skkn phuong phap giai bai tap dien phan
TRANSCRIPT
A
PAGE Phng phap giai bai tp in phn dung dich Trn Thi Thuy
PHN I: T VN
Trong qu trnh ging dy mn Ha hc trng THPT, c bit l trong qu trnh n luyn cho hc sinh thi hc sinh gii cc cp v cc k thi i hc, chuyn in phn dung dch l mt chuyn hay v kh quan trng nn cc bi tp v in phn thng c mt trong cc k thi ln ca quc gia.
Vi hnh thc thi trc nghim nh hin nay th vic gii nhanh cc bi ton Ha hc l yu cu hng u ca ngi hc; yu cu tm ra c phng php gii ton mt cch nhanh nht, i bng con ng ngn nht khng nhng gip ngi hc tit kim c thi gian lm bi m cn rn luyn c t duy v nng lc pht hin vn ca ngi hc.
Trong thc t ti liu vit v in phn dung dch cn t nn ngun t liu gio vin nghin cu cn hn ch do ni dung kin thc v k nng gii cc bi tp in phn cung cp cho hc sinh cha c nhiu. V vy, khi gp cc bi ton in phn cc em thng lng tng trong vic tm ra phng php gii ph hp.
Qua qu trnh tm ti, nghin cu trong nhiu nm ti h thng ha cc dng bi tp in phn dung dch v phng php gii cc dng bi tp cho hc sinh mt cch d hiu, d vn dng, trnh c nhng lng tng, sai lm v nng cao kt qu trong cc k thi. Trn c s , ti mnh dn chn ti Phng php gii bi tp in phn dung dch lm sng kin kinh nghim cho mnh. Vi hy vng ti ny s l mt ti liu tham kho phc v cho vic hc tp ca cc em hc sinh 12 v cho cng tc ging dy ca cc bn ng nghip.
PHN B. T CHC THC HIN TAI
I. Nhng thun li v kh khn khi gii bi tp in phn trong dung dch.
1. Thun li:
- HS vit c phng trnh in phn tng qut v tnh ton theo phng trnh .
- HS bit p dng cng thc Faraday vo gii cc bi tp in phn .
- HS vit c cc bn phn ng xy ra cc in cc.
2. Kh khn:
- Hc sinh t s dng cng thc h qu ca Faraday ( ne trao i) gii nhanh bi ton in phn .
- a s cc bi tp in phn thng tnh ton theo cc bn phn ng cc in cc nhng hc sinh thng ch vit phng trnh in phn tng qut v gii theo n.
- Hc sinh thng lng tng khi xc nh trng hp H2O bt u in phn cc in cc (khi bt u si bt kh catot hoc khi pH ca dung dch khng i).
- Hc sinh nhm ln qu trnh xy ra cc in cc.
- Hc sinh vit sai th t cc bn phn ng xy ra cc in cc tnh ton sai.
- Hc sinh thng b qua cc phn ng ph c th xy ra gia cc sn phm to thnh nh: 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.
II. PHNG PHP GII BI TP IN PHN TRONG DUNG DCH A . Mt s khai nim v s in phn:1) S in phn: La qua trinh oxi hoa-kh xay ra b mt cac in cc khi cho dong in mt chiu i qua hp cht nong chay, hoc dung dich cht in li.
2) Trong thit bi in phn :
- Anot (A) c ni vi cc dng cua mt chiu, y xay ra s oxi hoa .
- Catot (K)c ni vi cc m cua ngun in mt chiu , y xay ra s kh B .Cac qua trinh in phn: 1 in phn dung dch mui: 1.1 in phn cc dung dch mui ca Kim loi kim, kim th, Nhm
a. catot (cc m)
Cc ion kim loi kim, kim loi kim th v ion Nhm khng b in phn v chng c tnh oxi ha yu hn H2O; H2O b in phn theo phng trnh: 2H2O + 2e H2 + 2OH.
b. anot (cc dng):
- Nu l S2-, Cl-, Br-, I- th chng b in phn trc H2O theo th t tnh kh:
S2->I- > Br- > Cl- > H2O (F- khng b in phn )
Phng trnh in phn tng qut: S2- S + 2e; 2X- X2 + 2e
Sau khi ht cc ion , nu tip tc in phn th H2O s in phn theo phng trnh: 2H2O O2 + 4H+ + 4e
- Nu l cc ion: NO3-, SO42-, CO32-, PO43-...th chng khng b in phn m H2O b in phn.
