IN PHNI KHI NIM S in phn l qu trnh oxi ha kh xy ra b mt cc in cc
khi c dng in mt chiu i qua cht in li nng chy hoc dung dch cht in
li. S in phn l qu trnh s dng in nng to ra s bin i ha hc. Trong qu
trnh in phn, di tc dng ca in trng cc cation di chuyn v cc m (catot)
cn cc anion di chuyn v in cc dng (anot), ti xy ra phn ng trn cc in
cc (s phng in). Ti catot xy ra qu trnh kh cation (Mn+ + ne M) cn ti
anot xy ra qu trnh oxi ha anion (Xn- X + ne). Ngi ta phn bit: in
phn cht in li nng chy, in phn dung dch cht in li trong nc, in phn
dng in cc dng tan. II S IN PHN CC CHT IN LI 1. in phn cht in li nng
chy Trong thc t, ngi ta thng tin hnh in phn nhng hp cht (mui, baz,
oxit) nng chy ca cc kim loi c tnh kh mnh nh Li, Na, K, Ba, Ca, Mg,
Al a) in phn nng chy mui clorua (Ch p dng iu ch kim loi kim v kim
th) Tng qut: V d 1: in phn NaCl nng chy c th biu din bng s : Catot
( ) NaCl Anot ( + )
2| Na+ + e Na.................2Cl- Cl2 + 2e
Phng trnh in phn l: 2NaCl 2Na + Cl2 (pnc) Cn c mng ngn khng cho
Cl2 tc dng tr li vi Na trng thi nng chy lm gim hiu sut ca qu trnh
in phn. Mt s cht ph gia nh NaF, KCl gip lm gim nhit nng chy ca
h
b) in phn nng chy hiroxit Tng qut: Catot (-): 2M+ +2e2M Anot
(+): 2OH- -2e
(Ch p dng iu ch cc kim loi kim: Na, K)
V d 2: in phn NaOH nng chy c th biu din bng s : Catot ( ) NaOH
Anot ( + )
4| Na+ + 1e Na ........................ 4OH- O2 + 2H2O + 4e Phng
trnh in phn l: 4NaOH 4Na + O2 + 2H2O c) in phn nng chy oxit: (Ch
dng iu ch Al) V d 3: in phn Al2O3 nng chy pha thm criolit (Na3AlF6)
c th biu din bng s : Catot ( ) Al2O3 Anot ( + )
4| Al3+ + 3e Al ................................ 3/2 O2- O2 + 4e
Phng trnh in phn l: 2Al2O3 4Al + 3O2
* Vai tr ca criolit (Na3AlF6): + Criolit (Na3AlF6) c vai tr quan
trng nht l lm gim nhit nng chy ca Al2O3 t 2050oC xung khong 900oC.
+ + Lm tng dn in ca h. To lp ngn cch gia cc sn phm in phn v mi trng
ngoi.
* Ch nu anot lm bng than ch: Nu in cc lm bng graphit (than ch)
th s b kh sinh ra anot n mn.
Phng trnh phn ng in phn cho c 2 cc l:
Kh anot sinh ra thng l hn hp kh CO, CO2 v O2. n gin ngi ta thng
ch xt phng trnh: 2. in phn dung dch cht in li trong nc Trong s in
phn dung dch, ngoi cc ion do cht in li phn li ra cn c cc ion H+ v
OH- ca nc. Do vic xc nh sn phm ca s in phn phc tp hn. Ty thuc vo
tnh kh v tnh oxi ha ca cc ion c trong bnh in phn m ta thu c nhng sn
phm khc nhau. V d khi in phn dung dch NaCl, cc ion Na+, H+ (H2O) di
chuyn v catot cn cc ion Cl-, OH-(H2O) di chuyn v anot. Ion no trong
s chng s phng in cc in cc. C s gii quyt vn ny l da vo cc gi tr th
oxi ha kh ca cc cp. Trong qu trnh in phn, trn catot din ra s kh. V
vy khi c nhiu dng oxi ha th trc ht dng oxi ha ca cp c th ln hn s b
kh trc. Ngc li trn anot s din ra s oxi ha dng kh ca cp c th oxi ha
kh nh nht trc.
a) Kh nng phng in ca cc cation catot: catot c th xy ra cc qu
trnh kh sau y: Mn+ + ne M 2H+(axit) + 2e H2 Hoc ion hiro ca nc b
kh: 2H2O + 2e H2 + 2OHDng oxi ha ca nhng cp c th cng ln cng d b kh.
