In the Laboratory
W
How Many Atomic Layers of Zinc Are in a Galvanized Iron Coating? An Experiment for General Chemistry Laboratory Shui-Ping Yang Department of Chemistry, National Changhua University of Education, Changhua 50058, Taiwan;
[email protected] An experiment using a novel gasometric assembly to determine the thickness and number of atomic layers of zinc in a galvanized iron coating is described. How many atomic layers of zinc in a galvanized iron coating are there? Perhaps there would be hundreds, thousands, millions, or billions. This poses an interesting problem for undergraduate students. Students solved this problem by experimentation using three skills: a guided-inquiry approach, data processing, and guided problem solving. Some household products serve as reagents in the chemistry laboratory and have been compiled in general chemistry laboratory (GCL) textbooks (see 1, 2 ). Consumer products used as assays in GCL include white vinegar and antacid used for acid–base titration (3–7); bleach and vitamin tablets applied in oxidation–reduction titration (6–8); and aspirin tablets and cola drinks employed for spectrophotometry (3, 4). A few household products available for quantitative analysis have been newly published in the literature: examples are antacid (9), cereal (10), powdered drink mixes (11), imposter perfumes (12), pop rocks candy (13), malted barley (14), and diet tonic water (15). The inquiry-based approach has been integrated into the chemistry laboratory. Some educators have argued that inquiry-based activities greatly enhance pedagogical value in the chemistry laboratory (16). At least three inquiry-based approach textbooks for GCL have been published since 2000 (17–19). Several inquiry-based experiments for GCL pub-
lished in chemical journals include Web-based inquiry (20), graduate teaching assistant training (21), guided-inquiry format (22), classroom activity (23), discovery learning (24), and prompted inquiry-based learning (25). Students often learn chemistry problem-solving skills in the classroom rather than in the laboratory. However, problem solving integrated into GCL are available in refs 25 and 26. In addition, a cooperative learning project and water project, suitable for analytical chemistry laboratory, are available in refs 27 and 28, respectively. Instructional Strategies The methods for zinc content determination in the undergraduate chemistry laboratory include gravimetric, gasometric, volumetric, voltammetric, and spectroscopic analyses (29–33). In this article, a novel gasometric device is developed using a small-scale assembly made up of a graduated pipet, rubber tubing, a test tube, and detergent as illustrated in Figure 1. An ascending bubble layer inside the pipet is observable during the zinc reaction with acid. This experiment incorporates three questions with an inquiry-based approach, data processing, and problem solving: 1. What is the weight percent of zinc coating on galvanized iron substrates? 2. What is the thickness of zinc coating on galvanized iron substrates? 3. How many atomic layers of zinc coating on galvanized iron substrates?
Students carry out four procedures during the course of the experiment to answer the three questions as outlined in Table 1. In the first stage, students find suitable acidic concentrations through the guided-inquiry approach. In the second stage, students answer questions 1 and 2 regarding the weight percent and thickness of zinc coating through the data processing. In the third stage, students answer question 3 regarding the number of atomic layers of zinc coating through guided problem solving. Hazards Sulfuric acid is corrosive and may cause chemical burns and ruin clothing. Zinc metal is generally not hazardous in normal handling. Its contact with acids or alkalis generates flammable hydrogen gas that can accumulate in poorly ventilated areas. Hydrogen gas is highly flammable, readily forming explosive mixtures with air. There should be no open flames or electrical sparks in the area.
Figure 1. A novel gasometric device.
1792
Journal of Chemical Education
•
Vol. 84 No. 11 November 2007
•
www.JCE.DivCHED.org
In the Laboratory Table 1. Experiment Integrated into Laboratory Instruction Experimental Procedures
Instructional Strategies
Student Learning Objectives
Part A: Finding a suitable sulfuric acid concentration
Stage I: Guided-inquiry approach
Inquiry-based approach and reaction rate
Part B: Assembling the gasometric device and trial procedure
Stage II: Data processing
Data processing and assemblage of gasometric device
Part C: Exact procedure
Stage II: Data processing. Answer questions 1 and 2.
Data processing, vapor pressure, atmospheric pressure, Dalton’s law of partial pressures, ideal gas law, usage of vernier caliper and barometer, precision, and calculation of cone surface area
Part D: Problem solving for the number of zinc atomic layers
Stage III: Guided problem solving. Answer question 3.