V d 1:Vit PTHH xy ra khi in phn dung dch NaCl : NaCl Na+ + Cl- Catot (-) Anot (+) Na+ khng b in phn 2Cl- Cl2 + 2e
2H2O + 2e H2 + 2OH-
Phng trnh : 2Cl- + 2H2O Cl2 + H2 + 2OH- 2NaCl + 2H2O 2NaOH + Cl2 + H2 * Xy ra tng t khi in phn cc dung dch : NaCl , CaCl2 , MgCl2 , BaCl2 , AlCl3 Khng th iu ch kim loi t : Na Al bng phng php in phn dung dch .
V d 2 : Vit PTHH xy ra khi in phn dung dch Na2SO4 : Na2SO4 2Na+ + SO42- Catot(-):Na+, H2O Anot (+):SO42-, H2O Na+ khng b in phn SO42-khng b in phn
2H2O + 2e H2 + 2OH- 2H2O O2 + 4H+ + 4e
Phng trnh in phn: 2H2O 2H2 + O2* Xy ra tng t khi in phn cc dung dch: NaNO3, K2SO4 , Na2CO3 , MgSO4 , Al2(SO4)3....V d 3: in phn 100ml dung dch cha NaCl vi in cc tr ,c mng ngn, cng dng in I = 1.93A. Tnh thi gian in phn c dung dch pH = 12, th tch dung dch c xem nh khng thay i, hiu sut in phn l 100%. A. 50sB. 100s
C. 150s D . 200s
Hng dn gii
V dung dch c PH = 12 Mi trng kim .
pH = 12 [H+] = 10-12 [OH-] = 0,01 S mol OH- = 0,001 mol
NaCl Na+ + Cl- Catot (-) Anot (+) Na+ khng b in phn 2H2O + 2e H2 + 2OH- Cl- Cl2 + 2e 0,001 0,001
S mol e trao i l : n = 0,001 mol
p dng cng thc Faraday : n = It / F t= n F /I Chn p n A
p dng tng t gii bi tp V.7 1.2. in phn cc dung dch mui ca cc kim loi ng sau Al trong dy in ha
a. catot (cc m)
- Cc cation kim loi b kh theo phng trnh: Mn+ + ne M Sau khi ht cc ion , nu tip tc in phn th H2O s in phn theo phng trnh: 2H2O + 2e H2 + 2OH.
b. anot (cc dng): (Xy ra tng t mc.I.1b) V d 1 : Vit PTHH xy ra in phn dung dch CuSO4 : CuSO4 Cu2+ + SO42-
Catot(-):Cu2+ Anot (+):SO42-, H2O SO42- khng b in phn .
Cu2+ + 2e Cu 2H2O 4H+ + O2+ 4e
Phng trnh in phn : Cu2+ + H2O Cu + 2H+ + O2 CuSO4 + H2O Cu + H2SO4 + O2 Xy ra tng t khi in phn cc dung dch mui ca kim loi t Zn Hg vi cc gc axit NO3- , SO42- : Cu(NO3)2 + H2O Cu + 2HNO3 + O2 V d 2 : Vit PTHH xy ra in phn dung dch ZnCl2 : ZnCl2 Zn2+ + 2Cl- Catot (-) Anot (+)
Zn2+ + 2e Zn 2Cl- Cl2 + 2e
Phng trnh in phn: ZnCl2 Zn + Cl2
V d 3: in phn 100ml dung dch CuSO4 0,1M vi cc in cc tr cho n khi va bt u si bt bn catot th ngng in phn. Tnh pH dung dch ngay khi y vi hiu sut l 100%. Th tch dung dch c xem nh khng i. Ly lg2 = 0,3 A. pH = 0,1 B.pH = 0,7 C.pH = 2,0 D. pH = 1,3
Hng dn gii
n khi va bt u si bt kh bn catot th Cu2+ va ht .
in phn dung dch : CuSO4 :
CuSO4 Cu2+ + SO42-
Catot(-) Anot (+)
SO42- khng b in phn Cu2+ + 2e Cu 2H2O 4H+ + O2 + 4e
0,01 0,02 0,02 0,02
S mol e cho anot = s mol e nhn catot n H+ = 0,02 mol
[H+] = 0,02/0,1 = 0,2 pH = -lg0,2 = 0,7 Chn p n B
p dng tng t gii cc bi tp: V.3, V.4, V.5 1.3. in phn hn hp cc dung dch mui
* catot: Cc cation kim loi b kh theo th t trong dy th in cc chun (ion c tnh oxi ha mnh hn b kh trc): Mn+ + ne M
* anot : (Xy ra tng t mc I.1b)V d 1: Vit PTHH xy ra in phn dung dch hn hp NaCl v Cu(NO3)2 : NaCl Na+ + Cl- Cu(NO3)2 Cu2+ + 2NO3- Catot(-):Na+, Cu2+, H2O Anot(+):NO3-, Cl-, H2O Na+ khng b in phn NO3- khng b in phn Cu2+ + 2e Cu 2Cl- Cl2 + 2e 2H2O + 2e H2 + 2OH- 2H2O 4H+ + O2 + 4e
Phng trnh in phn: 2NaCl + 2H2O 2NaOH + H2 + Cl2 Cu(NO3)2 + H2O Cu + O2 + 2HNO3Phng trnh in phn tng qut: 2NaCl + Cu(NO3)2 Cu + Cl2 + 2NaNO3V d 2: (Trch i hc khi A- 2010)in phn (vi in cc tr) mt dung dch gm NaCl v CuSO4 c cng s mol, n khi catot xut hin bt kh th dng in phn. Trong c qu trnh in phn trn, sn phm thu c anot l
