Using a Teaching Model to Correct Known ... - ACS Publications

Research: Science and Education edited by

Chemical Education Research

Diane M. Bunce The Catholic University of America Washington, D.C. 20064

Using a Teaching Model to Correct Known Misconceptions in Electrochemistry Penelope Ann Huddle* and Margaret Dawn White Department of Chemistry, University of the Witwatersrand, P O Wits 2050, South Africa; *[email protected] Fiona Rogers St Mary’s School for Girls, Waverley, 2090, Johannesburg, South Africa

A paper presented by de Jong (1) examined the current crisis in chemical education in Europe and pinpointed three problem areas, one of which is the failure of students to understand the key chemistry concepts, namely, the mole, stoichiometry, chemical equilibrium, and electrochemistry (2). There are two major reasons that students experience problems with these concepts: the topics are very abstract, and the language of chemistry is new. Teachers use words from everyday language that have different meanings in the scientific context—called “portmanteau words” (3). Students tend to construct their own meanings for language that is used in the scientific context. Both de Jong (1) and Garnett and Treagust (4 ) pinpoint areas in electrochemistry where statements made by teachers are misinterpreted by students. The fact that students manifest alternate conceptions (misconceptions) in many abstract topics has been well documented (5). These alternate conceptions are extremely resistant to remediation (6 ), and effective learning is unlikely to occur if they are ignored (7). Moreover, if students believe a concept to be very complex this can also affect their performance and learning. More and more evidence (8) points to the value of using analogies in the form of concrete models when teaching theoretical chemical concepts, to aid in the development and refinement of ideas and for remediating misconceptions (9). Dagher (10) suggests that the use of an analogy provides students with a level of comfort and security that enables them to connect what they know with the world of theories and abstractions. This is supported by Gilbert (11), who states that “models are a visualisable intermediary between the imaginary world of theory and the world as experienced.” Recent research has focused on students’ conceptual difficulties with electrochemistry (4, 12–15). Several researchers have reported that students find the topic difficult (16, 17) and teachers experience problems teaching it (18). In an extensive study of the conceptual difficulties experienced in electrochemistry by senior high school pupils in Australia, Garnett and Treagust (4, 13) found that students exhibited serious misconceptions in this topic. Findings were similar when this study was replicated in America (19, 20). Research by members of this department (14, 15, 18, 21) has shown that school pupils, college students, and preservice teachers in South Africa have all manifested similar erroneous conceptions. In the studies in all three countries, three main misconceptions about current flow were identified:

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1. Current is believed to always involve movement of electrons, even in solution and through the salt bridge. 2. In an electrochemical cell, anions and cations move either until their concentration in both half-cells is equal or until one half-cell is strongly negatively charged and the other is strongly positively charged. 3. A lack of understanding of the significance of the signs of the anode and the cathode and what happens to these signs when changing from an electrochemical to an electrolytic cell. Many students interpret a negative electrode to imply that the electrode is negatively charged.

Furthermore, few students have a coherent concept of the purpose of the salt-bridge. Rationale for the Model In South Africa, with our “absolute shortage of science and mathematics teachers at the secondary level” (22) and 50% of those employed to teach physical science underqualified, there is a desperate need to find ways of teaching key concepts that make them easily intelligible to both students and in-service teachers. We tried for several years to devise a concrete model for teaching electrochemistry that specifically addressed these alternate conceptions. The model had to be one that could be simply and cheaply constructed and did not require electricity for its working, so that it could be used in all schools and teacher-training colleges in South Africa, including those that lacked electricity or sophisticated equipment. A successful model could possibly be implemented further in other developing countries. Therefore, the use of videos (23) or computer programs (24 ) for teaching this topic fell outside the ambit of our aims. A Concrete Model for Teaching Electrochemistry The model was devised by an HDipEd student after viewing the BBC TV Open Universities video Electrochemistry (23) and was modified and extended by us. It is a concrete teaching model (11) and serves as an introduction to a consensus model, which students believe to be important but find difficult to understand. The essential feature of the model is

Journal of Chemical Education • Vol. 77 No. 1 January 2000 • JChemEd.chem.wisc.edu

