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Aust. J. Ed. Chem., 2014, 73

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Guide for contributors to the Australian Journal of Education in Chemistry

Introduction

The Australian Journal of Education in Chemistry publishes refereed articles contributing to education in Chemistry. Suitable topics for publication in the Journal will include aspects of chemistry content, technology in teaching chemistry, innovations in teaching and learning chemistry, research in chemistry education, laboratory experiments, chemistry in everyday life, news and other relevant submissions.

Manuscripts are peer reviewed anonymously by at least two reviewers in addition to the Editors. These notes are a brief guide to contributors. Contributors should also refer to recent issues of the Journal and follow the presentation therein.

Articles Articles should not exceed six pages in the printed form including tables illustrations and references - ca. 5000 words for a text only document. Short, concisely written articles are very welcome. Please use headings and subheadings to give your article structure.

1. We prefer to handle all submissions electronically. Our preference is for Microsoft Word files in Mac format. However, you can send files from any common Windows, DOS or Macintosh word processor.

2. On another separate page provide an abstract of 50 to 100 words;

3. All photographs should be scanned and saved in JPEG format.

4. All chemistry structures, and schemes should follow the guidelines set for ACS publications. It is preferred that Schemes, Tables etc be arranged to fit

in a column 7 cm wide, although full page width will be accepted.

Reference Styles AusJEC reference styles are based on the most recent edition of the Publication Manual of the American Psychological Association OR the Journal of Chemical Education.

Copyright Your manuscript should not have been published already nor should it have been submitted for publication elsewhere. If AusJEC publishes your manuscript then it will become the copyright of the Royal Australian Chemical Institute. The RACI will, however, allow you to use the contents of your paper for most reasonable non-commercial purposes.

T h e A u s J E C T e a m

Editors Robert Bucat, School of Chemistry and Biochemistry, The University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia. Bucat@chem.uwa.edu.au Phone: (+61)(8) 9380 3158 Fax: (+61)(8) 9380 3432 Mauro Mocerino Department of Chemistry, Curtin University, GPO Box U1987, Perth WA 6845, Australia. M.Mocerino@curtin.edu.au Phone (+61)(8) 9266 3125 Fax (+61)(8) 9266 2300

Leslie Glasser Department of Chemistry, Curtin University, GPO Box U1987, Perth WA 6845, Australia. L.Glasser@curtin.edu.au Phone (+61)(8) 9266 3126 Fax (+61)(8) 9266 2300 David Treagust Science and Mathematics Education Centre, Curtin University, GPO Box U1987, Perth WA 6845, Australia. D.F.Treagust@curtin.edu.au Phone: (+61)(8) 9266 7924 Fax: (+61)(8) 9266 2503

All manuscripts should be sent to Mauro Mocerino AusJEC Reviewing Panel A.L. Chandrasegaran, Singapore Vicky Barnett, Australia Glen Chittleborough, Australia Deborah Corrigan, Australia Geoffrey T. Crisp, Australia Bette Davidowitz, South Africa

Onno de Jong, The Netherlands Kitty Drok, Australia Loretta L. Jones, USA Scott Kable, Australia Bob Morton, Australia Mark Ogden, Australia

W (Bill). P. Palmer, Australia Marissa Rollnick, South Africa Kim Chwee Daniel Tan, Singapore Roy Tasker, Australia Tony Wright, Australia Brian Yates, Australia

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Contents

* Revisiting the Daniell cell

Kidane Fanta Gebremariam, Per-Odd Eggen, Lise Kvittingen

5

* A Click Chemistry Organic Adhesives Experiment Adrian A. Accurso, M. G. Finn, Valery V. Fokin and David Díaz Díaz

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* The bench synthesis of silver nanostructures of variable size and an introductory analysis of their optical properties Aoife C. Power, Sinead Byrne, Stephen Goethals, Anthony J. Betts and John F. Cassidy

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* Playing games, learning science: promise and challenges Kim Chwee Daniel Tan & Yam San Chee

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* Ignitable liquids in fire debris investigation: A GC-MS practical for forensic chemistry Linda Xiao, Walter Stern and Philip Maynard

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* Thermodynamic aspects of the chemistry of copper, silver and gold Peter F. Lang and Barry C. Smith

34

* refereed papers Cover photographs: Images and UV-Vis spectra of solutions of silver colloids from Power et al. (p 14).

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In this issue.....

In the introduction to electrochemistry, it is very common for textbooks to portray a two-compartment representation of a Daniell cell to indicate the simultaneous processes, and to consider the direction of current flow. Gebremariam, Eggen and Kvittingen point out that this portrayal is a distortion from the original Daniell cell. Furthermore, they argue that this type of diagrammatic representation is pedagogically problematic at the introductory stages - especially with regard to recognition of the direction of electron flow (and, therefore, which electrode is the anode, and which the cathode). They suggest a simplified version with a graphite electrode inserted into a copper sulfate solution, and the zinc electrode inserted directly into a salt bridge gel. Such a cell can light an LED.

Accurso et al. offer an undergraduate click chemistry laboratory exercise that marries organic chemistry and materials chemistry - in particular, the world of metal adhesives. Cu(I)-catalysed azide-alkyne cycloaddition produces crosslinked networks of triazoles that bind copper surfaces. Apart from developing awareness of a type of chemical reaction, this experiment can aquaint students with concepts of adhesive formation, adhesive performance, green chemistry, and click chemistry. If the starting reagents are provided, the exercise is suitable for beginners in organic chemistry. Alternatively, it can be designed for advanced students if the synthetic operations are included.

A laboratory exercise in which students synthesise silver nanoparticles is proposed by Power. et al. The particle size is tunable, and can be monitored using UV-Vis spectrsocopy. The room-temperature synthesis is rapid and repeatable. The optical properties of silver nanoparticles is clearly contrasted with those of the bulk metal. Suitable for either undergraduates or secondary school students, this preactical can be geared to the educational context, depending upon the availability of instrumentation, the ability of the students, and the time available.

Tan and Chee report on the use of computer games to learn chemistry, as well as to experience the processes

of science. Intended for use by lower secondary school students in Singapore, Legends of Alkhimia is a multi-level game designed to assist the learning of the basic concepts involved in separation techniques, reactions of acids, bases and salts, and rates of reactions. The students construct their knowledge and experience scientific processes when they try to make sense of phenomena encountered in the game world and an in-game virtual laboratory. To try to resolve a problem, students travel to the virtual laboratory to hypothesize its source, and conduct experiments to generate possible solutions. Back in the game world, the students test their solutions, and perhaps need to reconsider if they fail. Through trial and error, incorrect decisions are regarded as opportunities for reflection and learning. Significant suggestions arise from evaluation of this strategy.

Xiao et. al. have developed a forensic chemistry laboratory exercise concerning ignitable liquids in fire debris investigations. Students use mock and real fire debris samples to learn how to collect samples, and how to extract and concentrate trace amounts of chemicals from a difficult matrix in preparation for GC-MS analysis with various solvents. They also had hands-on experience in the analysis of the chemicals, and interpretation of the results. Finally, they presented their findings in the form of an expert witness report.

Thermodynamics can be used to interpret chemical behaviours such as (i) How far does the reaction proceed before equilibrium is reached? (ii) What heat/energy effects accompany the reaction? (iii) Is the equilibrium position influenced by changes in temperature and, if so, how? The article by Lang and Smith shows how thermodynamic data can be used to understand chemical reactivity, and to define the stability of compounds, including transition metal complexes. This is illustrated by a survey of the chemistry of copper, silver and gold, which belong to the same group, as well as some comparison with nickel, palladium and platinum in another group.

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Revisiting the Daniell cell Kidane Fanta Gebremariam, Per-Odd Eggen, Lise Kvittingen*

Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim, Norway, lise.kvittingen@chem.ntnu.no

Abstract In this article we discuss the two-vial & U-tube Zn/Cu cell as depicted in textbooks today. We question its use as a model for a galvanic cell in the teaching of electrochemistry at an introductory level. Historical, pedagogical and chemical aspects of the Zn/Cu cell are considered in the discussion. Tentatively an alternative model is suggested, in which we identified the drawbacks of the current Zn/Cu cell model. Our intention is to revisit this commonly used model and provide a springboard for further improvements, hopefully through a multidisciplinary approach.

Keywords: Chemical model, electrochemistry, galvanic cell, Daniell cell

Introduction Diagrams and models, including the textbook model of a Zn/Cu galvanic cell, (often also called the Daniell cell), play a major role in understanding new concepts. In chemistry education, models strive to visualize the sub-microscopic level, illustrate a concept or a process in which simultaneous reactions take place, as well as to depict experimental set-ups on the macroscopic level, much of which is virtually impossible to explain in words alone. Diagrams and models are therefore used as tools to exchange ideas in the teaching and learning process. A useful model will channel the student’s observation to the most important parts of the subject matter. Some models, though they may appear simple to the expert, may challenge novices, with the result that little, or no, understanding is gained. Even worse, the student could end up with misunderstandings that may be difficult to rectify. Unsurprisingly, the use of models is a research field of its own.

Electrochemistry has a central place in chemistry curricula throughout the world. The topic has many abstract and dynamic concepts, and research has shown that electrochemistry is difficult to comprehend at the introductory level (1-11), which is in line with the experience of many teachers. The problems reported are linked to mechanisms in the reduction-oxidation reactions, the activities taking place in electrochemical cells, the purpose and function of the salt bridge, etc. (see references above).

Figure 1. An example of the textbook model “Daniell cell”

The two-vial & U-tube diagram of the Zn/Cu galvanic cell (see Figure 1), found in many introductory chemistry textbooks, is our primary concern here. Because of its visual simplicity, as well as ease of use in practicals, it appears frequently in chemistry textbooks and curricula, and has prevailed as the electrochemical cell representation of a galvanic/voltaic cell for almost half a century. The Zn/Cu cell depicted in Figure 1 is meant to facilitate the understanding of the chemical reactions taking place, the electric current produced and how these concepts are interrelated. We are, however, not convinced that the model serves this purpose as a model of a galvanic cell producing electricity, in particular at the introductory stage. To support our assertion we will first consider some historical and pedagogical aspects of this model. Secondly we will look at some chemical aspects.

Why reconsider the Zn/Cu cell? Historical and pedagogical aspects The Zn/Cu cell in Figure 1 is often called the Daniell cell, referring to the English chemist John Frederic Daniell (1790-1845). Naming after great scientists is known to give authority to a model, concept or equation. But in this case we believe that the connection between Daniell and the model is not appropriate.

Daniell announced his Constant battery in 1836 (12, 13), and a reproduction is presented in Figure 2. As can be seen, the Daniell´s original cell has little in common with the representation depicted in today’s textbooks (Figure 1). In his textbook (14) Daniell described many galvanic cells, but none therein resembles today’s textbook model. Nevertheless Daniell’s innovation was a cell consisting of two compartments, a feature that Figure 1 also shares. However, in Daniell´s cell, a porous ceramic (“earthen”) pot or an ox gullet separated the compartments, preventing polarization and evolution of gas, while allowing ions to pass across it. These improvements resulted in more efficient, longer lasting and safer cells, providing improved electrochemical yield compared to their forerunners, assets for which it is well worth remembering Daniell. Few of the features associated with the porous partition are emphasized in the two-vial & U-tube textbook model.

Furthermore we are concerned about the fact that graphical representations similar to Figure 1 are so

Cu +2e Cu2+ -Zn Zn + 2e

2+ -

CuZn

Zn Cu2+ 2+

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common in high school and university general chemistry textbooks. Developmental psychologists are concerned about “habituation” which, according to Uttal and Doherty, “relies on the fact that events become less interesting the more we see them. When we first see something new, we attend to it, perhaps looking at it for a long time. But if the event is repeated, we quickly get used to it, and it no longer grabs our attention” (15). When applied to the two-vial & U-tube cell, this becomes problematic, firstly from the point of view of its too early introduction, before the student has sufficient concepts to build an understanding on. Secondly that it is repeated over and over again, so that eventually when sufficient background knowledge has been acquired, the intended attention is less likely to be triggered.

The model cell depicted in Figure 1 has little in common with real battery cells. Whether or not a model or a representation that reminds students of similar items in the real world is advantageous, depends on their prior knowledge and concepts, as well as the intended use of the new concept. There are reports that indicate that although concrete visualizations are initially helpful, application to other domains appears challenging (16). Other reports claim that in a variety of cultures and at different educational levels many students favor simple, realistic looking mental models (17). Taking into account the well-documented problems of understanding in electrochemistry we are inclined to favor the latter view. Thus the model in Figure 1 might not be a good candidate when discussing galvanic cells at the introductory level.

Figure 2. A replica of one of Daniell’s original cells from 1836

Chemical considerations There are also chemical reasons to reconsider displaying Figure 1 as a galvanic cell to produce current at an introductory level.

The model in Figure 1 is both in its design and function not very similar to galvanic cells found outside the teaching environment (18). Although galvanic cells are by their nature separated into half-cells so that oxidation and reduction take place in the respective compartments, in Figure 1 this is rather prominent. The motive for this pronounced separation is probably that it encourages treating the oxidation and reduction reaction

separately, although anodic and cathodic processes are coupled, and can thus never be truly isolated. The functioning of the model in Figure 1 is also ambiguous compared to real life galvanic cells; for example the long and thin salt bridge results in a cell that hardly provides current, and this is precisely the opposite of the intention of a galvanic cell. It is also in contrast to Daniell’s achievement, which was a cell that had a bridge with a large area and short distance between the two electrolytes (12-13, 19-20), thus providing a high current. The frequently depicted glowing bulb connected to this model cell will never glow outside a textbook as this cell neither provides sufficient voltage nor current for a bulb, not even for a LED. When the two-vial U-tube model is built in the school laboratory, it can hardly be used for more than confirming expected voltages.

When discussing a galvanic cell, the direction of the reactions in each half-cell may be problematic to students. As the model includes both a copper electrode and a solution of a zinc salt, students will believe that these components are necessary for the cell reactions. But the zinc ions in the cell are products, and not reactants, and there is therefore no need to incorporate them into the model. Neither does the copper cathode take part in the cell reaction, thus replacing the copper electrode with a graphite electrode eliminates another source of misunderstanding and additionally makes the copper deposit much more visible.

The idea of getting rid of redundant species is not a new one; Dickerson et al. (21) wrote that “With a little reflection it should be apparent that neither the ZnSO4 nor the copper rod is essential” when discussing a useful cell. In recent years, however, galvanic/voltaic cells in textbooks have become almost synonymous with the two-vial & U-tube model.

The reader may argue that the point is to be able to understand and predict in which direction the electron transfer and the half reactions appear. This is true at some level in electrochemistry education, but we are here considering the teaching at an introductory level of galvanic cells as devices to produce electrical energy. In our opinion, the model in Figure 1 may instead be appropriate in a later stage, when discussing standard potentials, Nernst’s equation or considering the thermodynamics of the reactions taking place in the cell.

Simplifying the common Zn/Cu model when teaching galvanic cells at the introductory level. If the textbook model (Figure 1) as a model for a galvanic cell at the introductory level has the historical, chemical and pedagogical drawbacks we have stated, it could well be revised. Devising a diagram without limitations is, of course, difficult. Replacing a textbook model that has featured for so long may be unrealistic. Nevertheless we will attempt to suggest another model (Figure 3d) and explain how it is developed from Figure 1.

Earthenware ion bridge

Copper container withcopper salt solution(positive electrode)

+

_

Zn-electrodein dilute sulfuric acid(negative electrode)

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Figure 3. A stepwise transition from the two-vial & U-tube cell to a simpler model (a-d)

In a simplified form the main parts of a galvanic cell are; one compound/element to be oxidized (Zn in Figure 1), another to be reduced (Cu2+ in Figure 1), a means to divert the current into an external circuit (a metal wire in Figure 1) and a medium that allows ion transport (the U-tube salt bridge in Figure 1). Consequently we suggest to remove the Zn2+ solution, replace the Cu-electrode with an inert electrode (Figure 3a - b) and reduce the dominating feature of the salt bridge. As seen in Figure 3b there is no reason to keep an empty beaker (previously holding the Zn2+-solution). We therefore remove it and insert the zinc strip into the salt-bridge (Figure 3c), which contains a gel with a salt e.g. Na2SO4. But why make glassware (or plastic) curved when it can be replaced with a simpler geometrical form, a straight tube? Hence we obtain Figure 3d. Redundant parts, that we believe can confuse the students, have now been removed and the model in Figure 1 has been developed into the simpler model in Figure 3d.