A. kh Cl2 v O2. B. kh H2 v O2. C. ch c kh Cl2. D. kh Cl 2 v H2.
Chn p n: A
V d 3: in phn hon ton dung dch hn hp gm a mol Cu(NO3)2 v b mol NaCl vi in cc tr , mng ngn xp . dung dch thu c sau khi in phn c kh nng phn ng vi Al2O3 th A.b = 2a B.b > 2a C. b 2a Hng dn gii
Cu(NO3)2 Cu2+ + 2NO3- a a
NaCl Na+ + Cl-
b b
Catot(-) Anot (+)
Na+ khng b in phn NO3- khng b in phn .
Cu2+ + 2e Cu 2Cl- Cl2 + 2e
Phng trnh : Cu2+ + 2Cl- Cu + Cl2 (1)
a bNu d Cu2+ sau (1) : a > b/2 ( 2a > b ) th c phn ng : Cu2+ + 2H2O Cu + 4H+ + O2 Dung dch thu c c axit nn c phn ng vi Al2O3
Nu d Cl- sau (1) : a < b/2 ( b > 2a) c phn ng : 2H2O + 2Cl- 2OH- + H2 + Cl2
Dung dch thu c c mi trng baz C phn ng vi Al2O3 : NaOH + Al2O3 NaAlO2 + H2O Chn p n D .
p dng tng t gii bi tp V.2. V d 4: (Trch i hc khi A- 2010) in phn (in cc tr) dung dch X cha 0,2 mol CuSO4 v 0,12 mol NaCl bng dng in c cng 2A. Th tch kh (ktc) thot ra anot sau 9650 giy in phn lA.2,240 lt. B.2,912 lt. C.1,792 lt. D.1,344 lt.
Hng dn gii
NaCl Na+ + Cl-
CuSO4 Cu2+ + SO42- n e trao i) = It/F= 0,2 mol Catot (-) Anot (+)
(Cu2+; Na+, H2O) (SO42-, Cl-, H2O)
Na+ khng in phn SO42- khng in phn
Cu2+ + 2e Cu 2Cl- Cl2 + 2e
0,02 0,12 0,06 0,12
2H2O 4H+ +O2 + 4e 0,02 0,08
Vkh = (0,06 + 0,02). 22,4 = 1,792 lt p n C
p dng tng t gii bi tp V.8.V d 5: in phn 100 ml dung dch CuSO4 0,2M v AgNO3 0.1M vi cng dng in I = 3.86A.Tnh thi gian in phn c mt khi lng kim loi bm bn catot l 1.72g ?A. 250s B.1000s C.500s D. 750s
Hng dn gii
S gam kim loi Ag ti a c to thnh : 0,01.108 = 1,08 gam
S gam Cu ti a to thnh : 0,02.64 = 1,28 gam
V 1,08 < 1,72 < 1,08 + 1,28 in phn ht AgNO3 , V cn d mt phn CuSO4
Khi lng Cu c to thnh : 1,72 1,08 = 0,64 gam n Cu = 0,01 mol
p dng cng thc Faraday :
Cho Ag : 0,01 = 3,86.t1 / 96500.1 t1 = 250s
Cho Cu : 0,01 = 3,86.t2 / 96500.2 t2 = 500 s
Tng thi gian : 250 + 500 = 750 s Chn p n D .
