Theory - Testo 252 Bedienungsanleitung

Conductivity measurement

Theory

The molecules of three large groups of substances
(salts, acids and electrolytes) separate into
electrically charged ions when dissolved in water.
This process is called dissociation.
Example of dissociation:
Table salt (NaCl)
+ -
NACl NA + Cl
When an alternating electromagnetic field is
placed over the elelctrolyte, the electrodes can
move the ions. This movement of ionic charge can
be considered as an "electrical current", similar to
that of electrons in a copper wire. This
current is used to measure the electrolytic
conductivity.
As a result of this ionic current in the electrolyte, an
increase in the number of ions in the electrolyte (
higher concentration) causes an increase in the
electrolytic conductivity. This is only valid up to a
certain limit in the concentration. Should this limit
be exceeded, the ions will begin hindering each
other. This means that dissociation is incomplete
in high concentrations of matter; the conductivity
increases slower than the concentration of matter.
When the electrolyte is of a simple composition, i.e.
only water and one dissociated matter (e.g. table
salt NaCl), the concentration of the dissolved
matter can be calculated from the conductivity
value, (provided that the concentration is not too
high).
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