7/24/2019 Thi Ltttpt

1/3

thi l thuyt thc tp phn tch 1Kha 2011-2015Thi gian 120 pht

1.

Mt hn hp cha cc cation c nghi ngl Mn2+, Cu2+, Cd2+, Ni2+v Zn2+.Hy nghquy trnh chi tit tch nh danh cc ion ny (trong khunkhni dung thc tp c hc). Vit cc phng trnh phn ng minhha. (3im)-Tch v xc nh Mn(II): dng NH4Cl v NH3chnh pH n 9, thm 1 git H2O2,un nng nhkt ta MnO(OH)2en. Ly tm tch ta, ra ta sch. Thm 3git HNO3, un cho tan. Thm 1 mL pha long. Thm KIO4, un nngdungdch hng.Mn(II)Mn(NH3)6

2+MnO(OH)2.

MnO(OH)2Mn(II)MnO4-.

-

Tch Zn(II) khi cc nguyn tcn li v xc nh Zn(II): dung dch sau khitch Mn(II) c thm NaOH n pH 14, un si kn gn ht mu xanh. Lytm tch ta.M(NH3)n

m+ + NaOH M(OH)i+ CuO + ZnO2

2-.

Dung dch cha Zn(II). Dng HCl trung ha n pH 5, thm Na2S, ly tm lyta, ra sch ta. Thm CH3COOH, un nh, ly tm bta, ly phn dch trongcha Zn(II)

ZnO22-

+ HCl Zn(II); lng nhM(OH)I + HCl MCli.Zn(II) + M

i+ + Na2S ZnS + M2Si

ZnS + M2Si + CH3COOH Zn(II) + M2Si

Trung ha dung dch cha Zn(II) vpH 7 kt ta trng ZnS.-

Xc nh Cu: Kt ta M(OH)Ic ha tan trong 2 git HCl. Thm Na2SO3,un nh. Thm KSCNta trng. Ly tm ly ta, ra ta. Ha tan ta bng 1git HNO3, dung dch xanh, khi nu thm NH3 6M dung dchxanh m Cu(NH3)4

2+.

Cu(II) + Na2SO3 + KSCN

CuSCNCuSCN + HNO3Cu(II) + NO2

Cu(II) + NH3Cu(NH3)42+

.

-

Xc nh Co: Dung dch sau khi tch Cu(II) c thm ethylacetate, lc mnh.Dung dch tch thnh 2 pha, pha ethylacetate c mu xanh ca phcCo(SCN)4

2-.

7/24/2019 Thi Ltttpt

2/3

- Xc nh Ni(II): tch bphn pha ethylacetate, dng NH3chnh pH dung dch

vpH 8, thm dimethylglyoximkt ta Ni(DMG)2. Ly tm.- Xc nh Cd(II): tch bphn ta Ni(DMG)2, thm Na2Sta vng CdS.

2. C thxc nh chnh xc nng HCl bng cht gc Na2CO3c khng?Hy gii thch v phc tho quy trnh chun , iu kin chun v chncht chthph hp? (2im)C!

Na2CO3l 1 dibaz yu c pKb= 3.98 < 4 nn khng thchun ring tng ncn 99% xem xt chun tng 2 nc. pKb2= 7.65 l kh yu nn nu CNa2CO3=0.1 M th pKb+ pCo+ pD = 7.65 + 1 + 0.3 = 8.05 > 8 (khng chun c n99.9%). Tuy vy do H2CO3 dbay hi nn thot ra khi dung dch, ni rng

khong bc nhy nn thc tc thchun chnh xc. Quy trnh chun : phachdung dch cht gc nng 0.1M, CHClnn xp x0.1 M. Phng trnh chunHCl + Na2CO3 NaCl + CO2 + H2O. Np HCl vo buret, ly chnh xc10 mL vo erlen, chthmethylcam hoc pT 5.1. Chun c kt hp lc mnh,un nng nhn chthchuyn mu.

3. Chun xc nh ring NaHCO3v Na2CO3 trong hn hp. Hy nu tmtt nguyn l v cch thc hin chun ? Da vo nguyn l chun vthc t thc hin hy nh gi v chnh xc (ng + lp) ca kt

qu? (2im)Chun nc 1: CO3

2- + H+ HCO3-.: ch th pT 8.3 dng xc nh ring

Na2CO3.

Chun tng nc 1+2: CO32-

+ HCO3- + H

+ CO2+ H2O chthpT 5.1; 5.4

hoc methylcam dng xc nh tng Na2CO3v NaHCO3. Nng NaHCO3ctnh bng tng 2 nc tri nc 1. Chun nc 1 cn thc hin nhanh, lc thtnh. Chun tng 2 nc cn lc tht mnh, kt hp un nng khi ti gn imtng ng.Do khong bc nhy nc 1 hpkh c im cui nm trong bc nhy (theo

nh tnh ton l thuyt). Ngoi ra do smt mt CO2nn lm dch chuyn cnbng HCO3CO2+ CO3

2-+ H2O sang bn phi v nh vy php chun nc 1

lun mc sai s tha nng Na2CO3 lun cao hn thc t nng NaHCO3lun thp hn thc t.

7/24/2019 Thi Ltttpt

3/3

4.

Trong chun complexon, ti sao khi dng chthNET th phi dng mammoniac v khi dng chthXO th phi dng m acetate? (1 im)-

Ch th NET: mu ca dng phc thng l mu hng, mu ca ch th tythuc vo pH v thc tl mu chm trong khong 7-11. Thng dng khong

pH ny trong chun c mu tng phn. m ammoniac c m nng ttnht trong khong 9.25 1 nn lun i km vi chthNET.-

ChthXO: mu ca dng phc thng l mu hng tm, mu ca chthtythuc vo pH v thc tl mu vng trong khong 0-6. Trong thc tphn ngchun complexon vi mt skim loi chnh lng trong khong pH 4-6.Thng dng khong pH 4-6 trong chun c mu tng phn. macetate c m nng tt nht trong khong 4.75 1 nn lun i km vi chthXO.

5.

Nng Cu2+

c thxc nh bng chun complexon v chun oxyhakh. Bng l thuyt v thc nghim hc, hy nh gi chnh xc cakt quxc nh Cu2+bng hai php chun ny. (1.5 im)-

Chun Cu(II) bng complexon ti pH 8, chthmurexide l php chun trc tip, chuyn mu rt tng phn. EDTA l cht gc nn kt quCu(II) cchnh xc cao.

- Chun Cu(II) bng oxyha khl php chun gin tip thng qua iodine.Cht chun Na2S2O3 khng phi l cht gc, phi chun ha li cng qua 1

phn ng chun gin tip khc nn chnh xc ca nng thiosulfate rt

km. I2 trong cc phn ng chun ha thiosulfate v chun Cu(II) dbayhi nn gy sai shthng. Tm li chnh xc ca nng Cu(II) c c

bng cc phn ng chun gin tip v c lin quan ti I2l rt km.

6. nh lng ion Ca2+bng phng php trng lng. Hy vit phng trnhphn ng tokt ta ng thca Ca2+. (0.5 im).

Ca2+

+ H2C2O4+ (NH2)2CO + H2O

CaC2O4+ CO2 + 2NH4+

HT