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Transcript of giải nhanh kim loại
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I BI TP V XC NH TN KIM LOI
1) C th tnh c khi lng mol nguyn t kim loi M theo cc cch sau:
- T khi lng (m) v s mol (n) ca kim loi M =m
n
- T Mhp cht Mkim loi
- T cng thc Faraday M =m.n.F
I.t(n l s electron trao i mi in cc)
- T a < m < b v < n < m
Mn
a b< = n No duy nht m = 3 v n = 2 x = y = 0,1 mol
- T (1) M = 56 Fe v % M = 70 % p n D
V d 3: Hn hp X gm hai mui cacbonat ca 2 kim loi kim th hai chu k lin tip.
Cho 7,65 gam X vo dung dch HCl d. Kt thc phn ng, c cn dung dch th thu c
8,75 gam mui khan. Hai kim loi l:A. Mg v Ca B. Ca v Sr C. Be v Mg D. Sr v Ba
Hng dn:
- t cng thc chung ca hai mui l 3MCO . Phng trnh phn ng:
3 2 2 2MCO + 2HCl MCl + CO + H O
- T phng trnh thy: 1 mol 3MCO phn ng th khi lng mui tng: 71 60 = 11 gam
- Theo bi khi lng mui tng: 8,75 7,65 = 1,1 gam c 0,1 mol 3MCO tham gia
phn ng
M + 60 = 76,5 M = 16,5 2 kim loi l Be v Mg p n C
V d 4: Ha tan hon ton 6 gam hn hp X gm Fe v mt kim loi M (ha tr II) vo
dung dch HCl d, thu c 3,36 lt kh H2 ( ktc). Nu ch ha tan 1,0 gam M th dng
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khng n 0,09 mol HCl trong dung dch. Kim loi M l:
A. Mg B. Zn C. Ca D. Ni
Hng dn: nH2 = 0,15 mol
- nX = nH2 = 0,15 mol M X = 40
- ha tan 1 gam M dng khng n 0,09 mol HCl 2M
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+ M l kim loi c hiroxit lng tnh (nh Al, Zn)
M + (4 n)OH + (n 2)H2O MO2n 4 + H2 (da vo s mol kim loi kim hoc kim
th s mol OHri bin lun xem kim loi M c tan ht khng hay ch tan mt phn)
2) Mt s v d minh ha:
V d 1: Hn hp X gm Na, K, Ba ha tan ht trong nc d to dung dch Y v 5,6 lt kh
( ktc). Tnh V ml dung dch H2SO4 2M ti thiu trung ha Y
A. 125 ml B. 100 ml C. 200 ml D. 150 ml
Hng dn: nH2 = 0,25 mol
Ta c nOH = 2nH2 m nOH
= nH+ nH2SO4 = OHHnn
2 2
-+
= = nH2 = 0,25 mol V =
0,125 lt hay 125 ml p n A
V d 2: Thc hin hai th nghim sau:
Th nghim 1: Cho m gam hn hp Ba v Al vo nc d, thu c 0,896 lt kh ( ktc)
Th nghim 2: Cng cho m gam hn hp trn cho vo dung dch NaOH d thu c 2,24
lt kh ( ktc) Cc phn ng xy ra hon ton. Gi tr ca m l:
A. 2,85 gam B. 2,99 gam C. 2,72 gam D. 2,80 gam
Hng dn: nH2 th nghim 1 = 0,04 < nH2 th nghim 2 = 0,1 mol th nghim 1 Ba
ht, Al d cn th nghim 2 th c Ba v Al u ht
- Gi nBa = x mol v nAl = y mol trong m gam hn hp
- Th nghim 1:
Ba + 2H2O Ba2+ + 2OH + H2
x 2x x
Al + OH + H2O AlO2 +3
2H2
2x 3x
nH2 = 4x = 0,04 x = 0,01 mol
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- Th nghim 2: tng t th nghim 1 ta c: x +3y
2= 0,1 y = 0,06 mol
m = 0,01.137 + 0,06.27 = 2,99 gam p n B
