Dinh Luong

8/13/2019 Dinh Luong

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BI GING

HA PHN TCH


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1. i cng v phn tch th tch1.1.Bn cht ca phng php

xc nh nng ca mt dung dchcht A(gi l cht nh phn),ngi ta thm

dnmt dung dch cht B(gi l cht chunhay thuc th) bit nng vo mt thtch chnh xc dung dch cht A cho n khi

hai cht phn ng va vi nhau. T th tch dung dch cht B dng tnh

c nng ca dung dch cht A.


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D dich B

D dich A

- Cht A(cht nh phn) lcht cn xc nh nng

- Cht B(cht chun haythuc th) bit nng

- Cho hai cht phn ng va vi nhau vi nhng thtch xc nh

- Da vo nh lut ng

lng tnh nng cadung dch cht A.


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Theo nh lut ng lngta c :

VA. NA = VB. NB

NA =

Trong :

VA , VB : l th tch ca

dung dch A v B

NA , NB:l nng nglng ca dung dch

cht A v cht B

A

BB

V

NV .

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D dich B

D dich A


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1.2. Nhng khi nim c bn

1.2.1. S chun Qu trnh thm dn dung dch B vo

dung dch A gi l s chun .

1.2.2. im tng ngim tng ng l im m dung

dch cht A phn ng va vi dungdch cht B.


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V d : Khi chun HCl bng NaOH :

HCl + NaOH = NaCl + H2O

Khi lng NaOH phn ng ht vi lngHCl th trong dung dch ch c nc vmui NaCl.

Vy im tngng ng vi gi trpH = 7


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1.2.3. Cht ch th

pht hin im tng ngtrong phng php phn tch th tchngi ta thng dng nhng cht ch

th khc nhau.Cht ch thl nhng cht c mu

scthay i khi phn ng t n im

tng ng.


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1.2.4. im kt thc chun

im m cht ch th gy ra nhngbin i m mt quan st c, cho ta bitphn ng n vng gn im tng

ngth ngng chun c gi lim kt thc.

Ni chung, im kt thc thng khngtrngvi im tng ng. im kt thccng gnvi im tng ng th phpnh lng cng chnh xc.


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1.3. Phn loi cc phngphp phn tch th tch

Ty theo bn cht ca phn ng giathuc th v cht nh phn ngi ta chia

thnh cc phng php sau :

1.3.1. Phng php trung ha

Phn ng nh lng l phn ng traoi proton hay phn ng axit - bazHA + BOH = AB + H2O


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1.3.2. Phng php oxy ha khPhn ng nh lng l phn ng

trao i electron gia mt cht oxy hav mt cht kh

Ox1 + Kh2 = Kh1 + Ox2


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1.3.3. Phng php kt ta

Da vo phn ng kt ta gia thucth v cht cn nh lng to ra mthp cht t tan.

Thng dng nht l phng phpto thnh kt ta bc halogenua

X + Ag+ = AgX


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1.3.4. Phng php to phcDa vo phn ng to thnh phc cht

gia thuc th v cht cn nh lng.

Hay dng l phng php to thnh phcvi xyanua v complexon.

Na2H2Y + Men+ = Na2MeY + 2H

+


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2. Phng php trung ha

2.1. C s ca phng phpPhng php trung ha l phng php

phn tch nh lng da trn nhng phn

ng cho nhn proton gia axit bazHA + BOH = AB + H2O


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Nhn xt :- Trong qa trnh chun , pH ca dung dch

bin i.- Ti im tng ng c s bin i t ngtca pH v ta thu c mt dung dch c pH nhtnhhoc vng axit, hoc trung tnh, hoc

kim.- xc nh im tng ngngi ta phi dng nhng chtch th axit- baz hay gi lcht ch th pH.


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2.2. Cht ch th L nhng cht c mu sc thay i theo s bin

i pH ca mi trng.

L nhng cht hu c c tnh axit yu, baz yu .

Trong dung dch c cn bng sau :

HInd + H2O = Ind + H3O +

Ty thuc vo gi tr pH ca dung dch m chtch th dng axit hoc dng baz v mu ca

hai dng ny l khc nhau Khong pH chuyn mu :

pH = pKa(HInd)1 n pKa(HInd)+ 1

(Nng 2 dng axit v baz hn km nhau 10 ln)


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Mt s cht ch th thng dng


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Yu cu i vi cht ch th

Tan trong nc hoc trong cn nng l 104M n 105M mu phi xut

hin kh r Mu phi chuyn nhanh, r trong mt khong pH

kh hp Khong pH chuyn mu phi gn hoc cha gi

tr pH im tng ng ca phn ng chun( t nht phi nm trong bc nhy ca pH )

Bn vng iu kin thng.


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2.3. ng cong chun -Bc nhy pH - Cch chn cht ch th

2.3.1. Kho st ng cong chun axitmnh bng baz mnh

V d :Chun 100 ml dung dch HCl 0,1 N(CA) bng dung dch NaOH 0,1 N (CB).