Research: Science and Education

the use initially of a semipermeable membrane rather than a salt bridge to complete the circuit and demonstrate the maintenance of cell neutrality. The working of a semipermeable membrane is far simpler for students to understand than a salt bridge containing ions different from those present in the electrolytes. Once students have grasped the concept of maintaining electrical neutrality in a cell fitted with a semipermeable membrane, the salt bridge can be introduced. The model consists of two boxes joined together as shown (Fig. 1). Polystyrene balls of the same size are used for all atoms and ions; they are painted different colors for identification. Marbles are used to depict valence electrons. Prestik (“Blue Tack”) is used where necessary to hold marbles in indentations made in the polystyrene balls. Holes large enough to allow a polystyrene ball to pass through are cut out of the connecting sides of the boxes. Rulers are used to separate the “electrodes” from the “electrolyte solutions”. A hose-pipe cut longitudinally is inserted into the tops of the electrode compartments so that it slopes downward to allow spontaneous flow of the marbles from the “anode” to the “cathode” in the galvanic cell. Polystyrene balls are positioned in the boxes as shown in Figure 1. When demonstrating the model, students are told the following: The polystyrene balls, depending on their color, represent zinc, copper, or sulfate ions. In nature, individual atoms/ions do not have any color—the color is used to identify different atoms/ions.

Figure 1. Concrete model for teaching electrochemistry.

a

The marbles represent the electrons. When two marbles are inserted into the indentations in a polystyrene ball, the “cation” is converted into an “atom”, i.e., Cu2+ ion + 2e᎑ → Cu atom.

b

When two marbles are removed from the indentations in a polystyrene ball, the “atom” is converted into a “cation”. In nature, while the diameter of zinc and copper atoms/ ions is roughly the same (~120 pm), the sulfate ion is considerably larger (~200 pm). Also, Zn2+ and Cu2+ cations are smaller that Zn and Cu atoms. No water molecules are shown. If the concentration of the solutions at the start were 1.0 mol dm᎑3, then 55 water molecules would be required for every copper and sulfate ion. In a real situation there would be a vast number of ions. For simplicity only a few are shown. In this model, the cathode is on the right-hand side. It could be on either side—it makes no difference to the working of the model.

The Working of the Model A zinc atom is taken from the zinc electrode. The two valence electrons (i.e., marbles) are removed and placed at the top of the conducting wire (hose-pipe). The resulting zinc cation is placed in the solution compartment on the left. Two electrons (marbles) are then removed from the hose-pipe at the copper electrode and inserted into a copper cation taken from the right hand solution compartment. The resulting copper atom is placed in the copper electrode compartment (Fig. 2a). The attention of the students is then drawn to the

c

Figure 2. The working of the electrochemistry model.

fact that there are now five zinc cations and only four sulfate ions in the left-hand solution, while in the right-hand solution there are now six copper ions but seven sulfate ions. To reestablish neutrality either a sulfate ion could be pushed through the semipermeable membrane from right to left (Fig. 2b) or a zinc cation could be pushed through in the opposite direction (Fig. 2c). Either process will reestablish electrical neutrality. The whole process can be repeated several times, each time starting with the removal of two electrons from a zinc atom taken from the zinc electrode. Observers note that conduction of charge in solution and through the semipermeable membrane is by ions, not electrons—at no time do marbles (valence electrons) appear in the electrolyte compartments. This migration

JChemEd.chem.wisc.edu • Vol. 77 No. 1 January 2000 • Journal of Chemical Education

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of ions could also be through a salt bridge; either way, it is the manner in which electrical neutrality in the two solutions is maintained. For students who have difficulty with determination of cell potentials and cannot understand why it is the zinc atoms and not copper that lose electrons, the potential ladder of Runo and Peters (25) is very useful as a visual aid. The explanation given in the Open Universities video (23), involving the equilibria set up in each half-cell prior to connecting them, is too advanced and clouds the essential features of an electrochemical cell. Also, as equilibrium has been shown to cause students even more difficulties than electrochemistry (2), we felt that it was not expedient to mention it here. Placing the hose-pipe in the tops of the electrode compartments so that it slopes downward from the zinc to the copper is intentional, to show the difference in potential of the zinc and the copper and allow for the spontaneous flow of “electrons” down the “conducting wire” from the one “electrode” to the other.

