Hanna Instruments HI 4007 - Manual (Page 3)

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III. III. III. III. III. Theory of Operation Theory of Operation Theory of Operation Theory of Operation Theory of Operation:::::
The HI 4007 or HI 4107 chloride electrodes are potentio-
metric devices used for the rapid determination of free chlo-
ride ions in ground water, boiler water and drinking water.
The electrode functions as a sensor or ionic conductor. The
HI 4007 requires a separate reference electrode to complete
its electrolytic circuit. The HI 4107 has a reference electrode
incorporated in its design. The silver chloride pellet is prac-
tically insoluble in the test solutions being measured and
produces a potential change due to changes in the sample’s
ion activity. When the ionic strength of the sample is fixed
by the addition of ISA, the voltage is proportional to the
concentration of chloride ions in solution and the electrode
follows the Nernst equation.
E= E
a
+ 2.3 RT/nF log A
ion
E= observed potential
E
a
= Reference and fixed internal voltages
R= gas constant (8.314 J/K Mol)
n= Charge on ion (-1)
A
i
=ion activity in sample
T= absolute temperature in K
F= Faraday constant (9.648 x 10 4 C/equivalent)