Chemistry Reference
In-Depth Information
7000
7
6000
5000
6
4000
5
4
3000
3
2000
2
1000
1
0
0
0.2
0.4
0.6
0.8
1
c
OH
- (mol l
-1
)
4.8
Relationship between pseudo-limiting-current of the prewave at
E
=
0.45 V vs. SCE and the hydroxide concentration (pH) for various
hydrogen peroxide concentrations, recorded at a glassy-carbon
electrode rotating at 16.67 Hz. The numbered curves correspond to
hydrogen peroxide concentrations of (1) 0.02, (2) 0.05, (3) 0.1, (4)
0.2, (5) 0.3, (6) 0.4 and (7) 0.5 mol l
-
1
.
the relation is represented between the current signal at 0.45 V vs. SCE,
situated in the pseudo-limiting-current plateau, and the hydrogen peroxide
concentration for a large number of pH values in the range of 10-14.
Remarkable characteristics are the non-linear relation between the oxida-
tion current and the hydrogen peroxide concentration, which is more pro-
nounced when the pH is higher, and the strong increase of the current with
an increasing pH. The latter is an indication that there is a high probability
of hydroxide ions in the reaction sequence. The pH dependency is displayed
more directly in Fig. 4.8, which shows the relation between the oxidation
current in the pseudo-limiting-current plateau of the prewave and the con-
centration of the hydroxide ions [(1 ¥ 10
-4
-1 mol l
-1
) area] for different
hydrogen peroxide concentrations in the 0.02-0.5 mol l
-1
range.
The fact that the relation between the hydrogen peroxide concentration
and the oxidation current measured at
E
= 0.45 V vs. SCE is not linear
with all pH values could be due to the changes in the nature of the rate-
determining step, in the mechanism itself or in the reaction orders of the
components involved in the reaction.
The calibration curves in Fig. 4.7, registered at a constant pH, can be
divided into three groups. With the lowest pH values (10 to ca. 11.6), the
slope of the
I
LP
vs.
c
relation increases with an increasing hydrogen perox-
