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.



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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· 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



~ 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



Am= K /C



,"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.



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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(c:ath IDd1e)









Pt forO O 1 l , d u d t n , g

i f l e c I : f . ' o n ,







Using the above equations the tltermodfnamie

parameters AlI, A.G& . AS ofa cell reaction can be

determined,

















. . . . . . . . . . .. . . . .- I I ' .



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



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

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File1-Electrochemistry ppt 25