Phng trnh phn ng :

HCl + NaOH = NaCl + H2O


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K tht tin hnhqu trnh nh lng

Buret : Dd NaOH 0,1N

Bnh nn : Dd HCl 0,1N

Tin hnh chun bng

cch nh t t dd NaOHxung bnh nn

Tnh gi tr pH ti tng thiim

Xy dng ng congchun

Chn cht ch th thch hp

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Ddich NaOH 0,1 N

Ddich HCl 0,1N


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ng cong nh lng(ng cong chun )

1

7

14

4,3

9,7

pH

V NaOH ( ml )100


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NHN XT :

th biu din s thay i gi tr pH cadung dch vo lng NaOH cho vo dungdch HCl, gi l ng cong nh lnghayng cong chun

Trong qu trnh nh lng ban u pH bini t t, gn im tng ng ( khi thiuv tha 0,1 % NaOH ) c s bin i tngt ca pH ( t 4,3 n 9,7 ) gi l bcnhy pHca ng cong chun .


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Cch chn cht ch th:

Ba cht ch th phenolphtalein, metyl ,bromotymol xanh, u c khong pHchuyn mu nm trong bc nhycang cong nh lng nn u c thchn c ba cht ch th ny, tuy nhinkhong pH chuyn mu ca bromotymolxanh cha pH ti im tng ngnn

chn cht ch th ny l tt nht v sai sca php chun l nh nht.


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2.3.2. Kho st ng congchun axit yu bng baz mnh

V d :

Chun 100 ml dung dch CH3COOH0,1 N ( C

A

) c pKa =4,75 bng dung dchNaOH 0,1 N ( CB)

Phng trnh phn ng :

CH3COOH + NaOH = CH

3COONa + H

2O

Cch tin hnh tng t th nghim trn


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CU HI LNG GI

1. Kho st ng biu din nh lng v chncht ch th cho cc trng hp :a . Chun baz mnh NaOH 0,1N bng axit

mnh HCl 0,1Nb . Chun baz yu NH4OH 0,1N (c pKB=4,76) bng axit mnh HCl 0,1N

2. Mt hn hp gm hai axit HCl v CH3COOHcha bit nng . Bng dung dch NaOH 0,1Nv cc cht ch th bit, hy xc nh nng ca tng axit trong hn hp trn.


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NH LNGBNG PHNG PHP

OXY HA KH


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1. C s ca phng php

1.1. nh ngha

Phng php chun oxy ha - kh

l phng php da trn phn nggia cht oxy ha v cht kh ca haih oxy ha - kh khng lin hp.

Phng trnh phn ng :n2Ox1 + n1Kh2 = n2 Kh1 + n1Ox2


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1.2. c im ca phn ngoxy ha - kh :

Xy ra hon ton v theo mt t lng nht nh

Xy ra nhanh, nu chm cn phi tm iu kin

thch hp tng tc ca phn ng ln nhun nng, dng cht xc tc v.v

Phi chn lc, nu trong dung dch chun c

mt cc ion l phi tm cch che hoc tch n ra. Phi c cch v cht ch th thch hp xc nh

c im cui ca qu trnh chun .


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1.3. Cht ch th

* Cht ch th loi 1:

L cc cht hu c c tnh cht oxy

ha - kh c mu dng oxy ha v dngkh khc nhau v mu thay i phthuc vo th oxy ha ca dung dch


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Qu trnh oxy ha-kh ca cht ch th loi 1c biu din bng phn ng tng qut :

Ind ox + ne = Ind kh

Th oxy ha kh ca h oxy ha kh tnh theophng trnh Nerst :


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Mt s cht cht ch th thng dngChtchth Mu

Dngoxy ha DngkhE0(v)Khi [H+] = 1

trung tnh Khng mu + 0,24

Xanh metylen Xanh da tri Khng mu + 0,53

Diphenylamin Tm xanh Khng mu + 0,76

Eric glusin A Khng mu + 1,00

Ax phenylantranilic Tm Khng mu + 1,08

Feroin Xanh da tri + 1,14


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* Cht ch th loi 2

L cc cht c kh nng cho php nhn

ra im cui ca s chun , nhngs i mu khng ph thuc vo thca dung dch.

Th d :Dng dung dch KMnO4 chun

cc cht kh nh Fe2+,C2O42 , H2O2v.v, sau im tng ng nu dmt git dung dch KMnO4th dungdch s nhum mu hng.


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1.4. ng chun -Cch chn cht ch th

ng chun trong phng php oxyha kh l ng biu din s ph thucth oxy ha (E) ca dung dch vo th tch

(V) ca dung dch chun thm vo. ngchun cho bit bc nhy th ca qutrnh chun , qua s chn c chtch th thch hp cho qu trnh chun .

Mun v ng chun ta phi tnhc th ca dung dch sau mi ln thmthuc th (theo phng trnh Nests).