Theo dy th oxi ha kh th kh nng b kh ca cc ion kim loi nh sau: + dn
+ + Cc cation t Zn2+ n cui dy Hg2+, Cu2+, Fe3+, Ag+ d b kh nht v th
t tng T Al3+ n cc ion u dy Na+, Ca2+, K+ khng b kh trong dung dch
Cc ion H+ ca axit d b kh hn cc ion H+ ca nc
b) Kh nng phng in ca cc anion anot: anot xy ra qu trnh oxi ha cc
anion gc axit nh Cl-, S2-hoc ion OH- ca baz kim hoc nc 2Cl- Cl2 +
2e 4OH- O2 + 2H2O + 4e Hoc ion OH- ca nc b oxi ha: 2H2O O2 + 4H+ +
4e Dng kh ca nhng cp c th oxi ha kh cng nh cng d b oxi ha. Theo dy
th oxi ha kh th kh nng b oxi ha ca cc anion nh sau: + Cc anion gc
axit khng cha oxi d b oxi ha nht theo th t: RCOO-< Cl- .nKCl vi
in cc tr. Bit rng qu trnh in phn gm 3 giai on. Hy cho bit kh thot
ra mi giai on.
1. G1: Anot: Cl2 Katot: khng c kh; G2: Anot: O2 Katot: khng c
kh; G3: Anot: O2 Katot: H2.
2. G1: Anot: Cl2 Katot: khng c kh; G2: Anot: Cl2 Katot: H2; G3:
Anot: O2 Katot: H2. 3. G1: Anot: Cl2 Katot: khng c kh; G2: Anot:
Cl2 Katot: khng c kh; G3: Anot: O2 Katot: H2. 4. G1: Anot: Cl2
Katot: H2; G2: Anot: Cl2 Katot: H2; G3: Anot: O2 Katot: H2.Bi 2 (
thi tuyn sinh i hc khi B nm 2007). in phn dung dch cha a mol CuSO4
v b mol NaCl (vi in cc tr, c mng ngn xp). dung dch sau in phn lm
phenolphtalein chuyn sang mu hng th iu kin ca a v b l (bit ion
SO42- khng b in phn trong dung dch) A. b > 2a B. b = 2a C. b
< 2a D. 2b = a
Bi 3: in phn dung dch cha CuSO4 v MgCl2 c cng nng mol vi in cc
tr. Hy cho bit nhng cht g ln lt xut hin bn catot v bn anot. A. K:
Cu, Mg A: Cl2, O2 C. K: Cu, Mg A: Cl2, H2 B. K: Cu, H2 A: Cl2, O2
D. K: Cu, Mg, H2 A: Ch c O2
Bi 4: in phn c mng ngn in cc tr 100 ml dung dch cha CuSO4, NaCl
u c nng mol/l l 0.1M vi cng I = 0.5A sau mt thi gian thu c dung dch
c pH = 2. Thi gian tin hnh in phn l: A. 193s B. 1930s C. 2123s D.
1737s
Bi 5: in phn dung dch cha 7.45 gam KCl v 28.2 gam Cu(NO3)2 (in
cc tr, c mng ngn) n khi khi lng dung dch gim 10.75 gam th ngt mch.
Dung dch sau khi in phn cha nhng cht g sau y. A. KNO3 v KCl d C.
KNO3, Cu(NO3)2 cn d, HNO3 B. KNO3 v Cu(NO3)2 cn d. D. KNO3 v
KOH.
