Chemistry Reference
In-Depth Information
such a way that their corresponding electrical currents are equal but oppo-
site. This means that no net current will be measured. More generally, it is
possible that a net current
I
net
is measured which reflects the excess of
charge transfer not compensated by the opposite process (Equation 1.2):
I
=+
I
I
[1.2]
net
ox
red
where
I
ox
is the electrical current of the oxidation reaction (positive sign)
and
I
red
is the electrical current of the reduction reaction (negative sign).
The electrical current flowing through an electrical system is carried by
electrons. In solution, however, charges are moving through the transport
of ions instead of electrons. Making contact with the electrode is no
problem when using a conductor and connecting it to the electron-
conducting electrode; for the solution, however, this is not possible. To make
contact with the solution, a conductor must be immersed in it in order to
obtain electrical contact. However, this implies that a second interface is
created between the solution and this conductor surface. An interim con-
clusion is that for electrochemical measurements, at least two electrodes are
always necessary to realise and study an electron-transfer reaction.
A basic electrochemical cell always consists of at least two electrodes,
schematically shown in Fig. 1.1, where two metallic electrodes are immersed
R
2
O
1
e
-
e
-
O
2
R
1
1.1
Scheme of a potentiometric setup with an anode (electrode on the
right) at which oxidation reactions occur and a cathode (left elec-
trode) at which reduction reactions take place.
