282
5 – Applications
Based on segment (a) of figure 94, we obtain
s
2.3 log x
E
expt
Δ
Δ
=
. (
)
(
)
.
s
m V per decade
2 3 3 0
100
242
20 6
expt =
−
− −
=
for cell (Ia) at 230 °C.
Based on segment (b) of figure 94, we obtain for cell (Ib), at 190 °C,
. ( .
.
)
(
)
.
s
m V per decade
2 3 3 200 1 097
200
300
20 7
expt =
−
−
− −
=
b. The experimental slope is very close to the theoretical slope s th obtained
with an electrode reaction involving two electrons; that is,
s
F
RT
2
th =
2 for cell (Ia)
.
.
s
m V per decade
2 96 480
8 314 503
21 6
th =
=
#
#
2 for cell (Ib)
.
.
s
m V per decade
2 96 480
8 314 463
19 95
th =
=
#
#
c. For these conditions, we can propose the following electrode reaction:
O 2 + 2e m O 2
2−
where O 2
2−
is the peroxide ion.
7. The proposed reactions should involve a single electron and the peroxide
ion O 2
2−
. We can write
2 cell (Ia)
NO 2 + O 2
2− + e m NO 3
− + O
2−
2 cell (Ib)
NO + O 2
2− + e m NO 2
− + O
2−
The potential of each of these electrodes is proportional to
ln P
F
RT
NO x (x = 1
or 2) and does not depend on the oxygen partial pressure.
8. In the presence of only nitrogen dioxide NO 2 , a possible reaction involving
a single electron and no O 2 is
NO 2 + e m NO 2
−
9. To avoid the drawbacks of a sodium reference electrode, we can use the
following electrodes: Ag / AgCl + NaCl / NASICON
Ag,O 2 / Na
+
β-alumina