Phân Tích Cation

5/19/2018 Phn Tch Cation

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B CNG THNG

TRNG H CNG NGHIP TPHCM

Khoa Cng Ngh Ha Hc---

---

B Mn: C S L Thuyt Ha Phn Tch 1

Ti Tiu Lun:

CC PHN NG ION TRONG DUNG DCH NC

Ging vin hng dn:Gv. Th Long

Sinh vin thc hin:Nhm 6Lp:HPT8A


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TPHCM, ngy 20 thng 2 nm 2014


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LI NI U

Trc tin, chng ti xin chn thnh cm n s hng dn v gip

tn tnh ca ging vin ph trch b mn C Th Long. C l ngi trc

tip truyn t kin thc, to mi iu kin ti hon thnh chng tt bi

tiu lun cng nh gipchng ti hiu r hn v ngha ca vic nghin cu

ti.

Ha hc phn tch l mt trong 4 chuyn ngnh quan trng ca ha hc

v ngy cng ng vai tr quan trng trong cc lnh vc phc v nhu cu thc

tin nh y hc, mi trng, nng nghip,... Ha hc phn tch bao gm phn

tch nh tnh v phn tch nh lng.Nm trong khun kh phn tch nh tnh cc cht. Vi ti Cc phn

ng ion trong dung dch nc nhm i su vo nghin cu nhng vn

c bn sau:

- Nhng du hiu c trng ca phn ng ion trong dung dch nc

- Cc h thng phn tch cc cation v anion trong dung dch nc

- Phn tch cc cation bng h thng axit-baz

-

Phn tch cc anion bng h thng axit-baz

ti cung cp nhng kin thc cn thit, b ch v thc t cho

chng ti, lm c s quan trng cho vic thc hnh phn tch sau ny. Trong

qu trnh thc hin bi tiu lun nhm tham kho v s dng nhng ti

liu, bi vit v cc thng tin t cc gio trnh, sch tham kho sau:

1. Ha Hc Phn TchNguyn Tinh Dung Nh Xut Bn Gio Dc.

2. Bi Ging Ha Phn TchTh.S Nguyn B Sm- Trng i Hc Cng

Nghip Vit Tr.

3. C S Ha Hc Phn TchNguyn Minh Chu, T Vng Nghi Nh

Xut Bn Khoa Hc v K Thut.


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4. Cc bi vit, hnh nh t cc trang web: google.com.vn, Wikipedia ting

Vit-vi.wikipedia.org; coccoc.com;tailieutonghop.com;...

DANH SCH THNH VIN NHM 6

Tn MSSV Ni dung thc hin

Mai Kim Sang 12133461

- Chng 1: Nhng c trng ca

phn ng ion trong dung dch

nc

- Tng thp tiu lun

Hong Th Thu Tho 12031041

- Chng 2: Cc h thng phn tch

cc cation v anion trong dung

dch nc

Nguyn Phng Thanh 12056161 - Chng 3: Phn tch cc cation

trong dung dch nc theo h thng

axit - bazPhm Thanh Tm 12054831

Nguyn Nhc Thi 12147961 - Chng 4: Phn tch cc anion

trong dd nc theo h thng axit

bazNguyn Minh Qun 12144501


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MC LC


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Cc phn ng ion trong dung dch nc GVHD: ThLong

SVTH: Nhm 6 Lp HPT8A Trang 1

Chng 1: NHNG DU HIU C TRNG

CA PHN NG ION TRONG DUNG DCH NC

Hu ht cc cht v c tn ti trong dung dch nc di dng cc cht

in li. Chng in li hon ton hoc mt phn thnh cc ion. V vy phn ng

gia cc cht trong dung dch nc thc cht l phn ng gia cc ion. Phn

ng gia cc ion trong dung dch nc hu ht l cc phn ng thun nghch

v tn ti nhng du hiu c trng nht nh m trong phn tch nh tnh,

ngi ta li dng cc du hiu ny nhn bit s c mt ca mt hay mt

nhm ion no . Cc du hiu c trng bao gm:

1.1.

Xy ra sthay i mu sc ca dung dch.Trong mt phn ng ha hc n gin s thay i mu sc ca phn ng l

du hiud quan st nht nhn bit phn ng xy ra.

V d: Xt dung dch ng (II) hydroxit khi tin hnhngm 1 inh st

c lm sch vo trong cc ng dung dch ng (II) hydroxit bo ha. Sau 1

thi gian, ta thy dung dch mu xanh da tri ban u nht mu thm ch mt mu

du hiu chng t, phn ng xy ra.

Phng trnh phn ng: 2 2Fe Cu Fe Cu

Hnh nh dung dch CuSO4 trc v sau phn ng


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1.2. Mu sc ca cht kh thot ra.

Mu sc ca cc cht kh sinh ra trong qu trnh thc hin phn ng ha

hc cngd dngcho ta bit c phn ng ha hc xy ra.

V d:Phn ng gia kim loi Cu v dung dch axit HNO3 c, phn ngxy ra mnh lit v xut hin cht kh mu nu thot ra.

Phng trnh phn ng: 4 2 23 3 2 22Cu HNO Cu NO NO H O

Phn ng gia Cu v HNO3c, kh NO2thot ra mu nu

1.3. Xut hin mt pha mi: tokt ta hoc thot ra cht kh.

Kt ta l shnh thnh ca mt sn phm ho tan khng ng k, thu c

trong mt phn ng ho hc xy ra bi s trn ln 2 dung dch. Mu sc ca kt

ta thu c cng l mt du hiu c trng nhn bit cc ion no c mttrong

dung dch.

Vi hin tng hnh thnh pha kh trong qu trnh phn ng, ta cng c th

kt lun cc cht trong dung dch to thnh cht mi.

V d:Khi cho dung dch bc nitrat AgNO3phn ng vi dung dch axit

clohiric HCl, phn ng to thnh kt ta mu trng AgCltheo phng trnh ion:

Ag Cl AgCl


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1.4. Bin mt mt pha: ha tan kt ta.

Phn ng xy ra gia cc ion to thnh kt ta c sau kt ta tan l mt

trong nhng c trng ca phn ng trao i ion trong dung dch.

V d: trong phn ng gia CuSO4vi NH3 trong dung dch nc to snphm l Cu(OH)2v (NH4)SO4sau phn ng tip tc xy ra chng ta nhn bit

c v c hin tng l kt ta mu xanh m Cu(OH)2 tan ra to thnh dung

dch [Cu(NH3)4]SO4mu xanh dng.

Phng trnh phn ng:

2 2 24 3 2 4 42

2 22 3 2 3 44

CuSO NH H O Cu OH NH SO

Cu OH NH H O Cu NH SO

Hnh nh minh ha phn nggia CuSO4vi NH3

1.5. Vn tc ca qu trnh phn ng.

Tc phn ng l thay i nng ca mt trong cc cht tham gia

hoc sn phm trong mt n v thi gian.

Trong qu trnh din bin ca phn ng, nng cc cht phn ng gim

dn, ng thi nng cc sn phm tng dn. Phn ng xy ra cng nhanh th

trong mt n v thi gian nng cc cht phn ng gim v nng cc sn

phm tng cng nhiu.


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Chng 2: CC H THNG PHN TCH CATION V ANION

TRONG DUNG DCH NC

2.1. Mt s khi nim.

Thuc th phn tch:l mt hp cht ha hc c dng pht hin , xc

nh hay tch trong qu trnh phn tch ha hc ca mt cht hay hn hp nhiu

cht cgi l thuc th phn tch. Yu cu thuc th phn tch phi tinh khit

v c hiu.

Thuc th theo tc dng phn tch gm 3 loi:

- Thuc th nhm: l thuc th c tc dng ging nhau ln mt nhm cc

ion. V d: HCl l thuc th nhm Ag+, Pb2+, Hg2

2+

- Thuc th chn lc: l thuc th c tc dng ging nhau ln mt s ion

m ion ny c th thuc nhm phn tch khc nhau. Chng hn NH 3c

th to thnh phc tan hoc khng tan vi mt s ion nhiu nhm

phn tch.

- Thuc th c hiu hay thuc th ring bit: l thuc th ch cho phn

ng c hiu vi mt ion hoc mt cht. v d: h tinh bt cho mu

xanh ch vi iod; dimethyglyoxim trong mi trng amoniacto thnhch vi ion Ni2+cho mt kt ta mu hng.

2.2. Cc hthng phn tch cation v anion trong dung dch nc

Vic xc nh cc ion trong dung dch nc l mt trong nhng cng vic

cn c ca ngh phn tch. Cc ion trong dung dch s c phn chia theo cc

nhm thun li cho vic tch chng ra khi dung dch nc. Khi tin hnh

phn tch nh tnh ngi ta tin hnh theo hai cch:

- Phn tch ring phn

- Phn tch h thng


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2.2.1.Phn tch ring phn

Phn tch ring phnl xc nh mthay mt sion no trong hn hp

nhiu ion bng mt phn ng c hiu. C th ly tng phn ring dung dch phn

tch th ring tng ion, khng cn theo mt th t nht nh no.V d:tm Bi3+bng thuc th thioure c mu vng ti, Fe3+vi KSCN c

mu mu c trng.

Trong nhiu trng hp khng s dng c phng php phn tch ring

bit v khng phi tt c cc ion u c phn ng tht c hiu.

2.2.2.Phn tch h thng

Khi cn phn tch ton din 1 mu, ngi ta tin hnh phn tch h thng

l xc nh cc ion theo mt trtt nht nh. Mun phn tch hn hp nhiu ionngi ta thng dng cc thuc th nhm chia cc ion thnh nhiu nhm, mi

nhm c th c chia thnh cc phn nhm v cui cng c tch ring thnh

cc ion ring bit. Sau tin hnh chng minh s cmt bng cc phn ng c

trng thch hp.

Hin nay, i vi cc cation, ngi ta tm ra nhiu h thng phn tch,

mi h thng c nhng u im v nhc im ring. Ba h thng thng c

dng l h thng phn tch sunfua, h thng axit baz v h thng phn tch

photphat - amoniac.

Ty thuc vo thuc th s dng trong h thng phn tch nh tnh

cation chia lm 3 h thng c bn l:

a.

H thng phn tch sunfua cc cation

C s:da vo tnh tan ca cc kt ta gia cation vi cc thuc th nh

HCl, H2S, (NH4)2S/NaOH, (NH4)2CO3,... trong c s chnh l tnh tan ca mui

sunfua.