Bi 6: in phn dung dch hn hp cha 18.8 gam Cu(NO3)2 v 29.8 gam KCl
(in cc tr, mng ngn xp). Sau mt thi gian in phn thy khi lng dung dch
gim 17.15 gam so vi khi lng ban u, th tch dung dch sau in phn l 400
ml. Nng mol/l ca cc cht trong dung dch sau in phn l:
1. 2. 3. 4.
[KCl] = 0.375M; [KNO3] = 0.25M v [KOH] = 0.25M [KCl] = 0.5M;
[KNO3] = 0.25M v [KOH] = 0.25M [KCl] = 0.25M; [KNO3] = 0.5M v [KOH]
= 0.25M Kt qu khc.
Dng 2.3: Bi ton xc nh tn nguyn t thng qua in phn Loi 2.3.1: Bi
tp t lun Bi 1: in phn dung dch mui sunfat ca kim loi M (ha tr II).
Khi anot thu c 0.448 lt kh (ktc) th thy khi lng catot tng 2.36
gam.
1. Xc nh kim loi trong mui. 2. Tnh thi gian in phn, bit cng dng
in l 1A.Bi 2: in phn 200 gam dung dch mui MSO4 nng 4% n khi hai in
cc cng c kh thot ra th dng li. Ly catot ra ra sch, lm kh cn li thy
khi lng tng ln 3.2 gam.
1. Xc nh kim loi M. 2. Tnh thi gian in phn, bit cng dng in l 1A.
3. Tnh nng % ca cht tan trong dung dch sau in phn.Bi 3: in phn 200
gam dung dch mui MSO4 nng 7.75% n khi s mol ca axit trong dung dch
khng i th dng li. Khi lng catot tng ln 5.9 gam.
1. Xc nh kim loi M. 2. Tnh thi gian in phn, bit cng dng in l 1A.
3. Trung ha dung dch sau in phn cn bao nhiu gam dung dch NaOH 4%.Bi
4: (i hc Kinh t Quc dn nm 1999). in phn (dng in cc tr) dung dch mui
sunfat ca kim loi ha tr II vi cng dng l 3A. Sau 1930 giy thy khi
lng catot tng 1.92 gam.
1. Vit phng trnh phn ng xy ra ti mi in cc v phng trnh chung cho
qu trnh in phn. 2. Cho bit tn kim loi trong mui sunfat. 3. Hy tnh
th tch ca lng kh to thnh ti anot 25oC v 770 mmHg.Bi 5: in phn 784
gam dung dch R2(SO4)3 10% vi in cc tr, c mng ngn gia cc in cc v vi
cng I = 15A trong 3860 giy th ngng in phn. ng lc thu c 10.4 gam kim
loi catot.
1. Xc nh kim loi R (R l mt kim loi trong dy in ha v khng phi l
st).
2. Xc nh nng % cc cht cn li trong dung dch sau khi in phn.Bi 6:
Ha tan hn hp A gm kim loi M v oxit MO ca kim loi y (M ch c mt ha
tr) trong 2 lt dung dch HNO3 1M th c 4.48 lt (ktc) kh NO bay ra.
trung ha axit cn d trong dung dch B thu c cn 2 lt dung dch NaOH
0.5M khi ta thu c dung dch C.
1. Tnh s mol M v MO trong hn hp A. 2. in phn dung dch C vi in cc
tr trong thi gian 48 pht 15 giy th thu c 11.52 gam kim loi M bn
catot v 2.016 lt kh (ktc) bn anot. Xc nh kim loi M v cng dng in. 3.
Tnh thi gian in phn tip dung dch mt ht ion M2+. Cng dng in vn nh cu
trn.Bi 7: Trong 500 ml dung dch A cha 0.4925 gam hn hp gm mui
clorua v hydroxit ca cng mt kim loi kim. O pH ca dung dch A c pH =
12. Khi in phn 1/10 dung dch A (c mng ngn xp) cho n khi ht Cl- th
thu c 11.2 ml Cl2 ( 273oC v 1 atm).
