Chemistry Reference
In-Depth Information
6
5
4
y
= -0.9642x + 1.3496
R
2
= 0.9995
3
2
1
0
-5
-4
-3
-2
-1
0
Log
c
(mol l
-1
)
9.5
Logarithmic plot of the impedance at zero phase-angle shift as a
function of electrolyte concentration obtained from the
electrochemical cell with
A
=
314 mm
2
,
d
=
112 mm and
T
=
298.0 K.
this effect is less pronounced at higher concentrations can be explained by
interactions between the ions, which are much closer to each other at higher
electrolyte concentrations, thus making free diffusion towards the anode
(for Cl
-
) and the cathode (for Na
+
) more difficult.
Figure 9.5 shows the relationship between the logarithm of the obtained
impedance at the completion of the semi-circle (right-hand side of the semi-
circle in Fig. 9.2) as a function of the logarithm of the sodium chloride con-
centration. A linear relationship is observed with good correlation
coefficient and a slope of -1, indicating that the relationship between the
impedance (
R
) and the electrolyte concentration (
c
) is reciprocal. There-
fore Equation 9.1 can be re-defined to:
(
)
◊
RkdAc
=
,
-
1
[9.2]
1
where
k
1
is a factor containing the unknown parameters and relationships.
In Equation 9.2, the value of
k
1
is 20.0 ± 0.8, taking into account a tempera-
ture of 298.0 K and knowing that this factor is dependent on
A
and
d
, two
parameters that need to be investigated further in this work. The value of
k
1
= 20.0 is valid for
A
= 314 mm
2
and
d
= 112 mm.
9.2.4
Study of the influence of the electrode surface area
Similar to the experiments described in the previous section, but this time
with various surface areas of the palladium electrodes and at each elec-
