Proc. Natl. Sci. Counc. ROC(D)
Vol. 12, No. 3, 2002. pp. 100-105
Students’ Difficulties in Learning Electrochemistry
*
*
*
HUANN-SHYANG LIN , THOMAS C. YANG , HOUN-LIN CHIU , AND CHING-YANG CHOU
**
*Department of Chemistry
National Kaohsiung Normal University
Kaohsiung, Taiwan, R.O.C.
**Graduate Institute of Science Education
National Kaohsiung Normal University
Kaohsiung, Taiwan, R.O.C.
(Received October 17, 2002; Accepted March 25, 2003)
ABSTRACT
The purpose of this study was to investigate the difficulties students have in learning electrochemistry.
The answers on an open-ended test on electrochemistry obtained from 9th graders, 12th graders, and college
chemistry major students were compared and analyzed. The results of frequency analyses of student misconceptions
and data from interviews revealed that a larger percentage of college students had misconceptions about the function
of electrolytes in an electrochemical cell than did 9th or 12th graders. This study indicates that advanced study
in chemistry does not always result in better understanding of certain basic concepts. More importantly, if the
concepts are not clearly explained, students’ misconceptions may become firm and remain during their continued
study of chemistry even at the college level. It is also found that the students’ misconceptions likely result from
wrong impression given by pictures and statements in textbooks and improper classroom instructions.
Key Words: misconception, electrochemistry, science teaching
I. Introduction
Electrochemistry has been regarded as one of the most
difficult subjects to learn for both students and teachers
(Finley, Stewart, & Yarroch, 1982; Johnstone, 1980). As
Butts & Smith (1987) indicated, secondary school students
find that electrochemical cells and electrolytic cells are very
difficult for them to understand since these topics involve
concepts about electricity and oxidation-reduction, both of
which are very challenging.
If chemistry teachers can diagnose students’ difficulties in learning, and the origins of their misconceptions,
then their teaching effectiveness could be greatly improved.
In the 1980s, quite a few studies focused on the assessment
of student misconceptions in chemistry (Hackling & Garnett,
1985; Gorodetsky & Gussarsky, 1986; Mitchell & Gunstone,
1984). In the 1990s, a number of researchers (Garnett &
Treagust, 1992a, 1992b; Ogude & Bradley, 1994; Sanger
& Greenbowe, 1997a, 1997b) diagnosed student misconceptions in electrochemistry. It was found that the most
common misconceptions included the ideas that electrons
flow through a salt bridge and electrolyte solutions to
complete an electrical circuit, that anions and cations in
the salt bridge and the electrolyte solution transfer electrons
from the cathode to the anode, and that the half-cell potential
is an intrinsic property that can be used to predict the
spontaneity of an individual cell. In addition to the assessment for misconceptions, Sanger & Greenbowe (1997a)
reported that proper computer animations aimed at dealing
with misconceptions could reduce the number of students
who kept them.
In a review of the literatures, we found that student
misconceptions in electrochemistry are numerous and varied.
In general, students start to learn some basic concepts of
electrochemistry, including oxidations, reductions, cathodes,
anodes, electrolytes, salt bridges, and electrical current etc.,
at the age of 15 (i.e., 9th grade). They continue to study
advanced concepts, including the standard reduction
potential, electromotive force, and half-cell reactions in the
12th grade. In college, students are exposed to the principles
of electrochemical cells in general chemistry course in
greater depth and detail. We were curious about and
examined the growth of student understanding of the basic
principles of electrochemistry. We also tried to identify
the common misconceptions that occur in students of
different levels. In addition, we explored the reasons for
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Students’ Difficulties in Electrochemistry
students’ learning difficulties in electrochemistry.
II. Methodology
An open-ended paper-pencil test containing four items
(see Appendix) was used to assess students’ understanding
in the concepts of oxidation, reduction, and electrochemistry and to assess their explanations.