p dng tng t gii bi tp V.9 V d 6: (Trch i hc khi B 2009) in phn c mng ngn 500 ml dung dch cha hn hp gm CuCl2 0,1M v NaCl 0,5M (in cc tr, hiu sut in phn 100%) vi cng dng in 5A trong 3860 giy. Dung dch thu c sau in phn c kh nng ho tan m gam Al. Gi tr ln nht ca m l
A. 4,05 B. 2,70 C. 1,35 D. 5,40
Hng dn gii
S mol e trao i khi in phn : mol
n CuCl2 = 0,1.0,5 = 0,05 mol ; n NaCl = 0,5.0,5 = 0,25 mol
n Cu2+ = 0,05 mol , n Cl- = 0,25 + 0,05.2 = 0,35 mol Vy Cl- d , Cu2+ ht , nn ti catot s c phn ng in phn nc (sao cho s mol e nhn catot l 0,2)
Ti catot :
Ti anot :Cu2+ + 2e Cu 2Cl- Cl2 + 2e
0,05 0,1
0,2 0,2
2H2O + 2e H2 + 2OH- 0,1 (0,2-0,1) 0,1
Dung dch sau khi in phn c 0,1 mol OH- c kh nng phn ng vi Al theo phng trnh : Al + OH- + H2O AlO2- + 3/2 H2
0,1 0,1
mAl max = 0,1.27= 2,7 (g) Chn p n B
V d 8:: 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. ZnB. CuC. NiD. Pb Hng dn gii
Do hai bnh mc ni tip nn ta c: Q = I.t = M = 64 Cu Chn p n B p dng tng t gii bi tp V.10, V.11. .2. IN PHN CC DUNG DCH AXIT:
* catot: Cc ion H+ (axit) d b kh hn cc ion H+ (H2O): 2H+ + 2e H2Khi ion H+ (axit) ht , nu tip tc in phn th H2O s in phn theo phng trnh:
2H2O + 2e H2 + 2OH.
* anot: (Xy ra tng t mc2.1b)V d 1: Vit PTHH xy ra in phn dung dich HCl: HCl H+ + Cl- Catot(-) Anot (+) 2H+ + 2e H2 2Cl- Cl2 + 2ePhng trnh in phn: HCl H2 + Cl2 V d 2: Vit PTHH xy ra in phn dung dch H2SO4 H2SO4 2H+ + SO42- Catot(-) Anot (+)
2H+ + 2e H2 SO42- Khng in phn
2H2O 4H+ + O2 + 4e Phng trnh in phn: H2O H2 + O2
.3. IN PHN CC DUNG DCH BAZ
* catot:
- Nu to bi cc ion kim loi t Li+ Al3+ th H2O s b in phn :
2H2O + 2e H2 + 2OH - Nu to bi cc ion kim loi sau Al trong dy in ha : l cc baz khng tan in li yu khng xt qu trnh in phn.
anot: ion OH- in phn theo phng trnh sau: 4OH- 2H2O + O2 + 4e Nu tip tc in phn th H2O s in phn: 2H2O 4H+ + O2 + 4e
V d 1 : Vit PTHH xy ra in phn dung dch NaOH: NaOH Na+ + OH- Catot(-) Anot (+)
Na+ khng b in phn
2H2O + 2e H2 + 2OH 4OH- 2H2O + O2 + 4e
Phng trnh in phn: H2O H2 + O2
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 ltB. 156,8 lt v 78,4 lt C. 78,4 lt v 156,8 ltD. 74,7 lt v 149,3 lt Hng dn gii:mNaOH (trc in phn) = 20 gam
in phn dung dch NaOH thc cht l in phn nc
Phng trnh in phn: : H2O 1/2 O2 (anot) + H2 (catot)
mNaOH khng i mdd sau in phn = 80 gam mH2O b in phn = 200 80 = 120 gam
nH2O in phn = 20/3 mol VO2 = 74,7 lt v VH2 = 149,3 lt Chn p n D
4. IN PHN HN HP CC DUNG DCH IN LI ( dd mui, axit, baz)* catot: Th t in phn: ion c tnh oxi ha mnh hn b in phn trc:
* anot: Th t in phn: S2-> I- > Br- > Cl- > OH- > H2O theo cc phng trnh sau: S2- S + 2e 2X- X2 + 2e
4OH- 2H2O + O2 + 4e
2H2O O2 + 4H+ + 4e
V d 1: in phn hn hp cc dung dch: HCl, CuCl2, NaCl vi in cc tr, c mng ngn. Gi tr pH ca dung dch thay i nh th no trong qu trnh in phn:A. Tng B.Gim C.Tng ri gim D.Gim ri tng
Chn p n A
V d 2 : in phn 200 ml dung dch hn hp gm HCl 0,1M v CuSO4 0,5M bng in cc tr . Khi catot c 3,2 gam Cu th th tch kh thot ra Anot l A.0,56 lt B.0,84 lt C.0,672 lt D.0,448 lt
Hng dn gii
CuSO4 Cu2+ + SO42- 0,1 0,1
HCl H+ + Cl-
0,02 0,02
Catot(-) Anot (+)
SO42- khng b in phn .