The Essential Features and Scope and Limitations of the Model NOTE: Students should be asked where the model resembles and differs from reality before going through this list. Our students noted many of the similarities and differences themselves. 1. No electrons (marbles) ever appear in the solutions or move between the compartments other than via the external conducting wire (the hose-pipe). 2. One electrode (zinc) gets smaller while the other one (copper) increases in size. 3. Electrical neutrality in solution is maintained by ions, not electrons, moving from one compartment to the other. 4. There is an overall movement of negative charge in one direction (and positive ions in the opposite direction in the electrolytes) when the circuit is completed. 5. The model can be extended to explain why batteries run down by continuing the demonstration until there are no longer any copper cations left in the right-hand compartment. Note, however, that in reality a battery is run down when the concentration of ions becomes low, not when it has been totally depleted. 6. The model can also be used to explain electrolytic cells and the recharging of batteries. Garnett and Treagust (4 ) found that one of the misconceptions exhibited by students about electrolytic cells concerned the “swapping around” of the electrodes in electrochemical and electrolytic cells. One can reverse the actions in the model to demonstrate the copper atoms losing electrons and the zinc ions accepting them. By definition, oxidation is now occurring at the copper electrode, which becomes the anode while the zinc electrode becomes the cathode. Attention is drawn to the fact that the marbles now need to be pushed up the inclined hose-pipe—hence the need for an external energy source in electrolytic cells and when recharging batteries.

The main limitation of the model is that the actions are sequential and not simultaneous. The main strength of the model lies in its simplicity.

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The Pilot Sample Twenty-eight grade 12 pupils studying physical science in a private all-girls secondary school in Johannesburg, South Africa, were chosen to pilot the model. The teacher first set up a Zn|ZnSO4||CuSO4|Cu cell containing a voltmeter in the external circuit and a salt bridge connecting the two electrolyte solutions. She showed the pupils that the cell stopped working when the salt bridge was removed. She then set up the model alongside the cell and explained its working. She asked the pupils to compare the model and Zn|Cu cell and point out any physical differences. The pupils recognized most of the limitations of the model, namely, the lack of water molecules, the size, color, and number of particles, and the absence of a salt bridge. However, relative to previous years, the teacher found heightened interest in electrochemistry, especially by the weaker pupils. Despite her fears that using the model would require more time to teach this section, she found that less time was required because the pupils understood the processes so quickly and manifested fewer alternate conceptions. In a class test given at the end of the section, no pupils suggested that electrons moved in solution or through the salt bridge, and the results for the test were much better than in previous years. The University Sample Three 1996 Chemistry I classes at the University of the Witwatersrand, Johannesburg, were chosen for this study. Class I consisted of 67 Chemistry I (major) students who had scored at least 60% in mathematics and physical science in their final school examinations. Class II comprised 45 secondyear College of Science students who were studying Chemistry I over two years in a support program preparing them for entry into the university mainstream. Students in the College of Science do not attain the minimum requirements in their final school examinations to allow them direct entry into the university. They are predominantly black students who experienced years of poor or disruptive schooling during the latter years of apartheid rule in South Africa. Class III, the control group, contained 75 Chemistry I major students (the chemical engineers) of comparable ability to class I. (Test and examination scores for the two major classes had not varied by more than 3% during the past 10 years.) Class III wrote the pretest and attended lectures on electrochemistry by a lecturer who, like Sanger and Greenbowe (20), taught to actively confront and therefore to prevent or dispel known misconceptions in this topic. This class was never shown the model.

The Pretest Before any electrochemistry lectures were delivered to the three classes, they were given a pretest (see Box 1) involving eight tasks, which tested understanding rather than knowledge of the concepts of electrochemistry. Understanding of a topic should be retained indefinitely if a student found it intelligible, fruitful, and plausible when it was originally taught (26 ). All the students had been exposed to the topic at school but had not yet encountered it at university. Class II students may have had less exposure to the topic at school, as they generally had poorer schooling experiences. Students were asked to



Box 1. Electrochemistry Questionnaire Only tasks specifically addressed by the model are included here. TASK 1 In the circuit represented in the diagram, to get the bulb glowing brightly, the beaker could contain: (a) potassium sulphate dissolved in water (b) sugar dissolved in water (c) molten sugar (d) dilute sulfuric acid (e) molten potassium bromide (“molten” means the salt is heated sufficiently to melt)

Select the answer(s) you think are correct. Explain your choice. TASK 7 Look at the figure below and, using the table of reduction potentials, answer the questions that follow.

