file1-electrochemistry ppt 25
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Electrochemistry is a branch of chemistry that
studies chemical reactions which take place in a solution
at the interface of an electron conductor (a metal or a
semiconductor) and an ionic conductor (the electrolyte),
and which involve electron transfer between the
electrode and the electrolyte or species in solution.
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Flowof electricity through solution of electrolytes is due
to the migration of ions when potential difference is
applied between the two electrodes.
Cations are positively charged, which moves towards the
negatively charge particle known as cathode.
Anions are negatively charged, which moves towards the
positively charge particle known as anode.
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Unreg is tered vers ion .. p .__ ,....
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· The resistance of any conductor varies directly as itslength (I) and inversely as its cross sectional area (a).
R ai/a
R = pi/aWhere,
P is a constant, depending on the nature of the
material, specific resistance.
C...Reciprocal of specific resistance, 1/p is called specific
conductance.I = length of conductora = area of cross section
Unit: Q-1cm-1
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~ It is defined as the conduct ce of the volume of solution which
has one equivalent of electrolyte dissolved in it.
J\eq = Kx V
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Am= K /C
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,"Molar conductance of an electrolyte increases withincrease in dilution.
,'Due to the increase in the degree of dissociation of the
electrolyte.
Degree of dissociation
",.,The fraction of the total electrolyte in solution which
'exists in the form of its ions in,dilution.
"·The same amount of electrolyte is capable of furnishinga larger no of ions.
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I Increase in the number ofions on dilution is much less than the increase·
in.the volume of the solution so the number of ions per unit volume
decrease.
- Specific conductance deere ases"molar conductance Increases on
dilution.
On plotting concentration VSmolar conductance,
Strong electrolytes :
KCl, ReI, etc molar conductance shows certain limiting value when the
concentration approaches zero.
It is known as molar conductance at zero concentration (or) infinite
dihrtion. A O m
Weak electrolytes :
,C,R3e,OO,R, 'NH
40H', etc no irrdication of molar conductance attaining
a limiting value even when the concentration approaches zero.
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U n re gi s te re d ve rs iEle~ifOi(1h0R1tic-al-~ellco m
Co,n'versio'n ofchemical to
Electrical
energy
Eg. Dry cell
Electrical energy .to chemical
usinq 'external
source
Eg. lead storage
battery
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Pt forO O 1 l , d u d t n , g
i f l e c I : f . ' o n ,
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Using the above equations the tltermodfnamie
parameters AlI, A.G& . AS ofa cell reaction can be
determined,
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. . . . . . . . . . .. . . . .- I I ' .
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Power supply
Protected meta l
(+ ) Catbodie prot~ctjon (UP)
is a te 'cl tblque, to 'control the'I . . . 1 of ametal surface
bymaking itwork asa
_ ' I ' ~·Qf3D.
J This is achieved hy
placing ill contad with tlte
metal to be protected
anotber more easilf'"
corroded metal to ac t as the" . " _ . - ~ - .
a n o d e . of the
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Metal cladding• Coating of base metal by a dense, homogeneous layer of
cladding materials like pure metals (Ni, Pb, Ag, Pt) or alloys
like stai nless steel.
Electroplating• Deposition of coating metal on the base metal by passing a
di rect current through an electrolytic solution of soluble
salt of the coating metal.
Plastic coating• Plastic coated surface isolates the underlying metal from
the corroding environment & prevent the penetration of the