The reader may well ask: will this cell work (produce electricity) and is it really simpler to understand than the model in Figure 1? Firstly, a cell where Zn2+-salt and the Cu-electrode are replaced by e.g. table salt and an inert electrode can produce electricity as shown in previous reports (21, 22), and we encourage the reader to try. Secondly, whether Figure 3d or Figure 1 is easier to understand at an introductory level as a model of a galvanic cell producing electricity may be a matter of opinion.

Nevertheless the model depicted in Figure 3d has less parts, the students don´t have to question in which direction the half reactions proceed, the reddish deposit of Cu onto a grey/black graphite electrode is easy to spot, the model is more representative of batteries in general, it is less of a transgression on the historical origin of the Daniell cell and finally one can avoid the problems inherent with habituation when more elaborate treatment of electrochemical cells is to be conducted at a later state. We also believe this model can be used to teach topics such as potential calculations and Nernst’s equation, but this is outside the focus of this paper.

Conclusion In this paper we have questioned the textbook representation of the two-vial & U-tube galvanic cell as a source of electricity in the teaching of electrochemistry at an introductory level. The model, which is a central feature in many textbooks, is revisited drawing on historical, pedagogical and chemical aspects. We have also tentatively suggested an alternative model. Considering the long-standing use of the Zn/Cu cell model, suggesting changes to it, would reasonably not be easily understood; therefore we illustrate the steps from the textbook model to the alternative one. The effort of improving this teaching model can preferably be exerted by involving experts from multidisciplinary fields, such as chemistry, pedagogy and cognitive science.

V

Graphite rodZn

Cu2+

b)

V

Graphite rod

1.1V

Zn Cu2+

c)

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References 1. Garnett, P. J.; Treagust D. F. J. Res. Sci.Teach. 1992, 29, 121-

142. 2. Sanger, M. J.; Greenbowe, T. J. J. Chem. Educ. 1999, 76, 853-

860. 3. Sanger, M. J.; Greenbowe, T. J. J. Res. Sci. Teach. 1997, 34, 377-

398. 4. Sanger, M. J.; Greenbowe, T. J. J. Chem. Educ. 1997, 74, 819-

823. 5. Ogude, N. A.; J. Bradley, J. D. J. Chem. Educ. 1996, 73, 1145-

1149. 6. Lin, H.-S.; Yang T. C.; Chiu H.-L.; Chou C.-Y Proc.Natl. Sci.

Counc. ROC(D), 2002 12, 100-105. 7. De Jong, O.; Treagust D. The teaching and learning of

electrochemistry. In Chemical Education: Towards Research-based Practice. Gilbert J. K., De Jong, O., Justi, R., Treagust, D. F., Van Driel, J. H. Ed.; Kluver Academic Publishers. 2002; pp 317-337.

8. Ceyhun, Î.; Karagölge, Z. Aust. J. Ed. Chem. 2005, 65, 24-28. 9. Chou, C.-Y. Proc.Natl. Sci. Counc. ROC(D) 2002, 12, 73-78. 10. Özkaya, A. R. J. Chem. Educ. 2002, 79, 735-738. 11. Özkaya, A. R.; Üce, M.; Sariçayir, H.; Şahin, M. J. Chem. Educ.

2002, 8, 1719-1723. 12. Daniell, J. F. Philosophical Transactions of the Royal Society of

London. 1836, 126, 107-124.

13. Daniell, J. F. Philosophical Transactions of the Royal Society of London 1836, 126, 125-129.

14. Daniell, J.F. An introduction to the study of chemical philosophy: being a preparatory view of the forces which concur to the production of chemical phenomena, John W. Parker, West Strand, 1839, pp 429-450.

15. Uttal, D.H. and O'Doherty, K. Comprehending and Learning from 'Visualizations': A Developmental Perspective. In Visualizations: Theory and Practice in Science Education, Springer, Gilbert, J.K.; Ed. 2008, pp 53-72

16. Goldstone, R.; Sakamento, Y. Cognitive Psychology, 2003, 414-466.

17. Col, R.K. The Role of Models, Mental Models and Analogies in Chemistry Teaching. In Metaphor and Analogy in Science Education; Aubusson P.J.; Harrison, A.G., Ritchie, S.M.; Eds.; Springer, 2005, pp 210.

18. Boulabiar, A.; Bouraoui, K.; Chastrette, M.; Abderrabba, M. J. Chem. Educ. 2004, 81, 754-757.

19. Daniell, J. F. Philosophical Transactions of the Royal Society of London. 1837, 127, 141-160.

20. Daniell, J. F. Philosophical Transactions of the Royal Society of London. 1838, 128, 41-56.

21. Dickerson,R.E., Gray, H.B., Haight Jr, G.P: Chemical Principles 3 ed. 1979, p. 700.

22. Eggen, P-O.; Grønneberg, T .; Kvittingen,L.; J. Chem. Educ. 2006, 83, 1201-1203.

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A Click Chemistry Organic Adhesives Experiment Adrian A. Accurso,*,1 M. G. Finn,1 Valery V. Fokin1 and David Díaz Díaz*,2,3 1 Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, 92037 La Jolla, California, USA, aaccurso@scripps.edu 2 Institut für Organische Chemie, Universität Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany, David.Diaz@chemie.uni-regensburg.de 3 IQAC-CSIC, Jordi Girona 18-26, 08034 Barcelona, Spain, ddiazdiaz10@googlemail.com

Abstract Adhesives are important in a wide range of industries including packaging, electronics, automotives, furniture, and construction. Many chemistry students are unaware of the ubiquity of these materials or the countless ways they improve our daily lives. In this manuscript, we describe an undergraduate laboratory experiment in which the ability of organic compounds to form metal adhesive joints is demonstrated. The adhesive experiment, set up within two laboratory periods, is based on the Cu(I)-catalyzed azide-alkyne cycloaddition, which proceeds at room temperature without added catalysts to produce highly-crosslinked networks of triazoles that bind copper surfaces tightly.

Keywords: Representative elements, periodicity, principal component analysis, hierarchical cluster analysis

Introduction The practical demonstration of how physicochemical properties of specific organic compounds can lead to the fabrication of functional materials is an important lesson for chemistry students. Many laboratory exercises have been developed that teach timely materials chemistry techniques including epoxidation reactions [1-5], polymerization [6-11], and surface functionalization [12-14]. Organic adhesives provide a good example of a useful function generated from simple components. Although they are often taken for granted, they abound in modern life (e.g. structural urethanes that support car windshields, lightweight epoxies used in aircraft construction, superglues, polyvinyl acetate fiber adhesives used in bookbinding). New adhesives also play an increasingly important role in the development of green manufacturing processes [15-17].

This laboratory exercise bridges a gap between organic chemistry and materials science, in that small organic molecules are used to produce a metal adhesive with quantifiable properties. It is intended for advanced undergraduate students if the synthetic chemistry operations are included [18, 19], or for beginning organic chemistry students if the component molecules are pre-made. The design is based on ‘click chemistry’, an approach that emphasizes the development and use of only the most practical and reliable reactions to join together a variety of molecular building blocks [20]. We focus here on the Cu(I)-catalyzed azide-alkyne [3+2] cycloaddition (CuACC) reaction to generate 1,4-disubstituted 1,2,3-triazoles (Scheme 1), which proceeds with outstanding reliability and selectivity [21, 22].

Scheme 1. Synthesis of 1,4-disubstituted 1,2,3-triazoles 3 via CuAAC of alkynes 1 and azides 2.

The learning objective of this article is to demonstrate the creation of a useful bulk material property from

simple organic building blocks synthesized and assembled by upper-division undergraduate students. Based on previous publications in our group [23, 24], the proposed experiment acquaints students with concepts of adhesive formation, adhesive performance, green chemistry, and click chemistry. It also provides interesting and useful examples of organic synthetic reactions that can be implemented in the teaching laboratory.

2. Hazards Caution should be exercised when handling the chemicals, all of which can be irritants or harmful. Special vigilance is required to avoid the use of acid in the workup of synthetic reactions involving inorganic azide, which would generate the volatile and highly dangerous compound HN3. Operations involving the generation or handling of significant quantities (more than 100 mg) of organic azide compounds should be carried out behind a blast shield or blast-resistant fume hood sash, with eye and hand protection. All instructors and teaching assistant supervising the laboratory are encouraged to communicate clearly with each other and with the students concerning all potential hazards and prudent laboratory practices, which are comprehensively discussed in the Student Handout and Instructor’s Notes (Supporting Information)

3. Experiment, results and discussion 3.1. Synthesis of compounds Synthesis of the component monomers is shown in Scheme 2, involving standard reactions (i.e. sulfonylation, SN2 substitution and nucleophilic aromatic substitution) that are well within the reach of upper-division undergraduate organic chemistry students. However, any or all of these operations can be performed ahead of time by the instructors, depending on the emphasis to be placed on synthetic vs. materials chemistry. We divided the class into three groups, each assigned the synthesis of one component monomer. The yields reported in Scheme 2 were obtained by the students; complete experimental details and characterization data are provided in Supporting Information. Enough of each product was obtained for

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Scheme 2. Synthesis of adhesive monomers 7, 10, and 14. Commercially available compounds 15 and 16 are shown at the right.

use by the entire class in the subsequent adhesive formation and testing operations. Alternatively, commercially available N,N-di(2-propyn-1-yl)-2-propyn-1-amine (15) may be purchased and used in place of compounds 10 or 14. Therefore only the synthesis of compound 7 is absolutely necessary. In addition, (azidomethyl)benzene (16) can be purchased if an ineffective formulation is to be included for comparison.

3.2. Gluing copper plates The combination of component monomers to make metal-adhesive organic polymers was illustrated by dividing the class into groups tasked with the investigation of differing combinations of azides and alkynes. As shown in Figure 1 (top), the students prepared test samples consisting of cleaned rectangular copper plates crossed at right angles (comprising a cross-tensile peel test joint), glued by the deposition of

desired monomer mixtures and subsequent heat-promoted curing of the adhesive polymer. The amount of each monomer solution was adjusted to achieve the desired azide:alkyne molar ratio. In this case, the click reaction forms the functional group (1,2,3-triazole) that is largely responsible for adherence to the metal substrate. In brief, the adhesion process requires the metal to function in at least two crucial ways: (1) Providing the species (CuI ions) that catalyze triazole formation; and (2) the bulk metal must also bind to the growing polymer network by virtue of interactions with multiple triazoles and potentially also with alkyne groups. Finally, the polymer-forming process can also “etch” the surface by extracting metal ions, creating a surface binding region with a blurred boundary between the various copper species and the triazoles-based backbone (Figure 1, bottom). This is therefore a unique adhesive strategy with ample opportunity for discussion of a variety of chemistry and materials concepts.

Figure 1. Top: Experimental procedure to adhere the copper plates: (a) Copper plates with holes; (b) abrasion of the plates with steel wool just before gluing; (c) arrangement of 5-mm diameter O-rings in a 3 × 3 square (in one of the plates) to hold the THF solutions of the component monomers (1.0 M stock solutions in total azide or alkyne functional groups); (d) pipetting component mixtures into each O-ring; (e) removal of O-rings after solvent evaporation; (f) placement of the second cleaned plate over the adhesion area. After 2-4 minutes, the sample is placed in a laboratory oven preheated to 60 ºC for 1 h. Bottom: Illustration showing the proposed mechanism of copper adhesion by formation of 1,2,3-triazole-based polymeric networks as described in the text.

a b c d e f

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3.3. Measurement of adhesive strength and analysis of failure mode After cooling the samples down to RT, the students in pairs tested the strength of their adhesives using a simple apparatus involving a luggage scale, adding weight by pouring water into a bucket suspended from the bottom of the two-glued plates (Figure 2). The water should be added in 100 mL portions, and wait a fixed amount of time (i.e. 10 seconds) for the next addition. Water was added between readings with the bucket firmly on the floor, and care was taken to lift it slowly so as not to introduce a sudden stress. The final reading observed on the scale before the joint failed was recorded as the maximum load before failure. Reliability testing of adhesive joints was performed using two different approaches. In the first case, the reproducibility of the measurement for a single batch of adhesive monomers was determined by repeating the measurement at least three times. In addition, the performance of different combinations of adhesive monomers produced by different groups of students was recorded and compared.

Figure 2. Steps in the testing of adhesive strength: (a) Attaching the digital luggage scale to a 21'' chain holding the top plate; (b) the chains hooked onto the top plate; (c-g) attaching the chain holding the bucket to the bottom plate of the joint (the bucket should be a few inches off the floor); (h) adding slowly water to the bucket; (i) reading the load on the luggage scale when the bucket is lifted slowly off the ground; (j) plates after failure of the adhesive. Note: The lower chain contributes to the weight supported by the adhesive. Hence, it should be used the minimum necessary length of lightweight chain. See Supporting Information for expanded discussion.

In materials science the mode of failure of an adhesive is important in quality control testing. If failure occurs

in the bulk of the adhesive and material is left coating both plates the sample is judged to have undergone cohesive failure, which is indicative of a strong adhesive system. In contrast, if one adherend contains most of the polymer and the other shows bare metal then the sample underwent adhesive failure, which is symptomatic of a weaker adhesive product. In this experiment, after failure of the joints, they were visually examined to determine which mode of failure occurred and the extent of bending of the copper plates, which provide a qualitative indication of the adhesive strength. Table 1 provides a summary of the observed loading capacities obtained for triplicate experiments using several adhesive monomer combinations.

Crosslinked polymer systems (combinations of monomers containing some fraction of trialkyne monomers) displayed stronger adhesion than the combination of difunctional compounds, which would provide linear polymers. The strongest adhesives produced a greater degree of bending of the copper plates (uncharacterized here, but may be measured by the students). All the samples tested were found to have undergone adhesive as opposed to cohesive failure, indicating there is further room for improvement in the design of these materials. Note that, while the experimental error does not allow a firm correlation, the results suggest that greater adhesive power is obtained when the crosslinking percentage is at an intermediate value (entry 3 vs. 6). This is consistent with expectations that the ability of crosslinking to produce a stronger material is counterbalanced by increasing brittleness when crosslinking becomes too great. Brittle materials can experience bulk propagation of cracks and other stress-induced defects that harm overall adhesive performance.

The reported average values were calculated from the testing results obtained by different groups of students using the same batch of adhesive monomers. The spread of the reported values is due mainly to the simplification of the testing set up to facilitate the implementation of the experiment in any regular chemistry laboratory course. The major sources of error include movement of the chains and/or the bucket, fast addition of large amounts of water, and the small contact area used between the plates.

Table 1. Summary of loading capacities obtained for different adhesive monomer combinations.a

entry combination of monomers (molar ratios) b percent crosslinkingc maximum supported load

(kg) (N) (kPa) 1 10 + 16 or 14 + 16 0 no adhesion no adhesion no adhesion 2 7 + 10 (1:1) 0 weak adhesiond weak adhesiond weak adhesiond 3 7 + 10 + 15 (11:2:6) 75 1.37 ± 0.4 13 ± 4.0 21 ± 6.1 4 7 + 15 (3:2) 100 1.70 ± 0.4 17 ± 3.9 26 ± 6.1 5 7 + 14 (3:2) 100 1.67 ± 0.6 16 ± 5.4 25 ± 8.4 6 7 + 10 + 15 (5:2:2) 50 1.83 ± 0.6 18 ± 5.4 28 ± 8.4

a) The results are given as the average value obtained from triplicate experiments performed by the students. Supported loads are reported in kg, N, and kPa, using the standard conversions 1 N = 9.8 kg and 1 kPa = 1000 N/m2, where the glued area corresponded to 1.0 square inch (6.45 × 10-4 m2). b) See Scheme 1 for structures. c) The percentage of the monomer units having branched connectivity, assuming that all of the azide and alkyne groups form triazole linkages. d) “Weak adhesion” denotes average load values below 0.3 kg.

a b c d e

f g h j i

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4. General students’ perception A questionnaire was given to the students after the experiment and they were asked about their experience in terms of motivation and learning. Their feedback was very positive and highlighted the ease of the 2,4,6-trifluoro-1,3,5-triazine (12) route to compound 14, the novelty of the materials science aspects of the experiment, and an interest in learning more about click chemistry. Students were particularly impressed with the breadth of chemistry this experiment exposed them to in a limited number of laboratory periods, and also enjoyed the adhesive testing portion of the experiment. See the Supporting Information (Instructor’s notes) for the student survey.