Diagram of Pt, H2|H2SO4||ZnSO4|Zn cell

(a) Label the anode and cathode. (b) Show the direction of electron flow and movement of all ions. (c) Write the half-reaction occurring at the cathode and anode. (d) Calculate the voltmeter reading. (e) What is the function of the salt bridge? Explain. (f) Could the salt bridge be replaced by graphite (a semiconductor)? Explain. (g) What would the reading on the voltmeter be if the salt bridge were removed? Explain.

TASK 8 An enlargement of the left-hand electrode in Task 7 is given and students are asked to give a microscopic representation of what is occurring in the half-cell when the voltmeter registers a positive reading.

Box 2. Final Examination Question on Electrochemistry Use the data provided to explain why copper dissolves in nitric acid but not in hydrochloric acid. 3Cu(s) + 2HNO3(aq) + 6H+(aq) → 3Cu2+(aq) + 2NO(g) + 4H2O(ᐉ) Cu(s) + 2Cl᎑(aq) + 2H+(aq) → Cu2+(aq) + H2(g) + 2Cl᎑(aq) Half-Reaction

E°/V

Cu2+(aq) + 2e ᎑ → Cu(s)

0.34

2H+(aq) + 2e ᎑ → H2(g)

0.00

HNO3(aq) + 3H+(aq) + 3e ᎑ → NO(g) + H2O(ᐉ)

0.96

Draw a fully labeled diagram of an electrochemical (galvanic) cell for the reaction of copper with nitric acid. Use arrows to show the direction of movement of electrons and all ions. (Use a platinum electrode in the half-cell containing nitric acid).

complete the questionnaire during a 45-minute period with the lecturer in charge. No discussion among students was allowed. Results and Discussion TASK 1 (BOX 1). Of the 167 students in the three classes who took the pretest, most indicated that an aqueous solution containing ions would conduct electricity (option a, d, or e). No students selected option b or c (the aqueous sugar solution or molten sugar); that is, it seemed that all students appreciated that ions were required to transfer charge in solution to cause the bulb to glow. (Comparable experiments are carried out at school.) However, explanations by students revealed their misconceptions: for example, “current is a flow of electrons; these ions will be able to conduct the electrons and complete the circuit”; “potassium sulphate has delocalized electrons and positive protons that move to the opposite electrodes when a current is applied”; “anions produce electrons which conduct”; “H2SO4 is a proton donor, protons are transferred across the potential difference”; “KBr has many electrons freely available, therefore, electrons moving cause a change in potential”. One student gave the equation for the ionization of sulfuric acid as “H2SO4 → H3O+ + SO42᎑ + 2e᎑”. Thus, students knew that ions were required in the electrolyte, but the majority believed that their purpose was to furnish electrons (and occasionally protons) to transfer charge through the solution. TASKS 2–6. Tasks 2–6 did not address the documented misconceptions in this article and are therefore omitted from the discussion. TASKS 7, 8. Salient points from tasks 7 and 8 were analyzed separately for the three classes (Table 1). These tasks revealed that the students had very little understanding of what occurs at the microscopic level in electrochemical cells, especially in the electrolytes. Although most students could remember how to manipulate electrode potentials and write half-cell reactions, they had considerable difficulty identifying which ions were moving and the regions in which this movement occurred. Most students did not show any movement of ions. Some showed (unspecified) “ions” traveling along the conducting wire in the opposite direction to the electrons! A few wrote “ions” with arrows pointing into or out of the salt bridge. Seventy-three percent showed electrons moving along the conducting wire (though not necessarily from the anode to the cathode), 4% drew electrons in solution, and 20% showed electrons moving within the salt bridge. Few students had any idea of what was occurring at the standard hydrogen electrode. Some oxidized the platinum electrode to Pt2+ ions, and a few even managed to produce HO᎑ by removing H2 from H 3O+! Sanger and Greenbowe (19) similarly found students who had difficulties with inert electrodes. Thirty-eight percent of students correctly stated that the function of the salt bridge was to “transfer ions”. A further 16% were more vague and said it “completed the circuit”, “allowed current flow”, or “maintained neutrality of the solutions”. Some students actually stated that the salt bridge allowed for the transfer of electrons. To further probe their understanding of the working of a salt bridge, students were asked if it could be replaced by a graphite rod. While the majority of students who answered this question did not believe this was possible, only half of them gave the correct reason. Erroneous explanations included