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Theo h thng ny, cc cation c tch chia lm 5 nhm:

NhmThuc th

nhm

Cc cation

thuc nhmSn phm to thnh sau khi

tc dng vi thuc th

I HCl longAg+, Hg2

2+,

Pb2+

Ta clorua: AgCl, Hg2Cl2, PbCl2khng tan trong nc v cc axitlong

II

H2S trong mi

trng axit

(pH =0,5)

Sn2+

, Sn4+

,

Sb3+

, Sb5+

,

As3+, As5+,

Hg2+

, Cu2+

,

Cd2+

, Bi3+

,(Pb

2+)

Kt ta cc sunfua. Nhm ny chiathnh hai phn nhm:

+ Phn nhm IIA: Gm cc sunfuatan trong (NH4)2Sx v b oxi hoAsS4

3-, SbS4

3-, SbS3

2-

+ Phn nhm IIB: gm cc sunfuakhng tan trong (NH4)2Sxnh HgS,CuS, CdS, Bi2S3, (PbS)

III

(NH4)2S trong

mi trng NH3+ NH4Cl

Al3+, Cr3+,

Fe3+, Mn2+,

Co2+

, Ni2+

,

Zn2+

Kt ta Al(OH)3, Cr(OH)3,Fe(OH)3, MnS, CoS, NiS, ZnS.

Nhm ny cng chia thnh hainhm:

+ Phn nhm IIIA: gm cc kt tatan trong HCl nh Al(OH)3,Cr(OH)3, Fe(OH)3, MnS, ZnS.

+ Phn nhm IIIB: gm cc kt takhng tan trong HCl nh CoS, NiS.

IV

(NH4)2CO3

trong dd mamoniac didng cccacbonat khng

tan trong nc.

Ba2+, Sr2+, Ca2+To cc kt ta BaCO3, SrCO3,

CaCO3

NaH2PO4 trong

mi trng NH3+ NH4Cl

Mg2+ NH4MgPO4

VKhng c thucth nhm

Kim loi kimv NH4

+


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u im:cch phn chia cc nhm v cch tin hnh phn tch rt cht ch,

ph hp vi vic trnh by cc s s l thuyt, c bit l vic phn chia cc nhm

phn tch c nhiu im ph hp vi vic phn nhm trong bng h thng tun

hon Menelep, do lin hd dng gia cc phn ng hc trong gio trnhho hc v c vi phn ng phn tch, kt qu phn tch cc ion kh chnh xc,

pht hin trit cc cation, xc nh c cc ion trong phc cht.

Nhc im:H2S c, c mi trng thi gy kh kh chu cho ngi phn

ticch1; qu trnh phn tch ton b cation mt kh nhiu thi gian t 25-30 gi;

hay gp dung dch kt ta cng kt ca mt s sufua kim loi (NiS v CoS vi

SnS; ZnS vi CdS) gy kh khn trong vic x l hon ton sn phm.

b.

H thng cc cation theo phng php axit - bazC s:da vo tnh tan khc nhau ca cc hydroxit, sunfat, clorua,... c to

thnh gia cc cation vi axit -baz nh HCl, H2SO4, NaOH, NH4OH,...

Vic phn chia cc cation thnh tng nhm theo h thng ny c trnh

by trong bng sau:

NhmThucth

nhm

Cc cationthuc nhm

Sn phm to thnhsau khi tc dng vi

thuc th nhm

Nhmaxit

IKhng c thuc

th nhmKim loi

kim vNH4+

Khng to thnh kt takh tan vi mt thuc thno

IIH2SO4long v

ru etylicBa

2+, Sr

2+,

Ca2+, (Pb2+)

To kt ta mu trngBaSO4, SrSO4, CaSO4,

PbSO4

NhmBaz

III HCl long, nguiAg

+, Pb

2+,

Hg22+, Cu+,Au+

To cht t tan: AgCl,

PbCl2, Hg2Cl2, CuCl

IV NaOHd+ H2O2

Be2+

,

Al3+

,Cr3+

,

Zn2+, Sn2+,

Sn4+

, As3+

,

Al3+

, Sn2+

, Sn4+, to thnh

hiroxit lng tnh tantrong kim d AlO2

2-,

ZnO22-, SnO3

2-.


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As+, Sb

+,

As3+

, As4+

,

Ga3+, In3+,...

CrO2- s b oxi ho thnh

CrO4-mu vng.

AsO43-...

V NH4OH c dCd

2+

,Cu

2+

Hg2+, Co2+,

Ni2+

To cc phc amoniacatcmu cng thc chung

2

3 4( )M NH

VI

Dd NaOH v

H2O2sau lHNO3v H2O2

Fe2+

, Fe3+

,

Sb3+, Sb5+,

Bi3+

, Mn2+

,

Mg2+

To cc hiroxit khng tanc mu ring bitFe(OH)2,Fe(OH)3, Bi(OH)3,

Mn(OH)2, Mg(OH)2.

u im:h thng ny sdng c nhng c trngc bn ca ccnguyn t, quan hca chng vi cc axit, baz, tnh lng tnh ca cc hydroxit v

khnng to phc ca cc nguyn t; t c hi hn v thi gian thc hin phn

tch ngn hn t30-40% so vi hthng H2S.

Nhc im: h thng ny cn gii hn v s lng cc cation, cc tnh

cht ca cc tnh cht ca cc hyroxit ca cc cation nhm 4 v nhm 5 cha

c nghin cu k, cng nh cc iu kin tch, to kt ta ca chng; vic phn

tch nhm thiu cht chhn hthng H2S.c. Hthng phn tch photphatammoniac:

C s: da vo tnh tan ca cc mui photphat trong cc mi trng khc

nhau. H thng ny chia cc cation thnh 5 nhm phn tch:

- Nhm 1:gm cc cation kim loi kim v NH4+. Khng c thuc th

c trng cho nhm, cc hp cht chng c mt u c th tan to thnh

dung dch.

- Nhm 2:gm Ba2+, Sr2+, Ca2+, Mg2+, Fe2+, Fe3+, Al3+, Cr3+, Mn2+, Bi3+.

Nhm ny b kt ta bi thuc th nhm - amoni hyro phophat

(NH4)2HPO4trong dung dch amoniac c. c chia lm 2 phn nhm

nh:


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+ Phn nhm 2a: Ba2+, Sr2+, Ca2+, Mg2+, Fe2+, Mn2+- C kt ta

photphat tan trong axit axetic.

+ Phn nhm 2b: Fe3+, Al3+, Cr3+, Bi3+- C kt ta photphat khng

tan trong axit axetic.- Nhm 3: gm Cu2+, Cd2+, Hg2+, Co2+, Ni2+, Zn2+. Cc phophat ca

chng tan trong dung dch NH3to thnh cc amoniacat [M(NH3)4]2+

.

- Nhm 4: gm As3+, As5+, Sb5+, Sb3+, Sn2+, Sn4+. Cc ion thic v

antimon khi un nng vi HNO3th to thnh kt ta khng tan l acid

metastanic v acid metaantimon (H2SnO3, HSbO3). Cc hp cht Asen

(III) khi un nng vi HNO3th b oxy ho thnh H3AsO4.

-

Nhm 5:gm Ag+

, Hg22+

, Pb2+

b kt ta bi acid HCl di dng ccclorua t tan.

u im:Gim bt hi so vi 2 hthng trn.

Nhc im:Thi gian phn tch di v kh phc tp, c bit n hn ch

qu trnh phn tch ring phn nn khng c phbin so vi hai phng php

trn.

2.2.1Phn tch nh tnh anion

Vi cc anion th khng c mt h thng phn tch cht ch no m ch c

cc phng php phn tch ring l cho tng anion mt hoc tng nhm nh v th

pht hin mt anion no ngi ta phi dng nhiu phn ng c trng

kim tra li, m bo cho kt lun chnh xc, chnh v vy, phn tch nh tnh cc

anion thng phc tp hn cc cation. Da theo thuc th nhm anion c th

phn loi theo bng:

Nhm Ion

I

II

III

Cl- , Br-, I-, S2-, NO3-

PO43-, HCO3-, CO32-, AsO33-, AsO43-

SO42-, SO33-


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Bng phn loi thuc ththeo nhm anion:

STTThuc th

nhmNhm anion

Sn phm hoc du hiuphn ng

1HCl 2N hay

H2SO4

CO32-, CN-, S2-, SO3

S2O32-, NO2-, ClO-

To ra cc kh tng ngCO2 (khng mu, lm cnc vi trong); HCN (mihnh nhn); H2S (mi thi);SO2 (mi sc mnh); SO2 vS; NO v NO2 (mu nu ,kh th); Cl2 (mu vng lc,kh th)

2

BaCl2+ CaCl2Trong mi

trng trungtnh

AsO33-, AsO43-,CrO42,ClO-, MnO4-,

SO42-, PO43-, BrO3-,

IO3-, F-

To kt ta tng ngCa3(AsO3)2trng; Ca3(AsO4)2

trng; BaCrO4 vng;Ba(MnO4)2 ; BaSO4 trng;Ba(BrO3)2 trng; Ca3(PO4)2trng; Ba(IO3)2 trng; CaF2trng

3AgNO3+ HNO3

2NSCN-; Cl-; Br-; I-

To kt ta tng ngAgCN trng; AgCl trng;AgBr vng nht; AgI vng r

4Hn hp Mg

(NH4OH +

NH4Cl + MgCl2)AsO43-; PO43-

To kt ta tng ngMgNH4AsO4 kt ta mutrng; MgNH4PO4 kt tamu trng

5 KI + H2SO42N

CrO42-, AsO33-,

MnO4-, ClO-, ClO3-,

BrO3-, IO3-, NO2-

Gii phng I2( nhn bitbng mu trong dung dchnc, hoc trongchloroform, hoc th bnghtinh bt)

6 Dng dch I2S2-, SO32-, S2O32-,

AsO33- Lm mt mu I2

7

Dung dchKMnO4

+ H2SO42N

S2-, SO32-, S2O32-,

AsO33-, NO2-, Cl-,

Br-, I-, CN-, SCN-Lm mt mu KMnO4

8Khng c thuc

thNO3-, ClO4-


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Chng 3: PHN TCH CC CATION TRONG DUNG DCH NC

THEO H THNG ACID BAZ

3.1.

Nhm cation 1 (cc ion kim loi kim v NH4+): nhm ny khng c

thuc th nhm.3.1.1.Tnh cht acid baz

Hydroxit ca kim loi kim l cc baz mnh. Chng d tan trong nc. cc

cation khng th hin tnh acid baz.

