1942010_nhietnhomtimFexOy

8/12/2019 1942010_nhietnhomtimFexOy

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PHNG PHP TM NHANH CNG THC PHN T CA OXIT ST

TRONG PHN NG NHIT NHM

1. c im ca phn ng nhit nhm- Khi cho bt Al tc dng vi oxit st (FeO, Fe3O4, Fe2O3) nhit cao, ban u cn cung cpnhit cho phn ng xy ra, nhng sau , phn ng to nhiu nhit v xy ra nhanh.

- Trong phn ng, cho d s oxi ho ca st trong oxit l bao nhiu th cng s to thnh Fe,mc d oxit st cn d.

2. Cch tm nhanh cng thc phn t ca oxit st- Cn xc nh sau phn ng cht no ht, cht no d hay phn ng va

+ Nu Al d, cht rn sau phn ng tc dng vi dung dch NaOH s gii phng kh

+ Nu FexOyd, cht rn sau phn ng tc dng vi dung dch NaOH s khng c khthot ra v cht rn b ho tan 1 phn- Nu c vit phng trnh phn ng, t n, lp phng trnh v gii h th s mt rt nhiuthi gian. xc nh nhanh cng thc ca FexOyth cn tm t l mol gia Fe v O c trong

oxit.- p dng nh lut bo ton khi lng th khi lng ca oxi trong oxit st s bng lng oxic trong oxit nhm sau phn ng.V d 1 :Tin hnh phn ng nhit nhm 9,66 gam gm bt Al v FexOytrong iu kin khngc khng kh, thu c hn hp X. Nghin nh, trn u X ri chia thnh hai phn bng nhau.Phn mt ho tan ht trong dung dch HNO3un nng 1,232 lt kh NO duy nht ktc. Cho

phn hai tc dng vi lng d dung dch NaOH un nng thy gii phng 0,336 lt kh H2ktc. Cc phn ng xy ra hon ton. Cng thc ca st oxit l

A. FeO B. Fe2O3 C. Fe3O4 D. FeO hoc Fe3O4

Cch gii thng thng :Cc phng trnh phn ngot

x y 2 32yAl 3Fe O yAl O 3xFe (1)

Hn hp cht rn sau phn ng tc dng vi dung dch NaOH c kh thot ra nn cn d Al vFexOy ht. Cht rn X gm Fe, Al2O3v Al d.- Phn mt tc dng vi dung dch HNO3:

Al2O3 + 6HNO3 2Al(NO3)3 + 3H2O (2)

Fe + 4HNO3 Fe(NO3)3 + NO + 2H2O (3)

Al + 4HNO3 Al(NO3)3 + NO + 2H2O (4)

- Phn hai tc dng vi dung dch NaOH :

Al2O3 + 2NaOH 2NaAlO2 + H2O (5)

2Al + 2NaOH + 2H2O 2NaAlO2 + 3H2 (6)Gi s mol Al2O3, Fe v Al d trong mi phn ln lt l a, b v c theo cc phn ng ta c

NO

1,232n 0, 055 mol

22,4 ;

2H

0,336n 0, 015 mol

22,4 ; khi lng mi phn : 4,82 g

Theo cc phn ng ta c : 102a + 56b + 27c = 4,83 (I)Theo (3) v (4) : b + c = 0,055 (II)Theo (6) c = 0,01, tm c b = 0,045 v a = 0,02

Theo phn ng (1) ta c t l mol

2 3

Fe3 4

Al O

n 3x 0, 045 x 3 Fe On y 0, 02 y 4


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Cch gii nhanh :Ta c th tm tt bi ton theo s

