LV Nhien Cuu Kha Nang Xac Dinh Ion NO2

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M U

1.1. L do chn ti: Nh chng ta bit NO2- l cht gy c nht do tc dng chuyn t NO3- sang

NO2- ca vi khun. Mt liu nh mui NaNO2 cng c th gy t vong trong vi pht do

try tim mch, c th c cc triu chng km theo khc nh: au bng, i ma, tm ti. NO3- vo c th s tham gia phn ng d dy v ng rut do tc dng cu cc men

tiu ho sinh ra NO2-, NO2- sinh ra phn ng vi hemoglobin to thnh methemoglobin lm mt kh nng vn chuyn oxi cu hemoglobin. Khi dng thc phm hay ngun nc

cha hm lng nitrit vt qu gii hn cho php s gy ng c nn vic xc nh ion

ny c ngha rt quan trng trong vic nh gi cht lng nc, cht lng nng sn v rau qu.

Mt phng php phn tch nhanh xc nh NO2- l phng php trc quang. Phng php ny c u im l: kt qu mang tnh kh quan cao, thun li, thit b n

gin, t ng ho. Ngoi phng php ny ra chng ta cn c th s dng cc phng

php khc nh: phng php it(phng php oxi ho- kh) Do chng ti quyt nh chn ti Nghin cu kh nng xc nh ion nitrit bng cc thuc th I- v Griess-Ilosvay lm kho lun cho mnh. 1.2.Mc tiu ca ti:

- Bit c vai tr quan trng ca phng php trc quang trong ho hc phn tch.

- Nghin cu c kh nng xc nh ion nitrit bng phng php trc quang.

- Nghin cu c kh nng xc nh ion nitrit bng phng php

chun oxi ho kh. - So snh gia hai phng php xc nh nitrit trn.

1.3. Nhim v ca ti: - Nghin cu kh nng xc nh ion nitrit bng thuc th Griess.

- Nghin cu s nh hng ca mt s ion n vic xc nh ion nitrit bng

thuc th Griess (phng php trc quang).

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- Nghin cu c kh nng xc nh ion nitrit bng phng php It (phng php chun oxi ho kh). 1.4. Phng php nghin cu:

- Nghin cu bng phng php trc quang

- Kt hp vi mt s phng php khc nh: phng php oxi ho kh....


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CHNG 1: TNG QUAN

1.1. Gii thiu v thuc th Griess: Thuc th Griess l hn hp axit sunfanilic v -naphtylamin ho tan trong axit axetic 12%. 1.1.1. Axit sunfanilic: 1.1.1.1.Tnh cht: Axit sunfanilic c nhit nng chy cao, b phn hy 250-3000C, khng tan trong dung mi hu c m cng khng tan trong nc, khng tan trong dung dch

axit, tan trong benzen. Axit sunfanilic cn c tn axit p-aminobenzensunfonic. Axit sunfanilic c cu trc ion lng cc.

Trong dung dch axit, cu trc axit sunfanilic khng i, axit c 3SO l baz

yu c khuynh hng nhn proton t +OH 3 rt nh.

1.1.1.2.iu ch: Cho 50g(0,5mol H2SO4) vo bnh cu y trn kh c 250ml v thm dn tng t mt 15,5g anilin va mi ct. un cch du bnh cu 5h nhit 1850C. tin chc hon ton to thnh axit sunfanilic, ngi ta thm dung dch NaOH vo mu th nh ca hn hp phn ng, nu khng c mi anilin chng t phn ng

kt thc.

Sau khi lm lnh, rt khi phn ng ra cc 100ml nc, axit sunfanilic tch ra di dng kt ta khng mu.

1.1.2. -naphtylamin: 1.1.2.1.Tnh cht: L amin thm in hnh, nhit nng chy 500C. Tinh th khng mu lu s b thm mu do b oxi ha, t tan trong nc, tan nhiu trong axit, ct c bng hi nc.

1.1.2.2.iu ch: iu ch t naphtalen sau khi nitro ha v kh ha bng st trong axit clohiric.

1.1.3. Cc tiu chun ca mt thuc th hu c dng trong phn tch trc quang:


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- Khong cch gia cc cc i MR v HnR cng ln cng tt. i vi thuc

th hu c tt th = MR HnR > 100nm. (*) - Hiu gia cc h s hp th phn t ( = MR HnR) cng ln cng tt (**).

Hiu ny cng ln th nhy ca php xc nh cng cao.