1. Xc nh tn kim loi kim bit rng trong bnh in phn c vch ngn. 2.
Tnh thi gian in phn, bit cng dng in l 1A. 3. Bit 1/10 dung dch A th
tc dng va vi 25 ml dung dch CuCl2. Tnh nng mol/l ca dung dch
CuCl2.Bi 8: Ha tan 16 gam mui MSO4 vo nc thnh 2 lt dung dch A. in
phn dung dch A n khi hai cc cng c kh thot ra th dng li. Dung dch
khi c pH = 1, khi lng catot tng m gam.
1. Vit phng trnh phn ng. 2. Tm cng thc ca mui ban u, khi lng kim
loi trn catot v nng ca dung dch. 3. Tnh thi gian in phn, bit cng
dng in l 1A.Bi 9: (HQG thnh ph H Ch Minh nm 2001). Ha tan 4.5 gam
tinh th XSO4.5H2O vo nc thu c dung dch A (dung dch XSO4). in phn
dung dch A vi in cc tr. Nu thi gian in phn l t giy th thu c kim loi
ti catot v 0.007 mol kh ti anot. Nu thi gian in phn l 2t giy th thu
c 0.024 mol kh c hai in cc.
1. Xc nh XSO4.5H2O
2. Cho I = 1.93A. Tnh thi gian t.Loi 2.3.2: Bi tp trc nghim Bi
1: in phn vi in cc tr dung dch mui clorua ca mt kim loi ha tr II vi
cng dng in 3A. Sau 1930 giy, thy khi lng catot tng 1.92 gam. Kim
loi trong mui clorua trn l kim loi no di y. A. Ni B. Zn C. Fe D.
Cu
Bi 2: in phn 100 ml dung dch cha 2.7 gam mui clorua ca kim loi X
cho ti khi kh bt u xut hin catot th ngng in phn thu c 0.228 lt kh
anot (o ktc). Kim loi l: A. Cu B. Zn C. Al D. Mg
Bi 3: in phn 100 ml dung dch XSO4 0.2M vi cng dng in mt chiu I =
10A trong thi gian t, khi anot thot ra 224 ml kh ( ktc) th cng lc
kim loi bm vo catot c 1.28gm. Xc nh tn kim loi X. A. Fe B. Zn C. Cu
D. Mg
Tnh thi gian t, bit hiu sut phn ng t 100% A. 579 giy B. 386 giy
C. 193 giy D. 289.5 giy
Tnh nng ca dung dch sau in phn, bit th tch dung dch thay i khng
ng k. A. 0.15M B. 0.12M C. 0.1M D. 0.18M
Bi 4: in phn 100 ml dung dch XSO4 0.2M vi cng dng in I = 9.65A
sau 200 giy th dng li thy khi lng catot tng 0.64 gam. Xc nh tn kim
loi X. A. Ni B. Zn C. Cu D. Fe
Nu in phn dung dch ny n 500 giy th khi lng catot tng: A. 1.6 gam
B. 0.8 gam C. 0.96 gam D. 1.28 gam
Bi 5: in phn (c mng ngn) hon ton dung dch c cha 0.745 gam XCl,
cng dng in mt chiu I = 9.65A. Khi nc bt u b in phn c hai in cc th
mt 100 giy. Xc nh kim loi X. A. Li B. Na C. K D. Rb
Gi s th tch dung dch sau in phn l 100 ml. Tnh pH ca dung dch sau
in phn. A. 13 B. 12 C. 11 D. 10
3. IN PHN NNG CHY Loi 3.1: Bi tp t lun Bi 1: in phn mui clorua
kim loi nng chy, ngi ta thu c 0.896 lt kh (ktc) anot v 3.12 gam kim
loi catot. Hy xc nh cng thc mui in phn. Bi 2: in phn nng chy 4 gam
hydroxit ca kim loi thu c anot mt hn hp kh c th tch o ktc l 1.68
lt. Phn ng xy ra hon ton. Vit phng trnh phn ng in phn. Xc nh cng
thc phn t ca hydroxit. Bi 3: in phn nng chy mt hp cht oxit kim loi
thu c 10.8 gam kim loi catot v ng thi anot c 6.72 lt kh thot ra (o
ktc), phn ng xy ra hon ton.