Item 1 asked the students to predict whether there was
electric current in a cell containing Zn and Cu electrodes
and 1.0 M CuSO4 as electrolyte. In addition, students were
asked to explain the reasons for their prediction. Apparently,
the diagram used for Item 1 was different from a typical
diagram of a Galvanic cell shown in most high school or
college chemistry textbooks. It consisted of a single cell
with two electrodes and no salt bridge. The two electrodes
in the same beaker were connected by a wire and immersed
in the same electrolyte. The correct prediction of this item
should be that electrical current flows through this cell since
the electrons move from the Zn electrode to the Cu electrode
through the external wire and the cations in the solution
gain electrons that are plated onto the electrode. The electrolyte conducts electricity within the cell through the action
of dissolving ions. The movement of ions completes the
circuit and maintains electrical neutrality. Despite the fact
that there is only one cell but no salt bridge, the electrical
circuit is still complete in such a cell. A voltage meter
shown in the external circuit will detect the electromotive
force. We conducted the experiment and found that a
reading of 1.0 volt was shown on the meter. In addition,
the zinc electrode gradually dissolved in the CuSO4 solution.
Solid copper resulting from the reduction of Cu2+ was
observed at the copper electrode and on the bottom of the
beaker. The oxidation-reduction reaction lasted for about
20 minutes.
Item 2 asked the students what would happen if the
electrolyte consisting of 1.0 M CuSO4 was replaced with
electrolyte consisting of 1.0 M ZnSO4 in the cell shown
in Item 1. A prediction that the indicator of the voltage
meter would move was considered correct. Explanations
that were consistent with the following statements are
considered to indicate sound understanding. The ions of
Zn2+ in the electrolyte accept electrons and reduce to Zn.
As a result, the cathode becomes coated with Zn, and the
current stops. Then, no further oxidation-reduction reaction
or electromotive force is observed in the cell since the two
electrodes have the same standard reduction potential. When
we carried out this experiment, we found that the initial
voltage reading was 1.0 V. The reaction went on slowly
and lasted for more than 16 hours with a reading of
0.9 V.
Item 3 discerned students’ understanding of the difference in the voltage reading between a typical electro-
chemical cell with a regular salt bridge and an electrochemical cell with a copper wire used to connect the two half
cells. In a study by Ogude & Bradley (1994), a cell containing a copper wire showed no voltage at all. This was
mainly because no ions could carry an electrical charge
through the wire to complete the circuit. We, however,
were surprised by finding a net reading of 0.6 V in a similar
experiment. Why we obtained results different from those
of Ogude & Bradley (1994) needs further examination. For
this item, a reasonable prediction is that the electrochemical
cell with a regular salt bridge can provide a higher voltage
reading than the cell with a copper wire. A sound explanation would be that the ions can carry electrical charges
through the salt bridge to complete the electrical circuit,
while the cell with copper wire does not have the same
conductive capacity and mechanism.
Item 4 discerned students’ understanding of the difference in the voltage reading between a chemical cell with
Zn and Cu electrodes and a cell with two graphite electrodes.
It is apparent that there will be no voltage reading for the
later cell. This is because no oxidation or reduction will
occur. In contrast, the electrochemical cell with Zn and
Cu electrodes could have a net voltage reading resulting
from the oxidation of Zn and the reduction of Cu2+.
In order to identify the conceptual difficulties that
high school and the college students have, the same test
was administered to 182 9th graders, 75 college-bound 12th
graders, and 49 senior college students whose major was
chemistry. The 9th graders were picked from six classes
in three high schools. The 12th graders were from two
classes in two high schools, who had taken a curriculum
based on science or engineering. All the students who
participated in this study had learned the concepts that were
examined in the test. A longitudinal comparison of 9th,
12th, and senior college students’ conceptual difficulties
can help teachers understand what concepts are often
misunderstood by students of different levels. In addition,
for the purpose of exploring possible sources of and reasons
for student learning difficulties, three students from each
of the three levels who made wrong predictions and wrote
inappropriate explanations were randomly selected for a
semi-structured interview. Each of them was individually
interviewed for thirty minutes to solicit further explanations
of and reasons for their predictions. All the interviews were
audio-taped and transcribed.