V d 3: Ha tan hon ton 7,3 gam hn hp X gm kim loi Na v kim loi M (ha tr n
khng i) trong nc thu c dung dch Y v 5,6 lt kh hiro ( ktc). trung ha dung
dch Y cn dng 100 ml dung dch HCl 1M. Phn trm v khi lng ca kim loi M trong
hn hp X l:
A. 68,4 % B. 36,9 % C. 63,1 % D. 31,6 %
Hng dn: nH2 = 0,25 mol ; nHCl = 0,1 mol
- Gi nNa = x mol v nM = y mol 23x + My = 7,3 (1)
- Nu M tc dng trc tip vi nc 2H
x ny
n = + =0,0252 2 nOH
= 0,5 > nHCl = 0,1
loi
- Nu M l kim loi c hiroxit lng tnh (n = 2 hoc 3):
M + (4 n)OH + (n 2)H2O MO2n 4 +n
2H2
y (4 n)y ny/2
- Do OH d nn kim loi M tan ht v nOH d = x (4 n)y mol x (4 n)y = 0,1 (2)v x + ny = 0,5 (3) y = 0,1 mol
- Thay ln lt n = 2 hoc 3 vo (1) ; (2) ; (3) ch c n = 3 ; x = 0,2 ; M = 27 l tha mn
%M = 36,9 % p n B
III BI TON V KIM LOI TC DNG VI DUNG DCH AXIT
1) Kim loi tc dng vi dung dch axit:
a) i vi dung dch HCl, H2SO4 long:
M + nH+ Mn+ + n/2H2
(M ng trc hiro trong dy th in cc chun)
b) i vi H2SO4 c, HNO3 (axit c tnh oxi ha mnh):
- Kim loi th hin nhiu s oxi ha khc nhau khi phn ng vi H2SO4 c, HNO3 s t s
oxi ha cao nht
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- Hu ht cc kim loi phn ng c vi H2SO4 c nng (tr Pt, Au) v H2SO4 c ngui
(tr Pt, Au, Fe, Al, Cr), khi S+6 trong H2SO4 b kh thnh S+4 (SO2) ; So hoc S-2 (H2S)
- Hu ht cc kim loi phn ng c vi HNO3 c nng (tr Pt, Au) v HNO3 c ngui
(tr Pt, Au, Fe, Al, Cr), khi N+5 trong HNO3 b kh thnh N+4 (NO2)
- Hu ht cc kim loi phn ng c vi HNO3 long (tr Pt, Au), khi N+5 trong HNO3
b kh thnh N+2 (NO) ; N+1 (N2O) ; No (N2) hoc N-3 (NH4+)
c) Kim loi tan trong nc (Na, K, Ba, Ca,) tc dng vi axit: c 2 trng hp
- Nu dung dch axit dng d: ch c phn ng ca kim loi vi axit
- Nu axit thiu th ngoi phn ng gia kim loi vi axit (xy ra trc) cn c phn ng
kim loi d tc dng vi nc ca dung dch
2) Mt s ch khi gii bi tp:
- Kim loi tc dng vi hn hp axit HCl, H2SO4 long (H+ ng vai tr l cht oxi ha) th
to ra mui c s oxi ha thp v gii phng H2: M + nH+ Mn+ + n/2H2 (nH+ = nHCl +
2nH2SO4)
- Kim loi tc dng vi hn hp axit HCl, H2SO4 long, HNO3 vit phng trnh phn
ng di dng ion thu gn (H+ ng vai tr mi trng, NO3 ng vai tr cht oxi ha) v
so snh cc t s gia s mol ban u v h s t lng trong phng trnh xem t s no nh
nht th cht s ht trc ( tnh theo)- Cc kim loi tc dng vi ion NO3 trong mi trng axit H+ xem nh tc dng vi HNO3
- Cc kim loi Zn, Al tc dng vi ion NO3 trong mi trng kim OHgii phng NH3
4Zn + NO3 + 7OH 4ZnO22+ NH3 + 2H2O
(4Zn + NO3 + 7OH+ 6H2O 4[Zn(OH)4]2+ NH3)
8Al + 3NO3 + 5OH+ 2H2O 8AlO2 + 3NH3
(8Al + 3NO3 + 5OH + 18H2O 8[Al(OH)4] + 3NH3
- Khi hn hp nhiu kim loi tc dng vi hn hp axit th dng nh lut bo ton mol
electron v phng php ion electron gii cho nhanh. So snh tng s mol electron cho
