&periment%&'SCS&**+ -nalisisevel&.pdf, on -pril +', &'+/
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