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classes (I and III) fared similarly, whereas class II could not demonstrate the correct movement of Experimental Groups Control Group ions either in the salt bridge or in Class I Class I Class II Class II Class III Class III Item Pretest Final Pretest Final Pretest Final solution. However, in the exami(n = 58) (n = 67) (n = 41) (n = 45) (n = 68) (n = 75) nation the performances of the ex(%) (%) (%) (%) (%) (%) perimental groups (I and II) were 1. Electrons shown moving correctly along the 52 87 51 73 47 79 very similar and they had a compaconducting wire rable understanding of what was oc8 4 2. Electrons drawn in solution 7 0 12 2a curring at the microscopic level in 20 5 3. Electrons drawn in the salt bridge 26 0 17 4a the electrochemical cell. Surpris4. "Ions" shown moving in the salt bridge 62 54 51 58 60 53 (correctly or incorrectly) ingly, class II now exhibited a su5. Correct ions shown moving correctly in salt 22 64 0 56 23 28 perior ability to show the movebridge or across semipermeable membrane ment of ions correctly in solution. 6. Ions drawn in the electrolytes (correctly or 24 51 4 42 25 23 This may be because they manipuincorrectly) lated the model themselves rather 7. Ions shown moving correctly in both 12 21 2 31 15 16 than having it demonstrated to electrolytes them, as it was for class I. Just as 8. Ions drawn along the conducting wire 5 3 12 0 5 4 Sanger and Greenbowe (19) found Note: For each class, the number of students who take the pretest is smaller than the number of that demonstration of their comstudents who take the final exam because not all students attend lectures and tutorials. aIncludes 1 student (2% of sample) who did not attend the tutorial involving the model. puter animation by the lecturer was not wholly successful and they plan to give students access to it “a semiconductor will allow too slow a flow of current [or on the chem file server, so we plan to introduce the tutorial electrons]”; one student required a salt-bridge because both undertaken by class II into all Chemistry I courses so that all electrons and protons had to be transferred through it. students can manipulate the model themselves. Most students (66%) correctly stated that the reading The results of class III in the examination for items 4–8 on the voltmeter would drop to zero if the salt bridge were (Table 1) were comparable to those in the pretest: lectures removed, but again their reasons were vague—it had to be and tutorials alone resulted in minimal improvement of their there to maintain “current” flow. understanding of what was occurring at the microscopic level with respect to the movement of ions in and out of the salt Use of the Model bridge and within the electrolytes in an electrochemical cell. During lectures to class I, a Zn|Cu cell was demonstrated Active teaching by the lecturer to class III reduced the perusing first a salt bridge and then a piece of filter paper that centage of students who drew electrons in the salt bridge and had been dipped into a concentrated potassium chloride electrolytes in the examination but did not completely eradisolution to complete the circuit. The model was then demcate this problem, as was the case for class I students for whom onstrated to groups of about 20 students during a tutorial the model was demonstrated. session. To determine whether any conceptual change had In the examination, 64% of class I showed ions moving occurred, a question on electrochemistry (Box 2) was set for correctly through either a salt bridge or a semipermeable the final examination, which was written almost two months membrane and 21% showed the ions moving correctly in after instruction. This question was similar to tasks 7 and 8 both electrolytes. In the control group a mere 28% drew the of the pretest. The same examination question was set for class ions moving correctly through a salt bridge (a semipermeable III (the control class). For class II, four identical models were membrane was never chosen) and 16% showed the ions constructed for use by groups of students during a tutorial moving correctly in the electrolytes. on electrochemistry planned around the model. During this While 33% of students in class I drew electrons moving tutorial, they set up cells using filter paper dipped in various in the salt bridge or solution in the pretest, none did so in solvents (water, hexane, saturated KCl) as a salt bridge and their final examination. In class II, 2% still drew electrons in then manipulated the model themselves before answering the solution and 4% in the salt bridge. However, the one questions allied to it. An electrochemistry question similar to student (2%) who drew electrons in both the solution and that set for class I was given to class II students in their final the salt bridge did not attend the tutorial involving the examination (Box 2), written about six weeks after instruction. model. Thus, of the 127 learners comprising the pilot school The main difference between the questions given to the major sample (28), class I (58), and class II (41) who saw the model students (classes I and III) and class II is that the latter in operation, only one still drew electrons in the salt bridge (who came from poorer educational backgrounds) were given and none drew electrons in solution! In comparison, in the directed subquestions to guide them through the calculations control group after instruction, 4 students still drew electrons and diagrams. in the salt bridge and 3 drew them in solution. Even though the model does not show any water molComparison of Answers to Pretest and Examination ecules, the percentages of students in all three classes who Questions omitted the solvent from their drawings were comparable. Student responses to the pretest and examination questions Thus, the absence of water molecules in the model does not were analyzed. Table 1 shows that in the pretest the major seem to be a major problem. Table 1. Analysis of Electrochemistry Questions in the Pretest and Final Examination

