Hanna-instruments HI 4008 Manual do Utilizador descarregar pdf (Página 3)

III. III.

III.

Theory of OperationTheory of Operation

Theory of Operation

The HI 4108 or HI 4108 cupric electrodes are potentiometric

devices used for the rapid determination of free cupric ions

in samples and as a detector for the titration of cupric with

EDTA.

Cupric sensors are “electrodes of the third kind”

because they detect cations which also form low-solubility

salts with sulfide anions that also form low-solubility salts

with silver.

The electrode functions as a sensor or ionic conductor. The

HI 4008 requires a separate reference electrode to complete

its electrolytic circuit. The HI 4108 incorporates a reference

electrode. The mixed cupric sulfide/ silver sulfide mem-

brane produces a potential change due to changes in the

sample’s cupric ion activity. When the ionic strength of the

sample is fixed by the addition of ISA, the voltage is pro-

portional to the concentration of cupric ions in solution and

the electrode follows the Nernst equation.

E= E

+2.3 RT/nF log A

ion

E= observed potential

= Reference and fixed internal voltages

R= gas constant (8.314 volt coulomb/K Mole)

n= Charge on ion (2+)

=ion activity in sample

T= absolute temperature in K

F= Faraday constant (9.648 x 10

coulombs/mole)

1 2 3 4 5 6 7 8 ... 15 16

Sem comentários

Hanna-instruments HI 4008 Manual do Utilizador Página 3