Problem solving and atomic packing structure
Table 2. Weight Percent and Thickness of Zinc Coating Sample
Weight percent (%)
Thickness/cm
Gravi
Gaso
Avg
Gravi
Gaso
Avg
Wire D1.65
1.420
1.450
1.430
0.000635
0.000653
0.000644
Nail L38.1
0.726
0.678
0.702
0.000409
0.000382
0.000395
Nail L31.8
0.388
0.267
0.327
0.000169
0.000117
0.000143
Table 3. Number of Atomic Layers of Zinc Coating Sample
A-Axis Atomic Layers
C-Axis Atomic Layers
Gravi
Gaso
Avg
Gravi
Gaso
Avg
Wire D1.65
23500
24200
23800
28800
29600
29200
Nail L38.1
15100
14200
14600
18500
17300
17900
Nail L31.8
06280
04330
05300
07690
05300
06490
Results and Discussion In this experiment, three galvanized iron items are analyzed by gravimetry and gasometry. An iron wire with a 1.65 mm diameter, referred to as wire D1.65, and two iron nails of 1.5 in. (38.1 mm) and 1.25 in. (31.8 mm) length, referred to as nail L38.1 and nail L31.8, respectively, are examined. Students’ results are analyzed and discussed with various instructional strategies of guided-inquiry approach, data processing (involving questions 1 and 2), and guided problem solving (question 3). In evaluating the feasibility of this experiment, two comparisons—between gravimetry and gasometry and between students and instructor—are statistically analyzed. In addition, students’ learning impacts are summarized. All results and discussions are detailed in the Supplemental Material.W In the second stage, students answer questions 1 and 2 regarding weight percent and thickness of zinc coating through data processing. Students’ results are shown in Table 2. The results show that weight percents of three samples are 1.43%, 0.702%, and 0.327%, respectively. The latter two are smaller than 7–13% reported in ref 29. The zinc coating thicknesses of three samples are 0.000644, 0.000395, and 0.000143 cm (that is, 64400 Å, 39500 Å, and 14300 Å, respectively). These are smaller than penny shell thickness of 0.00116 cm (34). www.JCE.DivCHED.org
•
In the third stage, students answer question 3 by way of guided problem solving regarding the number of atomic layers of zinc coating. A student’s detailed answer is presented in the Supplemental Material.W Students solved this question in two ways. The first is to use short-edge lengths a and b in the unit cell positioned at the x and y axes of hexagonal close packing (as a-axis atomic layers) and the second is to utilize the long-edge length c in the unit cell positioned at the z axis (as c-axis atomic layers). Students’ results are shown in Table 3. Students’ results show that the number of atomic layers of zinc coating in the three samples cover a range of 23800–29200, 14600–17900, and 5300–6490 for the wire and the two nails, respectively. Conclusions Student results show that weight percents, thicknesses, and the number of atomic layers of zinc coating on galvanized iron substrates can be reproducibly obtained using the novel gravimetry and gasometry assembly. This experiment is an interesting challenge for undergraduate chemistry students. Students’ learning is diversified according to the guided-inquiry approach, data processing, guided problem solving, and experimental design. In evaluating this experiment, the average number of atomic layers of zinc coating obtained with gravimetry and
Vol. 84 No. 11 November 2007
•
Journal of Chemical Education
1793
In the Laboratory
gasometry are similar. The results obtained by the students and instructor are also similar; however, the students’ results are less precise relative to those of the instructor. Hence, this experiment is suitable for a second-semester general chemistry laboratory. Acknowledgments The author thanks the National Science Council of Taiwan for financially supporting this research by grant 93-2511S-018-011, Hon Man Lee for helpful suggestions, and Chung-Chia Li for testing this experiment.
9. 10. 11. 12. 13. 14. 15. 16. 17.
W
Supplemental Material
18.
Detailed student handouts, including prelab exercises and report sheet, and notes for the instructor, including a sample lab report, are available in this issue of JCE Online.
19.