Cu2+ + 2e Cu 2Cl- Cl2 + 2e
0,1 0,05 0,02 0,01
2H2O 4H++ O2 + 4e
0,02 0,08 mol
Khi catot thot ra 3,2 gam Cu tc l 0,05 mol S mol Cu2+ nhn 0,1 mol , m Cl- cho ti a 0,02 mol 0,08 mol cn li l H2O cho
T s in phn kh thot ra ti anot l : Cl2 0,01mol ; O2 0,02 mol
Tng th tch : 0,03.22,4 = 0,672 lt
Chn p n C .
V d 3: in phn 100 ml hn hp dung dch gm FeCl3 1M , FeCl2 2M , CuCl2 1M v HCl 2M vi in cc tr c mng ngn xp cng dng in l 5A trong 2 gi 40 pht 50 giy catot thu c: A.5,6 g Fe B.2,8 g Fe C.6,4 g Cu D.4,6 g Cu
Hng dn gii
Theo : n Fe3+ = 0,1 mol ; n Fe2+ = 0,2 mol ; n Cu2+ = 0,1 mol ; n HCl = 0,2 mol
Sp xp tnh oxi ha ca cc ion theo chiu tng dn : Fe2+ < H+ < Cu2+ < Fe3+
Th t b in phn catot (-) :
Fe3+ + 1e Fe2+ (1)
0,1 0,1 0,1
Cu2+ + 2e Cu (2)
0,1 0,2 0,1
H+ + 1e Ho (3)
0,2 0,2
Fe2+ + 2e Fe (4)
Theo cng thc Faraday s mol e trao i hai in cc :
n = It/96500 = 5.9650/96500 = 0,5 mol
V s mol e trao i ch l 0,5 mol Khng c phn ng (4) , kim loi thu c ch phn ng (2) Khi lng kim loi thu c catot l : 0,1.64 = 6,4 gam
Chn p n C.
p dng tng t gii bi tp V.12, I.13 * Lu : - Mi trng dung dch sau in phn:
+ Dung dch sau in phn c mi trng axit nu in phn mui to bi kim loi sau Al (trong dy in ha) v gc axit c oxi nh: CuSO4, FeSO4, Cu(NO3)2.....
+ Dung dch sau in phn c mi trng baz nu in phn mui to bi kim loi ng trc Al (Al, Kim loi kim, kim th) v gc axit khng c oxi nh: NaCl, AlCl3, KBr....
+ Dung dch sau in phn c mi trng trung tnh: in phn cc dung dch in li cn li nh : HCl, H2SO4, Na2SO4....
- Cc loi in cc:
* in cc tr: (v d : platin...)
* in cc tan: ( v d: bc, ng...) Chnh anot b oxi ha, n mn dn (tan dn). Cc ion khc c mt trong dung dch hu nh cn nguyn vn, khng b oxi ha.
V d: in phn dung dch CuSO4 vi bnh in phn c anot lm bng kim loi Cu:
Phng trnh in phn: Cu2+ + Cu Cu(r) + Cu2+
- ngha s in phn: phng php in phn c ng dng rng ri trong thc t sn xut v trong phng th nghim nghin cu nh dng iu ch kim loi tinh khit; iu ch mt s phi kim v mt s hp cht; tinh ch mt s kin loi hoc trong lnh vc m in...II. NH LNG TRONG QU TRNH IN PHN
* Mun tnh khi lng cc cht gii phng cc in cc ta c th tnh theo phng trnh in phn.
V d:
160(g ) 64(g) 11,2(lit) 1(mol)
a(g) x (g) y (lit) z(mol)
Khi bit cng dng in ( I) v thi gian in phn (t) ta c th tnh theo cng thc Faraday:
m = A I t / F n
Trong : m - khi lng cht (rn, lng, kh) thot ra in cc (gam).
A - Khi lng nguyn t (i vi kim loi) hoc khi lng phn t (i vi cht kh) n - s electron trao i
I - Cng dng in ( A)
t - Thi gian in phn (s)
F - Hng s Faraday F= 96500C
- S mol e trao i mi in cc : n= I t / F* T l A/n c gi l ng lng in ha (). Mt ng lng gam in ha c khi lng A/n (gam)
S ng lng gam n cht (hay ion ) X = S mol nguyn t( hay ion) X .n
Ta c : khi Q= 96500C hay 1F
III. CC BC THNG THNG GII MT BI TP IN PHN
Bc 1: Vit phng trnh in li ca tt c cc cht in phn; Xc nh cc ion mi in cc.Bc 2: Vit cc PTHH ca cc bn phn ng (Vit phng trnh cho, nhn e ca cc ion ti cc in cc); Tnh s e trao i mi in cc (Nu gi thit cho cng dng in v thi gian in phn) : ne (cho anot) = ne (nhn catot).Bc 3: Biu din cc i lng theo cc bn phn ng hoc theo phng trnh in phn chung.Bc 4: Tnh theo yu cu ca bi ton+ Trong nhiu trng hp, c th dng nh lut bo ton mol electron (s mol electron thu c catot bng s mol electron nhng anot) gii cho nhanh. IV. MT S KINH NGHIM GII BI TP TRC NGHIM IN PHN(1) H2O bt u in phn ti cc in cc khi:
+ catot: bt u xut hin bt kh hoc khi lng catot khng i ngha l cc ion kim loi b in phn trong dung dch b in phn ht. + Khi pH ca dung dch khng i c ngha l cc ion m hoc dng (hay c hai loi) c th b in phn b in phn ht. Khi tip tc in phn s l H2O b in phn.