1. Vit qu trnh in phn hp cht oxit. 2. Xc nh cng thc phn t ca
oxit.Bi 4: Khi in phn nng chy mt oxit kim loi thu c 0.224 lt kh (
ktc) anot, th khi lng catot tng ln 2.74 gam.
1. Tm cng thc ca oxit kim loi trn. 2. Ha tan kim loi thu c vo nc
c dung dch A. Cn bao nhiu ml dung dch HCl 0.1M trung ha 1/10 dung
dch A.Bi 5: Sn xut Al bng phng php in phn nng chy Al2O3. Hy cho bit
lng Al2O3 v C (anot) cn dng c th sn xut c 0.54 tn Al. Cho rng ton b
lng O2 sinh ra t chy cc dng thnh kh CO2. Bi 6: (i hc Ngoi thng nm
2001). Ngi ta dng than ch kh Al2O3 bng phng php in phn nng chy
Al2O3. thu c 6.75 kg Al, ng thi to ra hn hp kh A gm: 20% CO; 70%
CO2 v 10% O2 theo th tch.
1. Hy tnh khi lng than ch b tiu hao v lng Al2O3 b in phn. 2. Tnh
t khi hi ca hn hp kh A so vi H2.Loi 3.2: Bi tp trc nghim Bi 1: in
phn nng chayr2.34 gam NaCl vi cng dng in mt chiu I = 9.65A. Tnh khi
lng Na bm vo catot khi thi gian in phn l 200 giy. A. 0.23 gam B.
0.276 gam C. 0.345 gam D. 0.46 gam
in phn ht lng NaCl ban u vi cng dng in khng i th thi gian in phn
l: A. 500 giy B. 400 giy C. 300 giy D. 200 giy
Bi 2: in phn nng chy a gam mui G to bi kim loi M v halogen X ta
thu c 0.96 gam kim loi M catot v 0.04 mol kh anot. Mt khc, ha tan a
gam mui G vo nc sau cho tc dng vi dung dch AgNO3 d thu c 11.48 gam
kt ta. Cho bit X l halogen no: A. Clo B. Brom C. Iot D. Khng d
liu.
Cho bit M l kim loi no: A. Na B. Mg C. Al D. Khng d liu.
Bi 3: in phn nng chy hon ton 4 gam XOH, kim loi X bm vo catot
cho tc dng ht vi nc thu c 1 lt dung dch A c pH bng 13. Cho bit X l
kim loi g. A. K B. Li C. Na D. Rb
Nu cng dng in l 193A th thi gian in phn l bao nhiu. A. 50 giy B.