III. Results
Table 1 shows the percentages of students who made
wrong predictions or gave wrong explanations for test Items
1 and 2. It can be seen that two major misconceptions were
consistently held by the three grade levels of students. The
first one concerned the function of a salt bridge. 17.6%
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H.S. Lin et al.
Table 1. Percentage Distribution of Students’ Misconceptions Revealed by Items 1 and 2
(N = 182)
9th graders
(N=75)
12th graders
(N = 49)
College students
Item 1 wrong explanations
1. There must be a salt bridge to complete the circuit.
2. There must be an external battery to force chemical reactions to happen.
3. The reaction in the cell releases heat instead of electricity.
4. There is no any chemical reaction in the cell at all.
5. No explanation.
17.6
2.7
2.7
3.8
23.6
9.3
4.0
4.0
9.3
24.0
12.2
4.1
4.1
0
0
Item 2 wrong explanations
1. The direction of the indicator of the voltage meter will be reversed.
2. The electrolyte should contain Cu2+ if Cu is the cathode.
3. No explanation.
11.5
10.8
33.0
24.0
9.3
24.0
0
53.1
0
Students’ Misconceptions
Table 2. Percentage Distribution of Students’ Misconceptions in the Items 3 and 4
Students’ Misconceptions
(N = 182)
9th graders
(N=75)
12th graders
(N = 49)
College students
Item 3 wrong explanations
1. The principle and function of the salt bridge and the copper wire are similar.
2. Because the copper electrode does not dissociate ions into the solution,
the voltage will decrease.
3. No explanation.
19.8
0
8.0
0
14.3
8.2
33.5
16.0
0
Item 4 wrong explanations
1. Carbon can conduct electricity, so the cell will show a voltage reading.
2. The cell with two carbon rods will create electrolysis.
3. No explanation.
12.1
4.9
47.3
14.7
5.3
25.3
36.7
6.1
4.1
of the 9th graders, 9.3% of the 12th graders, and 12.2%
of the senior college students thought that a salt bridge was
indispensable for a galvanic for having a close circuit. They
believed that without a salt bridge, the cell could not work
properly.
Another major misconception held by the three groups
of students concerned the type of electrolyte used in a
Galvanic cell. About 10.8% of the junior high students,
9.3% of the senior high students, and 53.1% of the college
students explained that if the electrolyte does not contain
the cation of the cathode (i.e., Cu2+ for the Cu cathode),
then the cell will not have any electromotive force. We
were surprised that more than one-half of the college students
who were majoring in chemistry held the same misconceptions as the secondary school students did. While the
reasons they gave were different from those given by the
secondary school students, the college students firmly held
the same misconceptions.
Table 2 presents the percentages of students who had
major misconceptions as revealed by test Items 3 and 4.
For Item 3, 19.8% of the 9th graders, 8.0% of the 12th
graders, and 14.3% of the college students believed that
if the salt bridge in an electrochemical cell is replaced with
a copper wire, the net voltage will remain unchanged. They
thought that the function and principle of the salt bridge
are the same as those of the copper wire. In fact, the copper
wire does not contain ions dissociated from the electrolyte
inside the salt bridge. The ions play the important role of
carrying electrical charges to complete the electrical circuit.
Although copper is a conductor, it conducts electrons instead
of ions. In this case, there are no electrons going through
the solution (Ogude & Bradley, 1994). Apparently, the
copper wire is not able to transfer ions as the salt bridge
does since there is no electrolyte in it.
The major misconception of the students revealed by
Item 4 was that even if the Zn and Cu electrodes were
replaced with two carbon bars, the cell would still create
a net voltage. We were surprised by that 36.7% of the
college students held this misconception.
It should also be noted that 4.9% of the 9th graders,
5.3% of the 12th graders, and 6.1% of the college students
did not understand the difference between an electrochemical cell and an electrolytic cell. An electrochemical cell
creates electrical current through the chemical reactions of
oxidation and reduction. In contrast, an electrolytic cell
uses electrical current to decompose compounds into
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Students’ Difficulties in Electrochemistry
elements.