v nhn bin lun xem cht no ht, cht no d
- Khi hn hp kim loi trong c Fe tc dng vi H2SO4 c nng hoc HNO3 cn ch
xem kim loi c d khng. Nu kim loi (Mg Cu) d th c phn ng kim loi kh Fe3+
v Fe2+. V d: Fe + 2Fe3+ 3Fe2+ ; Cu + 2Fe3+ Cu2+ + 2Fe2+
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- Khi ha tan hon hon hn hp kim loi trong c Fe bng dung dch HNO3 m th tch
axit cn dng l nh nht mui Fe2+
- Kim loi c tnh kh mnh hn s u tin phn ng trc
- Nu bi yu cu tnh khi lng mui trong dung dch, ta p dng cng thc sau:
mmui = mcation + manionto mui = mkim loi + manion to mui
(manion to mui = manion ban u manion to kh)
- Cn nh mt s cc bn phn ng sau:
2H+ + 2e H2
NO3- + e + 2H+ NO2 + H2O
SO42 + 2e + 4H+ SO2 + 2H2O
NO3- + 3e + 4H+ NO + 2H2O
SO42 + 6e + 8H+ S + 4H2O
2NO3- + 8e + 10H+ N2O + 5H2O
SO42 + 8e + 10H+ H2S + 4H2O
2NO3- + 10e + 12H+ N2 + 6H2O
NO3- + 8e + 10H+ NH4+ + 3H2O
- Cn nh s mol anion to mui v s mol axit tham gia phn ng:
nSO42to mui = .a
2nX (a l s electron m S+6 nhn to sn phm kh X)
nH2SO4phn ng = 2nSO2 + 4nS + 5nH2S
nNO3to mui = a.nX (a l s electron m N+5 nhn to ra sn phm kh X)
nHNO3 phn ng = 2nNO2 + 4nNO + 10nN2O + 12nN2
3) Mt s v d minh ha
V d 1: Cho 3,68 gam hn hp gm Al v Zn tc dng vi mt lng va dung dchH2SO4 10 %, thu c 2,24 lt kh H2 ( ktc). Khi lng dung dch thu c sau phn ng
l:
A. 101,68 gam B. 88,20 gam C. 101,48 gam D. 97,80 gam
Hng dn: nH2 = nH2SO4 = 0,1 mol m (dung dch H2SO4) = 98 gam m (dung dch
sau phn ng) = 3,68 + 98 - 0,2 = 101,48 gam p n C
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V d 2: Ho tan hon ton 14,6 gam hn hp X gm Al v Sn bng dung dch HCl (d), thu
c 5,6 lt kh H2 ( ktc). Th tch kh O2 ( ktc) cn phn ng hon ton vi 14,6
gam hn hp X l:
A. 2,80 lt B. 1,68 lt C. 4,48 lt D. 3,92 lt
Hng dn: Gi nAl
= x mol ; nSn
= y mol 27x + 119y = 14,6 (1) ; nH
2
= 0,25 mol
- Khi X tc dng vi dung dch HCl:
V d 3: Cho 7,68 gam hn hp X gm Mg v Al vo 400 ml dung dch Y gm HCl 1M v
H2SO4 0,5M. Sau khi phn ng xy ra hon ton thu c 8,512 lt kh ( ktc). Bit trong
dung dch, cc axit phn li hon ton thnh cc ion. Phn trm v khi lng ca Al trong X
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l:
A. 56,25 % B. 49,22 % C. 50,78 % D. 43,75 %
Hng dn: nH+ = 0,8 mol ; nH2 = 0,38 mol nH
+phn ng = 0,76 mol < 0,8 mol axit d,
kim loi ht
- Gi nMg = x mol ; nAl = y mol % Al = %
p n A
V d 4: Cho 0,10 mol Ba vo dung dch cha 0,10 mol CuSO4 v 0,12 mol HCl. Sau khi cc
phn ng xy ra hon ton, lc ly kt ta nung nhit cao n khi lng khng i thu
c m gam cht rn. Gi tr ca m l:
A. 23,3 gam B. 26,5 gam C. 24,9 gam D. 25,2 gamHng dn: Cc phn ng xy ra l:
Ba + 2HCl BaCl2 + H2
0,06 0,12 0,06
BaCl2 + CuSO4 BaSO4 + CuCl2
