An
electrochemical
Sensor is a setup used for creating an
electromotive force in a conductor separating two
reactions. The current is caused by the reactions
releasing and accepting electrons in to the different
ends of the conductor. The most common example of an
electrochemical cell is a standard 1.5-volt
battery.
In each half-cell is a chemical undergoing
either oxidation or reduction. In a full electrochemical
cell one side must be losing electrons (oxidation) in to
its electrode, while the other half-cell gains electrons
(reduction.) If the atoms/ions involved in the reaction
are metal, the same metal is used for each electrode. If
the atoms/ions involved in the reaction at each
half-cell are not metal, obviously no electrode can be
constructed out of it. Nonreactive metals such as
platinum are used as a substitute. Finally a salt
bridge is necessary to provide electrical contact
between the cells--but without the solutions mixing.
This can simply be a strip of filter paper soaked in
saturated potassium nitrate (V) solution.
Different choices of substances for each half cell
results in varying potential differences. Each reaction
is undergoing an equilibrium reaction between different
oxidation states of the ions -- when equilibrium is
reached the cell cannot provide further voltage. In the
half-cell which is undergoing oxidation, the further the
equilibrium lies to the ion/atom with the more positive
oxidation state the more potential this reaction will
provide. Similarly, in the reduction reaction, the
further the equilibrium lies to the ion/atom with the
more negative oxidation state the higher the
potential.
This potential can be predicted quantitatively
through the use of electrode potentials (the voltage
measured when the substance is connected to hydrogen.)
The difference in voltage between electrode potentials
gives a prediction for the potential measured.
