232
5 – Applications
Figure 93 – emf as a function
of O 2 content in the presence
of (a) 40 ppm and (b) 4 ppm
of NO 2 , cell (Ia) at 230 °C,
(c) NO cell (Ib) at 190 °C.
Figure 94 shows the emf of these two sensors as a function of oxygen content
and in total absence of nitrous oxide.
Figure 94 – emf as a function
of O 2 content and in total absence
of nitrous oxide for (a) cell (Ia)
at 230 °C, (b) cell (Ib) at 190 °C.
a. Calculate the slopes of the lines.
b. Deduce the number of electrons exchanged in the electrode reaction.
c. Propose an electrode reaction compatible with the number of electrons
exchanged.
7. Based on the experimental results from the preceding questions, propose
electrode reactions compatible with the responses for cells (Ia) and (Ib).
8. In the presence of only nitrogen dioxide NO 2 , we observe that
2 the emf of cell (Ib) corresponds to the exchange of a single electron,
2 the emf is independent of the oxygen partial pressure.
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