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2. ng dng2.1. Phng php nh lng

bng Iot :Xc nh hmlng Vitamin C

Phng trnh phn ng:

C6H8O6 + I2 C6H6O6 + 2HI

Cch tin hnh

- Buret : Dung dch I2- Bnh nn : Dung dch vitamin C

+ ch th h tinh bt

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Ddich I2

Ddich vitamin C

+ Ho tinh bot


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Tin hnh chun cho n khi dung

dch trong bnh nn chuyn t khngmu sang mu xanh nht bn vngc th tch dung dch I2 phn ng.

Tin hnh lm 3 ln, ly kt qu trung bnhv tnh hm lng ca vitamin C ( g/l ).

Bit E vitamin C = 88

Vy :


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2.2. Xc nh kh ca nc

Nc trong t nhin ( sng, sui,ao, h... ) ngoi cc tp cht v c cnc nhiu tp cht hu c c ngun gcng vt, thc vt ... Nhng tp chthu c ny c tnh kh v chnh chnggy nn bn ca nc. Thngthng ngi ta hay dng phng

php oxi ha kh hay phng phpthuc tm xc nh kh canc.


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Nguyn tc :Dng phng php thatr xc nh lng cht kh.

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Ddich I2

Ddich vitamin C

+ Ho tinh bot

KMnO4

-Nc NC

-H2SO4


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PHNG PHP

CHUN TO PHC


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Phng php complexon

Da trn s to phc cng cua ca cc ionkim loi vi nhm complexon dn xut caaxt aminopolycacboxylic (ph bin dinatrica axt etylendiamin tetraaxetic - EDTA).

Ch th mu l nhng axt hu c yu hocbaz yu cha nhng nhm mang mu vch mu. Mu ca ch th v mu ca phcphi khc nhau, d phn bit.

pH phi thch hp cho ch th v phn ngto phc xy ra hon ton. Ch th thng dng: eriocromen T,

murexit, xylen da cam


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Complexon III (chelaton, trilon B) l

mui dinatri ca EDTA (etylen diamintetra axit axetic)

Vitttl Na2

H2

Y

Trong dung dch complexon III phn lytheo phng trnh sau :

Na2H2Y = 2 Na+ + H2Y

2


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Khng ph thuc vo ha tr ca ion kimloi, complexon u phn ng vi ion kimloi theo t l 1:1 theo cc phng trnhphn ng sau :

Men+ + H2Y2= MeY(n 4)+ 2 H+

Me2+ + H2Y2 = MeY2 + 2 H+

Me3+ + H2Y2 = MeY + 2 H+

Me 4+ + H2Y2 = MeY + 2 H+


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V d :Ca2+ + H2Y

2 = CaY2 + 2 H+Al3+ + H2Y2

= AlY

+ 2 H+

Th4+ + H2Y2 = ThY + 2 H+

Phn ng gia ion kim loi v complexon

thng gii phng ra ion H+

lm cho pHca dung dch thay i trong qu trnhchun do nh hng nhiu n khnng to phc ca ion kim loi v vy khi

chun phi gi cho pH ca dung dch trong mt khong pH nht nh thch hpcho s to phc, mun vy phi dngdung dch m.


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Cht ch th

Dng nhiu nht l cht ch th mu kimloi.

Cht ch th mu kim loi l nhng cht mu

hu c, c kh nng to phc mu vi ccion kim loi v trong nhng iu kin nhtnh mu ca cc phc khc mu cacht ch th t do.

Nhng cht ch th mu kim loi cdng trong chun complexon phi thamn cc iu kin sau:


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- Phc ca cht ch th vi ion kim loi phikhng bn bng phc ca complexon vi

ion kim loi.- Mu ca phc gia cht ch th vi ion

kim loi phi khc mu ca cht ch th t

do.- S i mu phi xy ra nhanh v r rt gnim tng ng ca qu trnh chun

- Cht ch th phi c phn ng c trngvi tng ion kim loi.


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Cc cht ch th kim loi

Eriocrom T en ( ETOO ) ; Murexit ;

Xylen da cam ; axit sunfosalixilic thy r c ch chuyn mu ca

cht ch th kim loi trong chun complexon ta ly mt v d c th :

chun Mg2 +bng complexon III pH = 11 vi cht ch th l ETOO(k hiu l HInd )


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* Trc khi chun :Trong dung dch c ion Mg2+v ETOO

Mg2+

+ HInd = MgInd+

+ H+

xanh nho* Khi chun

Mg2+ + H2Y2 = MgY2 + 2 H+

Khi H2Y2

phn ng ht vi ion Mg2+

tdo, mt git H2Y2 d s phn ng viphc MgInd+ (v phc MgInd+km bnhn phc complexonat magie MgY2 )theo phn ng :

MgInd+ + H2Y2 = MgY2 + HInd + H+ nho xanh

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Ddich I2

Ddich vitamin C

+ Ho tinh bot

- Mg 2+- ETOO

NaH2Y2-


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ng dng phng php chun complexon xc nh cng ca nc

cng ton phn ca nc l tngmui canxi v magie tan trong nc.Ta c th xc nh cng ton phnca nc bng complexon III vi chtch th Eriocrom T en.

(Xem THHH i cng)

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