Pin in ha v n mn kim loi
Pin in ha v n mn kim loi Din n ha hc thi @
Pin in ha v n mn kim loi
I. Pin in ha
1. Cu to v hot ng
- Kim loi mnh lm in cc m (anot) v b n mn.
- Kim loi c tnh kh yu hn c bo v.
- Cu mui c tc dng trung ha dung dch
2. Tnh sut in ng ca pin in ha
Epin = Ecatot Eanot = Emax - Emin
II. n mn kim loi
S n mn kim loi l s ph hu kim loi hoc hp kim do tc dng ca cc cht
trong mi trng xung quanh. l mt qu trnh ho hc hoc qu trnh in ho
trong kim loi b oxi ho thnh ion dng.
M ( Mn+ + ne
C hai kiu n mn kim loi l n mn ho hc v n mn in ho.
1. n mn ho hc
n mn ho hc l qu trnh oxi ho - kh, trong cc electron ca kim loi c
chuyn trc tip n cc cht trong mi trng.
My mc dng trong cc nh my ho cht, nhng thit b ca l t, ni hi, cc
chi tit ca ng c t trong b n mn do tc dng trc tip vi cc ho cht hoc
vi hi nc nhit cao. Nhit cng cao, kim loi b n mn cng nhanh.
2. n mn in ho
n mn in ho l qu trnh oxi ho - kh, trong kim loi b n mn do tc dng
ca dung dch cht in li v to nn dng electron chuyn di t cc m n cc
dng.
a) Th nghim n mn in hoNhng thanh km v thanh ng khng tip xc vi
nhau vo cc ng dung dch H2SO4 long. Ni thanh km vi thanh ng bng dy
dn cho i qua mt vn k. Kim vn k quay, chng t c dng in chy qua. Thanh
Zn b mn dn, thanh Cu c bt kh thot ra.
Gii thch : in cc m (anot), km b n mn theo phn ng :
Zn ( Zn2+ + 2e
Ion Zn2+ i vo dung dch, cn electron theo dy dn sang in cc
ng.
in cc dng (catot), ion H+ ca dung dch H2SO4 nhn electron bin
thnh nguyn t H ri thnh phn t H2 thot ra :
2H+ + 2e ( H2(b) C ch n mn in ha st (hp kim st trong khng kh
m)
Ly s n mn st lm th d. Trong khng kh m, trn b mt ca st lun c mt
lp nc rt mng ho tan O2 v kh CO2 trong kh quyn, to thnh mt dung dch
cht in li. St v cc tp cht (ch yu l cacbon) cng tip xc vi dung dch
to nn v s pin rt nh m st l anot v cacbon l catot.
Ti anot, st b oxi ho thnh ion Fe2+ : Fe ( Fe2+ + 2e
Cc electron c gii phng chuyn dch n catot.
Ti vng catt, O2 ho tan trong nc b kh thnh ion hiroxit : O2 +
2H2O + 4e ( 4OH(Cc ion Fe2+ di chuyn t vng anot qua dung dch in li
n vng catot v kt hp vi ion OH( to thnh st (II) hiroxit. St(II)
hiroxit tip tc b oxi ho bi oxi ca khng kh thnh st (III) hiroxit,
cht ny li phn hu thnh st II oxit.
G st mu nu, c thnh phn chnh l Fe2O3.xH2O.
c) iu kin xy ra s n mn in ho
Cc in cc phi khc cht nhau, c th l cp 2 kim loi khc nhau hoc cp
kim loi vi phi kim.
Cc in cc phi tip xc trc tip hoc gin tip vi nhau qua dy dn.
Cc in cc cng tip xc vi dung dch cht in li.
Thiu mt trong ba iu kin trn s khng xy ra s n mn in ho.
Cc diu kin m t trn ch l tuyt i ho, qu trnh n mn in ho xy ra
trong t nhin.
III. Chng n mn kim loi
S n mn kim loi gy tn tht to ln cho nn kinh t quc dn. Hng nm chng
ta phi sa cha, thay th nhiu chi tit ca my mc, thit b dng trong cc
nh my v cng trng, cc phng tin giao thng vn ti,...
Mi nm, lng st, thp b g chim n gn 1/4 lng c sn xut ra. V vy, chng
n mn kim loi l cng vic quan trng cn phi lm thng xuyn ko di thi gian
s dng ca cc my mc, vt dng lm bng kim loi. Di y l mt vi phng php
chng n mn kim loi.
1. Phng php bo v b mt
Dng nhng cht bn vng i vi mi trng ph ngoi mt nhng vt bng kim loi
nh bi du m, sn, m, trng men,... St ty l st c trng thic, tn l st c
trng km. Cc vt bng st thng c m niken hay crom.
2. Phng php in ho
Ni kim loi cn bo v vi mt kim loi hot ng hn to thnh pin in ho v
kim loi hot ng hn b n mn, kim loi kia c bo v. Th d bo v v tu bin lm
bng thp v v tu (phn chm di nc), ng thp dn nc, dn du, dn kh t di t,
ngi ta lp vo mt ngoi ca thp nhng khi km. Kt qu l km b nc bin hay
dung dch cht in li trong t n mn thay cho thp.
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