Ion NH4+c tnh acid yu v NH3l mt baz yu

9.244 3

+NH NH H logK

3.1.2.Tnh cht to phc

Thc t khng c cc phc cht bn to thnh bi cation nhm 1. Phc bn

nht l Li+- EDTA, c lg= 2.8. NH3to c phc cht vi cc kim loi khc

nhau: Cu+, Cu

2+, Co

2+, Co

3+, Cd

2+, Zn

2+, Ag

+, Hg

2+, Ni

2+. Cc phc ny b phn

hy trong mi trng acid do s proton ha ca NH3:

+ 9.243 4

NH H NH logK

3.1.3.Tnh cht oxi ha kh

Ch c mt trng thi oxi ha l M+. Th in cc cp oxi ha/kh rt thp

Cc kim loi nhm 1 l nhng cht kh rt mnh. Cc ion kim loi nhm 1 l cht

oxi ha rt yu.

3.1.4.Hp cht t tan

C mt s mui t tan tng t nhau ca K+v NH4+: KClO4, NH4ClO4,

K2Na[Co(NO2)6]. Ion Na+to c mt s rt t hp cht t tan: natri km uranyl

acetat, Na2SiF6, NaSbO3.

3.1.5.Phn ng ca cc ion

a. Natri

- Phn ng vi uranyl km acetat: Trong mi trng acid yu thuc th phn

ng vi ion Na+cho kt ta vng nht.

- Quang ph nhn thy: vng 587 589 nm. Mu la: vng, rt nhy.


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b.

Kali

- Phn ng vi natri cobantinitrit Na3[Co(NO2)6]: Cho kt ta vng.

- Phn ng vi natri hidrotatrat NaHC4H4O6: to kt ta trng tinh th

KHC4H4O6.- Quang ph nhn thy: 760 770 nm; Tm 404 nm; Mu la: tm.

c. Amoni

- Phn ng ui ion amoni

Do NH4+ l mt acid yu v NH3d bay hi nn khiun nng vi dung

dch kim thNH4+s b ui khi dung dch.Khi nung nng , cc mui amoni b

nhit phn to kh NH3.

Nu acid c tnh oxi ha th NH3thot ra b oxi ha cho nhng sn phmkhc nhau (N2, N2O,).

- Phn ng vi thuc th Nestler

Thuc th Nestler l dung dch kim ca mui kali iodomecuriat

(K2[HgI4] + KOH). Ion NH4+phn ng thuc th Nestler cho kt ta keo nu .

Nu nng NH4+rt b th ta c dung dch keo mu da cam.


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3.1.6.S phn tch cation nhm 1


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3.2. Nhm cation 2nhm kim loi kim th. Thuc th nhm ny l dung

dch H2SO4long v ru etylic.

3.2.1.Tnh cht acid baz

Cc cation nhm 2 u l cc acid rt yu. Cc hydroxit ca cc cationnhm 2 u l nhng baz mnh

2

2Ca H O CaOH H


Cc cation nhm 2 to c mt s rt t cc phc cht bn nhnchung

bn ca tng phc cht gim khi i t Ca2+n Ba2+.

Ion Ca2+

to c phc t bn vi ion SO42-. Phn ng ny dng tch

Ca2+ra khi Ba2+v Sr2+.

3.2.3.Hp cht t tan

Cc mui cacbonat sunfat, oxalat, photphat ca cation nhm 2 c mu

trng, cromat c mu vng.

- Cc mui cacbonat tan c trong cc acid, k c acid acetic do to thnh

H2CO3l acid yu v d phn hythnh CO2.

- Cc mui cromat: tan tng t BaCrO4n CaCrO4.

- Cc mui sunfat c tan tng khi i t BaSO4n CaSO4ng vi tch s

tan ca tng mui c trnh by bng sau:

Hp cht Tch s tan (T)BaSO4 1,10 x 10

-10

SrSO4 3,20 x10-7

CaSO4 9,10 x10-6

Bng th hin tan ca mui sunfat cation kim loi kim th

3.2.4.

Phn ng ca cc ion

a.

Vi dung dch K2CrO4v K2Cr2O7:

Trong mi trng axit axetic ch 2 ion Ba2+v Pb2+cho kt ta mu vng

BaCrO4v PbCrO4, cc ion Sr2+

v Ca2+ khng to thnh kt ta. Vi M2+l

Ba2+v Pb2+ ta c phn ng:


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M2+ + CrO42- MCrO4

2M2+ + Cr2O72- + H2O 2 MCrO4 + 2H

+

Trong BaCrO4khng tan trong kim, cn PbCrO4 tan trong cc dung

dich NaOH, KOH khi un nng theo phng trnh:

PbCrO4 + 4OH- PbO2

2- + CrO4

2- + 2H2O

b. Vi dung dch Na2S :

Vi dung dch ny ch ion Pb2+tc dng to thnh PbS mu en, thc t

khng tan trong cc dung dch HCl, H2SO4, ch tan trong cc dung dch HNO3un

nng.

Pb2+

+ S2- PbS

PbO22- + S2- + 2H2O PbS + 4 OH

-

c.

Vi dung dch (NH4)2C2O4:

Vi thuc th ny cc cation nhm 2 u cho kt ta trng tinh th. Cc kt

ta u kh tan trong dung dch axit axetic long. Dung dch l thuc th ny rt

nhy i vi ion Ca2+, nn ngi ta dng thuc th ny nhn ra cation Ca2+sau

khi tch n khi cc ion Ba2+ v Pb2+.

d.

Vi dung dch (NH4)2SO4:

Dung dch thuc th ny kt ta c SrSO4mu trng vi ion Sr2+:

Sr2+ + NH4SO4 SrSO4 + 2NH4+

Ion Ca2+ khng gy tr ngi cho vic tm Sr2+bng thuc th ny, v

CaSO4to vi thuc th mt mui phctan:

CaSO4 + NH4SO4 (NH4)2[Ca(SO4)2]

V vy sau khi tch Pb2+v Ba2+ra khi hn hp vi Sr2+v Ca2+, ta dng

dung dchNH4SO4lm thuc th nhn bit Sr2+trong hn hp vi Ca2+.


22/54



3.2.5.Quy trnh phn tch cc cati on nhm 2

Tch cation nhm 2 ra khi dunh dch, cho tc dng vi dung dch

H2SO4long, d v ru etylic, un nh, li tm, thu c kt ta 2 l hn hp

sunfat cc cation nhm 2 v dung dch cc cation cc nhm 3,4,5,6. Chuyn sunfatnhm 2 thnh cacbonat bng cch cho phn ng 4 ln vi dung dch Na2CO3un

nng. Ho tan kt ta cacbonat bng dung dch CH3COOH 6M. Thm vo dung

dch dung dch K2CrO4 kt ta BaCrO4v PbCrO4. Li tm, ly kt ta v

nc lc, chia i nc lc. Phn (1) tm Sr2+bng (NH4)SO4, phn (2) tm

Ca2+

bng dung dch (NH4)2C2O4. Cho kt ta PbCrO4v BaCrO4tc dng vi

dung dch NaOH tch Pb2+. Ly nc lc tm ion Pb2+bng dung dch Na2S.

Nu khi tc dng vi NaOH vn cn kt ta vng khng tan, l BaCrO4.Lu :

PbCrO4cn d dng tan trong dung dich CH3COOH v to thnh ion phc:

PbCrO4 + 3CH3COO- Pb(CH3COO)3

- + SO4

2

V vy ta c th thay dung dch NaOH bng dung dich NH4CH3COOH

tch PbSO4ngay t u khi hn hp vi 3 sunfat ca cc cation Ba2+

, Sr2+

,Ca2+

.

Phn ng ny c dng trong s di y


23/54




S phn tch cc cation nhm 2


24/54



3.3. Nhm 3: cc cation to c mui clorua ttan: Ag+, Pb2+, Hg22+

,Cu+,

Au+: Thuc th nhm ny l dung dch HCl long,ngui.

3.3.1. Tnh cht acid baz

a.

Ion Ag

+

Ion khng mu, c tnh acid yu. Khi kim ha dung dch th ban u xut

hin kt ta trng AgOH v sau chuyn nhanh thnh Ag2O mu nu

2Ag H O AgOH H

2 2AgOH Ag O H O

b. Ion Pb2+

Ion Pb2+

khng mu, c tnh acid yu. Khi kim ha dung dch, ban u to

kt ta mui baz v sau n Pb(OH)2.

+2 2

22

2 32

Pb H O Pb OH H

Pb OH H O Pb OH H

Pb OH H O Pb OH H

c.

Ion Hg2+

Trong dung dch nc, Hg2+

khng mu, c phn ng acid2 H

2Hg O HgOH H

Khi kim ha dung dch, ban u c kt ta mui baz v sau n HgO

mu vng. Kt ta tan trong acid .

3.3.2. Tnh cht to phc

a. Ion Ag+

Ag+to c kh nhiu phc cht bn vi cc phi t hu c v v c khc

nhau. Phc EDTA vi Ag+ c bn vo loi km nht trong s cc phc

complexonat kim loi (lg = 7,32). Ag+ to c phc bn vi ithizon, chit

c bng CHCl3, CCl4


25/54



b.

Ion Pb2+

Ch to c cc phc t bn: PbNO3+, PbCl

+, PbI2, PbI

+.Ch cng to

c cc phc tng i bn vi axetat,tatrat, xitrat, thiosunfat, phc vi EDTA,

phc vi xianuaPb4+

tn ti dng phc PbCl62-

, PbCl5-

trong dung dch HCl c.c.

Ion Hg2+

Ion Hg2+

to c phc bn vi rt nhiu cht, a s c s phi tr cc i

n=4. Cc phc vi sunfat, nitrat, florua t bn. Cc phc vi clorua, bromua, iodua,

xianua, thioxianat, nitrit, thiosunfat, sunfit, axetat, amin, EDTA, etilendiamin u

bn.Hg+cng to c cc hp cht ni phc vi nhiu thuc th hu c.

3.3.3. Tnh cht oxi ha kh

a.

Ion Ag+

Ion Ag+c tnh oxi ha tng i mnh. Tuy vy Agvn tan c trong

cc cht oxi ha mnh nh HNO3, H2SO4c nng, HCl khi c cht oxi ha

Tnh kh ca Ag tng lnkhi c mt ca cc cht to phc hoc to hp cht t tan

vi ion Ag+. Ion Ag+b kh bi nhiu cht kh: Sn2+, Zn, cc cht hu c,

b. Ion Pb2+

Ch c tnh kh, d tan trong HNO3, H2SO4c nng, tan chm trong HCl

c, HI c do to phc PbCl3-, PbI4-.