5. Summary and conclusions The synthetic procedures and adhesive failure experiments provide laboratory instructors with a simple, low-cost, and enjoyable two-part exercise that demonstrates the use of organic compounds in the production of high-value metal adhesive materials [25]. Students enrolled in CHEM 496 (Undergraduate Research) at The University of San Diego performed the syntheses and analyses described herein. Students worked in pairs and therefore each of the procedures was performed twice by undergraduates. As shown in Table 1, the adhesives were found to support between ca. 15 and 40 kPa during the laboratory experiment, providing for an informative range of results.

The experiment offers a good degree of flexibility that makes it adaptable to fit any time constraints and circumstances imposed by different lab courses (for example, selected synthesis and replication experiments may be left out, or additional variables of the students’ or instructor’s design may be included for comparison). The adhesive design offers several topics for more in-depth discussion regarding hyperbranched polymers and adhesion, since they show the unusual property of having glass transition temperatures far in excess of curing temperatures [26].

From a pedagogical point of view, the concept of using copper surfaces to catalyze the formation of their own adhesives via the formation of organic triazole-based polymers (a phenomenon that students can instantly relate), as well as the possible replacement of heavy metal alloys in metal adhesion, both comprise elements of environmentally-sound design that lend themselves to a motivating discussion within a variety of chemistry courses at several levels.

Acknowledgements We thank the National Institute of General Medical Sciences, the National Institutes of Health (GM 28,384), National Science Foundation (CHE-9985553), the W. M. Keck Foundation, The Skaggs Institute of Chemical Biology and the University of Regensburg for financial support. We are also indebted to Mr. Christopher Fish of the TSRI machine shop for assistance in producing the needed materials, Prof. Hyonny Kim (UCSD) for helpful suggestions, Prof. Peter Iovine and students at the University of San Diego, who helped to develop this activity.

Supporting Information Two files are provided: (1) The Instructor’s Notes contains 1H and 13C NMR spectra of synthesized monomers, TLC analyses of the reactions, synthetic procedures, product characterization, safety notes, adhesive test, possibilities for time optimization, CAS registry numbers of all chemicals and solvents used in this experiment, list of required materials, mechanistic considerations, answer to pre- and port-laboratory questions, additional comments for the instructor, and additional figures. (2) The Student Handout repeats some of this material in a form suitable for direct distribution to the students. This material is available free of charge to all readers from the authors or via the Internet at https://www.dropbox.com/sh/yad992jvtyykcac/AACX_nFrLdu5EfbgtgFDg7M2a?dl=0 Notes and references 1. Lang, P. T.; Harned, A. M.; Wissinger, J. E., Journal of Chemical

Education, 2011, 88, 652-656. 2. De Faveri, G.; Ilyashenko, G.; Watkinson, M., Chemical Society

Reviews, 2011, 40, 1722-1760. 3. Hollmann, F.; Arends, I.; Buehler, K.; Schallmey, A.; Buhler, B.,

Green Chemistry, 2011, 13, 226-265. 4. Broshears, W. C.; Esteb, J. J.; Richter, J.; Wilson, A. M., Journal

of Chemical Education, 2004, 81, 1018-1019. 5. Mohrig, J. R.; Nienhuis, D. M.; Linck, C. F.; Vanzoeren, C.; Fox,

B. G.; Mahaffy, P. G., Journal of Chemical Education, 1985, 62, 519-521.

6. Duval-Terrie, C.; Lebrun, L., Journal of Chemical Education, 2006, 83, 443-446.

7. Bennett, G. D., Journal of Chemical Education, 2005, 82, 1380-1381.

8. Moad, G.; Rizzardo, E.; Thang, S. H., Polymer, 2008, 49, 1079-1131.

9. Matyjaszewski, K.; Xia, J., Chemical Reviews, 2001, 101, 2921-2990.

10. Gilbert, R. G.; Fellows, C. M.; McDonald, J.; Prescott, S. W., Journal of Chemical Education, 2001, 78, 1370-1372.

11. Coessens, V. M. C.; Matyjaszewski, K., Journal of Chemical Education, 2010, 87, 916-919.

12. Sereda, G.; Rajpara, V., Journal of Chemical Education, 2010, 87, 978-980.

13. Roy, K.-M., in Ullmann's Encyclopedia of Industrial Chemistry; Wiley-VCH Verlag GmbH & Co. KGaA: 2000.

14. Aiyejorun, T.; Kowalik, J.; Janata, J.; Josowicz, M., Journal of Chemical Education, 2006, 83, 1208-1211.

15. Hjeresen, D. L.; Boese, J. M.; Schutt, D. L., Journal of Chemical Education, 2000, 77, 1543-1547.

16. Cannon, A. S.; Warner, J. C., in Green Chemistry Education; American Chemical Society: 2009; Vol. 1011, p 167-185.

17. Anastas, P. T., Green Chemistry Education; American Chemical Society: New Haven, CT, 2009.

18. Sharpless, W. D.; Wu, P.; Hansen, T. V.; Lindberg, J. G., Journal of Chemical Education, 2005, 82, 1833-1836.

19. Mendes, D. E.; Schoffstall, A. M., Journal of Chemical Education, 2011, 88, 1582-1585.

20. Kolb, H. C.; Finn, M. G.; Sharpless, K. B., Angewandte Chemie International Edition, 2001, 40, 2004-2021.

21. Bock, V. D.; Hiemstra, H.; van Maarseveen, J. H., European Journal of Organic Chemistry, 2006, 51-68.

22. Hawker, C. J.; Fokin, V. V.; Finn, M. G.; Sharpless, K. B., Australian Journal of Chemistry, 2007, 60, 381-383.

23. Diaz, D. D.; Punna, S.; Holzer, P.; McPherson, A. K.; Sharpless, K. B.; Fokin, V. V.; Finn, M. G., Journal of Polymer Science Part A: Polymer Chemistry, 2004, 42, 4392-4403.

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24. Liu, Y.; Díaz, D. D.; Accurso, A.; Sharpless, K. B.; Fokin, V. V.; Finn, M. G., Journal of Polymer Science Part A: Polymer Chemistry, 2007, 45, 5182-5189.

25. We are aware of no undergraduate laboratory experiments in chemistry or materials science curricula that explore the preparation and testing of organic metal adhesives. However, other examples of adhesive chemistry has attracted already the interest of journals devoted to education in Chemistry, see for example: (a) Sharkey, J. B., Journal of Chemical Education, 1987,

64, 195-200. (b) Doyle, D. J., Journal of Chemical Education, 1991, 68, 1012-1014. (c) Miyazaki, M.; Onose, H.; Moore, B. K. Am. J., Dentistry, 2000, 13, 101-104. (d) Unlu, N.; Gunal, S.; Ulker, M.; Ozer, F.; Blatz, M. B. J., Adhesive Dentistry, 2012, 14, 223-227. (e) Blum, I. R.; Lynch, C. D.; Wilson, N. H. F., European Journal of Dental Education, 2012, 16, E53-E58

26. Le Baut, N.; Diaz, D. D.; Punna, S.; Finn, M. G.; Brown, H. R., Polymer, 2007, 48, 239-244.

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The bench synthesis of silver nanostructures of variable size and an introductory analysis of their optical properties Aoife C. Power, a, c Sinead Byrne, a Stephen Goethals, a, d Anthony J. Betts b, c and John F. Cassidy a, c a School of Chemical and Pharmaceutical Sciences, Dublin Institute of Technology, Kevin St., Dublin 8, Ireland. b Directorate of Research & Enterprise, Dublin Institute of Technology, 143-149 Rathmines Rd., Dublin 6, Ireland. c Applied Electrochemistry Group, Focas Institute, Dublin Institute of Technology, Camden Row Dublin 8, Ireland. d KaHo Sint-Lieven, Technologie Campus Gent, Gebroeders Desmetsraat 1, 9000 Gent, Belgium. aoife.power@dit.ie

Abstract A laboratory practical was designed for use by both undergraduate and second level students to demonstrate the synthesis and characterisation of tuneable silver colloids. It clearly illustrates the novel optical properties of silver nanoparticles compared to the bulk metal. The synthesis is both rapid and repeatable, and can be conducted on the laboratory bench at room temperature.

Introduction For some time nanotechnology has been regarded as the next major scientific advance. References to nanoscience and nanotechnology are now ubiquitous throughout both scientific journals and popular science publications, as researchers dedicate more and more resources to the study and application of all things nano. This is particularly evident by the way that the controlled synthesis of nanoparticles (of various shapes and sizes) for use in a wide range of applications continues to progress and gather interest 1-2. Therefore the development of a secondary school / undergraduate laboratory practical based on a simple synthesis and characterisation of nanoparticles is not only highly relevant as an example of modern chemistry, but also appealing to students.

A simple and rapid practical is proposed, which allows students to both synthesise silver nanoparticles (with size control) and monitor size changes using UV-Vis spectroscopy. The submitted practical has an added advantage that it may be geared specifically to the educator’s needs, depending on the availability of instrumentation, ability of students and time dedicated for the practical / lesson.

Bulk silver is easily identified; its very appearance (silver grey colour) often used as a descriptor; as materials progress to the nanoscale however it is not unusual for their set physical properties to change as the influence of quantum mechanics on the material increases. This is clearly evident with silver colloids; a colloid is a type of mixture that appears to be a solution but is actually a mechanical mixture. A colloidal system consists of two separate phases: a dispersed phase (internal phase), and a continuous phase (dispersion medium). In a colloid, the dispersed phase is made of tiny particles or droplets that are distributed evenly throughout the continuous phase. The dispersed-phase particles are sized between 1 nm and 100 nm in at least one dimension. With silver colloids, because the silver nanoparticles they contain are smaller in dimension than the wavelength of visible light, they interact with light in different ways as demonstrated in figure 1.

It is well established that the colour 3-5 of the (suspended silver nanoparticles) colloids varies according to the morphology of the nanoparticles. Therefore it is possible to estimate the size of the colloidal nanoparticles by just observing their colour.

Figure 1. A sample set of the different coloured Silver colloids produced in the practical.

Materials The water used in the practical should be of high purity such as Millipore grade (with > 18.2 MΩ resistivity) or distilled. Silver nitrate (purum p.a. > 99.0%), sodium borohydride (reagent Plus 99%) polyvinyl alcohol, (99+% hydrolyzed, typical M.W. 89000-98000 gmol-1), tri sodium citrate, (purum p.a., ≥ 99.0%), hydrazine, (reagent grade, N2H4 50-60 %), crystal violet, (ACS reagent, ≥ 90.0% anhydrous basis), malachite green, (indicator Riedel-de Haën), Rhodamine 6G, (Dye content ~95 %), were all purchased from Sigma Aldrich and used as received without further purification. Students should prepare or be supplied with the following stock solutions, 1% PVA w/v (aqueous), 0.001M sodium borohydride, 0.001M Tri Sodium Citrate, 0.1M Hydrazine, 0.001M Silver Nitrate and for ‘junior’ laboratory sessions solution ‘A’ ( which contains 3 x 10-3M Silver Nitrate and 2.5 x 10-3 M Tri Sodium Citrate, 1:1 volume ratio). In ‘senior’ laboratory sessions students may prepare their own seed solution, as outlined in the experimental below and so do not require solution ‘A’.

Hazards Silver nitrate is corrosive, causing burns when in contact with the skin and eyes. Sodium borohydride is flammable and toxic. Sodium citrate may cause irritation to the skin, eyes and respiratory tract.

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Hydrazine hydrate causes burns and is toxic. Hydrochloric acid and sodium hydroxide are corrosive causing burns when in contact with skin and eyes. Students should wear the appropriate personal protection equipment (goggles, gloves, and lab coat), and follow all laboratory safety precautions.

Supplying the students with stock solutions of the proposed reagent concentrations significantly reduces the experimental risks. When preparing the sodium borohydride solution it is important to ensure that the volumetric flask is either left unstoppered or that the stopper is loosely fastened to avoid a build up of Hydrogen gas which can result in the failure of the vessel. Waste containers should be available for any waste solutions containing silver.

Experimental The synthesis methods proposed below are completely reliable, providing the practical is conducted with proper care (i.e. slow drop-wise addition of reagents where instructed and the use of properly cleaned glass ware). The prepared reagents, with the exception of sodium borohydride, will last several days to months if stored appropriately (e.g. photosensitive silver nitrate solutions should be stored in opaque vessels). As sodium borohydride decomposes in water (equation 1), it is necessary that the sodium borohydride solution should be freshly prepared the day of the practical. It should be noted that the best results are achieved when all reagent solutions are freshly made.

NaBH4 (aq) + 4H2O(l) → Na[B(OH)4](aq) + 4H2(g) (1)

Synthesis ‘junior lab’ – second level / 1st year undergraduate students The silver colloids were prepared by a two part process, consisting of nucleation and particle growth 1-2. Initially a seed solution was prepared by the chemical reduction of silver nitrate (AgNO3) with sodium borohydride (NaBH4) in the presence of a stabiliser and capping agent, Tri Sodium Citrate (TSC). The seed solution was then added, with constant agitation, to a mixture of TSC and hydrazine (H4N2) to produce a ‘growth’ solution. To this mixture set volumes of AgNO3 were added, producing the different colloids. The different volumes of excess AgNO3 that are added to the growth solution determine the colour, and therefore the size/shape, of the nanoparticles in the solution.

The principle behind this method is as follows: the seed solution that is added to the growth solution works like a sort of ‘frame’ or starting point. The excess AgNO3 that is added to the growth solution is also reduced by the TSC and H4N2 to silver atoms which interact with the existing seed nanoparticles, to give a gradual growth of the seed particles, to form nanoparticles of different sizes and shapes 6. (Please note; the green dispersion is most likely the product of the combined processes of particle growth (larger particles) and secondary nucleation (smaller particles), this accounts for the two distinct particle size ranges of the green colloid (figures 4 & 5b).

Seed production To 20 cm3 of solution A (ensure that the solution is being stirred continuously) slowly add (preferably drop wise) 6 cm3 0.001M sodium borohydride. Best results are observed using a clean 100 cm3 beaker as the reaction vessel. (Solution A is a 1:1 mixture of 0.003M AgNO3 and 0.0025M TSC)

Fabrication of coloured colloids To 5 cm3 1% PVA, first add 1 cm3 of the seed solution, followed by the addition of 3 cm3 0.1M TSC, and 5 cm3

0.1M H4N2 (again ensure this mixture undergoes constant agitation). To produce the coloured colloids, set volumes of 0.001M AgNO3 should be added to this ‘growth mixture’ as outlined in table 1, with best results observed using a clean 250 cm3 beaker as the reaction vessel. Table 1. Summary of volumes of 0.001 M AgNO3 and the resulting colloids.

0.001 M AgNO3 (cm3) ( X cm3)

Colour

~ 0.40 Yellow ~ 1.00 Orange ~ 1.30 Red ~ 2.50 Purple ~ 6.00 Blue

~ 20.00 Green

Synthesis senior lab – undergraduate students Again the silver colloids were produced using a two part process. Here the seed solution was once more prepared by the chemical reduction of AgNO3 with NaBH4 in the presence of polyvinyl alcohol (PVA) 7 a stabiliser and capping agent. It should be noted that this seed synthesis requires the student to show great care and patience with the addition of the reducing agent, in order to produce a suitable seed and hence coloured colloids.

Seed production To 2 cm3 of PVA (1% w/v) add 2 cm3 0.001M AgNO3 and mix well. To this mixture slowly add 2 cm3 of 0.001M NaBH4 drop wise ensure that the mixture undergoes constant agitation during the NaBH4 addition. Best results are achieved overall when the resulting seed solution is a golden yellow, although this colour change is almost immediately evident it its also important that the student adds the full volume of NaBH4 as failure to do so impinges the growth of further coloured colloids.

Fabrication of coloured colloids The production of the coloured colloids follows that of the ‘junior’ laboratory experimental outlined above in table 1.

Characterisation of the silver nanoparticles Characterisation of the silver nanoparticles can involve several techniques, dependent on availability of instrumentation, ability of students and time dedicated for the practical.

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The authors used UV-Vis, dynamic light scattering (DLS) and electron microscopy, which were conducted using a Perkin Elmer, Lambda 900 Spectrometer, a Malvern nano series Zetasizer and 100CX Transmission Electron Microscope (TEM) or Hitachi SU 6600 FESEM (STEM) respectively. The results presented below are for colloids produced via the senior lab practical, it should be noted that almost identical results are achieved with colloids produced via the junior practical.