(2) 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). (3) 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. (4) 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 nh: 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 .
(5) Khi lng catot tng chnh l khi lng kim loi to thnh sau in phn bm vo. - gim khi lng ca dung dch: m = (mkt ta + mkh) (6) Vit bn phn ng (thu hoc nhng electron) xy ra cc in cc theo ng th t, khng cn vit phng trnh in phn tng qut v s dng CT: . - Vit phng trnh in phn tng qut (nh nhng phng trnh ha hc thng thng) tnh ton khi cn thit. (7) 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: (*) (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.
(8) 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 . (9) Nu bi yu cu tnh in lng cn cho qu trnh in phn th p dng cng thc: Q = I.t = ne.F . (10) 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. (11) 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. (12) 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.
V. BI TP P DNG
V.1. Khi in phn cc dung dch: NaCl, KNO3, AgNO3, CuSO4 vi in cc tr, mng ngn xp. Dung dch c pH tng trong qu trnh in phn l:A. NaCl B. KNO3 C. AgNO3 D. CuSO4V.2.(Trch i hc khi B-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:A. b = 2a B. 2b = a C. b > 2a D. b < 2aV.3: in phn 100ml dung dch CuSO4 0.2M vi cng I = 9.65 A.Tnh khi lng Cu bm bn catot khi thi gian in phn t1 = 200s v t2 = 500s (vi hiu sut l 100%).A. 0.32g ; 0.64g B. 0.64g ; 1.28g C. 0.64g ; 1.32g D. 0.32g ; 1.28g
V.4.(Trch i hc khi B-2010): in phn (vi in cc tr) 200 ml dung dich CuSO4 nng x mol/l, sau mt thi gian thu c dung dich Y vn con mau xanh, co khi lng giam 8g so vi dung dich ban u. Cho 16,8g bt Fe vao Y, sau khi cac phan ng xay ra hoan toan, thu c 12,4g kim loai. Gia tri x la A. 2,25 B. 1,5 C. 1,25 D. 3,25
V.5. 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 sB. Cu v 2800 s C. Ni v 2800 sD. Cu v 1400 s V.6. (Trch i hc khi A-2007): in phn dung dch CuCl2 vi in cc tr, sau mt thi gian thu c 0,32 gam Cu catt v mt lng kh X ant. Hp th hon ton lng kh X trn vo 200 ml dung dch NaOH ( nhit thng). Sau phn ng, nng NaOH cn li l 0,05M (gi thit th tch dung dch khng thay i). Nng ban u ca dung dch NaOH l (cho Cu = 64)A. 0,15M. B. 0,2M.C. 0,1M. D. 0,05M.
V.7. in
HYPERLINK ""
HYPERLINK ""phn dung dch NaCl (d=1,2g/ml) ch thu c mt cht kh in cc. C cn dung dch sau in phn, cn li 125g cn kh. Nhit phn cn ny thy gim 8g. Hiu sut ca qu trnh in phn l:A. 25% B. 30% C. 50% D.60%V.8: in phn 2 lt dung dch hn hp gm NaCl v CuSO4 n khi H2O b in phn hai cc th dng li, ti catt thu 1.28 gam kim loi v ant thu 0.336 lt kh ( iu kin chun). Coi th tch dung dch khng i th pH ca dung dch thu c bng A. 2 B. 13 C. 12 D. 3
V.9: 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 gamB. 1,72 gamC. 2,58 gamD. 3,44 gam V.10. C hai bnh in phn mc ni tip nhau. Bnh 1 cha dung dch CuCl2, bnh 2 cha dung dch AgNO3. Tin hnh in phn in cc tr, kt thc in phn thy trn catot bnh 1 tng 1,6 gam. Khi lng catot bnh 2 tng:A. 2,52 gam B. 3,24 gam C. 5,40 gam D. 10,8 gam
V.11. Mc ni tip 3 bnh in phn A, B, C ng 3 dung dch tng ng CuCl2, XSO4, v Ag2SO4 ri tin hnh in phn vi in cc tr cng dng in l 5A. Sau thi gian in phn t thy khi lng kim loi thot ra ti catot bnh A t hn bnh C l 0,76g, v catot bnh C nhiu hn catot bnh B v bnh A l 0,485g. Khi lng nguyn t X v thi gian t l:A. 55 v 193s B.30 v133s C. 28 v 193s D. 55 v 965sV.12. in phn dung dch hn hp cha 0,15 mol FeCl3; 0,3 mol CuCl2; 0,1mol NaCl n khi catot bt u si bt kh th ngng in phn. Ti thi im ny, catot tng:A. 27,6 gam B. 8,4 gam C. 19,2 gam D. 29,9 gamV.13. Ho tan a mol Fe3O4 bng dung dch H2SO4 va , thu c dung dch X. in phn X vi 2 in cc tr bng dng in cng 9,65A. Sau 1000 giy th kt thc in phn v khi trn catot bt u thot ra bt kh. Gi tr ca a l A. 0,025.B. 0,050. C. 0,0125.D. 0,075.
