thuc hanh olympic.doc

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MT S BI TH NGHIM THC HNH THEO CHNG TRNH OLYMPICV Gio dc Trung hc B Gio dc v o to

Bi 1. Xc nh St c trong thuc vin cha StL thuyt St l mt thnh phn thit yu ca hng cu (hemoglobin), gip vn chuyn oxi trong mu n mi phn ca c th. N cng gi vai tr sinh t trong nhiu phn ng trao i cht. Thiu st c th gy bnh thiu mu l h qu ca mc hng cu trong mu thp. Thiu st l s suy dinh dng khong cht ph bin nht trn th gii. Mt cch gim s thiu ht st l cha tr bng vin cha st. Hot cht trong thuc vin cha st l st(II) hin din trong thuc vin kho st di dng st(II) fumarat. Ngoi hp cht hu c st(II) ny, thuc vin c cha cc cht khc nh nhng tc nhn lin kt. Cu trc ca axit fumaric l:OH O O OH

Axit fumaric St(II) v 1,10-phenanthroline to phc c mu vng cam/ [(C12H8N2)3Fe]2+. Mt quang (absorbance) ca phc ny, xc nh ti 510 nm trong dung dch m (pH=8) l mt php o hm lng st ca vin thuc. Do 1,10-phenanthroline ch lin kt vi st(II) v st(II) d b oxi ha thnh st(III), thm hidroxiamoni clorua (hydroxylammonium chloride) kh ton b st(III) thnh st(II). Mt s phn ng n gin l: 2 NH2OH + 4 Fe3+ N2O + 4 H+ + H2O + 4 Fe2+N N

1,10-Phenanthroline

1,10 phenantroline

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Thit b v Ha cht tin hnhTHIT B HA CHT

Cn Ci, chy s; Cc 100 mL; Thit b siu m (ultrasonic bath); Bp in; Phu Hirsch cha mt lp nh cht gip lc nhanh; Bnh nh mc 250 mL v 100 mL; Pipet; Quang ph k; Phng php tin hnh

Vin thuc cha Fe (II) HCl 4M; Dung dch 1,10-phenanthroline; Dung dch hydroxylammonium chloride;

Dng cn xc nh khi lng ca vin thuc cha st chnh xc n 1 mg. Vin thuc c tn cn thn thnh bt trong mt ci v chuyn nh lng vo cc 100 mL bng mt lng nh nc ct. Thm axit clohidric (5 mL, 4 M). un nng cc cht trong cc n khong 60 oC trn bp in. Dung dch i sang mu vng. t cc vo thit b siu m (ultrasonic bath) trong t nht 5 pht. Gi cc n nh bng mp xp (styrofoam). Phu Hirsch cha mt lp nh cht gip lc nhanh (Hi-flo filter aid) c lm m v p cht trn lc, dng phu ny lc huyn ph bng cch ht. Ra cht gip lc nhanh (Hi-flo filter aid) bng lng d nc ct. Nc lc c chuyn cn thn vo bnh nh mc (250 mL) v thm nc ct, khuy lin tc iu chnh th tch cui. Dng pipet ht 10 mL dung dch ny v cho vo bnh nh mc 100 mL. Li iu chnh th tch bng nc ct ng thi khuy u. T dung dch ny, dng pipet ly 10 mL v cho vo bnh nh mc 100 mL. Sau , thm dung dch 1,10-phenanthroline (10 mL) v dung dch hidroxi

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amoni clorua (hydroxylammonium chloride) (1 mL) . K tip, iu chnh th tch dung dch bng dung dch m (pH 8). Mt quang ca dung dch ny c o bng my so mu (quang ph k) ti 510 nm so vi nc trong cuvet 1,000 cm. Hy tnh lng st trong vin thuc cha st da trn hp th mol (h s tt, e) bit ca phc st(II) phenanthroline ti 510 nm. hp th mol ca phc st(II) phenanthroline ti 510 nm bng 11100 M-1cm-1. Quan trng lai b sai lch trong mt quang khi ni vi my so mu s dng, mt h s iu chnh c ghi trn my so mu hc sinh dng trong th nghim. Mt quang quan st c cn phi nhn vi h s ny thu c mt quang ng ca dung dch phc st.