0,06 0,06 0,06
Ba + 2H2O Ba(OH)2 + H2
0,04 0,04
Ba(OH)2 + CuSO4 BaSO4 + Cu(OH)2
0,04 0,04 0,04 0,04
Cu(OH)2 CuO + H2O
0,04 0,04
m (cht rn) = mBaSO4 + mCuO = (0,06 + 0,04).233 + 0,04.80 = 26,5 gam p n B
V d 5: Th tch dung dch HNO3 1M (long) t nht cn dng ho tan hon ton 18 gam
hn hp gm Fe v Cu trn theo t l mol 1 : 1 l: (bit phn ng to cht kh duy nht l
NO)
A. 1,0 lt B. 0,6 lt C. 0,8 lt D. 1,2 lt
Hng dn: nFe = nCu = 0,15 mol
- Do th tch dung dch HNO3 cn dng t nht mui Fe2+ ne cho = 2.(0,15 + 0,15) =
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0,6 mol
- Theo lbt mol electron nH+ = nHNO3 = mol VHNO3 = 0,8 lt p n C
V d 6: Ha tan 9,6 gam Cu vo 180 ml dung dch hn hp HNO3 1M v H2SO4 0,5M, kt
thc phn ng thu c V lt ( ktc) kh khng mu duy nht thot ra, ha nu ngoi khng
kh. Gi tr ca V l:
A. 1,344 lt B. 4,032 lt C. 2,016 lt D. 1,008 lt
Hng dn: nCu = 0,15 mol ; nNO3 = 0,18 mol ; nH
+ = 0,36 mol
3Cu + 8H+ + 2NO3 3Cu2+ + 2NO + 4H2O
0,36 0,09
Do H+ ht ; Cu d
VNO = 0,09.22,4 = 2,016 lt p n C
V d 7: Cho hn hp gm 1,12 gam Fe v 1,92 gam Cu vo 400 ml dung dch cha hn
hp gm H2SO4 0,5M v NaNO3 0,2M. Sau khi cc phn ng xy ra hon ton, thu c
dung dch X v kh NO (sn phm kh duy nht). Cho V ml dung dch NaOH 1M vo dung
dch X th lng kt ta thu c l ln nht. Gi tr ti thiu ca V l:
A. 360 ml B. 240 ml C. 400 ml D. 120 ml
Hng dn: nFe = 0,02 mol ; nCu = 0,03 mol ne cho = 0,02.3 + 0,03.2 = 0,12 mol ; nH+
= 0,4 mol ; nNO3 = 0,08 mol (Ion NO3 trong mi trng H+ c tnh oxi ha mnh nh
HNO3)
- Bn phn ng: NO3+ 3e + 4H+ NO + 2H2O
0,12 0,16
Do kim loi kt v H+ d
nH+ d = 0,4 0,16 = 0,24 mol nOH
(to kt ta max) = 0,24 + 0,02.3 + 0,03.2 =
0,36 V = 0,36 lt hay 360 ml p n A
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V d 8: Cho 24,3 gam bt Al vo 225 ml dung dch hn hp NaNO3 1M v NaOH 3M
khuy u cho n khi kh ngng thot ra th dng li v thu c V lt kh ( ktc).Gi tr
ca V l:
A. 11,76 lt B. 9,072 lt C. 13,44 lt D. 15,12 lt
Hng dn: nAl
= 0,9 mol ; nNO
3= 0,225 mol ; n
OH
= 0,675 mol
8Al + 3NO3+ 5OH + 18H2O 8[Al(OH)4] + 3NH3 (1)
B: 0,9 0,225 0,675
P: 0,6 0,225 0,375 0,225
D: 0,3 0 0,3
Do NO3 ht
Al + OH (d) + H2O AlO2 + H2 (2)
0,3 0,3 0,45
T (1) ; (2) V = (0,225 + 0,45).22,4 = 15,12 lt p n D
V d 9: Ha tan hon ton 100 gam hn hp X gm Fe, Cu , Ag trong dung dch HNO3
(d). Kt thc phn ng thu c 13,44 lt hn hp kh Y gm NO2, NO, N2O theo t l s
mol tng ng l 3 : 2 : 1 v dung dch Z (khng cha mui NH4NO3). C cn dung dch Z
thu c m gam mui khan. Gi tr ca m v s mol HNO3 phn ng ln lt l:
A. 205,4 gam v 2,5 mol B. 199,2 gam v 2,4 mol
C. 205,4 gam v 2,4 mol D. 199,2 gam v 2,5 mol
Hng dn: nY = 0,6 mol nNO2 = 0,3 mol ; nNO = 0,2 mol ; nN2O = 0,1 mol