PHN C: KT QUA THC HIN:
Vic vn dng sng kin kinh nghim ny bn thn ti t c mt s kt qu ht sc kh quan. Trc ht nhng kinh nghim ny rt ph hp vi chng trnh, SGK mi. Hc sinh c hng th hc tp hn, tch cc ch ng sng to m rng vn hiu bit, ng thi cng rt linh hot trong vic thc hin nhim v lnh hi kin thc v pht trin k nng.. Hc sinh c c hi khng nh mnh, khng cn lng tng, lo ngi khi bc vo gi hc. y cng chnh l nhng nguyn nhn i n nhng kt qu tng i kh quan ca t kho st va qua.Cu th:.Khi cha p dng sng kin kinh nghimi tngKt qu kim tra (im s bi kim tra)
LpTng
S bi8.0 10.06,5 7,95.0 6.43.5 4.90.0 3.4
SL%SL%SL%SL%SL%
12A146817,41021,71634,81226.100
12A53812,637,91436,91847,325,3
12A64424,524,51534,32147,749,0
Tng128118,61511,74535,25139.864,7
Trn TB: 71 chim 55,5%Di TB 57 chim 44,5
Khi p dng sng kin kinh nghimi tngKt qu kim tra (im s bi kim tra)
LpTng
S bi8.0 10.06,5 7,95.0 6.43.5 4.90.0 3.4
SL%SL%SL%SL%SL%
12A1461226,12043,51328,312,1
12A53825,3821,01539,51231,612,6
12A64436,8818,22045,41125,024,6
Tng1281713,33628,14837,52418,732,4
Trn TB: 101, chim 78,9%Di TB 27, chim 21,1%
PHN D: KT LUN
Trn y l mt s k nng v phng php gii mt s dng bi ton c bn v in phn dung dch. Qu trnh tm ti nghin cu ti gii quyt c nhng vn sau:
- Nghin cu c s l thuyt ca in phn dung dch; cc qu trnh xy ra trong .
- T rt ra cc bc thng thng gii mt bi ton in phn.
- Sp xp mt cch c h thng cc dng bi tp in phn dung dch
- a ra c cc dng bi tp c bn nht v hng dn gii chi tit, ngn gn cc dng bi tp .
Trong cc nm ging dy v n luyn thi vi vic p dng phng php trn ti thy kh nng gii bi tp in phn dung dch ca hc sinh c nng cao ; cc em hng th hn trong hc tp. cc lp luyn thi vi i tng l hc sinh trung bnh kh th s hc sinh hiu v c k nng gii c cc dng bi tp trn l tng i. Mc d ti c gng tm ti, nghin cu song khng trnh khi nhng hn ch v thiu st. Rt mong nhn c s quan tm ng gp ca cc bn ng nghip . Phu Binh ngay 15 thang 5 nm 2012 Ngi thc hin