Results and discussion

Colloid characterisation The Tyndall effect – Has a colloid been prepared? The Tyndall effect, also known as Tyndall scattering, is the scattering of light by colloidal particles or particles in suspension. It may be demonstrated using a laser pointer and several clear and coloured solutions, e.g. deionised water and a selection of dye solutions as well as prepared colloids, to demonstrate the observed scatter is a result of the presence of nanoparticles and not simply due to pigment.

The student should shine the laser through the solutions. In non colloidal mixtures only the points where it enters and exits the liquid is evident; the path the laser travels through the media is absent. If the solution is colloidal, the path of the laser is clearly illuminated (figure 2).

Figure 2.The glass on right contains only DI water, while glass on left contains silver colloid.

UV-Vis analysis The absorption spectrum of the ‘seed’ colloid, shown in Figure 3, indicates the production of the nanoparticles where the presence of a plasmon absorption band at ~ 400 nm is characteristic of silver nanoparticles 8.

Such plasmon bands are the result of the unique physical properties of the nanoparticles themselves. When an external electro-magnetic field such as light is applied to a metal, the conduction electrons move collectively so as to screen the perturbed charge distribution in what is known as plasmon oscillation. The Surface Plasmon Resonance (SPR) is therefore a collective excitation mode of the plasmon localized near the metal surface. In the case of a metal nanoparticle, the surface plasmon mode is 'restricted' due to the small dimensions to which the electrons are confined, i.e. the surface plasmon mode must conform to the boundaries of the dimensions of the nanoparticle 9. Therefore, the

resonance frequency of the surface plasmon oscillation of the metal nanoparticle is different from the plasmon frequency of the bulk metal. Surface interactions can alter the optical properties and influence the spectral profile of the light scattered by the SPR of the metal nanoparticles. This feature can be employed as an indicator in sensing interactions. Among the metal nanoparticles known to exhibit SPR, silver nanoparticles have an especially strong SPR. Particle size may be determined using Mie theory, which solves Maxwell’s equations 10 and in turn describes the extinction spectra (extinction = scattering + absorption) of spherical particles of arbitrary size 5, 11-12.

Figure 3. UV-Vis spectrum of stable aqueous colloidal Ag Seed solution, with λ max of 393 nm. [Ag+] = 0.001M (2.0 cm3), [PVA] = 1% wt/wt (2.0 cm3), [NaBH4] = 0.001M (2.0 cm3)

Figure 4. UV-Vis spectra of aqueous coloured Ag colloids. General make up of colloids [PVA] = 1% wt/wt (1.0 cm3), seed solution (1.0 cm3), [TSC] = 0.1M (3.0 cm3), [H4N2] = 0.1M (5.0 cm3) + [AgNO3] = 0.001M (X cm3). Please note that the value of X is stated in Table 1.

The excitation spectra of the different coloured colloids, which are presented in figure 4, are clearly influenced by the nanoparticles’ properties. It should be noted that for smaller particle size ranges such as the yellow colloid, a narrower/sharper absorbance band is observed. In contrast the blue colloid with a wider particle size range has clearly broader peaks. The λ max of the spectra also shifts position with changes in the nanoparticles size and shape.

The different nature of each colloid is also highlighted in the UV-Vis spectra of the green colloid where two distinct absorbance peaks are observed as a result of the interaction of two species (type) of nanoparticles i.e. the larger blue nanoparticles and the smaller yellow nanoparticles, (these are the most likely species contributing to the green as the peaks are seen to have

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similar λ max’s – Yellow 445 nm, Blue 670nm, Green band 1, 405 nm, band 2, 648 nm). The other colloids exhibit just one distinct band that can display a shoulder. However this could be attributed to band broadening due to the wider particle size range.

Dynamic light scattering, DLS Size analysis by DLS utilises the Brownian motion that particles, emulsions, and molecules in suspension undergo as a result of bombardment by solvent molecules. If the particles are illuminated with a laser, the intensity of the scattered light fluctuates at a rate that is dependent upon the size of the particles as smaller particles are “hit” more frequently by the solvent molecules and move more rapidly. Analysis of these intensity fluctuations yields the velocity of the Brownian motion and hence the particle size using the Stokes-Einstein relationship 13-14.

D = kBT / 6πηr (2)

Where D is the diffusion constant (m2s-1), kB is Boltzmann's constant (JK-1), T is the absolute temperature (K), η is the viscosity of the solvent (kgm-1s-1) and r is the particle radius (m). The typical graphical output of the zetasizer is shown below (figure 5a), whereas figure 5b is a graphical presentation of a combination of the size distributions of the different colloids.

Figure 5a. Distribution of particle diameters within the ‘seed’ Ag colloid.

Figure 5b. Distributions of particle diameters of the seed and coloured Ag colloids.

Table 2. Summary of Colloids UV-Vis λ max’s and DLS results.

Colour UV-Vis λ max

DLS Particle Size

Range

DLS Average

Size Range Seed 393 nm 5 – 14 nm 8 – 9 nm

Yellow 445 nm 6 – 28 nm 10 – 13 nm Orange 473 nm 11 – 38 nm 19 – 20 nm

Red 495 nm 11 nm – 60

nm 20-23 nm

Purple 555 nm 15nm – 50

nm 31-33 nm

Blue 670 nm 37 nm – 105 nm 58-60 nm

Green 405 nm &

648 nm 11 – 250

nm

91.1 % 20- 21 nm & 8.9 % > 60 nm

Electron microscopy. An image of the nanoparticles, (Figure 6) was obtained from the interaction of the coating and the beam of electrons transmitted through the coating. Before analysis, the colloidal samples (prepared in the same manner as outlined in Figure 2 and Table 1) were diluted in ethanol and sonicated for 30 mins, before being cast onto the TEM grid (Agar scientific, holey carbon 200 mesh (Cu)) by drop coating. The average diameters of the nanoparticles were determined, using Zeiss axiovision software 15 and correlated well with the DLS results.

Figure 6. On the left a TEM image of silver nanoparticles (yellow colloid) with an average diameter range of 10 – 13 nm, and on the right a STEM image of silver nanoparticles (blue colloid) with an average diameter range of 58-60 nm

Effect of ions on colloids stability Steric stabilisation and electrostatic stabilization are the two main mechanisms for colloid stabilisation. Electrostatic stabilisation is based on the mutual repulsion of like electrical charges. Different phases generally have different charge affinities, so that a charge double-layer forms at any interface. Small particle sizes lead to enormous surface areas (hundreds of m2/g), and results in this effect being greatly amplified in colloids. This can be better explained by the DLVO theory 14.

The Deryagin-Landau-Verwey-Overbeek (DLVO) theory suggests that the stability of a particle in solution is dependent upon its total potential energy function VT. This theory recognizes that VT is the balance of several competing contributions:

VT = VA + VR + VS

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VS (the potential energy due to the solvent) usually only makes a marginal contribution to the total potential energy over the last few nanometers of separation. More important is the balance between VA and VR; these are the attractive and repulsive contributions.

DLVO theory suggests that the stability of a colloidal system is determined by the sum of these Van der Waals attractive (VA), and electrical double layer repulsive (VR) forces that exist between particles as they approach each other due to the Brownian motion they are undergoing. This theory proposes that an energy barrier resulting from the repulsive force prevents two particles approaching one another and adhering together. Therefore if the particles have a sufficiently high repulsion, the dispersion will resist flocculation and the colloidal system will be stable. However if a repulsion mechanism does not exist then flocculation or coagulation will eventually occur. To maintain the stability of the colloidal system, DLVO theory states that the repulsive forces between the particles must be dominant.

The stability of many colloids of both natural and man-made origin can be improved by the presence of macromolecules or polymers, (e.g. fatty acids in milk are stabilised by the presence of casein). This is steric stabilisation. Polymers increase viscosity in the colloids, altering the sedimentation behaviour. This coupled with their high molecular weights results with only a small concentration being necessary to achieve this.

PVA is a well known and commonly used random block copolymer stabiliser. Only part of the macromolecule adsorbs to the particle allowing the rest to solvate and to expand away from the interface, preventing other particles from approaching. PVA is widely used for polymer nanocomposites. Due to the water solubility of PVA the nanoparticles can be produced in an aqueous medium making the preparation process non-toxic.

Therefore, the deliberate addition of ions to the colloidal system demonstrates the need of a stabiliser. With the addition of an acid or base (dilute HCl or NaOH), the colloids appearance changes as the larger particles aggregate in an uncontrolled manner. This first results in the colloid undergoing a colour change. If the concentration of ions is sufficient, the silver nanoparticles will aggregate completely to produce bulk silver; a black precipitate.

Motivation Continuing interest in the controlled synthesis of metal nanoparticles has resulted in the development of numerous experimental protocols for the production of defined nanostructures 1-2, 6. Consequently, this growing area of research is highly relevant to students and educators alike. This has led to a number of educational publications describing the synthesis of both semiconductor 16-17 and metal 6, 18-20 nanoparticles.

Here the authors describe a rapid, simple and robust methodology that may be carried out on bench, with comparatively mild reagents and without the need of ventilation6 or heating apparatus18, allowing for the

experiments use in both undergraduate and second level laboratories.

Student results Both second level and undergraduate students may perform this practical; in both cases a clear explanation of the Tyndall effect and an understanding of the localised plasmon resonance of metal particles on the nanoscale are required.

The experiment may be adjusted to suit the allocated laboratory time period. Variations of the practical have been successfully conducted in the Dublin Institute of Technology in laboratory sessions ranging from 2 – 3 hours, with over 500 students (groups of 20 -30 working in pairs) successfully completing it to date.

The most common factor for initial failure to produce the coloured colloids was the use of ‘dirty’ glassware where the students had neglected to ensure that the glassware was properly cleaned (and rinsed) prior to the practical (this had the benefit of clearly demonstrating to the students the importance of laboratory housekeeping).

The undergraduate students had already gained some useful knowledge that they were able to correctly apply when they were asked to characterise the colloids using UV-Vis spectroscopy. Students reported finding the experiment “somewhat challenging yet interesting and enjoyable”.

Supplemental Material Instructions for students and technical notes (including a complete risk assessment and introductory power point presentation) for the instructor are available at, https://www.dropbox.com/sh/9zf0cwe077xqhwo/mR0XZZGAFU

Acknowledgements The authors would like to thank E. O' Donoghue, P. Brien and C. Ní Néill for their assistance setting up and running the test practical sessions. A.C. Power thanks the ABBEST PhD Scholarship Programme of the Dublin Institute of Technology and everybody in the FOCAS Institute/DIT, particularly the members of the Applied Electrochemistry Group for their assistance during the experimental work.

References 1. D.M. Ledwith, A.M. Whelan, J.M. Kelly, J. Mater. Chem., 17,

2007, 2459–2464 2. D. Aherne, D.M. Ledwith, M. Gara, J.M. Kelly, Adv. Funct.

Mater., 18, 2008, 2005–2016 3. A. Shkilnyy. M. Souce. P. Dubois, F. Warmont, M.L. Saboungi,

I. Chourpa, Analyst, 134, 2009, 1868 – 1872. 4. M.E. Abdelsalam, S. Mahajan, P.N. Bartlett, J.J. Baumberg, A.E.

Russell, J. Am. Chem. Soc., 129, 2007, 7399 – 7406 5. K.L. Kelly, E. Coronado, L.L. Zhao, G.C. Schatz, J. Phys. Chem.

B, 2003, 107, 668-677. 6. A.J. Frank, N. Cathcart, K.E. Maly , V. Kitaev, J. Chem. Educ.,

2010, 87, 1098-1101 7. P.K. Khanna, N. Singh, S. Charan, V.V.V.S. Subbarao, R.

Gokhale, U.P. Mulik, Mater. Chem. Phys., 2005, 93, 117-121. 8. T. Li, H.G. Park, S. Choi, Mater. Chem. Phys., 2007, 105, 325-

330.

Aust. J. Ed. Chem., 2014, 73

19

9. Z.H. Mbhele, M.G. Salemane, C.G.C.E. van Sittert, J.M. Nedeljkovic, V. Djokovic, A.S. Luyt, Chem. Mater., 2003, 15, 5019-5024.

10. C.F. Bohren, D.R. Huffman, Absorption and scattering of light by small particles, New York; Chichester: Wiley, (1983)

11. Y. Kunieda, K. Nagashima, N. Hasegawa, Y. Ochi, Spectrochim. Acta, Part B, 64, 2009, 744–746.

12. E. Filippo, A. Serra, D. Manno, Sens. Actuators, B, 2009, 138, 625–630.

13. P. Atkins, J. de Paula, Atkins' Physical Chemistry, 7th ed., Oxford University Press, Oxford; New York, (2002), 845.

14. http://www.malvern.com/LabEng/industry/colloids/dlvo_theory.htm (accessed September 2011)

15. http://www.zeiss.com/c12567be0045acf1/ContentsFrame/cbe917247da02a1 cc1256e0000491172 (accessed December 2011)

16. K. Winkelmann, T. Noviello, S. Brooks, J. Chem. Educ. 2007, 84, 709.

17. E. M. Boatman, G. C. Lisensky, K. J. Nordell, J. Chem. Educ. 2005, 82, 949.

18. C. D. Keating, M.D. Musick., M. H. Keefe, M. J. Natan, J. Chem. Educ. 1999, 76, 949.

19. A. D. McFarland, C.L. Haynes, C. A. Mirkin, R.P. Van Duyne, H.A. Godwin, J. Chem. Educ. 2004, 81, 544A.

20. S. D. Solomon, M. Bahadory, A.V. Jeyarajasingam, S.A. Rutkowsky, J. Chem. Educ. 2007, 84, 322.

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Playing games, learning science: promise and challenges Kim Chwee Daniel Tan & Yam San Chee

National Institute of Education Nanyang Technological University, Singapore, daniel.tan@nie.edu.sg

Abstract Computer games can provide an immersive environment for players (learners) to experience scientific phenomena, reactions and properties according to related theories and laws, and provide a relevant context to assist learners to make sense of scientific concepts involved. Inquiry-based learning is also facilitated as players have to explore, discover, form hypotheses, experiment and make decisions based on outcomes generated in the game in the pursuit of an overall goal. Thus, science-based computer games can allow the player to learn to be a scientist, by thinking and acting as one in the game, instead of merely learning about science. This paper describes the development of a multi-player game, Legends of Alkhimia, and its associated instructional material to facilitate scientific inquiry and the learning of chemistry by lower secondary (Grades 7 and 8) students in Singapore. Challenges faced and lessons learnt in the implementation of game-based learning in the classroom are also discussed.

Introduction Constructivist theories of knowledge are based on the assumption that knowledge is constructed by the learner rather than being transferred from the teacher to the learner (Bodner et al., 2001). As learners have to personally make sense of what they are taught, teachers need to provide them with the appropriate experiences of the relevant phenomena, introduce the concepts, theories, procedures and language necessary for the understanding of the phenomena, and allow them to discuss their understanding with their peers and teachers (Driver, 1995; Driver et al., 1994). However, learners may not be provided the opportunities to meaningfully explore, negotiate and construct their understanding in school as much focus can be placed on the knowledge and skills that will be assessed (Rop, 1999). Learning is limited if they are required “to learn and think in terms of words and abstractions that they cannot connect in any useful way to images or situations in their embodied experiences in the world” (Gee, 2007, p. 73); they may not be able to understand and apply what is taught in a decontextualized manner. Computer games can be valuable tools to facilitate meaningful science learning if they encourage students to learn science and actively apply their knowledge during gameplay to solve problems, reflect on what they did, and discuss their actions and the consequences of these actions with their classmates and teachers (Squire & Jenkins, 2003).

Games for learning science Dempsey et al. (2002) define games as “a set of activities, involving one or more players…(with) goals, constraints, payoffs, and consequences…is rule-guided…(and) involves some aspect of competition, even if that competition is with oneself” (p. 159). Good games are motivating, fun, engaging and capture the attention of the players. These qualities of games, as well as their popularity, have attracted the attention of educators keen to explore the use of games to facilitate learning in schools (Dempsey et al., 2002; Oblinger, 2006; Sandford & Williamson, 2005). The types of games that have been used in educational settings include puzzles, bingo, word games, board games, card games and computer games (Crute, 2000; Dempsey et al., 2002; Gee, 2007; Rogers, Huddle, & White, 2000; Squire & Jenkins, 2003).

