Page 9 - Pharmaceutical Analytical Chemistry II - Pharm D Clinical- 07-PA202

Liquid junction Potential

It is the potential that arises at the interface between two electrolyte
solutions that differ in composition.
It results from differences in rate of migration "mobility" of ions across
the interface (liquid junction: fritted disk)
It causes interference in measuring the emf of the cell, i.e. it contributes
to the total cell potential
It could be eliminated BY using cell equipped with Salt Bridge
Salt Bridge: ionic solution that isolates the reactants but maintains

electrical contact between the two halves of the cell. Saturated solution
of KCl is the most widely used, because K+ and Cl─ have the same
mobility.

Relative Electrode Potential
"Electrode Potential"

It is defined as the potential of a cell consisting of the electrode in
question acting as the right-hand electrode [Cathode] and the
reference electrode (e.g standard hydrogen electrode 'SHE ')
acting as the left-hand electrode [Anode].
E.g. To obtain the potential of Ag/Ag+ electrode

Schematic representation of the cell:

SHE  Ag+ (0.02 M)  Ag

Ecell = Eright ─ Eleft
Ecell = EAg ─ ESHE

The potential of SHE is assigned a value of 0.00 V at all temp

Ecell = EAg ─ 0.000 = EAg

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