- Thc nghim v l thuyt v sai s cho bit t nu gi tr MR/HnR khc nhau khng qu 2 ln th xc sut sai s tng ln ng k. i vi cc thuc

th hu c tt th MR/HnR phi gp t 2 n 10 (***). 1.2. Tng quan v NO2-:

1.2.1.Tnh cht ca 2NO :

AXIT NITR Axit nitr ch tn ti trng thi kh v trong dung dch nc. trong pha kh c cn bng:

2 OHNONOHNO 222 ++

Dung dch nc ca axit nitr khng bn, nhanh chng b phn hu, nht l khi un nng:

OHNOHNOHNO 232 23 ++=

Bi vy khi kh NO2 tan trong nc th thc t to nn HNO3 v NO theo phn ng:

NOHNOOHNO +=+ 322 23

Trong dung dch nc, axit nitr l mt axit yu (Ka= 4,5.10-4), hi mnh hn axit cacbonic. Do khng bn, axit nitr rt hot ng v ho hc. N va c tnh

oxi ho va c tnh kh.

Tuy khng phi l cht oxi ho mnh nh axit nitric, axit nitr vi nit c s oxi

ho thp hn t ra c kh nng phn ng cao hn, ngha l n c th phn ng

nhit thp hn v vi tc ln hn. Axit nitr oxi ho c axit iothiric(HI) n I2, dung dch SO2 n H2SO4, ion Fe2+ n ion Fe3+..cn bn thn n bin thnh NO.

VD: OHINOHNOHI 222 2222 ++=+

Vi nhng cht oxi ho mnh nh KMnO4, MnO2, PbO2, axit nitr b oxi ho n axit nitric.

OHHNOMnHNOHMnO 23224 352562 ++=++ ++


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MUI NITRIT - Mui nitrit bn hn axit nitr nhiu. Hu ht mui nitrit d tan trong nc,

a s mui nitrit khng mu.

- Nh c cp electron t do nit, ion NO2- c kh nng to nn lin kt

cho- nhn vi ion kim loi. Mt phc cht thng gp l natri cobantinitrit

Na3[Co(NO2)6]. y l thuc th dng pht hin ion K+ nh to thnh kt ta K3[Co(NO2)6] mu vng.

- Nitrit kim loi kim bn vi nhit, chng khng phn hu khi nng chy

m ch phn hu trn 5000C. Nitrit ca cc kim loi khc km bn hn, b phn hu khi un nng, chng hn nh AgNO2 phn hu 1400C, Hg(NO2)2 750C. Trong mi trng axit, mui nitrit c tnh oxi ho v tnh kh nh axit nitr.

1.2.2.Vai tr, tc hi 2NO :

Trong h tiu ha ca con ngi, NO3- s b kh thnh NO2- mt trong nhng cht chuyn bin oxihemoglobin thnh methemoglobin lm gim h hp t

bo, nh hng n hat ng tuyn gip, gy t bin v kch thch cc khi u pht

trin. NO2- nng cao c th gy phn ng vi amin to thnh cht nitroamin, tc nhn chnh gy bnh ung th ngi.

Ngoi ra, c nc ngt c bit l dng c tr rt d mc phi bnh mu nu, nguyn nhn do tch ly qu mc NO2- trong nc.

Bn cnh NO2- cng c vai tr l: lm cho tht c mu bn vng, cung cp

m cho cy trng.

1.3. Phng php trc quang: Phng php trc quang l phng php ph bin, thng c s dng,

tuy n cha l mt phng php hon ton u vit nhng n c nhiu u im:

chnh xc, chn lc cao, thc hin nhanh, thit b n gin v t ng ho.

1.3.1. Phng php trc quang l g? Phng php trc quang l cc phng php phn tch quang hc da trn vic o

hp th nng lng nh sng ca mt cht xc nh mt vng quang ph nht nh.

1.3.2. Chc nng ca phng php trc quang:


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Phng php trc quang dng xc nh cc nguyn t, cc cht v hp cht c hm lng b, trung bnh v ln trong nhiu i tng khc nhau do n c

nhy, chnh xc v chn lc cao.

1.3.3. ng dng ca phng php trc quang: Phng php phn tch trc quang c dng rng ri trong phng th nghim, trong nghin cu khoa hc do phng php ny thc hin c nhanh,

thun li, thit b n gin v t ng ho.

1.3.4. Phn loi cc phng php trc quang: Phng php trc quang dng xc nh nng hp cht mu c chia lm 3 nhm:

1.3.4.1 Phng php so mu bng mt: - Cch tin hnh: Chun b mt dung dch tiu chun c nng bit v so

mu ca dung dch nghin cu vi dung dch tiu chun cho n lc c s cn bng

v cng mu ca hai dung dch, t suy ra nng ca cht cn xc nh.

- Phng php ny: + u im: Thc hin nhanh, n gin khng i hi cc thit b phc tp.

+ Nhc im: Kt qu khng tht s khch quan v ph thuc nhiu vo mt ngi quan st, nhy, chn lc v chnh xc khng cao.