Bi 2. Xc nh cc mu v c cha bitL thuyt C 12 mu cha bit ng trong ti bng cht do bao gm 9 dung dch cha bit, mi dung dch c ng trong ng nh git v 3 mu cht rn ng trong ba l ming rng. Tt c cc mu cha bit u c nh s vi 3 ch s. Hy kim tra cn thn cc m s mu theo danh sch cc mu v c cha bit ri vit s bo danh v tn ca mnh vo t giy. (Danh sch c km theo cc mu cha bit ca hc sinh). Mi l ng cht rn c khong 20 miligam di dng bt hoc tinh th ca mt hp cht tinh khit. Mi ng nh git cha khong 1,5ml dung dch ca mt hp cht tinh khit c ha tan trong nc ct. Nng ca cc dung dch cha bit nm trong khong t 0,05 n 0,5 M(mol/lit). Cc dung dch cha bit l nh sau: HCl NaOH Ch : H2O2 Na2CO3 H2SO4 Na2SO3 ZnCl2 BaCl2 NH4SCN K4Fe(CN)6

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(1) C 2 mu cha bit c lp li. (2) H2O kt tinh trong tinh th ngm nc c b qua trong cc cng thc cho trn. Trn bn th nghim ca hc sinh c mt hp nha ng cc dng c, mu cha bit v cc thuc th c s dng trong bi thc hnh ny. Danh sch cc dng c Dng c in cc dy Pt Hp ng pin Bn lm trng nh git Ko ct Tha cph Danh sch thuc th Thuc th KI FeCl3 S lng. 1 1 1 1 2 Dng c in cc dy Au Pin Bn mng bng nha mu en ng nh git (1 mL) S lng. 1 2 1 5

Nng . Thuc th 0.1M pp (phenolphtalein) 0.1M Dung dch tinh bt

Nng . 0.01 0.01

Mc c hi v an ton ca cc ha cht Ha cht Axit clohidric Axit sunfuric Dung dch Natri hidroxit Dung dch Hydroperoxit Dung dch Natri cacbonat Dung dch Bariclorua Dung dch Natrisunfit Dung dch Km clorua Dung dch Kali Cng thc HCl H2SO4 NaOH H2O2 Na2CO3 BaCl2 Na2SO3 ZnCl2 K4Fe(CN)6 c hi 36/37/38 35 35 22-41 36 20-25 31-36/37/38 22-34-50/53 32 an ton 26 26-30-45 26-36/37/39-45 26-39 22-26 45 26-36 26-36/37/39-45-6061 22-24/25

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hexaxyanoferat (II) Dung dch Amoni thioxyanat St (III) clorua (rn) Kali iotua (rn) Dung dch tinh bt Cht ch th Phenolphthalein Tin hnh

NH4SCN FeCl3 KI -

20/21/22-32-52/53 22-34 40

13-61 26-36/37/39-45 22-24/25 * 36/37

1. S dng bn thuc th c cp, cc phn ng gia cc mu cha bit vi nhau v thit b in phn n gin nhn bit cc mu cha bit v vit tr li ca em (di dng s vi 3 ch s - nh cch nh s mu ca cc mu cho) vo cc trng trong t phiu tr li.Ch : Sau khi kt thc cng vic hy cho hai dy vng (Au) v Platin(Pt) v cc pin vo ccti nilon ban u ca chng ri li tt c dng c v ha cht (k c cc mu cha bit) vo hp nha ng v tr ban u.

2. Trong bi thc hnh ny hc sinh thc hin mt lot php th xc nh (hoc khng nh) cc mu cha bit. Hc sinh cn nm c cc phn ng ho hc lin quan n cc php th tin hnh v vit c cc phng trnh phn ng: A. Vit phng trnh in phn xy ra dng ion rt gn c ghi trng thi tn ti khng nh mt mu cha bit l dung dch cha ZnCl2. B. Vit mt phng trnh phn ng dng lm sch kt ta Zn trn b mt in cc bng cc dng c v ha cht cho trong bi ny.

Bi 3. Xc nh cacbonat v hiro photphat trong mt mu lm cht mi L thuytNa2CO3, CaCO3 v Na2HPO4 l cc thnh phn chnh ca cc bt mi. Trong bi th nghim ny, phi xc nh cc ion cacbonat v hiro photphat trong mt mu mi bng hai chun axit-baz.223

u tin, thm mt lng chnh xc axit clohiric (c ly vi lng d) vo mu th. Phn ng xy ra, hiro photphat chuyn thnh H3PO4, cn cc ion cabonat chuyn thnh CO2 sau thot ra ht khi b un si. Cc ion canxi c ban u trong mu chuyn vo dung dch. V cc ion ny c th nh hng n kt qu phn tch nn chng c kt ta trong CaC2O4 v lc b trc khi chun . Tip n, axit photphoric va to thnh c chun bng dung dch NaOH c nng chnh xc vi hai cht ch th khc nhau l: Bromcrezon xanh (Bromocresol Green, BCG) v Thymolphthalein (TP). Bc th nht ca chun ny l: H3PO4 (v lng d HCl) c chun ti ion H 2PO4-, im kt thc bc chun ny c mi trng hi axit (pH khong ~4.5). im ny lm cho BCG chuyn t mu vng sang mu xanh. Bc th hai ca chun ny: tip tc bc trn cho ti khi to ra HPO42-. im kt thc bc hai ny xy ra khi TP khng mu chuyn sang mu xanh (mi trng c tnh kim, pH vo khong 10). Lng ion CO32- trong mu c tm ra khi da vo lng khc nhau gia: a) b) Lng cht chun ng vi lng ban u ca HCl ( dng ha tan mu) Lng cng ca cht chun ng vi im kt thc chun th hai (ch th TP). Lng ion HPO42- c tm ra khi da vo lng khc nhau gia lng cht chun dng t ti hai im kt thc chun (ch th TP v BCG). Thit b v Ha cht tin hnhTHIT B HA CHT