Nhanh chng tnh c 2 3Fe Al On 0, 045; n 0, 02 mol

x y 2 3 2 3O (trong Fe O ) O (trong Al O ) Al On n 3n 3.0, 02 0, 06

Do nFe: nO= 0,045 : 0,06 = 3 : 4 FexOyl Fe3O4. p n : CV d 2 : Sau phn ng nhit nhm hn hp cha Al v FexOy(khng c khng kh) thu c92,35 gam cht rn X. Ho tan X bng dung dch NaOH d thy c 8,4 lit kh (ktc) bay ra vcn li mt phn khng tan Y. Ho tan ht Y cn 240 gam axit H2SO498% (gi s ch to thnhmt loi mui st (III)). Cng thc ca FexOy l

A. FeO B. Fe2O3 C. Fe3O4 D. FeO hoc Fe3O4

Hng dn :

otx y 2 32yAl 3Fe O yAl O 3xFe

2 2 22Al 2NaOH 2H O 2NaAlO 3H

2 3 2 2Al O 2NaOH 2NaAlO H O

2Fe + 6H2SO4 Fe2(SO4)3 + 3SO2 + 6H2O

Theo cc phng trnh ho hc (hoc s dng phng php bo ton electron) tnh c :nFe= 0,8 mol; nAl d = 0,25 mol;2 3Al O

m 92, 35 0, 25.27 0, 8.56 40, 8 gam

S mol O trong FexOybng s O c trong Al2O3hay

2 3O Al O

40,8n 3.n 3. 1, 2 mol

102 ; Vy nFe: nO= 0,8 : 1,2 = 2 : 3 Fe2O3

V d 3 :Tin hnh phn ng nhit nhm hn hp gm Al v FexOythu c hn hp cht rnX. Cho X tc dng vi dung dch NaOH d thu c dung dch Y, phn khng tan Z v 0,672 litkh H2. Cho dung dch HCl vo Y n khi c lng kt ta ln nht, lc kt ta, nung tikhi lng khng i thu c 5,1 gam cht rn. Cho Z tc dng vi dung dch H 2SO4 c

nng, sau phn ng ch thu c dung dch E cha mt mui st duy nht v 2,688 lit kh SO2.Bit cc kh u o ktc, cc phn ng xy ra hon ton.

Cng thc phn t ca st oxit lA. FeO hoc Fe2O3 B. FeO hoc Fe2O4

C. Fe2O3hoc Fe3O4 D. Fe2O3

Cch gii nhanh:

otx y 2 32yAl 3Fe O yAl O 3xFe

2 2 22Al 2NaOH 2H O 2NaAlO 3H

o2 3

2t

2 4x y2 4 3 2d -

A l O N a O HA l HF e _ __ _ _

H SOFe OFe F e (SO ) SOA l

o2 3

2t

3x yd-

Al O NaOHAl H

Fe _____HNOFe O

NOAl

2

2 3

2 2 3

2 4x y4 2 4 3 2d-

HNaOHAl O

Al NaAlO Al OFe _____

H SOFe OFe FeSO / Fe (SO ) SOAl


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2 3 2 2Al O 2NaOH 2NaAlO H O

Cht rn X c nAl d = 0,2 mol;2 3Al O

m 0, 04 mol v Fe

- Trng hp 1 : Mui duy nht thu c l Fe2(SO4)3

2Fe + 6H2SO4 Fe2(SO4)3 + 3SO2 + 6H2O

2Fe SO

2 2 2, 688n n . 0, 08 mol3 3 22, 4

S mol oxi trong Al2O3(trong X) chnh bng s mol oxi trong FexOy.

2 3O Al On 3.n 3.0, 04 0,12 mol

Vy nFe: nO= x : y = 0,08 : 0,12 = 2 : 3 Fe2O3- Trng hp 2 : Mui duy nht thu c l FeSO4

2Fe + 6H2SO4 Fe2(SO4)3 + 3SO2 + 6H2O

Fe + Fe2(SO4)3 3FeSO4

Fen 0,12 mol . Vy nFe: nO= x : y = 0,12 : 0,12 = 1 : 1 FeO. p n : A

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1942010_nhietnhomtimFexOy