t vn : Cc phn ng to cht t tan dng c trong phn tch chun l rt t, ng thi cc phn ng kt ta thng km theo cc qu trnh ph lm sai lch tnh hp thc ca phn ng. V vy trong thc t phng php chun kt ta c ng dng trong phn tch chun .

nh ngha PP chun kt taPhng php chun kt ta da trn vic s dng phn ng kt ta v cc c trng l ha ca n lm nguyn tc chung cho qu trnh chun kt ta.

Kt ta c to thnh phi thc t khng tan Tc to thnh kt ta phi ln

Nguyn tc chung ca PP chun kt ta :

Phn ng phi chn lc

Phi c cht R thch hp xc nh im tng ng

1

Cc PP chun kt ta bng PP bc

3

Cc PP chun bng PP thy ngn

5

Click to add Title Cc PP chun khc

2.1 Cc PP chun bng PP bcL PP phn tch chun da trn vic dng dd chun Bc nitrat

Phng php Gay_Lussac

Phng php Mohr

Phng php Volhard

Phng php Fajans

Da trn phn ng gia ion bc v ion halogen c thc hin khng c cht ch th

Nhc im Do khng s dng cht ch th nn kh quan st c im tng ng ca php chun Do ch da vo th gic ch quan ca con ngi nhn bit thi im kt thc qu trnh chun ( thi im cn bng trong v cn bng c.) nn kt qu khng c chnh xc cao dn n sai s

Quy trnh n gin, d thc hin Da trn nguyn l ca phn ng n gin gia s kt hp ca ion Ag+ v ion X : Khng cn s dng cht ch th nn khng xy ra cc phn ng ph vi cht ch th.

u im

PP da trn vic s dng K2CrO4 lm cht ch th xc nh cc Halogenua bng AgNO3. Ti thi im cui chun c xut hin kt ta gch ca Ag2CrO4 Phng php ny ch yu c dng chun Clorua nhy ca cht R ph thuc vo nhiu yu t trong quan trng l nng ca cht R, pH ca dd, nhit

Nhc im Pp ny ch c s dng xc nh cc ion Cl v Br m khng c dng xc nh I v SCN Pp ny khng th dng trong mi trng Axit v kim Cc ion to vi ion cht R kt ta Cromat( Hg2+ , Pb2+ v Ba2+.) ngn cn s chun theo pp Mohr Khng th chun cc dd pp mu theo pp Mohr Nhiu ion cn tr vic chun theo pp Mohr

u im Thng dng chun ion Halogen Cl vi nng rt thp khong 0,001M m chnh xc cao. C s dng cht R to ra hin tng c trng ( xut hin kt ta mu gch: Ag2CrO4 ) quan st im cui ca qu trnh chun

Pp ny da vo phn ng chun gia ion Ag+ vo ion Thioxianat( SCN--) dng ion Fe3+ lm cht ch th:

Ti im cui chun c s xut hin mu caion phc FeSCN2+ Phng php ny c dng chun trc tip Thioxianat bng AgNO3 hoc chun cc Halogenua bng cch cho d AgNO3 ri chun Ag+ bng Thioxianat

Nhc im Gy sai s chun do tan ca AgCl > tan ca AgSCN nn ti im cui chun s xy ra phn ng gia AgCl v SCN

u im C th chun trong mi trng axit mnh, iu m khng th thc hin c vi pp Mohr Pp cn c p dng chun ngc 2 ion Br-- v Cl Cc ion khc ( Ba2+, Pb2+) cn tr vic xc nh theo pp Mohr, nhng trong nhiu trng hp li khng cn tr trong pp VolHard

Do mun lm xut hin mu ca phc FeSCN2+ th phi thm 1 lng thuc th SCN ln hn lng cn thit

Trn c s 1 s cht kt ta c kh nng hp th ln b mt cht hu c, lm cho n thay i cu to v c s i mu r rt. Pp ny da trn vic chun bng cc halogen bng dung dch chun AgNO3 bng cc cht ch th hp ph

Nhc im

u im Nu 3 pp trn ch chun 1 s ion nht nh th pp ny cho php chun c rt nhiu ion : Cl-- , Br--, SCN--, I--. Do chng to kt ta AgX t tan thi im Fcui > 1 cc ht keo AgX tch in dng nn c kh ncng hp ph nhng ion In ca cht ch th nn kt ta chuyn sang mu c trng, kt thc chun

i vi cc ion khc nhau th phi s dng cc cht ch th khc nhau i vi cc cht ch th khc nhau th phi chun dd phn tch nhng khong pH khc nhau. Qu trnh chun phc tp, i hi chnh xc cao Nng cc ion cn phn tch phi nm trong khong 0,005 0,025M (khng qu long cng khng qu c)

Cc pp chun bng pp thy ngn

Phng php thy ngn (I)

Phng php thy ngn (II)

Pp ny da trn vic dng dd chun mui thy ngn I. Khi ion [Hg2]2+ tng tc vi Cl--, Br--, I-- n to thnh kt ta Halogenua t tan Hg2Cl2, Hg2Br2, Hg2I2:

Trong phng php thy ngn I ngi ta dng cht ch th l dd st sunfuaxianua mu mu b mt mu khi d ion [Hg2]2+

Hoc diofenylcacbazon to vi ion [Hg2]2+ kt ta mu xanh

L pp chun da trn s to thnh hp cht thy ngn II km phn ly: HgCl2, Hg(CN)2, Hg(SCN)2

Trong phng php ny cht R l Natri nitropruxit phn ng vi Hg2+ to thnh kt ta trng hay difenylcacbazon to vi ion thy ngn d phc cht mu tm xanh

Nhc im Nhc im ca pp ny l tnh c ca thy ngn v vy khi lm vic vi mui ny cn ht sc cn thn Pp thy ngn (I) khi xc nh nh lng cc mui Clorua v Bromua tan hin cn rt t dng

u im Trong pp ny khng cn dng ha cht qu nh pp bc Trong mui thy ngn (I) t tan hn mui bc tng ng v vy m khi chun Cl- bng thy ngn (I) nitrat ta quan st c bc nhy chun r rt gn im tng ng Vic xc nh bng pp thy ngn (I) c th tin hnh trong cc dung dch axit bng cch chun trc tip

Phng php feroxianua : dng xc nh Zn2+ bng feroxianua kali vi ch th diphenylamin theo phn ng sau:

Chun ion Ba2+ bng sunfat vi ch th l rodizoonat natri lm ch th. Khi c mt Ba2+ th dung dch nhum mu , gn im tng ng mu bin mt.

Chun Pb2+ bng cromat : vi ch th Ag+, gn im tng ng s xut hin mu gch do :