Computer or video games are “digital applications that can be controlled by individuals or groups of players using a PC or a console such as a Playstation or Xbox machine” (Sandford & Williamson, 2005, p. 1). They allow inputs from one or more players and generate outcomes using the rules programmed into the applications (Oblinger, 2006). Many are “narratively driven, experientially immersive, and multi-media rich” (Barab & Dede, 2007, p. 1), allow players to take on the identity of characters in the game and experience new worlds and roles that would otherwise be inaccessible to them (Oblinger, 2006). For example, a computer game can allow a student to role-play a chemist, and this requires the student to act, think, use tools and solve problems like a chemist; they ‘learn to be’ a chemist instead of merely ‘learning about’ chemistry (Brown & Adler, 2008). These processes may not be emphasized in normal science lessons; the use of algorithms and memorization without clearly understanding the processes involved is quite common (Barrow, 1991). Computer games and simulations that have been developed for learning science include Racing Academy which requires players to apply physics, mathematics and design principles to build cars to race against each other (Sandford & Williamson, 2005), Environmental Detectives in which students play the roles of different parties involved in addressing a chemical spill on a college campus (Klopfer & Squire, 2008; Squire & Jenkins, 2003), and Supercharged in which players learn and apply electromagnetism principles to navigate mazes (Squire et al., 2004). In general, the studies showed that participants who played the games found the contexts fascinating and enjoyed interacting with the virtual worlds (e.g., Klopfer & Squire, 2008), and reported that the students who primarily engaged in gameplay had better understanding of the relevant science concepts than those who did not (e.g., Squire, Barnett, Grant & Higginbotham, 2004). Shaffer (2006) argues that computer games can help make learning relevant, authentic and motivating. Immersive environments allow learners to experience scientific phenomena and their behaviour according to related theories and laws, as well as help learners to think and talk about the phenomena “using their intuitive understandings developed in simulated worlds” (Squire et al., 2004, p. 1); these simulations and immersive

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experiences may not be possible with other types of games such as word, board and card games. Inquiry-based learning is facilitated in computer games as players have to explore, discover, form hypotheses, experiment and make decisions based on the simulated outcomes in the goal-driven contexts of the games (Gee, 2007; Mayo, 2007; Sandford & Williamson, 2005; Squire & Jenkins, 2003). Players learn by doing, trying alternative means, making mistakes, and then reflecting on the outcomes and consequences (Squire & Jenkins, 2003; Sandford & Williamson, 2005; Shaffer 2006).

Learning with Legends of Alkhimia This paper describes the development of a multi-player game, Legends of Alkhimia, and its associated instructional strategies to facilitate scientific inquiry and the learning of basic concepts involved in separation techniques, reactions of acids, bases and salts, and rates of reactions in lower secondary chemistry (Grades 7 and 8). The affordances and challenges faced in the implementation of game-based learning in the classroom are also discussed.

Legends of Alkhimia is a game that supports up to four players simultaneously, to be played over a local area network, typically in a computer laboratory in school. In the game, the students role-play as apprentices of a master chemist to tackle a series of challenges encountered at various game levels. The design of the game is based on the Performance–Play–Dialog (PPD) model (Chee, 2011, Chee & Tan, 2012; Chee, Tan, Jan, & Tan, 2012) where students construct their knowledge and gain competence in chemistry by performing as chemists. This performance is manifested in playing the game and dialoguing, facilitated by the teacher, to make sense of the chemistry phenomena experienced in the game world and in-game virtual laboratory. In general, a player will encounter a problem in the game world and needs to travel back to the in-game virtual laboratory to hypothesize the source of the problem and conduct experiments to generate possible solutions to the problem. He/She then goes back to the game world to determine if the proposed solutions will work. If the proposed measures fail, the player has to go back to the in-game laboratory to conduct further experiments to explore other possibilities and test them out again in the game world. Thus, students learn chemistry by playing the game, reflecting on their actions and the consequences of their actions, and deliberating on their experiences related to chemistry in the game, as part of a process of Deweyan inquiry. The game provides the context and motivation to learn, and students enact their developing competence in the way they play in successive levels of the game and dialogue on what they did and why in those levels. This approach is different from a traditional, didactic chemistry lesson where students passively receive knowledge from their teachers.

Legends of Alkhimia and its associated instructional material aim to facilitate lower secondary students’

(Years 7 and 8) understanding of scientific inquiry, separation techniques, and reactions of acids and bases as listed in the lower secondary science syllabus (Ministry of Education, 2007). The related learning outcomes are given in Figure 1. A few additional learning outcomes from the upper secondary chemistry syllabus (University of Cambridge Local Examinations Syndicate, 2008) are also included in the game. For example, the use of a separating funnel was included to give students some experience of its use in the in-game laboratory as actual practical work involving separating funnels is rare in Years 7 to 10, as well as to complete all the separation techniques that they have to learn in secondary chemistry; the researchers judged that Years 7 and 8 students are able to understand the critical concepts involved in the separation technique, that is, density and miscibility. The learning objective for acids, “investigate the properties of acidic and alkaline solutions”, is rather vague in the lower secondary science syllabus so details are taken from the upper secondary chemistry syllabus to clarify this learning objective. As chemical reactions are involved in the gameplay, that is, when the students try to defeat the different monsters they encounter, the effects of concentration, particle size and temperature on the rate of reactions from the upper secondary chemistry syllabus are also included to provide more options for the students to produce cartridges containing different types of reagents and use them on the monsters under different conditions to see the effects of these different cartridges. This will provide the context for the discussion on the factors affecting rate of reaction but not in detail as this topic is not assessed in Years 7 and 8.

The challenges in the six game levels developed are given in Table 1. The gameplay in Level 1 will be described in detail to illustrate the tasks, and the chemistry and inquiry processes involved in Legends of Alkhimia. In Level 1, players encounter silver-coloured monsters that they have to destroy (see Figure 2). However, they find that their weapons keep on malfunctioning when they shoot, and will wonder why this happens. They have to retreat to the in-game virtual laboratory where the master chemist suggests that their cartridges may have been contaminated. When they examine the original cartridges, they will notice that the cartridges contain a mixture of a dark-coloured solid in a blue liquid. They need to hypothesize that one component of the mixture could have caused the malfunction in their weapon, so they need to separate the mixture and then test out in the game world which component is responsible for the malfunction; the students will perform the separation processes with a purpose in mind. A flow diagram to illustrate the processes involved and the results obtained is given in Figure 3.

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Figure 1 Learning outcomes emphasized in the Legends of Alkhimia (Ministry of Education, 2007; University of Cambridge Local Examinations Syndicate, 2008)

Figure 2 Players fending off a monster attack in Level 1 of the game

The equipment available in the laboratory bench (see Figure 4) comprises two types of filter paper, a filter funnel and beaker combination, a separating funnel and beaker combination, and a beaker-tripod stand-bunsen burner combination. The students are encouraged to use of all of the equipment to separate the mixture to produce as many different types of cartridges as possible for use in the game. When the mixture is heated to dryness, the student will obtain a cartridge containing only a brown solid. If the student uses a separating funnel, a cartridge containing the original mixture would be obtained. Two cartridges, one containing the blue liquid and one containing the brown

solid, are obtained when filtration is carried out with a fine filter paper, whereas a cartridge with blue liquid with some brown solid and a cartridge with a brown solid are obtained when a coarse filter paper is used.

The in-game laboratory allows students to try out various means to separate the mixtures and discover the outcomes of their attempts, something which rarely happens in a normal science laboratory class because of time constraints and because the students are required to do the ‘correct’ experiments with little or no mistakes and seek the ‘right’ answers (Crawford 2000). In addition, doing ‘wrong’ experiments will incur additional cost in terms of equipment and reagents, and may have safety consequences. Thus, students usually learn only the ‘correct’ procedures in school; they are not asked to consider alternative procedures and compare them with the ‘correct’ procedure. The game encourages players to explore ‘wrong’ procedures and experience the outcomes with minimal real-world consequences (Gee 2007; Sandford & Williamson 2005). Mistakes made in the game are not considered as something to be avoided but as “opportunities for reflection and learning” (Gee 2007, p. 36); in order to really understand why a procedure is ‘correct’, one needs to realise or experience why it is better than the other procedures which are ‘wrong’ or unsuitable for a particular purpose.

Scientific inquiry • recognise that the study and practice of science involve three major elements: attitudes, processes or methods, and

products • recognise that the products of science are the tested data collected by scientists for centuries and explain with examples of

how people working with science have formulated concepts, principles and theories • show an awareness that science is not confined to the laboratory, but is manifested in all aspects of the world • use scientific inquiry skills such as posing questions, designing investigations, evaluating experimental results and

communicating learning • show an appreciation that scientific inquiry requires attitudes such as curiosity, creativity, integrity, open-mindedness and

perseverance • value individual effort and working in a team as part of scientific inquiry Separation techniques • show an awareness of basic principles involved in some separation techniques such as filtration, distillation, paper

chromatography and the use of a separating funnel* • explain how the properties of constituents are used to separate them from a mixture:

o magnetic attraction o filtration o evaporation o distillation o paper chromatography o using a separating funnel*

• show an awareness of the applications of the various separation techniques in everyday life and industries Properties of acids and alkaline solutions • investigate the effect of a variety of acidic, alkaline and neutral solutions on Universal Indicator paper and natural indicators

(i.e. obtained from plants) • investigate the effect on Universal Indicator paper when acidic and alkaline solutions are mixed • investigate the properties of acidic and alkaline solutions (action of alkalis on ammonium salts NOT required)

o describe the characteristic properties of acids as in reactions with metals, bases and carbonates* Speed of reaction* • describe the effect of concentration, particle size and temperature on the speeds of reactions* Note: * the learning objectives are taken from the upper secondary chemistry (Years 9 and 10) syllabus (University of Cambridge Local Examinations Syndicate, 2008)

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Table 1. Game challenges in the six levels of the Legends of Alkhimia

Level Challenges Chemistry concepts involved

1 Game world Virtual lab

• Weapons jammed when fighting metallic monsters

• Destroy metallic monsters • Separate/purify substances in the given

cartridges

• Separating substances based on their properties, e.g. particle size vs. pore size in filtration

• Reaction of acid with metal

2 Game world Virtual lab

• Weapons have no effect acidic monsters as cartridges contain acid

• Destroy acidic monsters • Separate/purify substances in the new

cartridges provided

• Separating substances based on their properties, e.g. differences in boiling points in simple distillation

• Reactions of acid with metals and bases • Factors affecting rate of reaction e.g. surface

area and concentration 3 Game world

Virtual lab

• Clean up contamination arising from the waste of the monsters and cartridges

• Neutralise acids and bases

• Acid-base reactions • Use of indicators • Effect of soluble and insoluble

base/carbonates in neutralization reactions 4 Game world

Virtual lab

• Destroy acid monsters in two different environments (hot and cold)

• Determine the effect of temperature on the rate of reaction

• Determine the effect of different substances on the rate of reaction

• Reactions of acid with metals and bases • Factors affecting the rate of reactions, e.g.

temperature and nature of the substances

5 Game world Virtual lab

• Destroy door to escape from room • Separate liquids to obtain fuel to destroy

door

• Separating substances based on their properties, e.g. differences in boiling points in simple and fractional distillation; differences in miscibility and density of liquids using a separating funnel

• Combustion of fuel

6 Game world • Destroy different types of monsters encountered in the previous levels

• Reactions of acid with metal and bases • Factors affecting the rate of reactions, e.g.

temperature and nature of the substances

Figure 3 Flowchart illustrating the processes involved in the in-game laboratory in Level 1

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Figure 4 A player performing an experiment at the laboratory bench in Level 1

When the students have finished their experimentation in the in-game laboratory, they re-enter the game world to encounter the silver-coloured monsters again with the different cartridges that they produced (see Figure 3). They will soon learn that the cartridge obtained containing the original mixture (obtained using a separating funnel) and the brown solid cartridge cause their weapons to malfunction. The cartridge with the blue liquid and lesser amount of brown solid (obtained using the coarse filter paper) will also cause the weapons to malfunction, albeit after a longer period of time. However, the blue liquid cartridge allows the weapons to be fired repeatedly and inflicts great damage on the monsters; eventually, the monsters are vanquished. The students will not know why the blue liquid is effective against the monsters, so this will be dealt with after the gameplay session where the students will describe and discuss what they did during gameplay; the blue liquid is supposed to be an acid which reacts with the silver-coloured monsters which are supposed to be metallic in nature and destroys them. Students are invited to speculate on what is going on, propose specific hypotheses, and cite any available evidence they can to support their hypotheses. Student peers are encouraged to interrogate and critique the work-in-progress hypotheses. The teacher facilitates this process as a classroom dialogue and introduces the relevant chemistry concepts at the appropriate junctures.

Implementation of the Legends of Alkhimia program The test of an early version of the Legends of Alkhimia program was conducted in November 2009 in School A, a typical government secondary school with a group of eight students, four boys and four girls, with two teachers, a male and a female, observing the session. This test was to assess the usability of the functions in the game and the learning activities which were integrated with the gameplay, as well as the playability of the game. A survey was administered to the students to collect their feedback. Six students found the game challenging and seven students indicated that they enjoyed the learning experience with Legends of Alkhimia. Six stated that the group discussion helped them better understand the game. Technical problems which arose were noted by the game development team

and were addressed in the following version of the game.

The first trial of the almost complete (beta) version of the Legends of Alkhimia program was conducted in July 2010, again in School A with the same two teachers, this time involving two Year 7 classes, an experimental and a control. A detailed account of this trial has been reported in another paper (Chee & Tan, 2012). The researchers found that the students who played the game had a better understanding of separation techniques and scientific inquiry than those who did not.

In January to March 2011, another trial of the Legends of Alkhimia program was conducted in School B, involving a class of 31 Year 8 students and one female teacher, Teacher C, who had no experience with game-based learning. This third trial, a continuation of the Legends of Alkhimia research, is the subject of this paper, and it focuses on teacher enactment and perception of game-based learning. The trial was conducted as an after-school enrichment program over seven 2-hour sessions and 1 one-hour session as the school could not accommodate the implementation of the Legends of Alkhimia program during curriculum hours. The students were in a science talent class (chosen from their performance in the school’s selection tests), and since the class would have additional hours of chemistry instruction, the Legends of Alkhimia program being an enrichment program, no comparable class was available as a control group in terms of additional instructional time as well as ability of students. Teacher C was interviewed on six occasions throughout the trial and her experiences and challenges faced when she implemented the Legends of Alkhimia program are discussed in the following section.

Challenges in game-based learning Are students learning? During interviews in all three trials, the students stated that they enjoyed playing Legends of Alkhimia and valued the opportunities to explore and experiment with the different apparatus and substances in the in-game laboratory. However, it was observed in the trials at Schools A and B that, while the students were engrossed in gameplay, they were not engaging deeply with the chemistry concepts. Teacher C was concerned that her students were focussed mainly on the playing of the game and getting the better of the monsters; she commented in an early session that many students “don’t really think very carefully about a lot of things…so they just do it”, relying much on trial-and-error. When the students were experimenting in the in-game laboratory, they did not seem to take the nature of the mixtures and equipment into much consideration. They also did not spend much time analysing and interpreting the results of their separation and thinking how the results could inform further experimentation; several students did not understand the relevance of what they were doing in the game, so they had difficulty explaining what they were doing apart from saying that they were trying out the available equipment. When they left the in-game laboratory and entered the game

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world, the students were so engaged with battling the monsters with the cartridges at their disposal that they did not seem to consider the outcomes of using different cartridges other than which was the most effective cartridge to use against the monsters. Klopfer and Squires (2008) also found that the students were very enthusiastic and excited participating in their augmented reality simulation, Environmental Detectives, but the students, too, did not seem to interact deeply with the content during the simulation sessions.

