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Au-K31-DHQN

ien cac solieu vao

N+5 +3e N+2

O0 +2e O-2

Fe -3e Fe+3

m/56 3m/56

Somol Fe =m/56, vay somol e nhng = 3m/56

0,1somol NO =0,1 . vay somol e nhan trong phan ng nay =0,3 (1)

0,3

16

12-m 12-m8

somol oxi =(12-m) / 16, vay somol e anhan =(12-m) / 8 (2)

T(1) va(2): tong somol e anhan =0,3 + 12-m8

Do tong somol e nhan =tong somol e nhng nen: 0,3 + 12-m =83m56 . Giai PT ta c m=10,08 (g)

m gam bt kim loi st ngoi khng kh mt thi gian, thu c 2,792 gam hnhp A gm st kim loi v ba oxit ca n. Ha tan tan ht hn hp A bng dung

dch HNO3long, thu c mt mui st (III) duy nht v c to 380,8 ml kh NOduy nht thot ra (ktc). Tr s ca m l?

Gii: Tng t m=2,24 (g).

m gam phoi bo st (A) ngoi khng kh, sau mt thi gian bin thnh hn hprn (B) c khi lng 13,6 gam. Cho B tc dng hon ton vi dung dch axit sunphuric c nng thy gii phng ra 3,36 lt kh duy nht SO2 (dktc). Tnh khi lng m ca A?Gii: Cng ging nh axit HNO3, H2SO4 c nng cng oxi ha Fe v cc oxit ca nn Fe+3.

Fe0 Fe, Fe xOy+O 2 Fe+3 , SO 2

H2SO4 +4+6

Quatrnh phan ng :

Thay cos thay oi sooxi hoa Fe, lu huynh, OxiFe -3e Fe+3 S+6 +2e S+4 O

0 +2e O-2

ta co: m Fe=m nFe=m/ 56

mFe +mOXI= moxit mOxi =moxit - mFe =13,6 - m n O=

13,6-m16

nS(+4) =n SO2=0,15

ien cac solieu vao

S+6 +2e S+4

O0 +2e O-2

Fe -3e Fe+3

m/56 3m/56

Somol Fe =m/56, vay somol e nhng = 3m/56

0,15somol SO 2 =0,15 . vay somol e nhan trong phan ng nay =0,3 (1)

0,3

16

13,6-m 13,6-m8

somol oxi =(13,6-m) / 16, vay somol e anhan =(13,6-m) / 8

13,6(g)m(g)

(2)

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Au-K31-DHQN

Ho tan m(g) hn hp gm Fe v cc oxit ca Fe trong HNO3 d thu c 4,48l NO2 v 145,2 g mui khan . Tnh m? Tng t: 46,4g.

Cho 20 gam hn hp X gm Fe, FeO, Fe3O4, Fe2O3 tan va ht trong 700 ml dung dchHCl 1M thu c 3,36 lt H2 (ktc) v dung dch D. Cho dung dch D tc dng vi NaOHd, lc kt ta v nung trong khng kh n khi lng khng i thu c cht rn Y.Khi lng Y l:Gii:Phn tch bi ton:Hn hp X tan trong HCl s to mui: mui Fe(II) v mui (III). Hai loi mui ny tc dngvi kim s to hai loi hidroxit: Fe(OH)2 v Fe(OH)3. Cc Hidroxit nynung trong khngkh uthu c Fe2O3.Quy i hh X v 2: Fe v Fe3O4

Gi s mol ca Fe v Fe3O4 ln lt l a, b. ta c : 56a + 232b =20 (1)

FeHCl Fe2+ , H2 (0,15 mol)

Fe2+ , OH-

Fe(OH)3 [O]

Fe2O3

Fe3O4 HCl

3Fe3+, 3H2O

Fe3+

S mol st = nH2= 0,15Vy nFe3O4= 20- 56*0,15 = 11,6Vy nFe3O4= 11,6 / 232 = 0,05Theo nh lut bao ton s mol nguyn t , ta c (tng s mol st trong chat tham gia = tng

s mol st sn phm)Tng s mol Fe = nFe + 3nFe3O4= 0,15 + 3*0,05 =0,3Vy s mol Fe2O3= 0,3/ 2 = 0,15.mFe2O3= 0,15* 160 = 24 (g). Ha tan hon ton 25,6 (g) cht rn X gm: Fe, FeS, FeS 2 , S bng dd HNO3 d, thot

ra V lt kh NO (sn phm kh duy nht ktc) v dd Y. Thm Ba(OH)2 d vo Y thu c126,25 g kt ta. Xc inh V ?

Gii:Quy i hh X v 2 nguyn t: Fe v SGi x, y ln lt l s mol ca Fe, S. Ta c: 56x+ 32y = 25,6 ( 1)

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Au-K31-DHQN

Cc qu trnh trao i e:Fe 3e = Fe+3

x 3x xS - 6e = S+6

y 6y 6y N+5 + 3e = N+2

z (mol) 3z znh lut bo ton e: 3x + 6y = 3z (2)Cho Ba(OH)2 vo Y thy xut hin kt ta, trong ddY cha SO42- , Fe3+.Vy cc kt ta l Fe(OH)3 v BaSO4.Theo nh lut bo ton s mol nguyn t:S mol S+6= s mol ion SO42- = s mol BaSO4 =6yS mol Fe3+ = s mol Fe(OH)3= xTa c : 107*x + 233*6y = 126,25 (3)

(1) V (3): x= 0,2, y = 0,45 (4)(2) V (4) : z= 1,1.V= 1,1*22,4 = 24,64 (l)