1.3.4.2. Phng php so mu quang in: - Phng php dng cc my c t bo quang in gi tt l cc phng php so mu quang in. Trong phng php ny c s cn bng cng dng sng da

trn hiu ng quang in.

- Phng php ny:

+u im: chn lc, chnh xc v nhy cao. Kt qu mang tnh kh quan cao.

+Nhc im: Ph thuc vo thit b my phn tch do i hi thit b hin i. 1.3.4.3. Phng php so mu quang ph Phng php ny: + u im: chn lc, chnh xc v nhy cao. Kt qu mang tnh kh quan cao.

+ Nhc im: Ph thuc vo thit b my phn tch do i hi thit b hin i.

1.3.5. Cc nh lut c s ca s hp th nh sng


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1.3.5.1. Cc nh lut c s - nh lut Buge-Lambe: Lng tng i ca dng sng b hp th bi mi

trng m n i qua khng ph thuc vo cng ca tia ti. Mi mt lp b dy nh nhau hp th mt phn dng sng n sc i qua dung dch nh nhau.

Biu thc ca nh lut:

A = lg(Io/I) = k. l A: l mt quang ca dung dch l: S phn ca lp dung dch k: ph thuc vo bn cht ca cht mu v bc sng ca nh sng i qua dung dch.

- nh lut Bia : hp th nh sng ca dung dch mu (gi l mt quang) t l bc nht vi nng ca dung dch cht hp th nh sng. Biu thc nh lng ca nh lut Bia :

A = lg(Io/I) = K. C Vi K l h s t l

C l nng ca hp cht mu - nh lut hp nht Buge-Lambe-Bia : "Khi chiu mt chm nh sng n sc

i qua dung dch mu th mc hp th ca dung dch mu t l thun vi cng dng sng v nng cc cht hp th".

Biu thc ca nh lut :

A = . l. C l h s hp th phn t gam ( 1,2. 105) C l nng (mol/l) l l chiu dy ca lp hp th (cm) - nh lut cng tnh : bc sng nht nh mt quang ca hn hp cc cu t khng tng tc ho hc vi nhau bng tng mt quang ca cc cu t ring bit.

Biu thc nh lut cng tnh :

A = 1. l. C1 + 2. l. C +... + n. l. Cn

1.3.5.2. Cc nguyn nhn lm sai lch nh lut Bia: + S c mt ca cht l trong dung dch mu + S Solvat ho


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+ Hiu ng lin hp

+ nh hng ca pH ca dung dch

+ nh hng ca n sc ca nh sng

+ nh hng ca s phn li ca phc mu

1.3.5.3. Cc phng php nh lng trc quang: a). Phng php dy tiu chun:

- c im ca phng php: + C th xc nh c ng thi mt s dung dch phn tch. + Nng dung dch khng cn nm trong khong tun theo nh lut Bia.

+ Nhc im ca phng php l dy dung dch tiu chun thng khng bn mu. khc phc iu ny ta dng knh mu hoc iu ch mt s cht v c bn mu.

- Ni dung ca phng php: + Chun b 10 dung dch chun c nng phc mu ln lt l: C1< C2

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* So snh vi 2 dung dch tiu chun: + Chun b 3 dung dch phc mu: 2 dung dch tiu chun (C1, C2 bit) v dung dch nghin cu (C1< Cx< C2) cc iu kin ti u nh nhau. + o mt quang 3 dung dch trn A1, A2 v Ax. Ta c:

A1 = .l.C1; A2 = .l.C2 v Ax = .l.Cx x 1 x 12 1 2 1

A - A C - C=

A - A C - C Cx = ?

c).Phng php ng chun: - c im ca phng php: + Phng php ng chun p dng thun tin cho php phn tch hng lot

mu v cho php tnh kt qu nhanh. + iu kin p dng: Xc nh nng nm trong khong tun theo nh lut Bia

- Ni dung ca phng php: + Pha ch mt dy dung dch chun c nng tng dn, cn lng thuc th v cc iu kin khc nh nhau (pH, dung mi, lc ion, bc sng). o mt quang ca dy dung dch chun v xy dng phng trnh ng chun A = f(C) x l bng ton hc thng k, ng chun thu c phi c dng:

A = (a a) + (b b).C (*) + Nu ng chun thu c c nhng im u hoc im cui (nng ) b lch khi ng thng ca (*) trn th th phi loi b cc gi tr . Tin hnh xy dng li phng trnh ng chun (nu cn). + Pha ch dung dch phn tch trong cc iu kin nh trn ri em o mt quang (Ax). Thay Ax vo (*) ta s tnh c Cx. - Vic x l thng k c th c thc hin tnh ton bng tay hoc s dng

cc phn mm chuyn dng nh Origin hay MS-Excel ca Microsoft. d).Phng php thm (phng php pha long):

- c im ca phng php: + Phng php thm cho php xc nh cht phn tch k c khi c mt cc ion cn tr.