3NOn - to mui = 2NOn + 3. NOn + 8. 2N On = 0,3 + 3.0,2 + 8.0,1 = 1,7 mol
mZ = mKl + 3NOm - to mui = 100 + 1,7.62 = 205,4 gam (1)
3HNOn
phn ng = 2. 2NOn + 4. NOn + 10. 2N On = 2.0,3 + 4.0,2 + 10.0,1 = 2,4 mol (2)
- T (1) ; (2) p n C
V d 10: Cho 6,72 gam Fe vo 400 ml dung dch HNO3 1M, n khi phn ng xy ra hon
ton, thu c kh NO (sn phm kh duy nht) v dung dch X. Dung dch X c th ho tan
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ti a m gam Cu. Gi tr ca m l:
A. 1,92 gam B. 3,20 gam C. 0,64 gam D. 3,84 gam
Hng dn: nFe = 0,12 mol ne cho = 0,36 mol; nHNO3 = 0,4 mol ne nhn = 0,3 mol
- Do ne cho > ne nhn Fe cn d dung dch X c Fe2+ v Fe3+
- Cc phn ng xy ra l:Fe + 4HNO3 Fe(NO3)3 + NO + 2H2O
0,1 0,4 0,1
Fe (d) + 2Fe3+ 3Fe2+
0,02 0,04
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Cu + 2Fe3+ (d) Cu2+ + 2Fe2+
0,03 0,06
mCu = 0,03.64 = 1,92 gam p n A
V d 11: Ho tan hon ton 12,42 gam Al bng dung dch HNO3 long (d), thu c dung
dch X v 1,344 lt ( ktc) hn hp kh Y gm hai kh l N2O v N2. T khi ca hn hp
kh Y so vi kh H2 l 18. C cn dung dch X, thu c m gam cht rn khan. Gi tr ca m
l:
A. 38,34 gam B. 34,08 gam C. 106,38 gam D. 97,98 gam
Hng dn: nAl = 0,46 mol ne cho = 1,38 mol ; nY = 0,06 mol ; M Y = 36
- D dng tnh c nN2O = nN2 = 0,03 mol
ne nhn = 0,03.(8 + 10) = 0,54 mol < ne cho dung dch X cn cha mui NH4NO3
nNH4+ = NO3= mol
- Vy mX = mAl(NO3)3 + m NH4NO3 = 0,46.213 + 0,105.80 = 106,38 gam p n C
(Hoc c th tnh mX = mKl + mNO3-to mui + mNH4
+ = 12,42 + (0,03.8 + 0,03.10 + 0,105.8 +
0,105).62 + 0,105.18 = 106,38 gam)
IV BI TP V KIM LOI TC DNG VI DUNG DCH MUI
1) Kim loi tc dng vi dung dch mui:
- iu kin kim loi M y c kim loi X ra khi dung dch mui ca n:
xM (r) + nXx+ (dd) xMn+ (dd) + nX (r)
+ M ng trc X trong dy th in cc chun
+ C M v X u khng tc dng c vi nc iu kin thng
+ Mui tham gia phn ng v mui to thnh phi l mui tan
- Khi lng cht rn tng: m = mXto ra mMtan
- Khi lng cht rn gim: m = mMtan mX to ra
- Khi lng cht rn tng = khi lng dung dch gim
- Ngoi l:
+ Nu M l kim loi kim, kim th (Ca, Sr, Ba) th M s kh H+ ca H2O thnh H2 v to
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thnh dung dch baz kim. Sau l phn ng trao i gia mui v baz kim
+ trng thi nng chy vn c phn ng: 3Na + AlCl3 (khan) 3NaCl + Al
+ Vi nhiu anion c tnh oxi ha mnh nh NO3-, MnO4-,th kim loi M s kh cc anion
trong mi trng axit (hoc baz)
- Hn hp cc kim loi phn ng vi hn hp dung dch mui theo th t u tin: kim loi
kh mnh nht tc dng vi cation oxi ha mnh nht to ra kim loi kh yu nht v
cation oxi ha yu nht
- Th t tng dn gi tr th kh chun (Eo) ca mt s cp oxi ha kh:
Mg2+/Mg < Al3+/Al < Zn2+/Zn < Cr3+/Cr < Fe2+/Fe < Ni2+/Ni < Sn2+/Sn < Pb2+/Pb < 2H+/H2