Trn Thi Thuy
TI LIU THAM KHO
1. L Xun Trng (ch bin), Sgk Ha hc 12 (nng cao)- NXB gio dc, H ni 2008.
2. thi i hc Cao ng cc nm 2007, 2008, 2009, 2010, 2011
3. Hong Nhm, Ha hc v c Tp 1 NXB gio dc, 2003.
4. Ng Ngc An, Phn ng oxi ha- kh v in phn- NXB gio dc, H ni 2006.
5. Nguyn Xun Trng, Bi tp Ha hc trng ph thng - NXB s phm, 2003.
6. Nguyn Xun Trng, n luyn kin thc ha hc i cng v v c trung hc ph thng NXB Gio dc, H Ni 2008.
MC LC
Trang
Phn A: t vn 1
Phn B: T chc thc hin tai 2
I. Nhng thun li v kh khn khi gii bi tp v in phn2
II. Phng php gii bi tp in phn trong dung dch 2
A. Mt s khai nim v s in phn
B.Cc qu trnh in phn2
.1. in phn dung dch mui31.1. in phn dung dch mui kim loi kim, kim th, Nhm31.2. in phn cc dd mui ca cc kim loi ng sau Nhm trong dy in 41.3. in phn hn hp cc dung dch mui5
2. in phn cc dung dch axit93. in phn cc dung dch baz9.4. in phn hn hp cc dung dch in li ( mui, axit, baz)
III. nh lng trong qu trnh in phn13
IV. Cc bc thng thng gii mt bi tp in phn14
V. Mt s kinh nghim gii bi tp trc nghim in phn dung dch14Bi tp p dng16
Phn C: Kt Qua 18
Phn D: KT LUN 19Ti liu tham kho19S LC L LCH KHOA HC
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I. THNG TIN CHUNG V C NHN
1. H v tn :
TRN TH THUY2. Ngy thng nm sinh : 05-10-1971
3. Nam, n :
N
4. a ch : p Ph Dng, X Ph Bnh, Huyn Tn Ph,
Tnh ng Nai
5. in thoi : C quan 061 3858 146
Di ng : 6. Fax :
E-mail :
7. Chc v : Gio vin Ho
8. n v cng tc : Trng trung hc ph thng Thanh Bnh,
X Ph Bnh, Huyn Tn Ph, Tnh ng Nai.
II. TRNH O TO
Hc v cao nht : i hc s pham
Chuyn ngnh o to : Ho hcIII. KINH NGHIM KHOA HC
Lnh vc chuyn mn c kinh nghim : Ging dy
S nm c kinh nghim : 20 nm
Cc sng kin kinh nghim c trong 5 nm gn y :
1 Tch cc ha hot ng ca hc sinh thng qua hot ng ging dy phn Hirocacbon
2-.Mt s phng php gii nhanh bi tp trc nghim ha hc THPT
3-S dng hiu qu dng dy hc mn ha hc trng THPT
4-. "Vn dng cc kin thc ho hc c bn gii thch cc hin tng thc t trong t nhin trong dy hc Ho hc " S GD&T NG NAI CNG HO X HI CH NGHA VIT NAM Trng THPT Thanh Bnh c lp T do Hnh Phc
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Tn Ph , ngy 16 thng 05 nm 2012
PHIU NHN XT, NH GI SNG KIN KINH NGHIM
Nm hc : 2011 - 2012
Tn sng kin kinh nghim : Phng php gii bi tp in phn dung dch
H v tn tc gi : Trn Th Thu n v : T Ha- Trng THPT Thanh Bnh, Tn Ph, ng Nai.
Lnh vc :
Qun l gio dc.. ( Phng php dy hc b mn ......( Phng php gio dc.. ( Lnh vc khc(1. Tnh mi
C gii php hon ton mi( C gii php ci tin, i mi t gii php c...(2. Hiu qu
Hon ton mi v trin khai p dng trong ton ngnh c hiu qu cao...( C tnh ci tin hoc i mi t nhng gii php c v trin khai p
dng trong ton ngnh c hiu qu cao...( Hon ton mi v trin khai p dng ti n v c hiu qu cao...( C tnh ci tin hoc i mi t nhng gii php c v trin khai p
dng ti n v c hiu qu cao... (3. Kh nng p dng
Cung cp c cc lun c khoa hc cho vic hoch nh ng li, chnh
sch :
Tt (
Kh (
t ( a ra cc gii php khuyn ngh c kh nng ng dng thc tin, d thc hin v d i vo cuc sng : Tt (
Kh (
t ( c p dng trong thc t t hiu qu hoc c kh nng p dng t hiu qu trong phm vi rng : Tt (
Kh (
t ( XC NHN CA T CHUYN MN TH TRNG N V
T TRNG
HIU TRNG
Trn Anh Nht Trng
S GIO DC V O TO NG NAI
n v : TRNG THPT THANH BNH
-------------------------------------------
M s : ...
SNG KIN KINH NGHIM
: Phng php gii bi tp in phn dung dch
Ngi thc hin : TRN TH THU
Lnh vc nghin cu :
Qun l gio dc .. (
Phng php dy hc b mn....(
Phng php gio dc(
Lnh vc khc.(
C nh km :
( M hnh ( Phn mm ( Phim nh( Hin vt khc
Nm hc : 2011 - 2012
PAGE 3Phu Binh ngay 15 thang 5 nm 2012