+ Phng php thm cng ch cho kt qu chnh xc trong khong nng tun

theo nh lut Bia.

- Ni dung ca phng php:


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+ Cho cng mt lng dung dch phn tch (Cx) vo hai bnh nh mc 1 v 2. Thm vo bnh 2 mt lng dung dch chun ca cht phn tch (Ca). Thc hin phn ng to phc trong c hai bnh vi cc iu kin ti u nh nhau v nh

mc n vch. em o mt quang ca hai dung dch bc sng ti u (max) v cng mt loi cuvet. + Tnh kt qu: Theo nh lut Buge Lambe Bia v nh lut cng tnh ta c:

Ax = .l.Cx (dung dch 1: khng thm dung dch chun) Aa = .l.Cx + .l.Ca (dung dch 2: c thm dung dch chun)

T ta c: xx a

a x

AC CA A

=

-

e). Phng php vi sai: - c im ca phng php: + Phng php vi sai c th cho php xc nh nng cht phn tch c nng

ngoi vng nh lut Bia nhng vn cho kt qu chnh xc. +Phng php vi sai cng hn ch nhng sai st gy ra bi cc ion l c trong dung dch

+ Phng php vi sai hn ch c sai s gy ra do lng thuc th d.

- Ni dung ca phng php: * Phng php vi sai nng ln:

+ Chun b 3 dung dch phc mu: 2 dung dch chun (C1< C2) v dung dch nghin cu (Cx) cc iu kin ti u. + o mt quang ca dung dch C2 so vi C1 A = .l.(C2 C1) + o mt quang ca dung dch Cx so vi C1 Ax = .l.(Cx C1)

T ta c: x 2 1x 1 +

A C CC CA

( - ) =

* Phng php vi sai nng b: + Chun b 3 dung dch phc mu: 2 dung dch chun c nng C0, C1 (C0

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T ta c: x 1 0x 1 + A C CC C

A( - )

= -

1.3.5.4. Nghin cu cc phn ng to phc mu: Phc mu trong phn tch trc quang cn tho mn cc yu cu sau:

- Phc mu phi c bn cao chuyn ht ion kim loi cn xc nh vo phc mu, phn ng to phc xy ra hon ton.

- Phc mu cn c thnh phn khng i.

- Phc mu cn c h s hp th phn t cng ln cng tt.

1.4. Phng php it(phng php phn tch th tch): 1.4.1. Tnh cht oxi ha kh ca it: It l cht oxi ha yu v iua l cht kh yu

I2(rn) + 2e 2 I VE 5345.00 = I2 c th oxi ha c cht kh trung bnh ( H2S, H2SO3, Sn(II),.) Ion ioua c th kh c cc cht oxi ha trung bnh tr ln ( +3Fe , H2O2, 72OCr , 4MnO ) It t tan trong nc nhng d dng tan trong KI do phn ng to phc vi ion ioua:

+ 32 )( IIddI (*) Th chun ca cp II 3/3 l 0.5355V

Bi v it t tan trong nc v li d thng hoa nn khi chun it thng dng d

KI v cn bng oxi ha kh ch yu trong dung dch l cn bng (*). 1.4.2. Phng php nh lng it:

- Phng php It thng c dng nh lng c cht oxi ha v cht kh. - Cc cht kh c th c chun trc tip bng it hoc cho tc dng

vi it ly d v sau chun lng d it bng natrithiosunfat Na2S2O3.

- Cc cht oxi ha c nh lng bng cch cho tc dng vi KI d trong mi trng

axit v sau chun lng it gii phng ra bng dung dch natri thiosunfat Na2S2O3.

1.4.3. Cht ch th dng trong chun it: - Khi cho h tinh bt vo dung dch it long th s xut hin mu xanh c trng.

H tinh bt l cht ch th rt nhy, cho php d dng xc nh it n nng 10-5M.


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- H tinh bt c t nht hai hp cht khc nhau l amiloz v

amilopectin. Amiloz to phc mu xanh m vi 3I , cn amilopectin to

phc mu tm nht. Tu theo loi h tinh bt m t l gia hai loi c khc

nhau. Chng hn khoai ty cha khong 20% amiloz v 80% amilopectin, cn h tinh bt ht cha hu ht l amilopectin.

