Concise Physical Chemistry

c13 JWBS043-Rogers September 13, 2010 11:27 Printer Name: Yet to Come

13 Coulometry and Conductivity

Aqueous solutions of some substances conduct electricity well and some conduct it

poorly. All aqueous solutions offerresistance Rto flow of electricalcurrent I. Good

conductors offer low resistance and poor conductors offer high resistance. In what

follows, we shall assume Ohm’s lawV=IR, whereVis the potential difference

forcing current to flow through the resistance.

13.1 ELECTRICAL POTENTIAL

A potential difference between two points separated by a distancelcan be maintained

by means of an electrochemical cell, commonly called a “battery” (Fig. 13.1):

φ=φ(0)−φ(l)

The potential differenceV=
φis called thevoltageorvoltage drop. We shall be

concerned with the influence of a potential difference on various chemical solutions,

especially salt solutions, placed between a pair of charged parallel plates. Solutions

of salts in water that conduct electricity are calledelectrolyte solutions. Like other

conductors, they offer some resistance to current flow.

13.1.1 Membrane Potentials

In mammalian cells, potential differences are established by a different mechanism. If

a membrane is permeable to ions of one charge but impermeable (or less permeable) to

Concise Physical Chemistry,by Donald W. Rogers

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