thi mn Phn Tch nh Lng Lp Ha 2006, 06/01/2009, 9:15

Thi gian: 120 pht (khng tnh 5 pht c ) Cu 1. (4 im)

Acid oxalic, H2C2O4, l mt acid yu 2 chc c pKa1=1.25 v pKa2 = 4.27 c xem l mt cht chun gc trong chun acid baz. Chun dung dch H2C2O4 0.1N bng NaOH 0.1N.

Hy: 9 Thit lp iu kin chun . 9 V ung cong chun . 9 La chn cht ch th ph hp. 9 Tnh cc sai s ch th m cc SV la chn.

Cu 2. (6 im) Hm lng Fe trong mt mu thin thch uc xc nh bng chun oxyha kh vi KMnO4.

Phn tch vin thc hin phn tch lp 3 ln nh sau: ha tan mi -g mu trong acid v dng ct Walden kh nh lng Fe3+ v Fe2+. Chun bng KMnO4 vi hn hp bo v Zymmerman, tn Vi mL.

Ln lp i Khi lng mu (mi) Th tch KMnO4 tiu tn (Vi)

1 0.4185 41.3

2 0.3529 35.2

3 0.4046 40.2

Nng KMnO4 c xc nh bng dung dch chun gc H2C2O4 (0.1000 0.0004)N. Ht 10 mL dung dch H2C2O4 dung dch chun gc vo erlen, thm 1 mL H2SO4 c, un nng n khong 70 oC. T buret cha KMnO4, chun chm H2C2O4 cho n khi dung dch trong erlen c mu hng bn trong 30s. Ghi ly th tch KMnO4 tiu tn. Chun lp 4 ln c th tch KMnO4 tiu tn l: 8.00; 8.03; 7.99; 7.97 mL. Cho VEVE o MnHMnO

oFeFe 51.1,77.0 2423 /8,/ == ++++ , [H

+] = 2N, pipet = 0.02 mL, cn = 0.0002 g, MFe2O3 = 159.69 (g/mol) 9 Hy nu cu to v cch s dng ct Walden 9 Vit cc phng trnh phn ng xy ra trong th nghim ny. 9 V ung cong chun gia Fe2+ v KMnO4 9 Vai tr ca hn hp Zymmerman. Gii thch 9 Vai tr ca H2SO4 v nhit trong phn ng chun gia H2C2O4 v KMnO4. Gii thch 9 Tnh % theo khi lng Fe2O3 trong mu thin thch c km theo sai s.

Ghi ch: Sinh vin uc php mang vo phng thi bng tm tt cc cng thc trong chng trnh phn tch nh lng do PGS. TS. C Thnh Long.