- nhy ca cht ch th tng ln nhanh khi c lng nh ioua. nhy gim khi tng nhit , 500C nhy gim 10 ln so vi nhy 250C. nhy cng gim khi c mt ru etylic v metylic. Khi t l ru etylic vt qu

50% th mu xanh khng xut hin. - Dung dch h tinh bt d b vi khun phn hy, v vy ch nn pha ch trc khi

dng. Dung dch ch th lu to vi it mu tm hoc hi , b mt mu rt chm khi tc dng vi Na2S2O3 v im tng ng xut hin khng r. Ngi ta thng

thm vo dung dch ny cc cht bo v nh HgI2, thimol, glixrin, fomamit.

- Khi chun it ch nn cho h tinh bt khi gn t n im tng ng, lc

dung dch chuyn sang mu vng rm, v phc ca it-h tinh bt t tan trong nc.

Cch pha ch dung dch h tinh bt bn: Nghin 2g tinh bt vo 10mg HgI2 vi mt t nc. huyn ph ny vo mt lt nc si. un si tip dung dch cho n trong sut, lm ngui, bo v trong bnh c nt nhm.

1.4.4. Cc ngun gc sai s khi chun it: - S oxi ha it bi khng kh:

4I- + 4H+ + O2 2I2 + 2H2O Phn ng xy ra rt chm trong mi trng trung tnh, nhng phn ng xy ra

nhanh khi nng ion hiro tng v khi c nh sng.

Phn ng cng xy ra nhanh khi c cc ion kim loi a ho tr lm xc tc(c bit l ng). Do , khng nn lu dung dch c cha I- d v axit qu thi gian cn thit phn ng xy ra hon ton. c bit l khng nn ch c nh sng. Khi

cn lu th phi ui ht oxi bng mt lung kh tr hoc CO2.

Cc vt NO, 2NO cn tr phn ng chun v NO2-

s oxi ha ion I- thnh I2.

- S mt mt it do thng hoa:


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Cn chun khi c lng d KI gim nng it xung thp hn tan ca n trong nc. Khng c un nng dung dch khi chun v phi phng s mt

it do vic dng kh tr ui oxi khng kh.

1.4.5. Phn ng gia it vi thiosunfat: Trong dung dch trung tnh hoc axit yu, phn ng gia it v thiosunfat

(khi c it d) xy ra nhanh chng v theo ng quan h hp thc to thnh tetrathionat 264OS

++ IOSIOS 32 2643232 (**) Phn ng trn xy ra qua cc giai an:

++

++

IOSOSIOSIIOSIOS

264

23232

323232 2

Cht trung gian khng mu S2O3I- phn ng c vi ion ioua:

++ IOSIIOS 32 26432

Khi nng ioua b ( 8 it phn ng vi ion OH- to thnh axit hopoioic:

++ IHOIOHI 2 ( 1110HOIK ) V khi c kim d th to thnh ion hipoioua:

OH- + HOI = H2O + OI- Hipoioua oxi ha thiosunfat mt phn thnh sunfat. Trong dung dch kim th s oxi

ha xy ra hon ton to thnh sunfat. V l do trn cn axit ha dung dch khi chun .


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+ Dung dch natri thiosunfat c bn cao nht khu vc pH t 9-10. Trong dung dch kim mnh thiosunfat b phn hy:

OHSOSOHOS 2232232 34263 +++

+ Trong dung dch nc cha kh cacbonic, th axit cacbonic cng phn hy chm thiosunfat:

Na2S2O3 + H2CO3 NaHCO3 + NaHSO3 + S + Khi axit qu ln th thiosunfat b phn hy to thnh axit sufur v lu hunh:

S2O32- + 2H+ H2SO3 + S

H2SO3 cng kh it nhng 1mol H2SO3 kh ht 1mol I3-

H2SO3 + I3- + H2O SO42- + 4H+ + 3I-

trong khi theo (**) th 1mol S2O32- ch kh 0,5mol I3-. Nh vy, khi 1mol thiosunfat chuyn thnh 1mol axit sunfur th phi tiu tn thm 0.5mol it. Trong trng hp phi chun it khi c axit ln th phi nh rt chm dung dch chun thiosunfat v phi khuy trn mnh. Nhng khng c chun dung dch thiosunfat trong axit mnh bng it.

Kt lun: Khi chun cc cht oxi ha mnh cn cho phn ng gia

cht oxi ha v ioua xy ra hon ton ri mi chun bng dung dch thiosunfat, nu khng cht oxi ha s oxi ha thiosunfat thnh hn hp

tetrathionat, sunfat v lu hunh.

1.4.6. Pha ch dung dch chun thiosunfat: C th tinh ch d dng natri thiosunfat bng cch lm kt tinh nhiu ln t

nc, lm kh khng kh, nghin thnh bt v cui cng sy kh trn CaCl2.6H2O. Tuy vy natri thiosunfat rn khi lu khng kh th b phn hy

mt phn thnh S v mt cht gn ging nh natri sunfit. Cc dung dch natri thiosunfat khi bo qun s thay i chun. Do , cn phi xc nh chun

sau khi pha ch, cng nh phi kim tra chun trong thi gian s dng.

