PHYSICAL CHEMISTRY IN BRIEF

CHAP. 11: ELECTROCHEMISTRY [CONTENTS] 361

11.3 Electric conductivity of electrolytes

Ohm’s law applies in electrolytes just like in first-class conductors:

R=

E

I

, (11.22)

whereRstands for resistance,Efor voltage, andIdenotes electric current.

Note:To be more precise, Ohm’s law applies in cases where no polarization of electrodes

occurs, see11.9. In order to suppress the effect of polarization, alternate current is used

when measuring resistance.

11.3.1 Resistivity and conductivity

Theresistivityρis the resistance of a conductor of unit length and unit cross-section. It is

defined by the relation

ρ=R

A

`

, (11.23)

whereAis the cross-section and`is the length of the conductor.
U Main unit:Ω m
Theconductivityκis the reciprocal value of resistivity.

κ=

1

ρ

. (11.24)

U Main unit:Ω−^1 m−^1 = S m−^1.

Example

The resistanceR= 100Ωwas measured in a potassium chloride solution. Each of the electrodes

had a surface area of 4 cm^2 , and the distance between them was 2 cm. Calculate the conductivity.

Solution

From relations (11.23) and (11.24) we obtain

κ=

`

R A

=

2 × 10 −^2

100 × 4 × 10 −^4

= 0. 5 S m−^1.