Literature Cited 1. Stratton, W. J.; Steehler, G. A.; Pienta, N. J.; Middlecamp, C. H. Chemistry in Context Laboratory Manual: Applying Chemistry to Society, 4th ed.; McGraw Hill: Boston, 2003. 2. Richardson, B. C.; Chasteen, T. G. Experience the Extraordinary Chemistry of Ordinary Things, 3rd ed.; John Wiley & Sons: New York, 1998. 3. Greco, T. G.; Rickard, L. H.; Weiss, G. S. Experiments in General Chemistry: Principles and Modern Applications, 8th ed.; Prentice Hall: Upper Saddle River, NJ, 2002; pp 65–70 (vinegar), 107–118 (aspirin tablet), 187–192 (antacid). 4. Hunt, H. R.; Block, T. F.; McKelvy, G. M. Laboratory Experiments for General Chemistry, 4th ed.; Brooks/Cole: Pacific Grove, CA, 2002; pp 97–104 (vinegar), 257–264 (cola drink). 5. Wentworth, R. A. D. Experiments in General Chemistry, 7th ed.; Houghton Miffin Company: Boston, 2003; pp 97–104 (vinegar). 6. Bettelheim, F. A.; Landesberg, J. M. Laboratory Experiments for General, Organic, and Biochemistry, 4th ed.; Harcourt College Publishers: Fort Worth, 2001; pp 239–246 (antacid), 507–514 (vitamin). 7. Zvi, S.; Pike, R. M.; Foster, J. C. Microscale General Chemistry Laboratory with Selected Macroscale Experiments, 2nd ed.; John Wiley: New York, 2003; pp 195–204 (vitamin), 249–258 (antacid). 8. Heasley, V. L.; Christensen, V. J.; Heasley, G. E. Chemistry and Life in the Laboratory, 5th ed.; Prentice Hall: Upper Saddle River, NJ, 2000; pp 79–84 (bleach).
1794
Journal of Chemical Education
•
20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31.
32. 33. 34.
Yang, S.-P.; Tsai, R.-Y. J. Chem. Educ. 2006, 83, 906–909. Hooker, P. J. Chem. Educ. 2005, 82, 1223. Sigmann, S. B.; Wheeler, D. E. J. Chem. Educ. 2004, 81, 1479. Mowery, K. A.; Blanchard, D. E.; Smith, S.; Betts, T. A. J. Chem. Educ. 2004, 81, 87. Davis, C. M.; Mauck, M. C. J. Chem. Educ. 2003, 80, 552. Pelter, M. W.; McQuade, J. J. Chem. Educ. 2005, 82, 1811. Herman, H. B.; Jezorek, J. R.; Tang, Z. J. Chem. Educ. 2000, 77, 743. Rudd, J. A., II; Greenbowe, T. J.; Hand, B. M.; Legg, M. J. J. Chem. Educ. 2001, 78, 1680. Bauer, R.; Birk. J.; Sawyer, D. Laboratory Inquiry in Chemistry, 2nd ed; Brooks/Cole: Pacific Grove, CA, 2005. Peck, M. L.; Williamson, V. M. Experiences in Chemistry I and II: Inquiry and Skill Building, 2nd ed.; Hayden-McNeil: Plymouth, MI, 2005. Wink, D. J.; Fetzer-Gislason, S; Kuehn, J. E. Working with Chemistry: A Laboratory Inquiry Program, 2nd ed.; W. H. Freeman: New York, 2005. Shive, L. E.; Bodzin, A. M.; Cates, W. M. J. Chem. Educ. 2004, 81, 1066. Roehrig, G. H.; Luft, J. A.; Kurdziel, J. P.; Turner, J. A. J. Chem. Educ. 2003, 80, 1206. Friel, R. F.; Albaugh, C. E.; Marawi, I. Chemical Educator 2005, 10, 176. Wilcox, C. J. Chemical Educator 2004, 9, 270. Sinex, S. A.; Gage, B. A. Chemical Educator 2003, 8, 266. Green, W. J.; Elliott, C.; Cummins, R. H. J. Chem. Educ. 2004, 81, 239. Selco, J. I.; Roberts, J. L., Jr.; Wacks, D. B. J. Chem. Educ. 2003, 80, 54. Giancarlo, L. C.; Slunt, K. M. J. Chem. Educ. 2004, 81, 868. Arnold, R. J. J. Chem. Educ. 2003, 80, 58. Burgstahler, A. W. J. Chem. Educ. 1992, 69, 575. Gillum, D. E.; Herrmann, M. S. J. Chem. Educ. 1990, 67, 62. Collado-Sánchez, C.; Hernández-Brito, J. J.; Pérez-Peña, J.; Torres-Padrón, Ma. E.; Gelado-Caballero, Ma. D. J. Chem. Educ. 2005, 82, 271. Novick, S. G. J. Chem. Educ. 1997, 74, 1463. Pomeroy, R. K.; Drikitis, N.; Koga, Y. J. Chem. Educ. 1975, 52, 544. Vanselow, C. H.; Forrester, S. R. J. Chem. Educ. 1993, 70, 1023.
Vol. 84 No. 11 November 2007
•
www.JCE.DivCHED.org