Khi pha ch dung dch chun thiosunfat phi ch mt s iu kin sau:


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- Nc dng pha ch phi c dit khun bng cch un si nc ct sch ri ngui, bi v vi khun c trong khng kh v trong nc s phn hy thiosunfat to

thnh tetrathionat v sunfat. Hot ng ca cc vi khun gim pH t 9-10. V vy, khi pha ch nn kim ho dung dch bng cch thm mt t Na2CO3. Hot

ng ca vi khun cng tng khi c chiu sng v khi tng nhit . dit vi

khun ngi ta cn cho thm mt t lng cht bo v (Clorofom, HgI2..). Nc khng c cha cc vt kim loi nng ( Fe3+, Cu2+ ) v chng lm xc tc cho qu trnh oxi ho thiosunfat thnh sunfat bi oxi khng kh.

- pha ch dung dch thiosunfat 0,1M cn cn 25g Na2S2O3.5H2O, ri ho tan trong 1lt nc ct sch c un si v lm ngui. Thm 0,1g Na2CO3, c th

thm vi git clorofom hoc HgI2(10mg/l). Nn lng mt ngy ri mi chun ho. - Cc dung dch long hn (C < 0,01M) c iu ch bng cch pha long

cc dung dch c hn, nhng cn lu cc dung dch ny d b phn hy hn v do ch nn dng trong vi tun l l cng v phi cho cht bo v.

1.5. So snh 2 phng php xc nh NO2- : - Phng php trc quang:

+ u im: thc hin nhanh, thun li, thit b n gin, t ng ho kt qu mang tnh kh quan cao, t sai s.

+ Nhc im: ph thuc vo thit b my phn tch. - Phng php it:

+ u im: Dng c, ho cht n gin, r tin.

+ Nhc im: Dung dch it d b nh hng ca cc hp cht v c Xut hin sai s do:

+ S oxi ho bi khng kh + S mt mt it do thng hoa


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CHNG 2: K THUT THC NGHIM

2.1. Dng c v thit b nghin cu: 2.1.1. Dng c:

- Cc dng c thu tinh: pipet, buret, erlen, bnh nh mc, cc thu tinh c th tch khc nhau, a thu tinh, phu lc.

- Cc dng c khc: kim tim loi 1ml, chia n 0,1ml

2.1.2. Thit b nghin cu: - Cn phn tch TE214S (c) chnh xc 0,1mg. - My o quang Motic o mt quang vi tn hiu 3 s l sau du phy,

Cuvet c b dy 1,00cm.

2.2. Ho cht: 2.2.1. Ho cht cn dng xc nh NO2-:

-

-naphtylamin, axit sunfanilic.

- NaNO2, KI.

- Mt s ho cht khc: CH3COOH, K2SO3, NaNO3, H2SO4

2.2.2. Pha ch dung dch: Tt c cc ho cht s dng trong kho lun u thuc loi tinh khit ho hc

hoc tinh khit phn tch.

- Dung dch axit sunfanilic: Ho tan 0,5g axit sunfanilic trong 100ml dung dch axit axetic 12%. Nc ct 1 ln. (dung dch Griess A)

- -naphtylamin : Ly 0,4g -naphtylamin sch ho vi vi git axit axetic c ri trn vi 300ml axit axetic 12%. (dung dch Griess B) Hn hp dung dch A v dung dch B theo t l th tch 1:1 gi l thuc th

Griess-Ilosvay (gi tt l thuc th Griess). - Axit axetic 12%: Ly 125ml axit c ho vi nc n 1000ml. - Dung dch gc KI 10-2M: Ho tan 1,660g KI trong 1000ml nc ct, ng trong

dng c sm mu. Chun li hng ngy bng phng php chun It

(cht chun gc l K2Cr2O7).


- 17 -

- Dung dch gc NaNO2 10-2M: Ho tan 0,69g NaNO2 tinh khit sy kh 1050C trong mt gi bng nc ct n vch 1000ml. Chun li hng ngy bng phng php chun It (cht chun l dung dch K2Cr2O7 trn).

- Cc dung dch chun NaNO2, KI khc c pha t dung dch gc. Dung dch

pha dng trong ngy.

2.3. Cch tin hnh xc nh NO2-: Dng pipet chuyn phn mu th c ly vo bnh nh mc 50ml. Sau

thm thuc th mu. Lc u v pha long vi nc ti vch, yn 30 pht. Quan st s xut hin mu.