40 giy C. 30 giy D. 60 giy
II MT S C S GII BI TP V IN PHN - Khi lng catot tng chnh l khi
lng kim loi to thnh sau in phn bm vo - m (dung dch sau in phn) = m
(dung dch trc in phn) (m kt ta + m kh) - gim khi lng ca dung dch: m
= (m kt ta + m kh) - Khi in phn cc dung dch: + Hiroxit ca kim loi
hot ng ha hc mnh (KOH, NaOH, Ba(OH)2,)
+ Axit c oxi (HNO3, H2SO4, HClO4,) + Mui to bi axit c oxi v baz
kim (KNO3, Na2SO4,) Thc t l in phn H2O cho H2 ( catot) v O2 ( anot)
- Khi in phn dung dch vi anot l mt kim loi khng tr (khng phi Pt hay
in cc than ch) th ti anot ch xy ra qu trnh oxi ha in cc - C th c cc
phn ng ph xy ra gia tng cp: cht to thnh in cc, cht tan trong dung
dch, cht dng lm in cc. V d: + in phn nng chy Al2O3 (c Na3AlF6) vi
anot lm bng than ch th in cc b n mn dn do chng chy trong oxi mi
sinh + in phn dung dch NaCl khng mng ngn to ra nc Giaven v c kh H2
thot ra catot + Phn ng gia axit trong dung dch vi kim loi bm trn
catot - Vit phn ng (thu hoc nhng electron) xy ra cc in cc theo ng
th t, khng cn vit phng trnh in phn tng qut - Vit phng trnh in phn
tng qut (nh nhng phng trnh ha hc thng thng) tnh ton khi cn thit - T
cng thc Faraday s mol cht thu c in cc - Nu bi cho I v t th trc ht
tnh s mol electron trao i tng in cc (ne) theo cng thc: ne = (*) (vi
F = 96500 khi t = giy v F = 26,8 khi t = gi). Sau da vo th t in
phn, so snh tng s mol electron nhng hoc nhn vi ne bit mc in phn xy
ra. V d d on xem cation kim loi c b kh ht khng hay nc c b in phn
khng v H2O c b in phn th in cc no - Nu bi cho lng kh thot ra in cc
hoc s thay i v khi lng dung dch, khi lng in cc, pH,th da vo cc bn
phn ng tnh s mol electron thu hoc nhng mi in cc ri thay vo cng thc
(*) tnh I hoc t - Nu bi yu cu tnh in lng cn cho qu trnh in phn th p
dng cng thc: Q = I.t = ne.F - C th tnh thi gian t cn in phn ht mt
lng ion m bi cho ri so snh vi thi gian t trong bi. Nu t < t th
lng ion b in phn ht cn nu t > t th lng ion cha b in phn ht - Khi
in phn cc dung dch trong cc bnh in phn mc ni tip th cng dng in v
thi gian in phn mi bnh l nh nhau s thu hoc nhng electron cc in cc
cng tn phi nh nhau v cc cht sinh ra cc in cc cng tn t l mol vi nhau
- Trong nhiu trng hp c th dng nh lut bo ton mol electron (s mol
electron thu c catot = s mol electron nhng anot) gii cho nhanh III
MT S V D MINH HA V d 1: in phn ha ton 2,22 gam mui clorua kim loi
trng thi nng chy thu c 448 ml kh ( ktc) anot. Kim loi trong mui l:
A. Na B. Ca C. K D. Mg
Hng dn: nCl2 = 0,02 Ti catot: Mn+ + ne M Theo lbt khi lng mM =
m(mui) m(Cl2) = 2,22 0,02.71 = 0,8 gam Ti anot: 2Cl Cl2 + 2e Theo
lbt mol electron ta c nM = M l Ca (hoc c th vit phng trnh in phn
MCln M = 20.n n = 2 v