Tnh kh ca ch tng ln trong cc dung dch to c mui ch kh tan.

c.

Ion Hg2+

Ion Hg2+

c th b kh thnh Hg22+

v sau n Hg.Hg ha tan trong cc

axit oxi ha nh HNO3, H2SO4c nng v I2(do to phc HgI42-bn). Ion Hg2+

b kh d dng bi cc kim loi, k c Cu, bi Sn2+, Fe2+,

Cc hp cht ca Hg22+

khng bn. Ion Hg22+

c khuynh hng t oxi ha

kh thnh hp cht tng ng ca Hg2+v Hg kim loi. Trong dung dchnc

phn ng ny xy ra chm. Tuy vy trong qu trnh to phc hay to hp cht kh

tan vi ion Hg2+th phn ng xy ra nhanh hn.

Khi un nng calomen Hg2Cl2 trong dd Cl- d s chuyn thnh phc

HgCl42-

v Hg.


26/54



3.3.4.Hp cht t tan

Hu ht cc mui Ag+u t tan tr mui nitrat, peclorat, florua, axetat

Cc mui bc halogennua c tan tng dn t iodua n clorua, do vy,

c th thy cc bc halogenua tan khc nhau trong dung dchamoniac: AgCl tannhiu, AgBr t tan hn v AgI hu nh khng tan.

Tr cc mui nitrat, axetat, peclorat hu ht cc mui ch u t tan, cc

mui ch halogenua u t tan: PbCl2, PbBr2, PbI.

Khi un nng nng tan ca nhng mui ny tng ln nhiu.Cc mui t

tan nht ca ch l PbCrO4mu vng, Pb3(PO4)2 mu trng, PbS mu en.

Hu ht cc mui ch u tan trong dd NaOH (tr PbS). Da vo y,

ngi ta phn bit kt ta sunfat ch v sunfat kim th bng tc dng ca NaOH.C nhiu hp cht t tan ca Hg2+: HgI2mu , Hg(SCN)2trng, HgS mu enl

hp cht t tan nhtca Hg2+khng tan trong HCl c, HNO3long, tan trong hn

hp (HNO3+ HCl) do tc dng oxi ha ion S2-

bi NO3-ng thi vi s to phc

ca Hg2+ vi Cl-. Hu ht cc hp cht ca Hg2+ u t tan tr cc mui nitrat,

axetat v peclorat. Hg2Cl2t tan mu trng, Hg2Br2, Hg2I2. Khi cho tc dng vi

vi NH3th Hg2Cl2chuyn thnh kt ta HgNH2Cl v Hg en.

3.3.5.

Phn ng ca cc ion

Cc cation ca nhm ny cho kt ta vi dung dch HCl long, ngui:

Ag+ + HCl AgCl + H+ TAgCl = 1 x 10

-10

Pb2+

+ 2HCl PbCl2 + 2H+ TPbCl2 = 2 x 10

-5

Hg22+

+ 2HCl Hg2Cl2 + 2H+ THg2Cl2= 1 x 10

-18

Nh vy, trong 3 clorua ni trn PbCl2kh kt ta nht. tan ca

PbCl2tng mnh theo nhit . Cn ch rng AgCl v PbCl2dtan trong dung

dch HCl c, v to thnh phc tan AgCl2-v PbCl3

-.


27/54



Cc mui clorua ca cc kim loicn li u c tan rt ln, v vy thuc

th nhm ca cc cation thuc nhm ny l dung dch HCl long, ngui. Bng

dung dch HCl long ngui, d va phi, chng ta tch c cc cation Ag+, Pb2+,

Hg22+

di dng kt ta ra khi hn hp cc cation khc. Ring cation Pb

2+

c tchs tan tng i ln nn khng kt ta hon ton s ln vo nhm phn tch th 2

khi dng thuc th nhm l dung dch H2SO4long, cng vi ru etylic.

c tnh ca cc mui clorua trn :

Cc kt ta clorua ca Ag(I), Pb(II) v Hg(I) kh tan trong nc v cc

dung dch axit v c long. Tuy nhin chng c cc c im khc nhau nh sau:

AgCl tan c trong dung dch NH3long v to phc bc (I) amoniac:

AgCl + 2 NH3 [ Ag(NH3)2]+

+ Cl-

Hg2Cl2tc dng vi NH3long to thnh 2 kt ta, 1 kt ta mu trng

NH2HgCl v 1 kt ta en Hg:

Hg2Cl2 + 2NH3 [NH2Hg]Cl + Hg + NH4Cl

PbCl2thc t khng tan trongNH3long. Phn ng ny dng nhn bit

Hg2Cl2khi c mt ng thi NaCl v PbCl2 (bng mu en kt ta ca Hg) v

dung dch NH3long dng tch AgCl ra khi hn hp 2 clorua cn li.

Da vo tan ca PbCl2tng theo nhit , c th dng nc khi un

nng tch PbCl2ra khi hn hp vi 2 clorua ca 2 kim loi cn li.

Sau y l phn ng ca cc cation nhm ny vi vi thuc th.

a. Vi H2S:

Cc cation ny to vi kh H2S hoc nc H2S cho kt ta rt kh tan Ag2S,

HgS v PbS, chng u mu en. Cc sunfua ny khng tan trong c HCl c,

Ag2S c PbS ch tan trong cc dung dch HNO3un nng, HgS ch tan trong nc

cng thu.

b.

Vi dung dch KI:

Ag+cho kt ta mu vng nht AgI ( T= 10-16) khng tan c trong NH3c

ch tan trong dung dch KCN v Na2S2O3v to thnh cc phc tan Ag(CN)2-v

Ag(S2O3)23-

.


28/54



Vi KI, ion Pb2+to thnh kt ta PbI2mu vng ti kh tan trong nc

lnh. Nhng khi un vi nc nng n tan nhiu thnh dung dch. ngui dung

dch , kt ta PbI2li xut hin di dng tinh th ln, vng ng nh rt c

trng.Vi dung dch KI, ion Hg2

2+lc u to thnh kt ta Hg2I2mu vng lc,

khi cho d thuc th, kt ta to thnh phc tan HgI42-

v Hg.

c.

Vi dung dch K2CrO4:

Ion Ag+to vi thuc th ny kt ta Ag2CrO4mu gch, tan c trong

dung dch axit axetic v cc axit v c long. Ion Pb 2+to vi thuc th ny kt

ta PbCrO4mu vng kh tan trong dung dch axit axetic long, nhng tan trong

dung dch axit v c. Ion Hg+

to vi thuc th ny kt ta Hg2CrO4mu khtan trong c axit HNO3long.

3.3.6.S phn tch cc cation nhm 3

Vic phn tch theo s c tin hnh nh sau: ly 1 n 1,5 ml dung

dch phn tch vo ng nghim, thm t t dung dch HCl long, lnh vo cho ti

d. Li tm, sau gn ly kt ta, thm vo 1- 1,5 ml nc ct, un nng. Sau

khi li tm gn ly nc lc (dung dch Pb2+) v ly kt ta 2. Thm dung dch KI

vo dung dch Pb2+, li tm ly kt ta vng tinh th gn nh bt. Ho tan kt ta

trong nc un nng ri ngui dung dch trong ng nghim. Sau mt lc thy

xut hin li cc tinh th ln mu vng, phn chiu nh sng rt p. Thm vo kt

ta 2 dung dch NH3thy xut hin kt ta mu en, chng t c Hg22+

. Li tm,

ly nc lc cha phc tan bc amoniac. Thm dung dch HNO3vo nc lc ,

thy kt ta trng xut hin li chng t c ion bc (I).


29/54




Dd phn tch + HCl long, d, lnh

Kt ta 1: AgCl,PbCl2, Hg2Cl2

+ H2O un nng

Dd Pb2+

+ KI

PbI2 ( mu vng)

Kt ta 2: AgCl,

Hg2Cl2

+ NH3

Kt ta 3:[NH2Hg]Cl

Hg( mu enca Hg)

Dung dch

+ DdHNO3

AgCl mutrng

Dd cc cation


30/54



3.4. Nhm 4: Cc cation to c hydroxit tan trong NaOH d: Be2+, Al3+,

Cr3+

, Zn2+

, Sn2+

, Sn4+

, Sb(III), Sb(IV), As(III), As(IV), Ga3+

, In3+

, .

Thuc th nhm ny l dung dch NaOH d v H2O2.

3.4.1.

Tnh cht acid baza.

Ion Zn2+

Dung dch nc ca ion Zn2+khng mu, c phn ng acid yu:

2 2

Zn H O ZnOH H

Khi kim ha Zn2+ trong kim d, cho ion ZnO22- khng mu. Khi kim

ha Zn2+bng NH3th ban u xut hin kt ta trng, sau tan ra do to phc

amoniacat.

b.

Ion Al3+

Dung dch nc ca Al3+c phn ng axit yu:

23 2

3 2 222

Al H O Al OH H

Al H O Al OH H

Nhm hidroxit c tnh cht lng tnh r rt.

c.

Ion Cr3+

Ion crom (III) Cr3+

, CrOH2+

mu xanh ve hoc tm. Dung dch nc ca

Cr3+c phn ng axit yu:

3 22

3 22 ( ) 22

Cr H O CrOH H

Cr H O Cr OH H

Hidroxit Cr(OH)3c tnh lng tnhtrong tnh axit v cng yu:

3( ) 33

( )3 2 2

Cr OH Cr OH

Cr OH H CrO H O


31/54




a.

Ion Zn2+

Zn2+to hp cht ni phc c mu vi nhiu thuc th hu c c dng

trong nh lng trc quang Zn

2+

. Zn

2+

toc nhiu phc cht khc nhau nh:- Phc t bn:phc vi axetat, clorua, florua, thioxianat, tatrat.

- Phc tng i bn: phc vi oxalat, sunfoxalixilat, axetylaxeton,

etilendiamin, amoniac.

- Phc rt bn: vi EDTA.

b.

Ion Al3+

Al3+c kh nng to phc vi nhiu cht, c bit l cc cht hu c c

nhm hidroxit nh xitrat, oxalat, tatrat, alizarin, aluminon. Phc vi EDTA khbn.Trong s cc phc cht v c, quan trng hn c l phc vi F-, cc phc vi

sunfat, hidrophotphat H2PO4-t bn hn.

c.