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CHNG 3: KT QU V THO LUN

3.1. Nghin cu kh nng xc nh ion nitrit bng thuc th It:

3.1.1. Nghin cu nh tnh NO2- bng thuc th It: Ly v 2 ng nghim ln lt cho cc ha cht sau:

- 1ml CH3COOH 1M + 1ml KI 10-3M. Quan st khng thy hin tng xy ra, dung dch khng mu.

- 1ml NaNO2 10-3M + 1ml CH3COOH 1M + 1ml KI 10-3M. Quan st thy mu c mu vng ca I2.

3I- + 4H+ +2NO2- I3- + 2NO + 2H2O Do : c th xc nh NO2- bng phng php it.

3.1.2. Xc nh nhy ca phn ng gia NO2- v I-: Pha mt lot cc dung dch trong bnh nh mc 10ml nh bng 3.1:

Bng 3.1: Kho st nhy ca phn ng gia NO2- v I-

STT bnh 1 2 3 4 5

Dung dch NaNO2 10-4M (ml) 0,1 0,2 0,50 1,0 1,5

Dung dch CH3COOH 1M (ml) 1,0 1,0 1,0 1,0 1,0

Dung dch KI 10-3M (ml) 1,0 1,0 1,0 1,0 1,0

nh mc bng nc ct n 10ml.

Nng NaNO2 sau khi pha (M) 1,0.10-6 2,0.10-6 5,0.10-6 1,0.10-5 1,5.10-5

Quan st thy bnh th 3 mi xut hin mu vng. Vy nng NaNO2 ti thiu tm thy vi thuc th It l 5,0.10-6M.

Do I2 to hp cht mu xanh thm vi h tinh bt nn chng ti tin hnh thm php xc nh tng t nhng c thm h tinh bt. Kt qu thu c nh bng 3.2:


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Bng 3.2: Kho st nhy ca phn ng gia NO2- v I-

vi s c mt ca h tinh bt STT bnh 1 2 3 4 5

Dung dch NaNO2 10-4M (ml) 0,1 0,2 0,50 1,0 1,5 Dung dch CH3COOH 1M (ml) 1,0 1,0 1,0 1,0 1,0 Dung dch KI 10-3M (ml) 1,0 1,0 1,0 1,0 1,0 H tinh bt (git) 1 1 1 1 1


Nng NaNO2 sau khi pha (M) 1,0.10-6 2,0.10-6 5,0.10-6 1,0.10-5 1,5.10-5 Quan st thy bnh th 2 xut hin mu xanh. Vy nng NaNO2 ti thiu

tm thy vi thuc th It khi c thm h tinh bt l 2,0.10-6M. Vy khi c mt h tinh bt lm tng nhy ca phn ng gia NO2- vi I-.

3.2. Nghin cu kh nng xc nh ion nitrit bng thuc th Griess- Ilosvay: 3.2.1. Nghin cu nh tnh NO2- bng thuc th Griess: Ly vo 2 ng nghim ln lt cho cc ha cht sau:

- 1ml axit sunfanilic (dung dch Griess A) + 1ml - naphtylamin (dung dch Griess B). Quan st khng thy hin tng xy ra, dung dch khng mu.

- 1ml NaNO2 10-3M + 1ml dung dch Griess A + 1ml dung dch Griess B. Quan st thy mu c mu hng.

u tin ion nitrit phn ng vi axit sunfanilic to thnh mui iazo:

Sau mui ny phn ng vi - naphtylamin to thnh hp cht azo c mu hng.

Do : c th xc nh NO2- bng phng php trc quang.


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3.2.2. Xc nh nhy ca phn ng gia NO2- v thuc th Griess-Ilosvay: a) Quan st bng mt thng:

Pha mt lot cc dung dch trong bnh nh mc 10ml nh bng 3.3:

Bng 3.3: Kho st nhy ca phn ng gia NO2- v thuc th Griess (quan st bng mt thng)

STT bnh 1 2 3 4 5 Dung dch NaNO2 10-4M (ml) 0,1 0,2 0,50 1,0 1,5 Dung dch Griess A (ml) 1,0 1,0 1,0 1,0 1,0 Dung dch Griess B (ml) 1,0 1,0 1,0 1,0 1,0


Nng NaNO2 sau khi pha (M) 1,0.10-6 2,0.10-6 5,0.10-6 1,0.10-5 1,5.10-5 Quan st thy bnh th 2 xut hin mu hng. Vy nng NaNO2 ti thiu

tm thy vi thuc th Griess Ilosvay l 2,0.10-6M. b) S dng my o quang Motic: Chng ti tin hnh o mt quang ca dy

dung dch trn. Kt qu thu c nh bng 3.4:

Bng 3.4: Kho st nhy ca phn ng gia NO2- v thuc th Griess (o mt quang)