M + n/2Cl2 tnh) p n B
V d 2: Tin hnh in phn (vi in cc Pt) 200 gam dung dch NaOH 10 % n
khi dung dch NaOH trong bnh c nng 25 % th ngng in phn. Th tch kh (
ktc) thot ra anot v catot ln lt l: A. 149,3 lt v 74,7 lt B. 156,8
lt v 78,4 lt C. 78,4 lt v 156,8 lt D. 74,7 lt v 149,3 lt Hng dn:
mNaOH (trc in phn) = 20 gam in phn dung dch NaOH thc cht l in phn
nc: H2O 1/2 O2 (anot) + H2 (catot) NaOH khng i m (dung dch sau in
phn) = 80 gam m (H2O b in phn) = 200 80 = 120 gam nH2O = 20/3 mol
VO = 74,7 lt v VH = 149,3 lt p n D V d 3: Sau mt thi gian in phn
200 ml dung dch CuSO4 ( d = 1,25 g/ml) vi in cc graphit (than ch)
thy khi lng dung dch gim 8 gam. lm kt ta ht ion Cu2+ cn li trong
dung dch sau in phn cn dng 100 ml dung dch H2S 0,5 M. Nng phn trm
ca dung dch CuSO4 ban u l: A. 12,8 % B. 9,6 % C. 10,6 % D. 11,8 %
Hng dn: nH2S = 0,05 mol - Gi x l s mol CuSO4 tham gia qu trnh in
phn: CuSO4 + H2O Cu + 1/2O2 + H2SO4 (1) m (dung dch gim) = m
Cu(catot) + m O2(anot) = 64x + 16x = 8 x = 0,1 mol - CuSO4 + H2S
CuS + H2SO4 (2) nH2S = nCuSO4 = 0,05 mol - T (1) v (2) nCuSO4 (ban
u) = 0,1 + 0,05 = 0,15 (mol) C% = p n B V d 4: in phn 100 ml dung
dch CuSO4 0,2 M vi cng dng in 9,65A. Tnh khi lng Cu bm vo catot khi
thi gian in phn t1 = 200 s v t2 = 500 s. Bit hiu sut in phn l 100 %
A. 0,32 gam v 0,64 gam B. 0,64 gam v 1,28 gam C. 0,64 gam v 1,60
gam D. 0,64 gam v 1,32 gam
Hng dn: nCuSO4 = 0,02 = nCu2+ Thi gian cn thit in phn ht Cu2+ l
t = s t1 < t < t2 Ti t1 2+ c 1/2 s mol Cu b in phn m1 =
0,01.64 = 0,64 gam v ti t2 Cu2+ b in phn ht m2 = 1,28 gam p n B V d
5: in phn 200 ml dung dch CuSO4 vi in cc tr v cng dng in 1A. Khi
thy catot bt u c bt kh thot ra th dng in phn. trung ha dung dch thu
c sau khi in phn cn dng 100 ml dung dch NaOH 0,1M. Thi gian in phn
v nng mol ca dung dch CuSO4 ban u l: A. 965 s v 0,025 M B. 1930 s v
0,05 M C. 965 s v 0,05 M D. 1930 s v 0,025 M Hng dn: nNaOH = 0,01
mol - Khi catot bt u c bt kh (H2) thot ra chng t CuSO4 b in phn ht
theo phng trnh: CuSO4 + H2O Cu + 1/2O2 + H2SO4 - nNaOH = nOH = 0,01
mol nH2SO4 = 0,5.nH+ = 0,5.nOH = 0,005 (mol) nCu = nCuSO4 = 0,005
(mol) = 0,005 t = 965 s v CM(CuSO ) = M (hoc c th da vo cc phn ng
thu hoc nhng electron in cc tnh) p n A V d 6: in phn 200 ml dung
dch hn hp AgNO3 0,1 M v Cu(NO3)2 0,2 M vi in cc tr v cng dng in bng
5A. Sau 19 pht 18 giy dng in phn, ly catot sy kh thy tng m gam. Gi
tr ca m l: A. 5,16 gam B. 1,72 gam C. 2,58 gam D. 3,44 gam Hng dn:
nAg+ = 0,02 mol ; nCu2+ = 0,04 mol - Ta c ne = mol - Th t cc ion b
kh ti catot: Ag+ + 1e Ag (1) sau (1) cn 0,06 0,02 = 0,04 mol
electron 0,02 0,02 0,02 Cu2+ + 2e Cu (2) sau (2) cn d 0,02 mol Cu2+