However, this is to be expected as the students are unaccustomed to this mode of learning and may have not developed the capacity to engage in inquiry. Lessons in School C do not normally encourage “situated and embodied thinking and doing” (Gee, 2007), so students are used to passively receiving knowledge re-presentation from their teachers rather than actively thinking and constructing knowledge for themselves. The Legends of Alkhimia program is designed to facilitate students’ inquiry, thinking and talking in ways that are relevant to the discipline (Shaffer, 2006), and develop the relevant process skills, dispositions and habits of mind in lower secondary science (Ministry of Education, 2007). The initial period of a new way of learning is difficult for students (and teachers), so they need time to be accustomed to the required thinking, talking and doing, and to value these processes. Thus, additional time within the two-hour session had to be allocated after the gameplay for students to review and make sense of what happened in the in-game laboratory and game world in order for them to discuss and reflect on what they had done (Chee et al., 2012; Sandford & Williamson, 2005). Squire et al. (2004) emphasize the need for structures to help reduce student difficulties and help them to see how they are learning science through the game, so log sheets were designed for this purpose (see Appendix 1). These log sheets were distributed before gameplay session started and required students to note down the equipment that they used in the in-game laboratory and the results of each experiment using specific equipment. With the log sheets, discussions can be centred on whether a particular experiment is successful, and if unsuccessful, the reasons why and how to address the shortcomings. Squire et al. (2004) also found that log sheets were required to reinforce the purpose of the activities as students were not critically reflecting on what they were doing in the game. In addition, they also suggest that the teacher project relevant game scenarios during the reflection part of the session to facilitate more focussed thinking. For example, the teacher can carry out experiments in the in-game laboratory and lead the students in the discussion of the results obtained, the concepts involved and possible alternative separation routes. Through these discussions, the students should gain a better understanding of the inquiry process, and the procedures and reactions

involved in the various levels that they had played, and be able to apply this understanding when playing later levels of the game, in the classroom or in the laboratory.

Understandably, some students complained about the need to reflect on their gameplay and discuss issues, especially in the first few sessions when they were still not used to the Legends of Alkhimia program. Playing the game was fun for the students but the thinking and reflection after the playing was tedious to some of them so they did not take this part seriously. To motivate these students, assessment of their performance in the Legends of Alkhimia program was required as Teacher C commented that students expect to be rewarded with good grades for putting in time and effort into thinking. However, she agreed that the majority of the students enjoyed exploring and thinking about what they did during the game, and discussing these with their classmates. She also mentioned that she had to be very familiar with the game in order to help students make connections between gameplay and chemistry concepts at the various game levels.

One very important observation that Teacher C made was that students could not see the impact of the cartridges on the monsters as chemical reactions, so the learning of the reactions involved was not impactful. Some students viewed the cartridges as projectiles, causing ‘physical’ damage to the monsters (making holes in them) rather than the contents of the cartridge reacting with the material of the monsters, which was the intention of the researchers. Thus, the instructional material was revised to make the links between the game and real chemistry more explicit. For example, demonstrations of acid reactions (and separation processes) were included in the lesson plans (an example is given in Figure 5) to help students experience the real-life equivalent of the phenomena that they encountered in the game world (and in-game laboratory). In Level 1, the teacher can demonstrate to students, using a visualizer, the reaction between an acid (the content of the cartridge) and a metal (the material of the monster). As an extension, the teacher can also demonstrate the testing of hydrogen and/or the reaction of different metals with acid and complete the demonstrations with equations of the reactions. Students may be able to make more sense of the demonstrations and equations as they have played the game and experience the situations where the reactions are involved (Gee, 2007). It was unfortunate that none of the researchers realised that close-up animations showing the effect of the content of the cartridges on the monsters were necessary, and so, were not considered during the developmental phase of the game. Virtual effects showing the contents of the cartridge splashing or scattering onto the monsters and reacting with the substance of the monsters could have parallel real-life reactions and create greater impact on the students’ experience of the relevant reactions during gameplay.

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Activity Time/min Resources Remarks/ Rationale 5

5.1

5.2

Teacher demonstration of real chemistry (Whole-class) The teacher demonstrates separation of soil and water using filters of different pore sizes. Questions: • How does the apparatus work? • What is the principle behind the separation

techniques? What can be successfully recovered? Why? Are there alternative methods to separate soil and water – distillation – can compare pros and cons.

Learning points: • The size of the pores in the filter paper and

the size of the particles in the mixture determine what passes through the filter paper.

The teacher demonstrates reaction of acids with metals (HCl with magnesium, zinc and copper). Learning points: • Different metals react differently with the acid • Metals react with acid to produce hydrogen and

salt • Hydrogen extinguishes a lighted splinter with a

‘pop’ sound (explosion)

30

(15)

(15)

Material: Muddy water Apparatus: Filter paper, filter funnel, conical flask, sock/cloth Acid: 0.1M HCl Metals: magnesium, zinc, copper Apparatus: (Experiment) test-tubes, splinter, matches/lighters; (Demo) petri dish, visualiser or overhead projector.

Possible alternative conception: • Solute particles will be

filtered off, especially in the filtration of a mixture consisting of a solution and an insoluble substance

Figure 5. Abridged version of the lesson plan for Level 1 focusing on teacher demonstrations

Teachers’ struggles with game-based pedagogies Expository teaching is the general mode of teaching in secondary chemistry focussing on students’ mastery of content (Chee et al., 2012) and Teacher C agreed with this assertion; when she taught in the classroom, she would present the concepts explicitly, clearly and linearly with students taking notes. Thus, teachers face challenges and tensions when they implement game-based learning because students are expected to learn by doing in the game instead of receiving the knowledge from them. Teacher C mentioned that she seemed to be “a bit lost” at what to do during gameplay as it is not easy for her to refrain from telling students the right answers when she sees students struggling during the in-game laboratory or the reflection sessions, or taking what she considers to be a long time to come up with a solution. She was anxious that her students might not learn what they were supposed to learn and tended to believe that leaving students to work out the answers for themselves might not be effective; neither was it an efficient use of (precious) time. In addition, there was the worry that students would not know how to play the game successfully if they were not first taught the content involved (Chee et al., 2012). Teacher C stated that her students felt confused as the way of doing things was new, there were so many thing happening at the same time and so many possibilities, as well as no clear way of doing things; the students had to try many things out and make sense of what was happening, so she believed that learning was more difficult and confusing for them. Teachers need to be convinced that students are able to perform and gain competency through gameplay as they are supported by the design of the game and the facilitation of the teacher (Gee 2007). Towards the end of the Legends of Alkhimia trial in School B, Teacher C mentioned that she had learned to

trust the students more, and that the students were able to learn the required concepts with the appropriate scaffolding and take charge of their own learning; she saw more students being able to explain what they were doing in the game using the appropriate chemistry concepts.

The additional time required to enact the Legends of Alkhimia program compared to the normal frontal teaching of the required concepts could be a potential concern for teachers. Thus, when the Legends of Alkhimia program is introduced to more schools, teachers will be given the option to choose the levels that they think are more important for their students’ learning. This was in line with Teacher C’s feedback that she would only use certain levels if she were to use the Legends of Alkhimia program during curriculum time with future classes. The researchers believed that the inquiry and learning processes would not be as effective if only certain levels were played by the students but agreed that this would be a pragmatic compromise to encourage more teachers to experiment with the Legends of Alkhimia program. The researchers would also explore implementing the Legends of Alkhimia program in informal learning environments such as in science centres to address the issues of time constraints and teachers’ and students’ unfamiliarity and reluctance to engage in game-based learning during curriculum time.

Support for teachers who are interested in implementing game-based learning is essential as the practices involved are different from the normal teaching and learning activities in school, and require teachers to adopt a mind-set of learning by doing science rather than teaching for content mastery (Chee et al., 2012). The support can be in the form of opportunities to

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observe other teachers enacting game-based learning in real classroom settings, listening to the success and ‘horror’ stories shared by the teachers facilitating the game sessions, discussing issues of learning and implementation, and inviting other teachers to observe and comment on their own enactment of such lessons. These will be built into the Legends of Alkhimia program when it is introduced into schools; hopefully, a community of teachers who are interested in game-based learning will be established so that they can learn from and support each other in their endeavours. Otherwise, there is a high possibility that a lone teacher who adopts innovative pedagogy such as game-based learning will not persist with it in the future (Chee et al. 2012).

Conclusion Game-based learning has the potential to facilitate contextualized learning that is fulfilling and motivating (Shaffer 2006). The Legends of Alkhimia program is an attempt in this direction to facilitate the acquisition of inquiry skills as well as the learning of chemistry concepts. Students who were involved in the three trials of the game found it interesting and engaging, and the results from surveys and a conceptual test indicated that they gained a better understanding of the inquiry process and chemistry concepts involved. Teachers play a critical role in game-based learning as they provide support and focus for student reflection and learning during the game sessions. As the adoption of game-based pedagogies may require a drastic change in beliefs of instructional practice, how students learn and should be taught in schools, support needs to be given to teachers by game developers and researchers in the initial stages, and at a later stage, by a community of peers who were earlier adopters of game-based learning. Such support could include in-service courses on the theoretical basis of game-based learning and the skills required to facilitate such learning, observations of actual game-based learning sessions in school, colleagues sharing their experiences in using games for students to learn with, and peer observations and coaching during the teacher’s own implementation of game-based learning with her/his classes.

Acknowledgments The work reported in this paper was supported by a research grant (NRF2007–IDM005–MOE–006CYS) from the National Research Foundation, Singapore. The authors acknowledge with gratitude the contribution of the research and game development team members: Ek Ming Tan, Mingfong Jan, Rahul Nath, Yik Shan Wee, Cher Yee Ong, Won Kit Ho, Simon Yang, Andy Lim, Henry Kang, Ittirat Vayachut, and Aldinny Abdul Gapar.

References Barab, S., & Dede, C. (2007). Games and immersive participatory

simulations for science education: An emerging type of curricula. Journal of Science Education and Technology, 16(1), 1-3.

Barrow, G. M. (1991). Intellectural integrity or mental servility. Journal of Chemical Education, 68(6), 449-453.

Bodner, G., Klobuchar, M., & Geelan, D. (2001). The many forms of constructivism, Journal of Chemical Education, 78(8), 1107.

Brown, J. S., & Adler, R. P. (2008). Minds on fire: Open education, the long tail, and learning 2.0. Educause Review, 43(1), 16-32.

Chee, Y. S. (2011). Learning as becoming through performance, play, and dialog: A model of game-based learning with the game Legends of Alkhimia. Digital Culture & Education, 3(2), 98-122

Chee, Y. S., & Tan, K. C. D. (2012). Becoming chemists through game-based inquiry learning: The case of Legends of Alkhimia. Electronic Journal of e-Learning, 10(2), 185–198.

Chee, Y. S., Tan, K. C. D., Jan, M. F., & Tan, E. M., (2012). Learning chemistry performatively: Epistemological and pedagogical bases of design-for-learning with computer and video games. In K. C. D. Tan & M. Kim (Eds.), Issues and challenges in science education research: Moving forward (pp. 245–262). Dordrecht: Springer.

Crawford, B. A. (2000). Embracing the essence of inquiry: New roles for science teachers. Journal of Research in Science Teaching, 37(9), 916-937.

Crute, T. D. (2000). Classroom nomenclature games - BINGO. Journal of Chemical Education, 77(4), 481-482.

Dempsey, J. V., Haynes, L. L., Lucassen, B. A., & Casey, M. S. (2002). Forty simple computer games and what they could mean to educators. Simulation & Gaming, 33(2), 157-168.

Driver, R. (1995). Constructivist approaches to science teaching. In Steffe, L.P. & Gale, J. (Eds.), Constructivism in education (pp. 385-400). Hillsdale, New Jersey: Lawrence Erlbaum Associates.

Driver, R., Squires, A., Rushworth, P., & Wood-Robinson, V. (1994). Making sense of secondary science: Research into children’s ideas. London and New York: Routledge.

Gee, J. P. (2007). What video games have to teach us about learning and literacy. New York: Palgrave Macmillan.

Klopfer, E., & Squire, K. (2008). Environmental Detectives—the development of an augmented reality platform for environmental simulations. Educational Technology Research and Development, 56(2), 203-228.

Mayo, M. J. (2007). Games for science and engineering education, Communications of the ACM, 50(7), 30-35.

Ministry of Education (2007). Science Syllabus: Lower Secondary: Express/Normal (Academic). Singapore: Author.

Oblinger, D.G. (2006). Games and learning. Educause Quarterly, 3, 5-7.

Rogers, F., Huddle, P. A., & White, M. D. (2000), Simulations for teaching chemical equilibrium, Journal of Chemical Education , 77(7), 920-926.

Rop, C. J. (1999). Student perspectives on success in high school chemistry. Journal of Research in Science Teaching, 36(2), 221-237.

Sandford, R., & Williamson, B. (2005). Games and learning. Bristol: NESTA Futurelab.

Shaffer, D. W. (2006). How computer games help children learn. New York: Palgrave Macmillan.

Squire, K., & Jenkins, H. (2003). Harnessing the power of games in education. Insight, 3, 5-33.

Squire, K., Barnett, M., Grant, J. M., & Higginbotham, T. (2004). Electromagnetism supercharged! Learning physics with digital simulation games. Paper presented at the International Conference of the Learning Sciences 2004 (ICLS 04), Santa Monica, CA.

University of Cambridge Local Examinations Syndicate. (2008). Chemistry: GCE Ordinary Level (Syllabus 5072). Cambridge: Author.

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Appendix 1 Game log for students for Level 1

Initial Cartridge

(I) Cartridge Content

• Part Substance A: Liquid, blue

• Part Substance B: Solid particles, brown

Apparatus Used Effects in Lab Used Effects in Lab

1

2

3

4

5

6

Cartridges Obtained

Effects in Mission

Effects in Mission

A

B

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Ignitable liquids in fire debris investigation: A GC-MS practical for forensic chemistry Linda Xiao*, Walter Stern and Philip Maynard

Centre for Forensic Science, School of Chemistry and Forensic Sciences, University of Technology, Sydney, PO Box 123, Broadway, 2007, NSW, Australia, linda.xiao@uts.edu.au

Abstract We have developed an ignitable liquids in fire debris investigation experiment for the forensic sample preparation and GC-MS analysis in the forensic chemistry laboratory. Students were given several mock fire debris samples plus a few real samples from a Forensic and Scientific Services. Students will learn how to collect samples; extract the fire debris fit for GC-MS analysis with various solvents; carry out the instrument analysis and interpret the results obtained.

Keywords: ignitable liquids, fire debris, GC-MS, forensic chemistry

Introduction Arson, the crime of maliciously lighting fires, is a major problem in all industrial countries. Damage from fire is Australia's most costly public safety problem. Losses due to fire, in life and injury, are exceeded only by those due to traffic accidents [1-2]. The cause of a significant proportion of all fires investigated is found to be arson or suspected arson [1]. Arson investigation is a complex subject that requires information from many different sources, including the topic of chemical analysis [3]. This paper focuses on a small but significant aspect of the overall investigation, the chemical analysis of fire debris for the presence of ignitable liquids [4]. One of the many objectives of a fire cause and origin investigation is to determine whether ignitable liquids were deliberately used to accelerate the spread of the fire [5]. An accelerant is usually an ignitable liquid and it is used to initiate or speed the spread of fire. It is commonly a petroleum hydrocarbon mixture, such as petrol, kerosene, mineral turps or diesel, all readily available, and all good at producing a rapid, intense, hot fire [6]. Finding accelerant present indicates both intent and preparation, provided the materials found are not normal to the premises where the fire occurred.

If the presence of an accelerant is suspected at the fire scene then debris samples from various areas should be submitted to the laboratory to determine the presence, distribution and identity of the liquid. This information will support the investigator's own understanding of the ignition and propagation of the fire [7]. Using methods adapted for student use from American Society for Testing and Materials (ASTM) standard E 1618-10 [8] and Australian Standard AS 5239-2011 [9], the gas chromatography-mass spectrometry (GC-MS) technique is used to analyse for the ignitable liquids [10]. The students focus on the extraction, analysis and identification phases of the investigative process described in the Standards. Mock arson cases and some real case samples obtained from a forensic fire examination company were set up in standard packaging [11], in order to create an educational and practical laboratory experience for a chemistry laboratory.

This laboratory exercise is part of a programme to develop the attributes expected of a graduate from the degree; communication skills, discipline knowledge, and development of critical thinking. The mission for the forensic students is to analyse the samples submitted according to common forensic procedures. Students are required to decide whether a fire debris sample is positive or negative for the presence of flammable liquids, and if positive identify the flammable liquid or liquids. An expert witness report is to be composed which includes the information on techniques applied, results of the examination and interpretations of findings. Students learn the concepts of gas chromatography, sample preparation, data acquisition, and data analysis.

Experimental Equipment: GC/MS system-HP 6890 gas chromato-graph with HP 5973 mass selective detector and ChemStation software (Agilent). Operation conditions: ionization energy +70eV; helium carrier gas constant flow of 1mL/min; injector 280˚ C; transfer line 250˚ C; initial oven temperature 90˚ C for 2 min, ramp at 10˚ C/min to 200˚ C, and then 200 to 290˚ C, hold for 3 min: split injection of 1 µl, solvent delay for 1.75 min. Capillary column-HP MS 5, crosslinked 5% phenylmethyl silicon, 30 m x 0.25 mm id x 0.25 µm film thickness (Agilent) was used.