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Statistical Analysis It was not possible to perform a logistic regression analysis of the data, as the students in class III did not identify themselves in the pretest scripts and pairing of their results was not possible. Therefore, 2 × 2 contingency table χ2 tests were run. Because these showed no significant difference between the results of classes I and II in the pretests, the results of these classes were combined for further analysis. Also, there was no significant difference between the experimental and control groups in the pretest (.137 < p < 1.000) for any item in Table 1 except item 7 (see Table 2). However, the difference between the experimental and control groups in the final exam (post-test) for items 4–7 of Table 1 was highly significant (0.000 < p < .048); that is, the experimental groups had a greater ability to show the correct movement of ions in the electrolytes and through a salt bridge or semipermeable membrane. A one-tailed Z-test of the differences in the proportion, P, of correct responses between the pretest and exam (post-test) scores for classes I and II (Table 3) showed a highly significant improvement for all items in Table 1 (0.000 < p < .007). For class III a highly significant improvement was obtained only for item 1 (the ability to draw the electrons moving correctly along the conducting wire). Z=

P post,i – P pre,i , where s = s

Table 2. Comparison of Exam Scores in Experimental Classes (I + II) and Control Class (III)

1

0.037

.871

4.227

.058

2

0.009

1.000

1.404

.333

3

2.457

.137

4.687

.048

4

0.195

.740

14.590

0.000

5

0.332

.692

22.968

0.000

6

0.372

.566

14.586

0.000

7

10.550

.001

12.117

.001

8

0.072

1.000

3.611

.094

Note: Values of p less than .05 are considered significant.

alternate conceptions and assisted pupils to visualize what was occurring at the microscopic level in an electrochemical cell, and found them more responsive to this section than in previous years. This research also showed that chemistry students at a South African university manifest many of the alternate conceptions in electrochemistry found by Garnett and Treagust (4) and Sanger and Greenbowe (19) in studies of Australian and American students, respectively. These misconceptions may not be apparent by simple multiple choice questioning. Explanation of the choice of answer is essential to probe the level of understanding of the students. Use of the model led to significant improvement in the students’ understanding of what was occurring at the microscopic level in an electrochemical cell and helped to address known alternate conceptions documented in this paper. Of the 127 students who saw the model in operation, only one still drew electrons moving in the salt bridge or solution. The improved ability of these students to show what was occurring at the microscopic level in the cells is very encouraging. Dagher (10) pointed out that the contribution of instructional analogies to conceptual change is most likely to be of a covert nature, leading to small but substantive shifts in students’ understanding of concepts. Expecting all conceptual change to be of a radical nature is equivalent to expecting all worthwhile

