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Chemistry LibreTexts

Pre- or Post-test Questions

There are several concepts that students need to grasp in this experiment as outlined below, (all the suggested readings above will help students answer these questions below):

  1. What is a cyclic voltammogram and how does one identify the reversibility of an electron transfer reaction by cyclic voltammetry? Students are required to read the references on cyclic voltammetry as noted above, (Kissinger et al., discuss the how to measure peak potential differences, and it illustrates examples of reversible, irreversible and quasireversible cyclic voltammograms). Kissinger et al. shows that the irreversible cyclic voltammogram only has an anodic peak observed. For the reversible cyclic voltammogram shows the cathodic and an anodic peak observed. The peak potential difference between the anodic and cathodic peak relates to the supporting electrolyte effect on the cyclic voltammogram as described by Zhang et al. The P3MT electrode was shown by Zhang et al., that the smallest peak potential difference response to catechol was in sulfuric acid compared to a bare electrode. This assists the students with understanding electrocatalytic ability of P3MT electrode compared to a bare electrode and this helps the student with answering part II.
  2. Why use the modified polymer electrode or the sonogel-carbon modified electrode with titanium oxide to detect catechol compared to the use of a bare carbon electrode? Catechol and ascorbic acid is detected at the modified electrode and no response of catechol and ascorbic acid at the bare sonogel-carbon electrode. The electron faster is easier and better at the modified electrodes P3MT and SGC/TiO2 compared to the bare electrode.
  3. Which electrode has the greatest stability the P3MT sonogel-carbon electrode or the SGC/TiO2 electrode over 20 cyclic voltammogram scans to detect catechol in the presence of ascorbic acid? Students typically get results as cyclic voltammograms displayed by Figure 2(b)., above that illustrate the problems of poor stability over 20 scans. The P3MT black polymer falls into the sulfuric acid over several scans where the SGC/TiO2 electrode can be used over and over without breaking down over time.

More examples of data compiled by students are shown below:

Cyclic voltammogram of 5mM catechol in 10 mM H2SO4 (100 mV/s) vs. Ag/AgCl /3 M NaCl, on SGC/TiO2 modified electrode (Reversible catechol).

Cyclic voltammogram of 5 mM ascorbic acid in 10 mM H2SO4 (100 mV) vs. Ag/AgCl/3M NaCl on SGC/TiO2 modified electrode (Irreversible ascorbic acid).

1 SGC/TiO2 and 2 P3MT: cyclic voltammogram of 5 mM catechol + 5 mM ascorbic acid in 10 mM H2SO4 (100 mV/s). This data allows the student to see that the SGC/TiO2 can distinguish there is ascorbic acid and catechol present where with the P3MT electrode there is no peak for ascorbic acid and the peak difference (cathode –anode) is much greater for catechol detection.