Ion Cr3+

Cr3+ to c cc phc clorua CrCl2+, CrCl2+ t bn.Cc phc vi sunfat

tng i bn. Cc phc vi oxalat, xitrat, xianua, EDTA kh bn.


a.

Ion Zn2+

Km c tnh kh mnh.2 2Zn Zn e 0,762 /

oE VZn Zn

Trong mi trng axit: 222

Zn H Zn H

Trong mi trng kim:

24 O 2 22 2

Zn OH Zn H O e 1,2162 /

2

oE VZnO Zn

Km tc dng c vi cc axit. Km tht nguyn cht tan rt chm trong

HCl. H2SO4long. Km thng mi cha tp cht (Cu, Cd, Pb) tan nhanh trong

cc axit trn do c hnh thnh trn b mt kim loi cc cp pin: Cu Zn, CdZn,

trong Zn ng vai tr Catot.


32/54



Km d tan trong HNO3 (vi nng HNO3 long dn) v H2SO4 c,

nng:

2 24 O 24 2 2

23 2 O 8 3 2 43 2

24 O 10 4 53 2 2

24 O 10 4 33 4 2

Zn SO H Zn S H O

Zn N H Zn NO H O

Zn N H Zn N O H O

Zn N H Zn NH H O

Trong mi trng bazyu, km khng phn ng v c hnh thnh lp oxit

bo v t tan.

b.

Ion Al3+

Al c tnh kh mnh. Al kh c hu ht cc ion kim loi nng thnh kimloi tng ng (Ag, Cu, Sn, Hg,). Tuy vy pH = 5 11, Al b bao ph bi lp

oxit bo v ngn cn hot ng ca n.

c. Ion Cr3+

Crom l mt kim loi c tnh kh mnh. Trong khng kh Crom b bao ph

bi mt lp oxit bo v ngn khng cho kim loi ny b n mn tip tc. Kim loi

c tnh th ng trong HNO3.

Ion Cr2+c tnh kh mnh, b oxi ha nhanh trong khng kh , phn ng

chm vi ion H+:

2 32 2 22

Cr H Cr H logK=13

Phn ng xy ra nhanh khi c mt cht xc tc Pt. Cr2+kh c hu ht

cc cht oxi ha khc ClO4-, NO3

-, Sn2+,

Ion Cr3+

b Zn hoc hn hng km kh trong mi trng axit thnh Cr2+.

Ion Cr2O72- c tnh oxi ha mnh trong mi trng axit.2 3O 14 6 2 7

72 2Cr H e Cr H O Eo=1,33V

Ion CrO42-ch b kh bi cc cht kh rt mnh. Cr3+ch b oxi ha trong

mi trng axit bi cc cht oxi ha rt mnh ( MnO4-, BiO3

-, S2O8

2-,).


33/54



3 2 2 22 3 7 O 6 O 1472 8 2 2 4

3 2 32 3 O 4 O 3 i 273 2 2

xtAgCr S O H O Cr S H

Cr Bi H Cr B H O

Trong mi trng kim, ion CrO2-b oxi ha d dng ( bi H2O2, Cl2,

Br2,) thnh CrO42-mu vng.

22 O 3 8 2 O 6 42 2 4 2

2O O O ( )2 4 2 4 2

22 O 3 2 2 O 42 2 2 4 2

Cr Br OH Cr Br H O

Cr Mn H O Cr MnO OH

Cr H O OH Cr H O

3.4.4.Hp cht t tan

Zn to c nhiu hp cht t tan: hidroxit, cacbonat, oxalat, xianua,

photphat, asenat, borat. ZnS kh tan nht trong s cc mui kh tan ca km. ZnS

kt ta c ngay c trong mi trng axit. ZnS tan trong axit mnh, khng tan

trong axit axetic v tan t trong kim :

222

ZnS H Zn H S

2 24 O 22 2

ZnS OH Zn S H O logK= -6,9

Mt s hp cht t tan ca nhm c ngha phn tch l nhm hidroxit,nhm photphat, nhm oxinat Al(Ox)3 tan c trong clorofom. Na3[AlF6],

Al[AlF6], AlAsO4cng u t tan.

Kt ta Al(OH)3bt u xut hin pH = 4 v ha tan thnh AlO2- pH =

10 13. Cc axit v c v nhiu axit hu c ha tan nhm hidroxit d dng. Ion

NH4+l axit qu yu khng ha tan c Al(OH)3v NH3l baz yu nn cng ha

tan Al(OH)3 khng ng k. Khi cho ion AlO2- tc dng vi cc axit rt yu

(NH4+, CO2+ H2O,) th c kt ta nhm hidroxit xut hin:

( )2 4 2 3 3

+CO 2 ( ) +HCO2 2 2 3 3

AlO NH H O Al OH NH

AlO H O Al OH

Ion Al3+phn ng vi cc dung dch cacbonat, sunfua, xianua, kim hoc

amoni sinh ra kt ta hidroxit m khng sinh ra cc mui tng ng:


34/54



2 33 O 2 3 ( ) 3 O3 2 3 2

2 33 2 3 ( ) 32 3 2

33 3 ( ) 3

2 3

C Al H O Al OH C

S Al H O Al OH H S

CN Al H O Al OH HCN

Crom to c cc hp cht t tan Cr(OH)3, CrPO4,Cr(VI) to c mt

s hp cht t tan quan trng trong ha hc phn tch: Ag2CrO4 gch,

Ag2Cr2O7, BaCrO4, PbCrO4 vng, SrCrO4 vng, cc cromat Cu2+

, Hg2+

, Fe3+

cng t tan.

Cc cromit kim loi kim d tan trong nc nhng cc cromit magie, km,

mangan, st u kh tan, v vy nu cho kim d tc dng vi dung dch Cr3+khi

c mt Mg2+

, Mn2+

, Fe2+

, Zn2+

th crom s tch hon ton hoc mt phn didng kt ta cromit ca cc kim loi . Tng t nhm, cc cacbonat, sunfua

kim to vi Cr3+kt ta hidroxit mu lc thm

3 22 3 O 3 Cr(OH) 3 O3 2 3 2

3 22 3 6 Cr(OH) 32 3 2

Cr C H O C

Cr S H O H S

3.4.5.Phn ng ca cc cation

Cc cation nhm ny tc dng vi cc dung dch NaOH, KOH d to thnhcc dung dich mui tan v hiroxit ca n lng tnh:

23 2 2 23 2 2

2 2 34 3 2

2 2 22 2 2

Al OH OH AlO H O

Cr OH OH CrO H O

Sn OH OH SnO H O

Zn OH OH ZnO H O

Nhng v ion CrO2-d to kt ta vi cc cation khc nh Mn2+, Fe3+.... nn

ngi ta dng dung dch NaOH d v thm H2O2 oxi ho CrO2- ln CrO4

2-

ng thi thuc th oxi ho Sn(II) ln SnO32-, Fe2+ln Fe3+, Sb(III) ln Sb(V).


35/54



a.

Tch Al(III) v Sn(IV):

Thm lng ddung dch NH4Cl vo dung dch kim dca cc cation

nhm ny v un nh th Al(OH)3v Sn(OH)4 s kt ta li, trong khi CrO42-

vn khng thay i, ZnO22-

s chuyn thnh [ Zn(NH3)4]2+

:NH4

+ + OH- NH3 + H2O

AlO2- + NH4

+ + 2H2O Al(OH)3 + NH3

SnO32- + 2NH4

+ + H2O Sn(OH)4 + 2NH3

ZnO22- + 4NH4

+ [Zn(NH3)4]2+ + 2 H2O

b.

Nhn bit Al3+:

Ho tan kt ta Al(OH)3v Sn(OH)4bng dung dch HCl long, sau

thm vo dung dch vi ht Zn, un nh kh Sn4+v Sn.

Sn4+ + 2Zn Sn + 2Zn2+

Lc, thu c dung dch cha Al3+v Zn2+, H+. Thm dung dch NH3vo

kt ta Al(OH)3, dng li tm ly kt ta ri nhn bit nhm bng dung

dch thuc th hu c alizarin s thu c kt ta sn nhm mu da cam rt

c trng.

c.

Nhn bit Sn(IV):

Ly kt ta Sn v Zn d, ho tan ht trong dung dch HCl 6M un nng thu

c dung dch cha Sn2+v Zn2+. Thm t t dung dch HgCl2vo dung dch

theo thnh ng nghim tm Sn2+.

SnCl2 + 2HgCl2 Hg2Cl2 + SnCl4

Nhn ra bng kt ta Hg2Cl2mu trng.

d. Nhn bit CrO4

2-:

Bn thn dung dch mu vng sau khi thm kim dv H2O2vo dung dchphn tch chng t c ion Cr3+:

2 Cr(OH)3 + 3 H2O2 + 4OH- 2CrO4

2- + 8H2O

nhn bit CrO42-ta dng phn ng sau: thm vo dung dch cha CrO4

2-

v v [Zn(NH3)4]2+

) vi git H2O2, thm vo 0,5 ml ruisoamilic, thm vo


36/54



thnh ng nghim dung dch H2SO4long v lc n khi lng axit d ta thy lp

ru isoamilic c mu xanh ca Cr2O5. C chca phn ng ny kh phc tp n

nay cha r rng.

e.

Nhn bit [Zn(NH3)4]2+

:

Thm vo dung dch cha ion ny v CrO42-dung dch Na2S, ZnS kt ta

trng s xut hin.


Lu :

Hiroxit Cu(OH)2cng c tnh lng tnh, tuy tnh axit khng ng k so vi

tnh baz. Nu trong dung dch phn tch c ion Cu2+, sau khi thm thuc th

nhm 3 l dung dch H2O2v NaOH dth dung dch nhm 3 c ion CuO22-

mu

xanh lam. Sau khi thm NH4Cl cn c Cu(NH3)42+. S c mt ca ion hon

ton ngn cn s pht trin ion km bng Na2S v khi CuS mu en s kt ta.

loi tr nh hng ca Cu(NH3)42+

ta lm nhsau:

Thm vo dung dch c mu xanh ca phc ng amoniacat vi git dung

dch KCN n khi dung dch ht mu xanh, v khi ion CN -kh Cu(II) v Cu(I)

v to phc Cu(CN)43-khng mu:

Cu(NH3)42+ + 2CN- Cu(CN)2 + 4NH3

2Cu(CN)2 2CuCN + (CN)2

CuCN + 3 CN- 2 Cu(CN)43-

Phc Cu(CN)43+

rt bn v khng mu nn khng cn tr s nhn bit ion

Zn(NH3)42+bng dung dch Na2S.