Reagents: Petrol, kerosene and diesel were commercial grade. Pentane (AR), Tenax TA 60/80, dimethyl-sulfoxide (AR) and carbon disulfide (AR) were purchased from Sigma-Aldrich.

Hazards: Caution must be used when working with ignitable liquids: pentane, petrol, kerosene and diesel are highly ignitable solvents, while carbon disulfide was only handled by the instructor because of the risk of the highly toxic solvent. These chemicals should be handled in a fumehood while wearing appropriate gloves, eye protection, and a laboratory coat.

Procedure I. The carpet samples were burned by lab staff one week prior to the laboratory session. Carpet pieces were cut into 50 x 50 mm and left in an individual paint can. Two millilitres of the ignitable liquid either mixture or single solvent were poured over

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the carpet in the can and allowed to soak for a few minutes. At the end of this time the ignitable liquid was ignited and the lid put back on the can. The carpet pieces were stored in a capped can and sealed. The quantity of ignitable liquid remaining was detectable, but not enough to cause ignition or explosion at any stage of the experiment. The fire debris samples were stored at room temperature until needed for the practical class.

Procedure II. The case debris samples (100 g) were collected at two different and independent fire scenes. The samples were collected in both cases in an area indicated by intense low burning to be the likely position of origin of the fire. The samples were each placed into unglued and unlined metal cans, labelled, sealed and taken to the chemistry laboratory where they were kept at cool temperatures till extracted.

The three samples were extracted by placing inside each can a strip of activated charcoal (obtained from Albrayco Technologies), and then leaving the cans at 60˚ C for 16 hours. During this period volatile components were adsorbed onto the activated charcoal. The charcoal strip was then removed from each of the three cans, cut in two and the six halves of the three samples were placed inside six separate 5 mL glass GC vials, to each of which was added 1 mL solvent. Carbon disulfide was used as the solvent in one vial of each of the three fire samples. Likewise, pentane was used as the solvent for each of the three remaining vials from the three fire samples.

Procedure III. The Tenax TA absorbant was activated before the class by heating overnight in the oven. The Tenax was removed from the oven and allowed to cool. 0.3 g of Tenax TA was weighed out into a clean scintillation vial for each sample. The sample tin was opened and the (uncapped!) scintillation vial and Tenax was quickly placed inside. The tin was again sealed. The sample tins were placed in the convection oven at 80˚ C for 60 minutes. Remove the tins from the convection oven and allow to cool for 5 mins and then remove the scintillation vial from each tin, cap it and allow to cool to room temperature. For each sample, 4 mL of pentane was added to the scintillation vial, and the vial recapped and swirled gently for 30 seconds. The solution was taken up with a Pasteur pipette for each sample. The solution was filtered through a plug of cotton wool into a GC vial, until there was 1.5 mL of solution in the GC vial. The GC vial was capped. In each case, the volatile components were then highly concentrated and ready for instrument analysis. Petrol, kerosene and diesel standards were prepared by injecting 10 µl of each ignitable liquid into 1 mL of pentane in GC/MS vial. 1 mL of pentane was added to a GC/MS vial as blank. The GC/MS instrument run was programmed.

Results and Discussion Total ion chromatogram (TIC) and a series of extracted-ion chromatograms were obtained for each injection. The extracted-ion chromatograms are designed to separate various classes of hydrocarbons and assist in the identification of a flammable liquid amongst

interfering hydrocarbon peaks, such as pyrolysis products, which may contain a number of the same hydrocarbons, but in different ratios, one to another. Partly evaporated samples give more of the higher boiling components and less of the lower boiling components.

Total ion chromatograms and ion extractions of petrol, kerosene and diesel The chromatogram of pure petrol shows a multitude of peaks of different proportions from which at least ten known components shown in Table 1 must be present, in correct relative proportions, to be identified as petrol. The most common compounds to observe in GC/MS chromatograms of petrol are in fact; benzene, toluene, xylene, alkylbenzenes, naphthalene and methyl-naphthalene isomers. As such, it is expected to see the petrol standard chromatogram with the most intense peaks at the beginning of the chromatogram (around 4 minutes) as shown in Figure 1 and extracted ions as shown in Figures 2-3. Table 1. Known peaks present in petrol samples

m/z values Aromatics Naphthalenes Ions extracted 91, 105, 119

and 128

Toluene Xylenes (3) C3-alkylbenzenes (5)

Naphthalene

Figure 1. TIC chromatogram of petrol standard

Figure 2. Petrol standard alkane and alkene extracted TIC chromatograms

Analysis of a standard kerosene sample shows a number of evenly-spaced major peaks, which are the C9 – C17 straight chain alkanes, with a number of minor intermediate peaks as shown in Figures 4-7. The identity of each of the even shaped major peaks is shown in Table 2.

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Figure 3. Standard petrol aromatics, styrenes and napthalenes extracted TIC chromatograms

Figure 4. TIC chromatogram of the kerosene standard

Figure 5. Kerosene standard alkanes chromatogram

Figure 6. Kerosene standard alkenes chromatogram

Figure 7. Kerosene standard naphthalenes chromatogram

Table 2. Components present in kerosene samples

m/z values Alkanes Ions extracted

43, 57, 71, 85 and 99 C10-C17 straight chains

The chromatogram of diesel also shows evenly spaced major peaks, in this case the C10 –C24 straight chain alkanes as shown in Figure 8. The m/z values for the hydrocarbons are shown in Table 3. The relative quantities of the alkanes in kerosene and in diesel are observed to be in a normal or bell-shaped curve.

Figure 8. TIC and extracted ions chromatograms of the diesel standard

Table 3. Components present in diesel samples

m/z values Alkanes Ions extracted

43, 57, 71, 85 and 99 C10-C23 straight chains

Total Ion Chromatograms and Ion Extractions of Set up Unknown Samples Analysis An example of TIC of a weathered petrol and kerosene mixture unknown sample is shown in Figure 9. The extracted-ion chromatograms of the sample (Figure 9) are labelled for their target hydrocarbons and have a list of m/z values which have been extracted. The most important diagnostic compounds for positive identification of petrol in fire debris samples are C2 to C5 alkylbenzenes, naphthalene, and methyl-naphthalenes. The characteristic features of the hydrocarbon composition of kerosene are the distribution of n-alkanes in the range of n-C10 to n-C17. The extracted TIC chromatograms indicate that the alkane, alkene and naphthalenes show a resemblance to kerosene and the aromatics chromatogram resembles petrol and styrenes chromatogram. m/z values of 43, 57, 71, 85 and 99 are indicative of alkanes, namely CnH2n+1.

Figure 9. TIC and extracted ions chromatograms of weathered petrol and kerosene mixture (unknown)

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Total Ion Chromatograms and Ion Extractions of Real Case Samples Analysis The three samples were extracted by placing inside each can a strip of activated charcoal and then leaving the cans at 60˚ C for 16 hours. During this period volatile components would be adsorbed onto the activated charcoal. The unknown fire samples were extracted by various solvents such as CS2 and pentane. The results were very similar to each other. However due to the toxicity of the CS2 solvent, the students were only given samples extracted by pentane. The TIC and extracted-ion chromatograms for the three samples (A, B and C) are shown in Figure 10, 11 and 12. The extracted-ion chromatograms of the sample A exhibits the distinct hydrocarbon pattern of kerosene. The extracted-ion chromatograms of the sample B exhibits the distinct hydrocarbon pattern of petrol and the extracted-ion chromatograms of the sample C exhibits only intensive styrene peaks. The compound was most likely a thermal decomposition product of household organic polymers.

Figure 10. TIC and extracted ions chromatograms of sample A

Conclusion The goals of the exercise presented here were to teach students the concepts of extraction and concentration of trace amounts of chemicals from a difficult matrix, to give them hands-on experience at the analysis of those chemicals and to have the students present their results in the form of an expert witness report. Students were able to accomplish the experimental goals in the time allowed and analyse the data to produce high-standard reports.

Acknowledgements We wish to thank the Forensic Science students at UTS who have trialled this exercise. The exercise results shown in this paper were provided by Bianca Cavasinni.

Figure 11. TIC and extracted ions chromatograms of sample B

Figure 12. TIC and extracted ions chromatograms of sample C

References [1] Dehaan, J.D. 6th edition. New Jersey: Brady Prentice Hall,

2006. [2] Leong, G.B. and Silva, J.A. Journal of Forensic Sciences,

1999, 44(3): 558. [3] Bertsch, W., Holzer, G and Sellers, C.S. Chemical Analysis for

the Arson Investigator and Attorney, Heidelberg: Huthig Buch Verlag GmbH, 1993.

[4] Stern, W., Presented at the New South Wales Chapter, International Association of Arson Investigators. 1988.

[5] Cafe, T, Firepoint Magazine: Journal of Australian Fire Investigators, 1998.

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[6] Sutherland, D.A., Fire & Arson Investigator. 2000, 21. [7] Bertsch, W., Analytical Chemistry News & Features, 1996,

541A. [8] E 1618-10 Standard Test Method for Ignitable Liqid Residues

in Extracts from Fire Debris Samples by Gas Chromatograph-Mass Spectrometry. ASTM International, 100 Barr Harbor Drive, West Conshohoken, PA 19428 USA.

[9] AS 5239-2011 Australian Standard: Examination of ignitable liquids in fire debris. Standards Australia , GPO Box 476 Sydney NSW 2001, Australia.

[10] Orf A. C., Morris M and Chapman J. Chem. Educator, 2009, 14, 10.

[11] E 1412-00 Standard Practice for Separation of Ignitable Liquid Residues in Extracts from Fire Debris Samples by passive Headspace Concentration with Activated Charcoal. ASTM International, 100, Barr Harbor Drive, West Conshohoken, PA 19428 USA.

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Thermodynamic aspects of the chemistry of copper, silver and gold Peter F. Lang and Barry C. Smith

School of Sciences, Birkbeck College (University of London), Malet Street, London WC1E 7HX, p.f.lang@gmail.com

Abstract Chemical reactivity is the core of chemical science. This article shows how thermodynamic data are used to understand chemical reactivity and define the stability of compounds including transition metal complexes. This is illustrated by a short survey of the chemistry of copper, silver and gold. A brief examination of the chemistry of nickel, palladium and platinum is provided as a comparison and additional aid to the understanding of the influence of thermodynamics on chemical reactivity.

Introduction A very important part of chemistry involves learning about different kinds of chemical reactions. When studying why and how a chemical reaction occurs one may also want to know the following: (a) How far does the reaction proceed before equilibrium is reached? (b) What heat/energy effects accompany the reaction? (c) Is the equilibrium position influenced by changes in temperature and, if so, how? (d) How fast does the reaction occur and how is the speed of the reaction affected by factors such as temperature and concentration? (e) Does the reaction take place in one step or are there a number of steps? (f) If there are a number of steps, which is the rate determining step?

Thermodynamic interpretations of chemical behaviour answer the questions (a), (b) and (c) above and provide useful clues to why some compounds may not exist (Ives, 1971, Dasent, 1982). The discussion extended here emphasizes some of the similarities and differences in behaviour between copper, silver and gold which belong to the same group. A brief comparison is made with another transition metal group to see what inferences can be drawn.

The coinage metals, copper, silver and gold, have been known since ancient times. They are in the same group (subgroup 1B) in the periodic table. They have characteristic lustres and they are very malleable and ductile. They are good conductors of heat and at room temperature possess the lowest electrical resistivities. The three metals have many uses, from electrical components to medicines. Gold salts have been known to be able to treat rheumatoid arthritis for over eighty years (Clegg, 1964) and copper and silver also have many medicinal uses (British Medical Association, 2010). Within the past few years, research interests in subgroup 1B have increased especially in the nano-technology, biochemical and medical fields, for example, in research into the targeting of cancer cells with gold (Wieder et.al, 2006). Although the behaviour of each individual metal has been described in depth in numerous publications, there are not many detailed discussions in general chemistry text books on their differences in behaviour.

Reactions of Copper, Silver and Gold with oxygen and the halogens Since each element of subgroup 1B follows a transition metal with a completed d shell they might be expected to behave as non-transition metals, react in a similar manner and to form M+ ions with the loss of the single s electron in the outermost shell and have the +1 oxidation state as the most common oxidation state. However, the +1 oxidation state is not always the preferred oxidation state and their reactions are much more complicated.

All three metals react differently with oxygen and the halogens. Copper forms stable univalent and bivalent oxides and halides but not the univalent fluoride (CuF) or the bivalent iodide (CuI2). Silver forms a univalent oxide, univalent halides and also AgF2. Gold does not burn in air and the oxide of gold, Au2O3, precipitated by the action of alkali on aqueous gold (III) solutions, decomposes at temperatures above 160oC. Copper and silver form many more ionic compounds than gold. The better known ionic gold compounds are the monohalides and trihalides but not AuF or AuI3.

Thermodynamic data (Johnson, 1982, Wagman et al., 1982, Chase, 1998) for the oxides and halides of copper, silver and gold are presented in Table 1. These compounds are thermodynamically stable. This means that they are in a state of equilibrium and we do not observe any spontaneous change (and they are stable with respect to spontaneous dissociation and disproportionation). Consider the following:

Cu2O(s) → CuO(s) + ½Cu(s)

2CuCl(s) → CuCl2(s) + ½Cu(s)

2CuO(s) → Cu2O(s) + ½O2(g)

CuCl2(s) → 2CuCl(s) + ½O2(g)

At constant temperature, ∆G = ∆H - T∆S (G for the above reactions are all positive). A negative value ∆G corresponds to a loss in the free energy of the system as a result of a change. Free energy loss is useful energy or work that can be gained from the change and is a measure of the affinity of the change. Hence, a condition for the thermodynamic stability of the four compounds are:

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2∆Gfө [CuO(s)] < ∆Gө

f [Cu2O(s)] < ∆Gөf[CuO(s)]

2∆Gfө [CuCl2(s)] < ∆Gө

f [CuCl(s)] < ∆Gөf [CuCl2(s)]

Silver(I) forms a stable oxide, but thermodynamic data for silver (I) peroxide and silver(III) oxide show significant positive standard Gibbs function of formation, so that these compounds, as expected, are thermodynamically unstable. AgF and AgF2 are examples of univalent and bivalent silver salts co-existing. The ∆Gf

ө data are not available and, since at low temperatures ∆S is very small (Johnson, 1982), in the cases below the standard enthalpy of formation values can be taken as a fairly reliable guide. Both are stable with respect to disproportionation:

2AgF(s) → AgF2(s) + Ag(s) [1] -204.6x2 -360 0

AgF2(s) → AgF(s) + ½F2(g) [2] -360 -204.6 0

The figures above (see Table 1) show that the enthalpy for reaction [1] is positive and the standard enthalpy for reaction [2] is even more positive at +155.4 kJ mol-1. Gold monohalides, which have low enthalpies of formation, decompose fairly easily and all dissociate into the elements at elevated temperatures. However, the enthalpy values can only serve as a guide and not as conclusive evidence of thermodynamic stability. Table 1. Thermodynamic data (kJ mol-1)

Compound ∆fH˚ ∆fG˚

CuO -156.1 -128.3 Cu2O -170.7 -147.9 CuF2 -538.9 -491.6 CuF -280.3 -259.5 CuCl -138.1 -120.9 CuCl2 -205.9 -161.7 CuBr -104.6 -100.8 CuBr2 -141.8 CuI -67.8 -69.5

AuF3 -363.6 AuCl -34.7 AuCl3 -117.6 AuBr -14 AuBr3 -53.3 AuI 0

Ag2O2 -24.3 27.6 Ag2O -31.1 -11.2 Ag2O3 33.9 121.4 AgF2 -360 AgF -204.6 AgCl -127.1 -109.8 AgBr -100.4 -96.9 AgI -61.8 -66.2

Aqueous Chemistry of Copper In aqueous solution, the behaviour of copper (I) and copper (II) are very much different from the behaviour in the solid state. There is a strong tendency for Cu+ to disproportionate to Cu2+ as in the following:

2Cu+ → Cu2+ + Cu

The standard enthalpies of hydration (Greenwood and Earnshaw, 1984) of Cu+ and Cu2+ are -580 kJ and -2100 kJ respectively. The enthalpy of hydration of Cu2+ is sufficiently high to ensure that Cu2+ is more stable in aqueous solution. This increase in hydration energy of Cu2+ can be accounted for by considering the Born model. In his model on ion-solvent interaction, Born (1920) regarded the ion as a charged sphere and the solvent as a dielectric continuum. Although this is not exact and the effects of molecular structure in the solvent is not accounted for, it is useful in providing a measure of influence of strong electrostatic ion-solvent interaction.

