課程名稱︰分析化學二
課程性質︰必修
課程教師︰陳俊顯
開課學院：理學院
開課系所︰化學系
考試日期（年月日）︰104/3/29
考試時限（分鐘）：105分鐘
試題 :
課號：203 21220, spring 2015, Exam #1 (2015-03-29) 10:20 ~ 12:05 (滿分125分：
乘30%為期末總成績積分)
姓名(name)：__________ 學號(student ID)：__________
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會向同學宣布。
I.(63%) Multiple Choice Questions (Select one answer and write it on this sheet
above the underlines.) (3 points for a correct answer, -1 point for a
wrong answer, mark △ if you think that there is no correct answer)
(單選，每題 3 分，錯倒扣 1 分，若你認為選項中沒有正確答案，則打△)
1. Which of the following defines where the electrochemical reduction taking
place in an electrochemical cell?
a) Cathode. b) Anode. c) Working electrode.
2. For a spontaneous reaction, the value of Ecell is defined by anode cathode.
a) E_anode - E_eathode.
b) E_eathode - E_anode.
c) E_indicator - E_reference.
3. What is the purpose of using "saturated" electrolytes in reference
electrodes?
a) To reduce the resistance of the reference electrode.
b) To make sure that the concentration ratio of supporting electrolyte to the
analyte is more than 100.
c) To obtain a constant value of the reaction quotient in the Nernst equation
that describes the reference electrode.
4. The reference electrode is preferably nonpolarizable. A polarizable
reference electrode is detrimental for electrochemical studies because
a) the potential of the reference electrode is easily changed.
b) the iR drop is large.
c) the charging current is large.
5. The purpose of a Luggin capillary for the reference electrode is to minimize
a) the distance from the reference to the working electrode.
b) the current going through the reference electrode.
c) the contamination to the solution under study.
6. When using Clark oxygen electrodes, the configuration of 2 electrodes,
instead of a 3-electrode system, works alright because
a) the potential applied to the working electrode is not scanned.
b) the redox current at the working electrode is very small.
c) there is an Ag guard electrode to amplify the current signal.
7. If the problem of uncompensated iR_un become more and more serious, what
would be observed for a reversible electrochemical reaction?
a) Peak current becomes larger.
b) E_cathodic peak becomes more negative.
c) Peak separation (|E_(cathodic peak) - E_(anodic peak)|) becomes smaller.
8-10. Answer questions 8-10 based on the glucose sensors discussed in class.
8. In our lecture, we discussed a glucose sensor that relies on the ubiquitous
O2. The sensor monitors the amount of produced H2O2 to derive the
concentration of glucose. What is the drawback of this sensor design?
a) The amount of O2 in the atmosphere is too much.
b) The reduction of H2O2 requires a very negative E_wk which reduces other
electroactive species in the blood sample.
c) The concentration of dissolved O2 in the blood sample is sometimes not
enough for the sensing reaction.
9. In our lecture, we discussed a glucose sensor that contains glucose oxidase
and a dimethyl ferrocene. Which of the following is an electroactive species
in this sensing device?
a) Dimethyl ferrocene. b) Glucose oxidase. c) H2O2
10. Which statement is true about the glucose sensor that contains glucose
oxidase and a dimethyl ferrocene?
a) The redox current decreases with an increasing temperature because the
analyte diffuses away from the electrode.
b) Coulometric measurements is temperature-independent.
c) Coulometric signal is obtained from the integration of the voltammogram.
11. Regarding the double layer charging current in CVs, which of the following
describes the correlation between i_dl and the scan rate, v (V/s)?
-1/2 1/2 1
a) i_dl 正比於 v . b) i_dl 正比於 v . c) i_dl 正比於 v .
12. Based on Randles-Sevcik equation, which of the following correlation
between i_peak and the scan rate, v (V/s) is correct?
-1/2 1/2 1
a) i_peak 正比於 v . b) i_peak 正比於 v . c) i_peak 正比於 v .
13. The figure shows the behavior of Pt and Ag electrode at whick reduction of
H3O+ to H2(g) occurs. The experiment is conducted in an O2-free and pH 3.2
equeous solution. Which of the following statements is correct?
a) The reaction of hydrogen reduction is "overpotential" at bothPt and Ag
electrodes.
b) The reaction of hydrogen reduction is "overpotential" at Pt electrodes and
"underpotential" at Ag electrodes.
c) The reaction of hydrogen reduction is "underpotential" at both Pt and Ag
electrodes.
d) The reaction of hydrogen reduction is "underpotential" at Pt electrodes and
"overpotential" at Ag electrodes.
http://imgur.com/pIpxyfq
14. In 1-M NH3/1-M NH4Cl solution, Cu2+ is reduced to Cu+ near -0.3 V (versus
SCE), and Cu+ is reduced to Cu in theamalgam near -0.6 V. Which of the
following might be true if Pt, rather than Hg, is used as the working
electrode?
a) Cu+ → Cu2+ + e- takes place at +0.3 V (versus SCE).
b) Cu2+ + e- → Cu+ takes place at -0.3 V (versus SCE).
c) Cu+ + e- → Cu(s) takes place at -0.6 V (versus SCE).