Cn Phu lc; Cc 100 mL; ng ong; Bp in; Bnh hnh nn (Erlenmeyer);

Bt mi cha Na2CO3, CaCO3 v Na2HPO4 HCl 1M; Nc ct Dung dch K2C2O4 15%; Dung dch NaOH;

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Bnh nh mc 100 mL; Pipet;

Dung dch Thymolphthalein (TP) Dung dch BromoCresol Green (BCG)

Qui trnh tin hnhBc 1. Ha tan mu v ui CO2 Thm ng 10,00 mL dung dch HCl nng khong 1 mol/L (xem tr s chnh xc ny c ghi trn nhn ca l) vo mu bt mi c trong cc c y bng mt knh ng h thy tinh (mi thao tc phi chnh xc: ly dung dch bng mt pipet! Khng c b np y cc ra trnh tht thot ha cht! ). Sau giai on thot kh mnh kt thc, dng bp in cn thn un nng dung dch trong cc (vn phi y cc bng mt knh ng h) ti khi ht kh thot ra. Tip n, un cn thn dung dch cn li trong cc cho si trong khong 2-3 pht. Bc 2. Kt ta canxi Nhc cc khi bp in. Dng nc ct ra phn hi nc ngng t mt knh ng h cho chy vo cc. Dng ng ong ly 1-2 mL dung dch K2C2O4 15%. Cho t t lng ny theo thnh vo cc (mt khong 10 n 20 pht) cho ti lc kt ta hon ton. Dng khong thi gian ch i ny xc nh nng chnh xc ca dung dch NaOH (theo phng php di y). Bc 3. Xc nh nng chnh xc ca dung dch NaOH Dng mt pipet ly 10,00 mL dung dch HCl ri cho vo bnh nh mc 100 mL, thm nc ct cho n vch, lc bnh trn u. Rt dung dch NaOH y buret. Dng pipet ly 10,00 mL dung dch HCl trong bnh nh mc cho vo mt bnh hnh nn (Erlenmeyer). Thm vo erlenmeyer ny 1-2 git dung dch Thymolphthalein ri chun bng dung dch NaOH ti khi mu xanh xut hin trn vng xoy ca dung dch v bn ch trong khong 5 - 10 giy. Ti y v phn sau: Hy lp s chun mc cn thit. Cn lu rng tr s th tch dung dch cn dng nhiu nht v t nht ch cch nhau c 0,10 mL. S liu th tch dung dch bo co c chnh xc ti 0,01 mL.

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3.1a Hy in y vo bng trong Phiu tr li. 3.1b Hy tnh nng ca dung dch NaOH (theo mol/L). Bc 4. Lc b canxi oxalat Sau khi kt ta c hu ht CaC 2O4, dng phu lc dung dch vo bnh nh mc 100 mL. Nc lc ny hi b c do c mt lng nh canxi oxalat nhng khng gy nh hng ti vic chun . Dng nc ct ra sch kt ta ri b giy lc c kt ta vo thng ng rc. Thm nc ct vo bnh ng nc lc cho ti vch v lc u. Bc 5. Chun mu dng Bromocresol Green Dng pipet ly 10,00 mL nc lc thu c sau bc 4 cho vo mt Erlenmeyer ri thm tip vo 3 git dung dch BCG. Hy chun b mt Erlenmeyer khc c dung dch i chng gm 3 git dung dch NaH2PO4 15%, 3 git dung dch BCG v 15-20 mL nc ct. Dng dung dch NaOH chun dung dch nc lc ti khi mu ca dung dch ny trng vi mu ca dung dch i chng th dng. 3.2 Hy in y vo bng trong Phiu tr li. Bc 6. Chun mu dng Thymolphthalein Dng pipet ly 10,00 mL nc lc thu c sau bc 4 trn cho vo mt Erlenmeyer ri thm tip vo 2 git dung dch TP. Dng dung dch NaOH chun dung dch nc lc ti khi mu xanh xut hin v bn trong khong 5 10 giy th dng. 3.3 Hy in y vo bng trong Phiu tr li. Bc 7. Cc tnh ton 3.4. Hy tnh khi lng ca CO32- trong mu dng. 3.5. Hy tnh khi lng ca HPO42- trong mu . Bc 8. Cc cu hi thm cho bi th nghim ny Hy tr li cc cu hi sau y vo Phiu tr li. 3.6a. Hy ch ra mt phn ng (vit phng trnh) lm cn tr s phn tch mu