37/54




Dd phn tch + H2O2

+ NaOH d, un k

AlO22-, CrO4

2-,

SrO32-, ZnO22-

+ NH4Cl, to

CrO42-,

[Zn(NH3)4]2+

Chia lm 2phn

P1+ H2O2+H2SO4 l

+ ru amylic

Cr2O5

Lp ru mu xanh

P2+ Na2S

Kt ta ZnS mutrng

Kt taAl(OH)3,Sr(OH)4

+ HCl long

Al3+, Sn4+

+ Zn ht

Al3+, Zn2+

+ NH3 l, d

Al(OH)3

+alizarin

Kt ta sn nhmMu c rt

Sn vZn2+d

+ HCl

SnCl2

+ HgCl2

Hg2Cl2mu trng

Kt ta

nhm khc


38/54



3.5. Nhm 5: cc cation c hydroxit tan trong NH3hoc tan trong hn hp

NH3 + NH4Cl do to phc amin: Cu2+

, Co2+

, Ni2+

, Cd2+

, Hg2+

. Thuc

th nhm ny l dung dch NH3c.

3.5.1.

Tnh cht acid baza.

Ion Cu2+

Trong dd nc ion Cu2+c mu xanh lc. Dd c phn ng axit:

22

Cu H O CuOH H

Khi kim ha dd, miu xut hin kt ta mui baz, sau l hidroxit

mu xanh nht:

2 22 224 2 4

222 22 4 4

Cu SO OH Cu OH SO

Cu OH SO OH Cu OH SO

Khi un nng s chuyn thnhoxit CuO mu en. Trong dd kim rt mnh,

Cu(OH)2tan mt phn thnh anion CuO22-

mu xanh nht.

22 22 2 2Cu OH OH CuO H O

b.

Ion Cd2+

Ion Cd

2+

khng mu. Dd nc c phn ng axit yu:

22

2 2 222

Cd H O Cd OH H

Cd H O Cd OH H

Khi thm NaOH vo dd mui Cd2+, xut hinkt ta hidroxit mu trng.

Khi un nng kt ta ha vng do mt dn nc v sau chuyn thnh oxit mu

nu. Trong dd kim mnh, kt ta tan mt phn do to thnh cc phc hidroxo

Cd(OH)42-

, Cd(OH)53-

, v.vc.

Ion Ni2+

Ion Ni2+c mu xanh ve, dd nc c phn ng axit yu:

22

Ni H O NiOH H


39/54



Khi kim ha dung dch mi u c kt ta bazo, sau c kt ta hidroxit

Ni(OH)2mu xanh nht, tch ra pH = 7.Niken hidroxit tan trong axit, khng tan

trong kim d. Kt ta cng tan trong NH3v cc mui amoni do to phc amin.

d.

Ion Co

2+

Dung dchCo2+c mu hng nht, c phn ng axit yu:

22

Co H O CoOH H

Khi kim ha dung dch Co2+ mi u c kt ta mui baz sau l

Co(OH)2mu hng b oxi ha trong khng kh thnh Co(OH)3mu nu, t tan hn

nhiu.


a.

Ion Cu2+

Cc phc cht ca Cu(I) vi Cl-, NH3, CN-, S2O3

-u khng mu. Phc

cht ca Cu(I) vi NH3 tng i bn, phc cht ca Cu(I) vi CN- rt bn n

mc m cc mui sunfua Cu(I) khng th kt ta khi c CN-d. Cc phc vi Cl-,

Br-, F

-,t bn.

Cc phc cht ca Cu2+vi cc phi t khc nhau thng c mu c trng

(xanh, vng, nu).

b.

Ion Cd2+

Ion Cd2+to c nhiu phc cht vi cc phi t khc nhau vi s phi tr

cc i thng bng 4.Ion Cd2+ to c cc hp cht ni phc c mu vi nhiu

thuc th hu c. Cc phc vi Cl-, Br-, SCN- t bn. Phc tng i bn vi

amoniac, phckh bn vi CN-, EDTA.

c.

Ion Ni2+

Cc phc rt t bn: phc vi Cl-

, Ch3COO-

, F-

. Phc tng i bn: phcvi NH3, oxalat, thioxianat, pirophotphat, xitrat, sunfoxalixilat. Phc rt bn: phc

vi xianua, EDTA


40/54



d.

Ion Co2+

Phc t bn: cc phc vi axetat, sunfat, thiosunfat. Phc tng i bn:

phc vi amoniac, oxalat, xitrat, pirophotphat. Phc kh bn: phc vi xianua,

etylendiamin, trietylentetramin,3.5.3.Tnh cht oxi ha kh

a. Cu

Ion Cu2+

khngbn, n d dng t oxi ha kh:

22Cu Cu Cu

Cc axit oxi ha nh HNO3, H2SO4c, nng ha tan nhanh Cu.

Ion Cu2+b kh thnh Cu bi nhiu cht kh: Al, Fe, Zn, CdMt s cht kh

c Cu2+do sn phm kh l Cu(I) to c hp cht t tan hay phc bn.

b.

Cd

Cd c tnh kh mnh: 0,402 /

oE VCd Cd

. Cd c th kh c cc kim

loi nng nhng ion Cd2+li b Al, Zn kh thnh kim loi.

c.

Ni

2 2Ni e Ni 0,23oE V

Phn ng xy ra chm theo hai chiu.Ni tan chm trong dd HCl, H2SO4

long, tan d trong cc axit oxi ha.

d.

Co

Coban c nhiu trng thi oxi ha c tnh kh tng i mnh, d tan trong

cc axit long. Trong mi trng axit, Co3+l cht oxi ha rt mnh. Co2+c tnh

kh tng i yu.

3.5.4.Hp cht t tan

a s mui Cu(I) t tan, mu trng. Nhiu mui Cu(II) t tan. Cc mui

Cd2+

t tan thng gp l: cacbonat, oxalat, photphat, asenat

C nhiu hp cht t tan ca Ni: hidroxit, cacbonat, oxalat, sunfua

Hidroxit tan trong NH3v NH4+do to phc amin:


41/54



2

6 22 3 3 6Ni OH NH Ni NH OH

Cc hp cht Co(II) thng c mu hng hoc xanh. Cc hp cht ca

Co(III) c tan b hn cc hp cht tng ng ca Co(II).


c im ca cc cation nhm ny l s to phc vi dung dch NH3, v

vy, sau khi tch chng khi cc cation nhm 4, ta thu c dung dch phc

amoniac ca cc cation nhm ny. Tip theo ta thm dung dch ( NH4)2S vo

kt ta cc sunfat nhm ny gm: CdS, NiS, CoS, CuS, HgS. Sau y l tnh cht

cc sunfat nhm ny:

a.

CdSMu vng ti, c tch s tan T = 7,9 x 10-27. CdS tan trong dung dch

H2SO43M ...NiS v CoS u c mu en v c chung tnh cht l khng kt ta

c t dung dch axit bng kh H2S. Chng ch kt ta c t dung dch axit

bng dung dch Na2S hoc bng dung dch (NH4)2S. Nhng khi NiS v CoS kt

ta, chng nhanh chng b lo ho, chuyn dng tinh th, thay i cu trc phn t

c tch s tan nh i nhiu ln n mc khng tan c trong dung dch HCl c,

ch tan c trong dung dch HNO3un nng.

Hp cht Tch s tan T

CoS 4,0 x 10-12

CoS 2,0 x 10-25

NiS 3,2 x 10-19

NiS 1,0 x 10-24

NiS 2,0 x 10-26

Bng tch s tan cc dng NiS v CoS

b.

CuS

CuS mu en c tch s tan rt nh TCuS= 6,3 x 10-36, v vy, c th kt ta

t dung dch c axit kh cao bng chnh kh H2S. CuS ch tantrong dung dch


42/54



HNO3un nng theo phn ng oxi ho - kh trong ion sunfat b oxi ho thnh

S hoc kh SO2hoc SO42-

.

3CuS + 8HNO3 3 Cu(NO3)2 + 3S + 2NO + 4H2O

c.

HgSHgS mu en l sunfua c tan nh nht ( THgS= 1,6 x 10

-52). Khng tan

c trong dung dch HNO3un nng, ch tan trong dung dch nc cng thu.

Chnh v vy HgS kt ta c trong cc dung dch axit mnh c nng cao

bng dung dch kh H2S.

3HgS + 6HCl + 2HNO3 3HgCl2 + 3S + 2NO + 4H2O

3.5.6.Phn ng nhn bit cc cation nhm 5

a.

Cation Cd2+

Dung dch H2S trong nc (nc H2S) y c CdS mu vng t dung

dch axit c pH ln hn hay bng 0.

b.

Cation Cu2+

Thuc th thng dng i vi ion Cu2+tn ti trong dung dch axit l dung

dch NH3c. Dung dch thuc th ny to phc Cu(NH3)42+mu xanh lam m

rt c trng.

c.

Cation Ni2+

Phn ng c trng ca Ni2+l phn ng ca n vi thuc th hu c

imetylglioxim (H3CCNOH)2 trong dung dch amoniac to thnh kt ta mu

cnh sen sm rt c trng. y l phc vng cng khng tan trong NH3nhng tan

trong cc dung dch axit v c long. C th pht hin Ni2+bng phn ng nh

git dng thuc th ny khi c mt trong dung dch hn hp hu ht cc cation

khc

Phn ng tin hnh nh sau: Nh ln trn giy lc mt git dung dch

Na2HPO4, chm vo gia git mt git dung dch phn tch ri nh ln gia vt

chm dung dch imetylglioxim. Nu c mt ion Ni2+s thy mt vt hng hoc

cnh sen xut hin.


43/54



d.

Cation Co2+

Dung dch thuc th SCN-to vi ion Co2+ion phc Co(SCN)42-

mu xanh

c chit bng ru isoamylic. Phn ng rt nhy v rt c trng vi ion

Co

2+

. Ch cc ion Fe

3+

v Cu

2+

ngn cn. Fe

3+

c tch trong nhm 4.Cu2+c che bng dung dch Na2S2O3. V vy, ta tm Co

2+khi c mt Cu nh

sau: thm dung dch Na2S2O3vo ri thm ln lt dung dch SCN-v ru

isoamylic, lc hn hp. Nu c mt ion Co2+lp ru isoamylic s ho xanh.

e.