15. For a Galvanic cell, the positive electrode
a) is where the current comes out.
b) carries out oxidation reactions.
c) is the working electrode.
16. When we apply Nernst equation to experiments using a 3-electrode
electrochemical cell, the location of the concentration term refers to the
reactants and products
a) in the bulk solution.
b) in the diffusion layer.
c) at the working electrode
17. If the voltammetry of Cu(CN)4 2- + 2e- Cu(s) + 4CN2- is carried out
without using supporting electrolyte, which of the following is correct?
[i_m: the measured current; i_d: the current driven by concentration
gradient]
a) |i_m| > |i_diff|
b) |i_m| = |i_diff|
c) |i_m| < |i_diff|
18. In class we used examples of the reduction of Cu2+ and Cd2+ to illustrate
"polarization". Which region in the Figuresshows "kinetic polarization"?
a) 1 b) 2 c) 3
http://imgur.com/HiFXcmB
19-20. In the left is a cyclic voltammogram obtained from a Pt working
electrode in an acidic solution.
19. The oxidation state of the surface Pt atoms is NOT zero at
a) 1. b) 2. c) 3.
20. Which of the following can increase the range of potential window for Pt
electrodes?
a) Perform the experiments in nonaqueous solutions.
c) Use solutions with a smaller pH.
b) The solutions are purged with N2(g) to remove di-oxygen.
http://imgur.com/BfaxSkC
21. In an unstirred solution containing 1 mM ferrocene (Fc) and supporting
electrolyte, what is the waveform looked like for the voltammogram obtained
by IDA electrodes?
a) Similar to those obtained by RDE. (The current reaches a plateau, not a
peak.)
c) Similar to those obtained without using RDE. (The current increases fast and
decreases not as fast.)
b) Similar to surface waves.
有關於 II~IV 的評分：需要敘述的地方，描述必須完整，才能獲得高分；僅提供關鍵字
、文義不明的句子則不給分。
II.(28%) Concentration profiles.
http://imgur.com/HHqiXjB
(i)(18%)OSWV: For a 1.0-cm^2 gold working electrode, qualitatively draw the
concentration profiles for the cases of (a) prior to the
experiment, (b) prior to E_peak, and (c) after E_wk passing and
the current value decreases to that of the baseline. [Two
traces are necessary for the cases of (b) and (c).] (d) Comment
on the reason why the voltammogram is peak-shaped. (e) For the
situation (c), draw i(t) of the forward potential step. You
need to explain how the concentration files are obtained.
(ii)(10%)CV: For a gold working electrode with a radius of 5.0 μm under an
unstirred condition, the CVs show features of steady-state
voltammograms, similar to those obtained by using rotating disk
electrodes. Starting from the definition of (a) "concentration
gradient" and (b) "diffusion length", (c) correlate the shapes
of CVs with the radii of working electrodes.
III.(10%) Half-wave potential, E_1/2.
(i)(3%) Define by words E_1/2 of a steady-state voltammogram (i.e., an RDE
experiment) for O + e- → R.
(可提供圖的輔助，但計分依據為文字敘述的正確與完整。)
(ii)(3%) Draw the concentration profile at E_1/2.
(iii)(4%) Starting from writing down the Nernst equation, describe the
significance of E_1/2.
IV.(24%) 3-eleetrode electrochemical cells.
This scheme is utilized in our lecture to discuss how the 3-electrode
configuration is better than the 2-electrode one. The x- and y-axes
represent the wk-to-ctr distance andpotentials, respectively. ref*
in the scheme indicates the perfect position for the reference
electrode. By having the reference electrode superimposed with the
working electrode, the expected E_wk can be equal to true E_wk. This
superimposition is of course impossible. Please use this scheme to
respond the following questions.
(i)(10%) Although the configuration of 3-electrode cells offers good control
over the accuracy of our lecture still gives instructions about (1)
placing the working and reference electrode as close as possible and
making sure that the amount of the supporting electrolyte is
sufficient.
Please (a) use the scheme below and indicate an arbitrary wk-to-ref
distance for the reference electrode and (b) use the scheme to
explaun why the statements of (1) and (2) are important principles to
keep the true from significant deviations.
http://imgur.com/zGT8tjf
http://imgur.com/Eygux9i
(ii)(14%) For a reaction O + e- → R (C_O* = 1 mM, C_R* = 0.0 M), voltammogram
(1) is typical under normal conditions.
(a) When the amount of electrolytes is insufficient, which
voltammogram will be the most likely one?
(b, 5%) Draw the schemes at -0.44 V under (b1) normal conditions and
(b2) electrolyte-insufflcient conditions.
(c, 3%) Draw the schemes at E'_peak under electrolyte-insuffcient
conditions.
(d, 6%) Explain in words the changes in (d1) the peak position and
(d2) the peak width. (Please ignore the changes in y-axis, i.e., the
value of redox current. 計分為問題 b 與 c 的說明，選圖正確但說明錯
誤，則不給分。)
http://imgur.com/yjYgQ4V