STT bnh 1 2 3 4 5

Dung dch NaNO2 10-4M (ml) 0,1 0,2 0,50 1,0 1,5 Dung dch Griess A (ml) 1,0 1,0 1,0 1,0 1,0 Dung dch Griess B (ml) 1,0 1,0 1,0 1,0 1,0


Nng NaNO2 sau khi pha (M) 1,0.10-6 2,0.10-6 5,0.10-6 1,0.10-5 1,5.10-5 Mt quang 0,009 0,020 0,051 0,096 0,142 T kt qu thu c chng ti v th s ph thuc mt quang vo nng ,

kt qu c trnh by hnh 3.1 sau y:


- 21 -

Hnh 3.1. th biu din s ph thuc mt quang vo nng nitrit T th thu c chng ti thu c phng trnh ng chun: A = 9440,2.C + 0,0013

H s hp th phn t gam ca phc ca NO2- vi thuc th GriessIlosvay

l = 9440,2 (l.mol-1.cm-1). Trong phn tch trc quang, nhy l nng thp nht ca cht c pht

hin khi mt quang l 0,001. Vy ta c:

-7minmin

A 0,001C = = = 1,059.10 M.l 9440,2

Trong l h s hp th phn t gam, l l chiu dy cuvet(1,0cm). Nh vy nhy ca php phn tch NO2- bng phng php trc quang vi

thuc th GriessIlosvay l: 1,059.10-7 M. Ta thy nhy ca phng php trc quang l tt hn rt nhiu so vi

phng php so mu bng mt thng.

3.2.3. So snh nhy ca phn ng NO2- vi hai thuc th I- v Griess: - Thuc th It: CNaNO2min = 2.10

-6 M (c thm h tinh bt)

- Thuc th Griess: CNaNO2min = 1,059.10-7

M (phng php o quang) Da vo kt qu trn ta thy phng php o quang vi thuc th Griess

Ilosvay xc nh c nng NaNO2 nh hn khong 20 ln ln so vi phng

php dng thuc th It. Do ti chn phng php trc quang.

Tuy nhin pha ch thuc th Griess - Ilosvay phc tp hn rt nhiu so vi thuc th I-


- 22 -

3.3. Nghin cu s nh hng ca mt s ion n vic xc nh ion nitrit bng thuc th Griess Ilosvay theo phng php trc quang:

Cc ion gy cn tr phn ng gia ion nitrit vi thuc th Griess l SO32-, I-

lm gim nhy ca phn ng. V vy chng ti tin hnh kho st s nh

hng ca ion SO32-, I- n nhy ca phn ng gia NO2- vi thuc th Griess

Ilosvay nh bng 3.5 sau: Bng 3.5: Kho st nh hng ca ion I, SO32- n nhy ca phn ng

gia NO2- v thuc th Griess STT bnh 1 2 3 4 5

Dung dch NaNO2 10-4M (ml) 0,1 0,2 0,50 1,0 1,5 Dung dch KI 10-3M (ml) 1,0 1,0 1,0 1,0 1,0 Dung dch K2SO3 10-3M (ml) 1,0 1,0 1,0 1,0 1,0 Dung dch Griess A (ml) 1,0 1,0 1,0 1,0 1,0 Dung dch Griess B (ml) 1,0 1,0 1,0 1,0 1,0


Nng NaNO2 sau khi pha (M) 1,0.10-6 2,0.10-6 5,0.10-6 1,0.10-5 1,5.10-5 Quan st thy bnh th 3 mi xut hin mu hng. Vy nng NaNO2 ti

thiu tm thy l 5,0.10-6M. Vy khi c mt cc ion I-, SO32- lm nh hng n nhy ca phn ng.


- 23 -

KT LUN

Qua nghin cu cc c im ca phn ng gia NO2- vi thuc th I- v thuc th Griess Ilosvay chng ti c nhn xt nh sau:

- Phng php xc nh NO2- vi thuc th Griess Ilosvay c nhy cao hn phng php dng thuc th I- khong 20 ln.

- Cc ion SO32- v I- c nh hng n nhy ca phn ng nhng vi nng

kh ln so vi nng NO2-.


- 24 -

TI LIU THAM KHO

1. Nguyn Tinh Dung (2003), Ho phn tch III, NXBGD. 2. Trn T Hiu (2003), Phn tch trc quang ph hp th UV-VIS, NXB HQG H Ni. 3. Hong Nhm (2004), Ho v c II, NXBGD. 4. Trn Th Phng (2008), Xc nh hm lng cc anion v c trong nc thi k

tc x trng HSP ng Thp, Kha lun tt nghip, i hc ng Thp.

5. H Vit Qu (1999), Cc phng php phn tch quang hc trong ho hc, NXB HQG H Ni.


Documents

LV Nhien Cuu Kha Nang Xac Dinh Ion NO2