CHM171L / A11 Physical Chemistry Laboratory 2
Quarter S.Y. 2010-2011
Conductimetry: Determination of the Electrical Properties of
, Palomaria, Ralph Matthew
, Regulacio, Anna Rafaela
Professor, CHM171L/A11, School of Chemical Engineering, Chemistry and Biotechnology, Mapua Institute of Technology;
CHM171L /A11 , School of Chemical Engineering, Chemistry and Biotechnology, Mapua Institute of Technology
The conductivity (or specific conductance) of an electrolyte solution is a measure of its
ability to conduct electricity. The SI unit of conductivity is siemens per meter
(S/m).Conductivity measurements are used routinely in many industrial and environmental
applications as a fast, inexpensive and reliable way of measuring the ionic content in a
solution. For example, the measurement of product conductivity is a typical way to monitor
and continuously trend the performance of the water purification systems.
In many cases, conductivity is linked directly to the total dissolved solids (T.D.S.). High
quality deionized water has a conductivity of about 5.5 μS/m, typical drinking water in the
range of 5-50 mS/m, while sea water about 5 S/m (i.e., sea water's conductivity is one
million times higher than deionized water). Conductivity is traditionally determined by
measuring the AC resistance of the solution between two electrodes.
The electrical conductivity of a solution of an electrolyte is measured by determining the
resistance of the solution between two flat or cylindrical electrodes separated by a fixed
distance. An alternating voltage is used in order to avoid electrolysis. Typical frequencies
used are in the range 1-3 kHz. The dependence on the frequency is usually small. The
resistance is measured by a conductivity meter. A wide variety of instrumentation is
commercially available. There are two types of cell, the classical type with flat or cylindrical
electrodes and a second type based on induction. Many commercial systems offer
automatic temperature correction.
The conductivity of a solution depends on:
• The quantity of ions. The more ions a solution contains, the higher will be its conductivity.
• The kind of ions. The smaller and more mobile an ion, the better will be its
electrical conductivity. Thus H3O+, OH-, K+ and Cl- ions all conduct very well.
• The solvent. The more polar the solvent, the better the ionisation of the solutes it
contains. In relation to this, water is an ideal solvent, while methyl alcohol is also good.
• The temperature. Ionic mobility increases with rising temperature.
According to the type of ion, the conductivity increases by 1-3% / ºC.