P post,i 1– P post,i P pre,i 1– P pre,i + n post,i n pre,i

A final test to analyze the difference between the posttest–pretest proportion differences between classes I plus II and class III (Table 4) confirmed that there was a highly significant difference between the experimental and control groups for items 3–7 in Table 1; that is, the experimental groups who had been shown the model had a significantly greater ability (0.000 < p < .007) to show what was occurring at the microscopic level in an electrolytic cell. Summary and Conclusion A model for teaching electrochemistry is presented. Both the scope and the limitations of the model are given. Piloting of the model in a secondary school showed that it reduced

Table 3. One-Tailed Z-Test of Difference in Proportion of Correct Responses between Exam Scores and Pretest Scores Item

Experimental Groups ( I + II) Ppost– Ppre

S

Z

1

0.47059

0.061622

7.63669

2

0.08235

0.033761

3

0.29412

0.051329

4

0.24706

0.067691

5

0.44706

0.067595

6

0.49412

7

0.41176

8

0.07059

Control Group (III) p

Ppost– Ppre

Final Exam (nI + II = 85, nIII = 72) χ2 p

Pretest (nI + II = 85, nIII = 67) χ2 p

Item

S

Z

p

Table 4. Difference in "Post"– "Pre" Proportion Differences between Classes I + II and Class III Item 1

Z ᎑2.23986

p .025

0.000

0.34287

0.076721

4.46906

0.000

2.43926

.007

0.04789

0.042089

1.13772

.128

2

᎑0.92033

.357

5.73007

0.000

0.11070

0.058267

1.89982

.029

3

᎑2.70840

.007

3.64978

.001

᎑0.07027

0.083621

᎑0.84039

.200

4

᎑3.17503

.001

6.62377

0.000

0.02508

0.073560

0.34099

.367

5

᎑4.43553

0.000

0.066380

7.44380

0.000

0.14905

0.078531

1.89794

.029

6

᎑3.92152

0.000

0.054856

7.50631

0.000

0.01741

0.061840

0.28158

.389

7

᎑5.10866

0.000

0.027782

2.54081

.006

0.01803

0.037316

0.48330

.314

8

᎑1.45487

.146

Note: “Post” refers to the final examination. Values of p less than .05 are considered significant. Values less than .01 are highly significant.

Note: Values of p less than .05 are considered significant. Values less than .01 are highly significant.


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science to be revolutionary. It is thus unlikely that demonstration of the model would lead to total eradication of the targeted misconceptions in a class of students. The model does not address misconceptions related to electrolytic and concentration cells (4, 18), but does go some way toward giving students an initial understanding of what is occurring in an electrochemical cell at the microscopic level and may make them more receptive to teaching of more difficult concepts in this topic. Sanger and Greenbowe (19) used computer animations as a tool to enhance students’ ability to visualize and understand chemical concepts at the molecular level. In the absence of available computer technology, we believe that this model can contribute to students’ ability to visualize particulate behavior in electrochemical reactions and, in so doing, address known alternate conceptions. Acknowledgments

7. 8. 9. 10. 11.

12. 13. 14. 15. 16. 17. 18.

We wish to thank Ian McKay for his innovative model incorporating a semipermeable membrane for use in teaching electrochemistry, which led to the model presented in this paper. We also thank Data Management and Statistical Analyses (DMSA) at Wits for the statistical analysis.

19.

Literature Cited

20.

1. De Jong, O. Characteristics of Chemistry Education in Research in Europe: A Three-Context View; Paper presented at the Third Conference on Research in Chemical Education, LublinKazimierz, Poland, September 1995. 2. Hackling, M. W.; Garnett, P. J. Eur. J. Sci. Educ. 1985, 7, 205– 214. 3. Rutherford, M.; Nkopodi, N. Int. J. Sci. Educ. 1990, 12, 443– 456. 4. Garnett, J. D.; Treagust, A. J. Res. Sci. Teach. 1992, 29, 1079– 1099. 5. Osborne, R. J.; Bell, B. F. Eur. J. Sci. Educ. 1983, 5, 1–14. 6. Novak, J. D. Studies Sci. Educ. 1988, 15, 77–101.

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