In order to understand why the students gave wrong
explanations, individual follow-up interviews were conducted after the paper-pencil test. In the interviews, these
students gave a variety of reasons. For example, although
college students Huang and Hu both believed that the cell
with two identical carbon rods in Item 4 could create a
voltage reading, Huang explained that some reactions
occurred in the half cell while Hu thought that the voltage
of the cell had nothing to do with the types of electrodes
in this case.
College student Huang: In the case where Zn and Cu are
used as electrodes, its anode reaction is Zn → Zn+2
+ 2e−, and the cathod reaction is Cu+2 + 2e− → Cu.
If Zn and Cu are replaced with two carbon rods, the
anode reaction is OH−1 → O2 + e−, while the cathod
reaction remains uncharged.
Interviewer: Why is it unchanged?
College student Huang: The H2O solution in the left side
of the cell will serve as the anode and discharge
electrons while the Cu+2 ions in the right side of the
cell will serve as a cathod to receive the electrons.
However, the net voltage reading will be smaller than
the original cell that uses Zn and Cu as electrodes.
College student Hu: The voltage reading will be the same
because the voltage has nothing to do with the types
of electrodes. It is only influenced by the concentration of the electrolytes.
It was found from interviews that student misconceptions about electrochemistry likely stemmed from inappropriate interpretations of textbooks and classroom instructions.
For instance, their typical thinking about the salt bridge
was greatly influenced by the pictures of electrochemical
cells they had seen in textbooks.
Interviewer: Why do you think the voltage meter (in Item
1) will not show a reading?
Junior high student Wang: Because this picture has only
one beaker. The Galvanic cell that I have ever seen
always has two half cells and a salt bridge.
Interviewer: Why is it necessary to have two cells and
a salt bridge?
Junior high student Wang: That’s what the textbook says.
It’s a standard format for a Galvanic cell. My physical
science teacher also taught the same thing that the
textbook said.
The following answers of a senior high school student
further revealed the typical conception of a Galvanic cell.
Interviewer: Don’t you think that putting the two elec-
trodes into the same beaker still create electrical
current?
Senior high student Chen: No, I don’t think so.
Interviewer: What are your reasons?
Senior high student Chen: I have never seen a single
Galvanic cell in my junior and senior high school
textbooks that uses one cell only. The pictures in
textbooks all show that two half cells and one salt
bridge are required.
It can be seen from the above selection of student
explanations that student misconceptions in electrochemistry likely result from their over-simplification and generalization of the information in textbooks and classroom
instructions.
IV. Discussion and Implications for
Chemical Education
Sanger & Greenbowe (1997b) reported that student
misconceptions about the mechanism of current flow in a
cell with a salt bridge and electrolyte are that “electrons
can either attach themselves to ions in solutions or they
can flow by themselves without assistance from ions.” This
study found two major misconceptions are commonly and
consistently held by 9th graders, 12th graders, and college
students in Taiwan.
(1) A salt bridge is absolutely essential in a Galvanic cell.
(2) The electrolyte must contain the cation that corresponds to the electrode in a Galvanic cell (e.g., Cu2+
for a Cu cathode).
A comparison of the percentages of students holding
the two major misconceptions reveals that more advanced
study in chemistry does not necessarily result in better
understanding of some particular basic concepts. In fact,
if these concepts are not thoroughly clarified, students’
misconceptions may become more firm and widespread as
they progress in their studies in chemistry from secondary
school to college. This speculation is supported by the
finding that about one-half of the college chemistry majors
in this study held a misconception, while only about onetenth of the high school students had the same misconception.
This finding indicates that chemistry teachers should give
multiple examples and explanations when they teach. For
instance, when the functions of a salt bridge and electrolytes
are taught, examples showing what types of electrolytes
(e.g., CuSO4 and ZnSO4) are appropriate (or not) for a
specific electrode (e.g., Cu) and why should be given.