Phn ng ca cation Hg2+

Pha long dung dch axit cha ion Hg2+ri cho mt l ng mng nh vo.

Sau mt lc ly n ra, nu c Hg2+l Cu ban u mu s chuyn sang sng nh

bc, do Hg b y ra to thnh hn hng vi Cu:Cu + Hg2+ Hg(Cu) + Cu2+

3.5.7.Phn tch cc cation nhm 5

Sau khi tch cc cation nhm 5 ra khi nhm 4 ta c dung dch cc

cation ny trong mi trng (NH3+ NH4+). Thm vo dung dch (NH4)2S

kt ta tt c cc sunfua ca cc cation nhm 5, ta c kt ta mu en. Ra kt

ta vi ln bng dung dch NH4Cl ph keo sunfua v loi b kt ta d. un

nng kt ta vi dung dch HCl hoc H2SO4long 1,5M. Thu c dung dch

cha Cd2+. Pha long dung dch bng nc H2S nu c Cd2+ta c kt ta

mu vng ti.

Ho tan cc sunfua khc trong kt ta en bng dung dch HNO3long un

nng. Chia dung dch thu c thnh 4 phn v ln lt tn cc cation Cu2+, Hg2+,

Co2+

v Ni2+

nh trnh by trn.


44/54



3.6. Nhm 6: cc cation to c hydroxit t tan trong nc, tan trong

acid: Fe3+

, Fe2+

, Mg2+

, Mn2+

, Bi2+, cc cation ca cc nguyn t t

him,Thuc th nhm ny l dung dch NaOH v H2O2, sau l

HNO3v H2O2.3.6.1.Tnh cht acid - baz

a. Ion Fe2+

, Fe3+

Dung dchFe2+mu xanh nht, c phn ng axit yu.

22

Fe H O FeOH H

Dung dchFe3+c phn ng axit mnh hn.

3 2

2Fe H O FeOH H

Khi kim ha dung dchFe2+ thy xut hin kt ta trng Fe(OH)2nhanh

chng b oxi ha thnh Fe(OH)3mu nu trong khng kh. C hai hidroxit trn

u tan rt t trong kim d.

b.

Ion Mg2+

Dung dchnc ca ion Mg2+khng mu, c phn ng gn nh trung tnh:

22

Mg H O MgOH H logK= -12,8

Mg(OH)2t tan trong nc, tan c trong dd mui amoni:

22 2 22 4 3 2Mg OH NH Mg NH H O logK= -1,48

c. Ion Mn2+

Dung dchnc ca Mn2+mu hng nht, c phn ng axit yu:

22

Mn H O MnOH H logK= -10,6

Khi kim ha dung dchthy xut hin kt ta trng Mn(OH)2d tan trongcc axit long v mui amoni, tan t trong kim do to thnh phc hidroxo, d b

oxi ha trong khng kh thnh MnO(OH)2hay H2MnO3mu nu rt t tan trong

nc v kh tan trong axit.


45/54




a.

Ion Fe2+

, Fe3+

Cc phc ca Fe2+vi clorua, sunfat, thiosunfat, thioxianat t bn. Cc phc

vi oxalat, axetat, tatrat, sunfoxalixilat tng i bn. Cc phc rt bn vixianua, EDTA, dimetylglioximrt bn.Cc phc cht ca Fe3+nhiu hn v bn

hn cc phc cht tng ng caFe2+.

b.

Ion Mg2+

Cc phc cht ca ion Mg2+ thng rt t bn: phc vi sunfat, florua,

axetat, clorua, amoniac, mt s phc tng i bn nh phc vi EDTA.

c.

Ion Mn2+

Mn2+

to c cc phc cht t bn vi axetat, thioxianat, amoniac, oxalat,sunfat, phc cht tng i bn vi EDTA.

Mn(III), Mn(IV) thng tn ti dng phc bn v rt bn.


a.

Fe

Fe c tnh kh mnh: 2 2Fe e Fe . Fe tan c trong cc axit long,

kh c nhiu ion kim loi thnh kim loi tng ng (Ag, Sb, Pb).Trong mi

trng axit, Fe3+c tnh oxi ha v Fe2+c tnh kh.

b.

Mg

2 2Mg e Mg

Magie c tnh kh cc mnh. N kh chm ion H+ ca nc ( khi nh

sch lp oxit trn b mt). Mg tan trong cc axit. N kh c phn ln cc ion

kim loi thnh kim loi tng ng.

c.

Mn

Mn c tnh kh mnh. Mn(III) c tnh oxi ha mnh, Mn(IV) c tnh oxi

ha tng i mnh, Mn2+c th b oxi ha thnh MnO2bi nhiu cht oxi ha

mnh nh HNO3c, MnO4-Mn(VI) MnO4

2-c tnh oxi ha trong mi trng

kim.Mn(VII) th hin tnh oxi ha rt mnh trong mi trng axit.


46/54



3.6.4.Hp cht t tan

a.

Fe

Cc mui fer t tan: Fe2O4, FeCO3, FeCrO4, FeS, oxinatCc hp cht t

tan ca Fe(III) u kh tan hn cc hp cht tng ng ca Fe(II).b.

Mg

Mt s mui t tan ca Magie: asenat, oxalat, cacbonat, florua, photphat

Khi thm chm mui kim ca cc axit yu vo dung dchMg2+th c kt

ta Mg(OH)2 xut hin, khi thm thuc th th c th xut hin mui t tan v

trong thc t thng xut hin hn hp hidroxit v mui t tan ca magie.

c.

Mn

C nhiu hp cht t tan ca Mn2+

: cacbonat, asenat, photphat, oxalat,

sunfuaMnS mu hng nht, tng i t tan, tan d trong cc axit long.


c im ca cc cation nhm ny l to hiroxit M(OH)nch c tnh baz

khng tan trong thuc th kh kim d. V vy, thuc th nhm ny v cc cation

nhm ny l dung dch NaOH d c mt H2O2. Tc dng ca H2O2 l oxi ho

Cr3+thnh CrO42-, oxi ho Sb(III) ln Sb(V) v hiroxit Sb(OH)3cng lng tnh.

Khi di tc dng ca thuc th nhm ni trn, Mn(II) s to thnh MnO2mu

en:

Mn2+ + H2O2 + 2OH- MnO2 + 2H2O

Khi cho tt c cc cation nhm ny s tn ti di dng kt ta mu en.

Khi dng thuc th nhm l dung dch kim d v H2O2, cc cation nhm 5: Cu2+,

Cd2+

, Hg2+

, Ni2+

, Co2+

cng c kt ta di dng hiroxit M(OH)ncng vi cc

cation nhm 6 trn y.

3.6.6.Tch cc cation nhm 6 khi cc cation nhm 5

Ho tan kt ta cc hiroxit cation nhm 5,6 cng MnO2bng dung dch

H2O2v HNO3:

M(OH)n + nH+ Mn+ + nH2O

MnO2 + H2O2 + 2H+ Mn2+ + O2 + 2H2O


47/54



un si k dung dch phn hu H2O2d. Trung ho va ht lng axit

dbng cch thm tng git dung dch NaHCO3vo lc u cho n khi dung

dch thong c ca cc vt hiroxit cc kim loi mi to thnh. Thm vo dung

dch lng d dung dch NH3 kt ta ht hiroxit nhm 6 (Fe(OH)3, MnO2,Sb(OH)5, Mg(OH)2, Bi(OH)3). Li tm tch nhm 5 di dng dung dch phc

amoniacat Cu(NH3)42+

, Cd(NH3)42+

, Ni(NH3)62+

, Co(NH3)62+

.

3.6.7.Nhn bit cc nhm cation nhm 6

a.

Nhn bit Mg2+

Sau khi tch cc cation nhm 6 khi cc cation nhm 5, nhm 6 tn ti d-

i dng hiroxit M(OH)nv MnO2. Trong s cc hiroxit ca cc kim loi thuc

nhm 6 ch c mt mnh Mg(OH)2c tan ln nht. Tch s tan ca n l6.10-12v vy ch mt mnh Mg(OH)2tan c trong dung dch NH4Cl:

Mg(OH)2 + 2NH4+ Mg2+ + 2NH3 + 2 H2O

nhn bit Mg2+ta tin hnh nh sau: cho kt ta nhm 6 tc dng vi

dung dch NH4Cl, lc ly nc, cho tc dng vi dung dch Na 2HPO4, ion Mg2+

s

cho kt ta tinh th MgNH4PO4.

b. Nhn bit Sb(III) v Sb(V)

Sau khi ho tan kt ta hiroxit cc kim loi nhm 6 v MnO2bng dung

dch HNO3c mt mt t dung dch H2O2ta c dung dch cha ion Sb(III) v

Sb(V). Chia dung dch thu c thnh cc phn nh. tm Sb, ngi ta dng

dung dch thuc th hu c rodamin B. Dung dch nc ca thuc th ny c

hunh quang mu vng. Khi thm thuc th vo dung dch cha ion SbCl6-ta

thu c mt dung dch mu tm v mt phc ion lin hp c chit bng benzen

to thnh dung dch mu cnh sen trong benzen. Lc ta thy dung dch nc

c hunh quang mu tm cn lp benzen trn c mu cnh sen rt c trng.

c.

Nhn bit Fe3+

Ly mt phn dung dch nhm 5 cho tc dng vi dung dch KSCN hoc

NH4SCN ta c dung dch c mu mu m rt c trng.

d.

Nhn bit Mn2+


48/54



Ly mt t dung dch nhm 6 (vi git) cho tc dng vi mt dung dch

gm 2 ml dung dch (NH4)S2O8hoc K2S2O8vi git dung dch AgNO3(lm cht

xc tc) v un nng nh, ion Mn2+s b oxi ho to thnh MnO4-mu tm rt

c trng:2Mn2+ + 5S2O8

2- + 8H2O 2 HMnO4 + 10 SO42- + 14H+

e.

Nhn bit ion Bi3+

Ly mt t dung dch nhm 5, c thm 1 ml dung dch SnCl 2, nu thu c

mt dung dch c mu vng ti ca ion BiI4-l c mt ion Bi3+. S c mt ca

SnCl2l cn thit v trong dung dch c mt HNO3, khi ta thm dung dch KI vo,

n s b oxi ho thnh I2 mu vng, nu. SnCl2s kh I2 thnh I-khng mu,

khng gy nh hng n qu trnh tm ion Bi3+.