0,02 0,04 0,02 m (catot tng) = m (kim loi bm vo) = 0,02.(108 + 64)
= 3,44 gam p n D V d 7: Ha tan 50 gam tinh th CuSO4.5H2O vo 200 ml
dung dch HCl 0,6 M thu c dung dch X. em in phn dung dch X (cc in cc
tr) vi cng dng in 1,34A trong 4 gi. Khi lng kim loi thot ra catot v
th tch kh thot ra anot ( ktc) ln lt l (Bit hiu sut in phn l 100 %):
A. 6,4 gam v 1,792 lt B. 10,8 gam v 1,344 lt C. 6,4 gam v 2,016 lt
D. 9,6 gam v 1,792 lt
Hng dn: nCuSO4.5H2O = nCuSO4 = 0,2 mol ; nHCl = 0,12 mol - Ta c
ne = mol - Th t in phn ti catot v anot l: Ti catot: Cu2+ + 2e Cu
Cu2+ cha b in phn ht m (kim loi catot) = 0,1.64 = 6,4 gam 0,1 0,2
0,1 Ti anot: 2Cl Cl2 + 2e ne (do Cl nhng) = 0,12 < 0,2 mol ti
anot Cl b in phn ht v 0,12 0,06 0,12 n nc b in phn ne (do H2O nhng)
= 0,2 0,12 = 0,08 mol 2H2O O2 + 4H+ + 4e 0,02 0,08 V (kh thot ra
anot) = (0,06 + 0,02).22,4 = 1,792 lt p n A V d 8: C 200 ml dung
dch hn hp Cu(NO3)2 v AgNO3, in phn ht ion kim loi trong dung dch cn
dng cng dng in 0,402A trong 4 gi. Sau khi in phn xong thy c 3,44
gam kim loi bm catot. Nng mol ca Cu(NO3)2 v AgNO3 trong hn hp u ln
lt l: A. 0,2 M v 0,1 M B. 0,1 M v 0,2 M C. 0,2 M v 0,2 M D. 0,1 M v
0,1 M Hng dn: - Ta c ne = 0.06mol - Ti catot: Ag+ + 1e Ag Ta c h
phng trnh: 2x+y=0,06 va 64x+108y=3,44 x x (mol) Cu2+ + 2e Cu CM
Cu(NO3)2 = CM AgNO3 = 0,1 M p nD y y (mol) V d 9: Ha tan 4,5 gam
tinh th MSO4.5H2O vo nc c dung dch X. in phn dung dch X vi in cc tr
v cng dng in 1,93A. Nu thi gian in phn l t (s) th thu c kim loi M
catot v 156,8 ml kh ti anot. Nu thi gian in phn l 2t (s) th thu c
537,6 ml kh . Bit th tch cc kh o ktc. Kim loi M v thi gian t ln lt
l: A. Ni v 1400 s B. Cu v 2800 s C. Ni v 2800 s D. Cu v 1400 s Hng
dn: Gi nMSO4 = nM2+ = x mol
V d 10: Mc ni tip hai bnh in phn: bnh (1) cha dung dch MCl2 v
bnh (2) cha
dung dch AgNO3. Sau 3 pht 13 giy th catot bnh (1) thu c 1,6 gam
kim loi cn catot bnh (2) thu c 5,4 gam kim loi. C hai bnh u khng
thy kh catot thot ra. Kim loi M l: A. Zn B. Cu C. Ni D. Pb Hng dn:
- Do hai bnh mc ni tip nn ta c: Q = I.t = 1,6.2.F/M M = 64 Cu p n B
V d 11: in phn nng chy Al2O3 vi anot than ch (hiu sut in phn 100 %)
thu c m kg Al catot v 67,2 m3 ( ktc) hn hp kh X c t khi so vi hiro
bng 16. Ly 2,24 lt ( ktc) hn hp kh X sc vo dung dch nc vi trong (d)
thu c 2 gam kt ta. Gi tr ca m l: A. 54,0 kg B. 75,6 kg C. 67,5 kg
D. 108,0 kg Hng dn: 2Al2O3 4Al + 3O2 (1) ; C + O2 CO2 (2) ; 2C + O2
2CO (3) - Do X = 32 hn hp X c CO2 ; CO (x mol) v O2 d (y mol) -
2,24 lt X + Ca(OH)2 d 0,02 mol kt ta = nCO2 trong 67,2 m3 X c 0,6
CO2 - Ta c h phng trnh: 44.0,6+28x+32y =32.3v 0,6 + x + y = 3 x =
1,8 v y = 0,6 T (1) ; (2) ; (3) mAl = 7.56kg p n B