The potential at a distance r from the centre of a charged sphere in a vacuum is q/4πεor and the work required to bring up an element of charge dq from infinity to a distance r is qdq/4πεor. The total work required to charge up a sphere of radius R from 0 to Ze is:

∫ Ze qdq/4πεoR = Z2e2/8 πεoR (A)

because the potential at the surface of the sphere is q/4πεoR. If the sphere is placed in a continuous dielectric and assuming there is no change in the structure of the dielectric and the dielectric constant of the medium D is constant everywhere, the potential at distance r from a sphere with charge q is q/4πεoDr. The work of charging up the ion at constant temperature and pressure is:

∫ Ze qdq/4πεoDr = Z2e2/8 πεoDr (B)

The difference between (A) and (B) is the difference between the amount of work for creating an ion in a vacuum and in solution. This difference is the Gibbs free energy of hydration:

∆Gө(hydration) = N Z2e2/8 πεor(1 – 1/D)

N is the Avogadro number. This model predicts an inverse dependence of free energy of hydration on ionic radius and is in broad agreement with observation. The ionic radius of Cu2+ is smaller than that of Cu+ and the hydration enthalpy increases as the charge on the ion is doubled.

Ionization Energies of Copper, Silver and Gold The first comprehensive survey of ionization energies of the elements was completed by Moore (1949, 1952, 1956) who produced an excellent three volume work. This was later followed by a critical survey by Moore of ionization limits for atoms and atomic ions. This work included ionization energies derived from spectroscopy and calculations ranging from rough approximations to highly complex quantum mechanical equations (Moore, 1970). Recently, the CRC Handbook of Chemistry and Physics (2011-2012) presented extensive authoritative data with reference to Moore and other up to date works. We consider that successive ionization energies can often provide a dependable guide to chemical behavior as in the case of copper, silver and gold. It must said that ionization energies form only a component of many factors that determine chemical behavior and the following discussion should only be

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taken as a guide to the chemistry of copper, silver and gold.

The first, second and third molar ionization energies of the transition metals are shown in Table 2. The values, taken from the CRC handbook, are converted from electron volts (eV) to kJ mol-1 by multiplying them with the electron charge (1.6022x10-19 C) and the Avogadro number (6.022x1023 mol-1). There are two slightly different values of the third ionization energies of gold reported in the literature. The first reported value is 2895 kJ mol-1 (Greenwood and Earnshaw, 1984) and the second reported value (Korgaokar, Gopalaraman, Rohatgi, 1981) (which is given below) is 3280 kJ mol-1.

In contrast to some of the transition metals which have complicated ionization pathways (Lang and Smith, 2003), the gaseous atoms and ions of copper, silver and gold have similar configurations in the ground, first, second and third ionised states. All 3 metals follow the ionisation processes:

M(d10s1) → M+(d10s0) → M2+(d9s0) → M3+(d8s0)

Of all transition metals, only mercury and zinc have higher first ionization energies than gold. The first ionization energy of copper and silver are respectively 145 kJ and 159 kJ lower than that of gold. We assume that this trend in first ionization energies is related to the ratio of distance between the electron and nucleus (or “size”) of the atoms and that the dimension of the unit cells in the solid state is a good indication of the ratio of the distance (or “size”). At room temperature, all three metals have a cubic close packing structure and the cell constant ‘α’ of copper, silver and gold are 3.6148Ǻ, 4.0857Ǻ and 4.0782Ǻ (Donohue, 1974) (equal to 361.48pm, 408.57pm and 407.82pm) respectively. Thus, the ratio of the cell constants are 1:1.13 between copper and silver and 1:0.998 between silver and gold. Since the “size” of the silver atom has increased appreciably over copper it is not surprising that the first ionization energy of silver is just lower than that of copper. Whereas, the “size” of the gold atom is smaller than that of silver but its nuclear charge is about 1.7 times greater than that of silver, the first ionization energy of gold is much higher.

Silver has the highest second ionization energy, followed by copper and gold when compared to other transition metals. The sum of I1 and I2 of gold is highest

amongst all transition metals, followed by that of mercury, silver and copper.

The most stable oxidation state of silver is I at least partly because its first ionization energy is lower (than that of both copper and gold) but its second ionization energy is higher than any transition metal including copper and gold. The first ionization energy of copper is only higher than that of silver by 14 kJ but both the sum of I1 + I2 and the second ionization energy of copper is lower than that of silver. Hence, it is reasonable to assume that the stability of the II oxidation state decreases from copper to silver to gold.

The high first and second ionization energies as well as the sum of I1 and I2 of gold is a major factor why gold is inert, does not burn in oxygen and is more likely to form covalent complexes. However, gold has the lowest value of I3 and the sum of I1, I2 and I3 for gold is also lowest of the 3 metals and gold does form some ionic compounds with a valency of +3. The values of ionization energies of the 3 metals do correlate with the most familiar valencies of 2, 1 and 3 for copper, silver and gold, respectively. The relatively high first ionization energies and the high values of the sum of I1 and I2 account for the lower reactivity of copper and silver compared to some other transition metals.

Complex formation A complex is formed when a neutral central atom or positive ion is surrounded symmetrically by a shell of ions or molecules commonly described as ligands. Transition metal atoms/ions act as Lewis acids (with empty orbitals of the atom/ion) which accept electron pairs from donor molecules or ions. Copper, silver and gold all form complexes in the I, II and III oxidation states. Silver(III) is more stable than copper(III), but there are many more gold(III) complexes than silver(III) or copper(III). In contrast, silver(I) form many complexes that are linear or with long zigzag chains. Gold(I) also form complexes with a co-ordination number of 2 (linear complexes). All three metals form octahedral, tetrahedral and planar complexes and examples are given in Table 3. More examples, including different stereo-chemistry and types of complexes, can be found in Advanced Inorganic Chemistry (Cotton, Wilkinson, Murillo, Bochmann, 1999). The most common stereochemistry of copper(I) complexes is tetrahedral.

Table 2. First, Second and Third Molar Ionisation Energies (in kJ/mol) 3d Sc Ti V Cr Mn Fe Co Ni Cu Zn I1 633 659 651 653 717 762 760 737 745 906 I2 1235 1310 1410 1591 1509 1562 1648 1753 1958 1733 I3 2389 2653 2828 2987 3248 2957 3232 3395 3555 3833

4d Y Zr Nb Mo Tc Ru Rh Pd Ag Cd I1 600 640 652 684 702 710 720 804 731 868 I2 1179 1264 1351 1559 1472 1617 1744 1875 2072 1631 I3 1980 2218 2416 2618 2850 2747 2997 3177 3361 3616

5d La Hf Ta W Re Os Ir Pt Au Hg I1 538 659 728 759 756 814 865 864 890 1007 I2 1067 1447 1553 1791 1949 1810 I3 1850 2248 3280 3300

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Table 3. Examples of complexes of copper, silver and gold Copper Silver Gold Tetrahedral [Cu(Cl)4]2- [Ag(SCN)4]3- [Au(diars)2]+

Octahedral [Cu(NH3)6]2+ [AgF6]3- [AuBr6]3- Square planar [Cu(py)4]2+ [AgF4]- [AuBr4]-

There are numerous copper(II) complexes. The d9 configuration makes copper(II) subject to distortion if placed in an environment of cubic symmetry. When 6 coordinate, the octahedral shape is usually distorted. For square planer complexes with the metal ion possessing a d9 configuration, the odd d-electron will occupy the d(x2-y2) orbital.

Thermodynamic stability of a compound is determined by a number of factors(such as ionization energy and lattice energy), and, for example, as shown by the Born Haber cycle the bigger the electron affinity and lattice energy or the smaller the ionization energy terms the greater the stability. For transition metal complexes there is an extra important factor that confers thermodynamic stability. When a ligand approaches the central atom/ion, the degeneracy of the 5d orbitals is partly removed by the electrostatic field. The orbitals are split into 2 groups and the difference in energy of the 2 sets of orbitals is known as crystal field splitting or ligand field splitting. This is represented by the crystal field splitting parameter Δ or 10Dq. A detailed description on ligand field/crystal field theory is beyond the scope of this work. An extensive discussion is provided by Cotton (1990). If most or all the d electrons in the central metal atom/ion occupy the set of orbitals with lower energy the complex gains extra stability through CFSE or crystal field stabilisation energy. Table 4 (Johnson, 1982) shows the amount of CFSE in an octahedral and tetrahedral environment as a function of Δ or 10Dq. Table 4. CFSE in an octahedral or tetrahedral environment as a function of Δ*

Configuration Octahedral Tetrahedral d0 0 0

d1 2/5 3/5

d2 4/5 6/5

d3 6/5 4/5

d4 3/5 2/5

d5 0 0

d6 2/5 3/5

d7 4/5 6/5

d8 6/5 4/5

d9 3/5 2/5

*refers to high spin configurations only (since only d8 and d9 are relevant for copper, silver and gold complexes).

For common ligands in complexes, the order of increasing splitting (Δ or 10Dq) follows the series of ligands commonly called the spectrochemical series. The value of crystal field splitting in some cases can be of the order of 400 kJ/mole or more (Jones, 2001),

hence extra thermodynamic stability is conferred on many transition metal complexes. For example, the ligand field splitting for [Cu(NH3)6]2+ and [Cu(en)3]2+ are 182 and 198 kJ per mole respectively. The extra stabilisation energy gained from crystal field splitting equal (0.6 x 182) 109 and (0.6 x 198) 119 kJ per mole (to 3 significant figures) respectively and these values are significant.

Since ligand field splitting of d orbitals increases down groups (Jones, 2001) (i.e. greater for heavier transition metals), this orbital splitting has a higher energy for gold(II) then copper(II). Hence, gold(II) complexes are more likely to oxidise or disproportionate than copper(II) complexes.

Comparison with the Platinum Subgroup The platinum subgroup is next to subgroup 1B. It may be instructive to make a brief comparison to see if there are significant differences and similarities between the 2 subgroups (with different electronic configurations). Both copper and nickel are more ionic whereas gold and platinum are inert and are more likely to form covalent complexes using the available d orbitals for bonding. As shown in Table 2, I1 of copper and gold are higher than the respective I 1 of nickel and platinum. But, the sum of I1 and I2 of all three metals of the platinum subgroup are less than that of subgroup 1B by 5% or more. I3 of nickel and palladium are also lower than that of copper and silver. Hence, it is not surprising that elements of the platinum subgroup prefer oxidation states of II or higher. Higher oxidation states are more common with the heavier elements of both groups. For example, Pt4+ is more stable than Pd4+ and similarly Au3+ is much more stable than Ag3+. The magnitude of the first and second ionisation energies is a major factor that accounts for the stability of Ag+ but not Pd+ and that Pd2+ is much more stable than Ag2+. The relative values of the sum of I1 and I2 also influence both copper and nickel to favour a valency of 2 even though their electronic configurations are different. Unlike subgroup 1B, none of the three metals in the platinum subgroup form univalent halides but all form divalent halides. None of the members of the subgroup form univalent oxides (as compared to Cu2O and Ag2O) but do form well characterized oxides including NiO, PdO, PtO2, PtO3 (Cotton, Wilkinson, Murillo, Bochmann, 1999) in which the metal may have the oxidation states of II, IV or VI.

All three metals in the platinum subgroup form octahedral, tetrahedral and planar complexes and examples are shown in Table 5. However, planar palladium and platinum complexes are more common than tetrahedral ones.

Table 5. Examples of complexes of nickel, palladium and platinum

Nickel Palladium Platinum

Tetrahedral [Ni(Cl)4]2- [Pd(PF3)4] [Pt(PF3)4]

Octahedral [Ni(NH3)6]2+ [PdCl6]2- [PtF6]-

Square planar [Ni(CN)4]2- [Pd(CN)4]2- [PtCl4]2-

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Table 4 shows that for complexes with the same shape and same oxidation state, say an oxidation state of M(II), and with similar ligands on the spectrochemical series, those of the platinum subgroup (d8 configuration) are in general more stable than ones in subgroup 1B (d9 configuration). A good example is a comparison between [Cu(NH3)6]2+ and [Ni(NH3)6]2+ both of which are octahedral. Δ or 10Dq are 182 and 130 kJ/mole for [Cu(NH3)6]2+ and [Ni(NH3)6]2+ respectively. Hence, the CFSE for the 2 complexes are (182 x 3/5) 109 kJ and (130 x 6/5) 156 kJ (to 3 significant figures), which shows the nickel complex is more stable.

Conclusion Chemical reactivity is the core of chemical science. We have shown in this article how straight forward thermodynamic data are used to understand chemical reactivity and in many cases can define the stability of compounds including transition metal complexes. From the beginning of life on earth, biological systems have taken advantage of particular properties of metals and developed molecules such as haemoglobin (containing an iron complex) and haemocyanin (containing a copper complex) (Avila, 1995) which allow evolution of many organisms to take place. Thermodynamics contribute to the understanding of the evolution of these biological systems and allows compounds and complexes to be designed for both chemical and biological systems.

References Avila, V. L. (1995) Biology, Investigating life on earth. Jones and

Bartlett: Boston and London, 571-573. Born, M. (1920) Free energy of solvation, Zeit. Physik, 1, 45. British Medical Association/Royal Pharmaceutical Society (2010)

British National Formulary, 60th ed., London, 13.7, 13.10, A8.3. Chase Jr., M.W. J. (1998) Chem. Phys. Ref. Data ; monograph nr. 9,

NIST-JANAF Thermochemical Tables.

Clegg, H. (1964) Today’s Drugs, British Medical Association: London, 304-307.

Cotton, F. A. (1990) Chemical Applications of Group Theory, 3rd edn., Wiley: New York, 253-304

Cotton, F.A., Wilkinson, G., Murillo, C.A., Bochmann, M. (1999) Advanced Inorganic Chemistry 6th edn., Wiley: New York, 836-850, 854-873, 1063-1106.

Dasent, W. E. (1982) Inorganic Energetics: An Introducton, CUP: Cambridge, 1-32.

Donohue, J. (1974) The Structure of the Elements, Wiley: New York, 220-223.

Greenwood, N.N., Earnshaw, A. (1984) Chemistry of the Elements, Pergamon: Oxford, 1368, 1372.

Haynes, W.M.(ed); (2011-2012) CRC Handbook of Chemistry and Physics, 92nd edn., CRC: Boca Raton, FL,; 10:196-10:198.

Ives, D.J.G. (1971) Chemical Thermodynamics, Macdonald: London, 5-73.

Johnson, D.A. (1982) Some Thermodynamic Aspects of Inorganic Chemistry, 2nd edn., CUP: Cambridge, 1-12, 141-150, 258-269.

Jones, C.J. (2001) d and f-Block Chemistry, RSC: Cambridge, 105, 109-110.

Korgaokar, A.V. Gopalaraman, C.P. Rohatgi, V.K. (1981) Threshold ionization energies of Au2+, Au3+, Au4+. Int. J. Mass Spectro. Ion. Phys., 40, 127-134.

Lang, P.F. Smith, B.C. (2003) Ionization Energies of Atoms and Atomic ions. J. Chem. Educ., 80, 938-946.

Moore, C.E. (1949, 1952, 1956), Atomic energy Levels; NBS Circular 467, U.S. Department of Commerce: Washington DC; (a) vol. 1. (b) Vol. 2. (c) vol.3.

Moore, C.E. (1970) Ionization Potentials and Ionization Limits Derived from the Analysis of Optical Spectra; NSRDS-NBS 34, U.S. Department of Commerce: Washington DC.

Wagman, D.D., Evans, W.H., Parker, V. B., Schumm, R. H., Halow, I., Bailey, S. M., Churney, K. L., Nuttall, R. L., (1982) J. Chem. Phys. Ref. Data; 11, supplement 2, NBS Tables of Chemical Thermodynamic Properties.

Wieder, M.E., Hone, D.C., Cook, M. J., Handsley, M. J., Gavrilovic, J., Russell, D.A. (2006) Intracellular photodynamic therapy with photosensitiozer-nano particle conjugates and cancer therapy using a “Trojan horse”, Photochem. Photobio. Sci. ; 5, 723-726.