Bi3+ + 4I- BiI4-


49/54



Chng 4: PHN TCH CC ANION TRONG DUNG DCH

NC THEO H THNG AXIT BAZ

4.1.

Nhm 1: gm cc anion halogenua: Cl-, Br-, I-, S2-, CN-,

SCN-

,...

Anion nhm 1 to kt ta khng tan trong HNO3vi thuc th AgNO3v

khng to kt tavi Ba2+.

4.1.1.Tnh cht ch yu ca anion nhm 1

Tnh cht ch yu ca anion nhm 1 c trnh by bng sau:

Anion

Thuc thCl

- Br

- I

- S

-

AgNO3/ HNO3AgCl2

trng

AgBrtrng

ngAgIvng

Ag2Smu

en

Kt ta ca Ag+

trong NH3

Tan, to phc

[Ag(NH3)2]+

Tan, to phc

[Ag(NH3)2]+

Khng tan Khng tan

Nc Clo ca

Ag+trong dung

mi hu c

KhngC mu bng

nht do Br2

C mu

tm do I2b

y ra

Khng

KMnO4,

K2Cr2O7Khng

Gii phng

Br2I2thot ra

Gii phng S

t do

Cht kh KNO2

hoc NaNO2Khng Khng I2thot ra Khng

Dung dch Pb2+ PbCl2trng AgBr2trng

PbI2vng,

tan trong

nc nng

PbSen

HCl Khng Khng Khng H2Sthi

Na2[Fe(CN)5NO

] trong kimKhng Khng Khng

To phc

[Fe(CN)5NO]

2- tm


50/54



4.1.2.Phn tch mt s anion nhm 1

a.

Kim tra s b

Axit ha dung dch mu bng HNO3 2N sau thm t t thuc th

AgNO3.Nu c S

2-

th kt ta Ag2S mu en xut hin, nu c I

-

th c kt tavng xut hin, Nu c Br- th c kt ta AgBr ng trng xut hin v cui cng

nu c mt Cl-th c kt ta trng AgCl xut hin.

b.

Pht hin anion S2-

- Cch 1: Tm t giy lcbng dung dch Pb(CH3COO)2 trong kim d,

sau nh git dung dch ln t giylc, nu c S 2-th giy lc xut hin

vt loang en ca PbS.

- Cch 2: Cho HCl vo dung dch mu, nu c S

2-

th H2S s bc ln c mitrng thi c trng. Nu cho hi ca H2S tip xc vi giy lc c tm Pb

2+

th c vt en xut hin.

c.

Pht hin I-

Tm h tinh bt (dung dch 1% trong nc) ln giy lc, sau thm 1 git

dung dch HCl 2N, 2 gii dung dch HNO2v 1 git dung dch mu. Nu giy lc

xut hin mu xanh l c I-, v I2gii phng ra tc dng vi h tinh bt c mu

xanh.

2 2 4 2 22 2 2

I NO H I NO H O

d. Pht hin Br-

Ly 1 ml dung dch mu cho vo ng nghim, sau cho thm 1 ml H 2SO4

v 2ml Benzen ri thm 2-3 git nc Clo, nu c mu vng trn lp benzen th c

Br-. Nu c mt I-th u tin I2 gii phng ra s lm lp benzen c mu nu, ta

thm tip vo 2-3 git nc clo, lc k th mu nu bin mt, mu vng xuthin chngt c Br-

e.

Pht hin Cl-

Axit ha dung dch mu bng HNO36N, sau thm AgNO3, un si, kt

ta s xut hin, tch v ra sch kt ta. Ha tan hon ton bng NH31/1, nu


51/54



cn kt ta th tch ra, ly phn dch tin hnh axit ha bng HNO3, nu ly kt ta

trng tch ra l c Cl-

4.2. Nhm 2: gm cc anion: SO42-

, SO42-

, S2O32-

, PO42-

, CrO42-

, Cr2O72-

,

SiO32-

, BO

2-

, B4O72-

,...Anion nhm 2 to kt ta vi Ag+v Ba2+, kt ta tan trong HNO3.

4.2.1.Tnh cht ca anion nhm 2

a.

Vi thuc th BaCl2

Anion nhm 2 tc dng vi thuc th to thnh hp cht t tan, Da vo tan,

ngi ta chia anion nhm 3 lm 3 phn nhm nh:

- Phn nhm 1: To kt ta khng tan trong nc v khng tan trong

CH3COOH long, HNO3long gm cc anion: SO42-, SiF6, IO3-.- Phn nhm 2: To kt ta khng tan trong nc v CH3COOH nhng tan

trong HNO3long, gm cc anion: CrO42-, SO3

2-, S2O32-.

- Phn nhm 3: Ta kt ta km tan trong nc, nhng tan trong CH 3COOH

v HNO3long gm: PO42-, AsO4

3-, CO32-, SiO3

2-, BO2-, B4O7

2-.

b. Vi thuc th AgNO3:

- Vi thuc th AgNO3to kt ta vi anion nhm 2 khng tan trong nc

nhng tan trong dung dch NH3v HNO3long.

- a s cc kt ta c mu trng v mt s t c mu khc bit:

+ Mu trng: Ag2SO3, Ag2S2O3, Ag2CO3, Ag2SiO3,...

+ Mu vng: Ag3PO4, Ag3AsO3,...

+ Mu gch: Ag2CrO4

+ Mu : Ag2Cr2O7

+ Mu nu: Ag3AsO4, Ag3[Fe(CN)6].

4.2.2.Phn tch mt s anion nhm 2:

a.

Pht hinSO42-

Kim tra mi trng dung dch mu, nu thy axit th tin hnh trung ha

bng Ba(OH)2, thm thuc th BaCl2nu thy kt ta th c anion nhm 2. Lc,


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ra sch kt ta, sau ha tanbng HNO3nu kt ta khng ht l khng c

SO42-, nu khng tan ht v khng phi dng keo l anion nhm 2 c c SO4

2-.

b. Pht hin S2O3

2-

-

Bng phn ng vi thuc th KMnO4trong mi trng H2SO42N, nu cS2O3

2- th mu tm s b mt.

- Cho dung dch mu tc dng vi AgNO3s c kt ta trng xut hin l

Ag2S2O3. Nu gia nhit s thy kt ta en ca Ag2S tc l c S2O32-

c.

Pht hin SO32-

Cho dung dch mu tc dng vi thuc th Sr(NO3)22N c kt ta

SrCO3(ion S2O32-khng cho kt ta nu c mt). Tch v ra kt ta bng nc

nng. Thm 1-2 gii dung dch I20,1N nu thy mt mu I2l c SO32-

d.

Pht hin CO32-

Cho dung dch mu tc dng vi axit v c (HCl, HNO3) nu thy kh bc

ln ta cho i qua dung dch Ba(OH)2hay Ca(OH)2, c kt ta trng xut hin th

c anion CO32-.

e. Pht hin anion PO43-

- Tt nht l cho tc dng vi thuc th hn hp Magie, nu c kt ta trng

NH4MgPO4l c ion PO43-.

- Dng thuc th amoni molipdat (NH4)2MoO4trong mi trng HNO3, nu

c kt ta vng l c mt PO43-.

f. Pht hin BO2-

- Dng hn hp ru CH3OH v H2SO4c: C cn dung dch mu sau

tm ru metylic CH3OH v thm H2SO4c:

hp cht B(CH3O)3 l eterboric, nu cho nn ngn la th ngn la s b

nhum mu xanh tc l c ion BO2-

g.

Pht hin SiO32-

Tt nht l dng axit v c cho vo dung dch mu, nu c kt ta dng keo

th chc chn c SiO32-

.


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4.3. Nhm 3: gm cc anion NO3-, NO2

-, (SO4

2-),...

Anion nhm 3 khng to kt ta vi c hai cation Ag+ v Ba2+. Trong

SO42-l trng hp c bit ca anion nhm 2 v BaSO 4khng tan trong HN3 v

Ag2SO4ch kt ta nng ln (T = 1,6.10

-5

).4.3.1. Phn ng ca nhm anion NO-2

Axit HNO2l axit yu khng bn. Nu axit ha dung dch cha ion

NO2- v gia nhit th HNO2s phn hy.

3HNO2 HNO3+ 2NO + H2O

Cc mui nitric a s tan tt trong nc, km tan ch c AgNO2.

a.

Vi thuc th KI

Trong mi trng axit nh NO2-

tc dng vi I-

gii phng I2 lm choDung dch c mu nu tm

2NO2 + 2I- + 4H+ 2NO + I2 + 2H2O

b.

Vi thuc th Diphenylamin

Trong mi trng axit H2SO4, nu c NO2- s tc dng vi thuc th

Dephenylamin c mu xanh tm c trng.

c.

Vi thuc th Naftyl amin.

Trong mi trng axit H2SO4, ion NO2-phn ng iazo ha vi thuc

th lm cho dung dch c mu tm ( hay Anh o ).

4.3.2.Phn ng ca NO3-

Axit HNO3 l axit mnh c tnh oxi ha, cc mui nitrat hu ht tan tt

trong nc

a. Vi thuc th Diphenylamin

Cho mt lng nh diphenylamine vo 1ml H2SO4 c sau cho dung

dch mu vo, nu c ion NO3-th dung dch c mu xanh tm c trng.

b.

Phn ng nitro ha.

un cn 1ml dung dch mu, cho thm vo cn kh 1ml H 2SO4c, 1ml

benzen v khuy, dm cn thn. Sau khi hn hp chia thnh 2 lp ta ly 1 git


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lp dung mi benzen cho ln giy lc v cho t bc hi. Nu c NO3-ta s ngi

thy mi c trng ca nitro benzen bc ln.

4.3.3.Phn tch nh tnh anion nhm 3

a.

Pht hin anion NO2-

:Dng phn ng thuc th KI trong mi trng axit , nu c NO2

-th dung

dch c mu tm.

b. Pht hin anion NO3-.

- Nu trong mu khng c ion NO2-th ta dng thuc th diphenylamine nu

dung dch mu xanh tm l c NO3-.

- Nu trong dung dch c mu NO2- th phi loi NO2

-bng cch un dung

dch mu vi NH4Cl :NaNO2+ NH4Cl N2

-+ NaCl + H2O

Hoc dng Urea trong mi trng axit :

2HNO2 + CO(NH2)22N2-+ CO2+ H2O

Dung dch sau khi loi NO2- cho tc dng vi Diphenylamin , nu xut hin

mu xanh tm l c NO3-.

---Ht---

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