Using a single example in teaching is likely to result in
student misconceptions as those found in this study. Further
research could develop more test items to investigate students’ understanding of electrodes and electrolytes in electrochemical cells.
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H.S. Lin et al.
The finding that students typically believed that a salt
bridge is necessary in a Galvanic cell should be noted by
chemistry teachers. About one-sixth of the ninth graders,
one-tenth of the 12th graders, and one-eighth of the college
chemistry majors believed that a salt bridge is absolutely
necessary in a Galvanic cell to create electromotive force.
The follow-up interviews revealed that these students’
conceptions were likely influenced by textbooks and classroom instructions. All the students who were interviewed
expressed that their explanations regarding the Galvanic
cell were based on the pictures and statements they had
seen and read, respectively, in textbooks and on their
teachers’ instructions. It seems that textbook writers and
chemistry teachers should be particularly careful when
explaining the structure and principles of a Galvanic cell.
After introducing examples of Galvanic cells, open discussion and further practice in designing a variety of Galvanic
cells might help students construct their own understanding
and to try out their own hypotheses. In addition, introducing
the students to Volta’s 1799 experiment may reduce the
number of students who hold the typical misconceptions
since Volta did not use any salt bridge in his demonstration
of the electrochemical cell. Further studies on applying
conceptual change teaching approaches are encouraged.
neutrality in operating electrochemical cells. Journal of Chemical
Education, 71(1), 29-34.
Sanger, M. J., & Greenbowe, T. J. (1997a). Common student misconceptions in electrochemistry: Galvanic, electrolytic, and concentration cells. Journal of Research in Science Teaching, 34(4), 377-398.
Sanger, M. J., & Greenbowe, T. J. (1997b). Students’ misconceptions in
electrochemistry: Current flow in electrolyte solutions and the salt
bridge. Journal of Chemical Education, 74(7), 819-823.
Appendix
The Open-Ended Test Items 1 to 4
1. In the following diagram, Zn and Cu electrodes are connected at one
end by an electrical wire and a voltage meter. The other end of each
electrodes is immersed into a solution consisting of 1.0 M CuSO4. Do
you think the voltage meter will show a reading or not? Please explain
as well as you can.
Acknowledgment
The authors sincerely thank the National Science Council,
R.O.C., for financial support through project NSC 89-2511-S-017-048.
References
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of important and difficult science content. Science Education, 66(4),
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Garnett, P. J., & Treagust, D. F. (1992a). Conceptual difficulties experienced by senior high school students of electrochemistry: Electric
circuits and oxidation-reduction reactions. Journal of Research in
Science Teaching, 29(2), 121-142.
Garnett, P. J., & Treagust, D. F. (1992b). Conceptual difficulties experienced by senior high school students of electrochemistry: Electrochemical (galvanic) and electrolytic cells. Journal of Research in
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Gorodetsky, M., & Gussarsky, E. (1986). Misconceptions of the chemical
equilibrium concept as revealed by different evaluation methods.
European Journal of Science Education, 8(4), 427-441.
Hackling, M. W., & Garnett, P. J. (1985). Misconceptions of chemical
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Johnstone, A. H. (1980). Chemical education research: Facts, findings,
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Mitchell, I. J., & Gunstone, G. F. (1984). Some student conceptions
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Ogude, A. N., & Bradley, J. D. (1994). Ionic conduction and electrical
2. In the above diagram, if the electrolyte is replaced with a 1.0 M ZnSO4
solution, do you think that the voltage meter will show a reading or
not? Please explain as well as you can.
3. If the salt bridge in the following diagram is replaced with a copper
wire, do you think that the voltage reading will be different from the
voltage reading obtained when a salt bridge is used? Please explain
in your own words.
4. In the above diagram, if the Zn and Cu electrodes are replaced with
two similar carbon rods, do you think that the voltage reading will be
different from the voltage reading obtained when the original Zn and
Cu electrodes are used? Please explain in your own words.
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Students’ Difficulties in Electrochemistry
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