Oxidation-Reduction Alexander Darmanin, Marcus Pabian & Lyn Cheah
Chemistry Stage 6 Syllabus 9. 2 Production of Materials 4. Oxidation-reduction reactions are increasingly important as a source of energy • identify the relationship between displacement of metal ions in solution by other metals to the relative activity of metals • explain the displacement of metals from solution in terms of transfer of electrons • account for changes in the oxidation state of species in terms of their loss or gain of electrons
Oxidation-Reduction In oxidation-reduction reactions (redox), changes of oxidation states occur between chemicals. 3 Cu. Cl 2(aq) + 2 Al(s) → ? • What happens in this reaction? • What IS an oxidation state? • What happens to the oxidation states? • What do YOU know about oxidation-reduction reactions?
Go! • Materials 1 x 150 ml beaker 1 x glass stirring rod 1 x Balance machine Calculate the grams of Copper chloride Cu. Cl 2 granules 1 x 0. 25 g Aluminum foil 50 ml distilled water 50 ml graduated cylinder • See work sheet for instructions Results visible in 5 min • Safety Wear lab coat, glasses and gloves Cu. Cl 2 is not that strong but don’t get It on you – when done use safe disposal bin NOT sink
Think Which of the following best describes a reduction? A. The loss of electrons during a chemical reaction. B. The gain of electrons during a chemical reaction. C. The formation of copper during a chemical reaction. D. The loss Al during a chemical reaction. Which of the following best describes oxidationreduction reactions? A. A reaction that involves the transfer of electrons from one species to another. B. A reaction that involves the formation of gases hydrogen and oxygen when two solutions are mixed. C. A reaction that involves the formation of solids when two solutions are mixed. D. A reaction that involves the neutralisation of H+ ions in solution.
Results – what actually happens after 20 minutes
Results In terms of electron transfer: • In this reaction the Cu 2+ ions have been converted into copper atoms • This requires Cu 2+ ion to gain two electrons • Cu 2+(aq) + 2 e- → Cu(s) • Electrons come from the Al 3+ The net result: • Copper ions come out of solution as Cu metal • Al goes into solution as an Al 3+ ion • 3 Cu 2+(aq) + 2 Al(s) → 3 Cu(s) + 2 Al 3+(aq) Half reactions: • Oxidation is the loss of electrons - Al is oxidised • Reduction is gain of electrons - Cu 2+ is reduced Simulation: Reduction of zinc by oxygen: http: //www. youtube. com/watch? v=e 6 Xxz-VBE 6 s
Dominant student misconceptions Oxidation and reduction misconceptions (taken from Garnett & Hackling, 1995 pp 84): 6. The oxidation state of an element is the same as the charge of the monatomic ion of the element. 7. A polyatomic species can be assigned an oxidation state and this equals the charge on the species. 8. In all chemical equations the "addition" and "removal" of oxygen and hydrogen can be used to identify oxidation and reduction. 9. In all chemical equations the change in the charges of polyatomic species can be used to identify oxidation and reduction. 10. Oxidation and reduction processes can occur independently. What where your Misconceptions? ? ? MORE MISCONCEPTIONS, FULL EXPLANATIONS, SOURCES + SIMULATIONS AT http: //oxidationreductionactivity. wordpress. com
Think What best describes an oxidation? What best describes a reduction? “Not all redox reactions involve oxygen, but all oxidation and reduction reactions involve transfer of electrons between substances” -Chemistry and chemical reactivity (6 th edition) – first year chemistry textbook at UWS “the increase in oxidation state, is the only one that is universal to all oxidations” - Silverstein, 2011 “The only way oxidation-reduction equations can be identified with certainty is from changes in oxidation states” - Garnett, Garnett & Hackling, 1995
Oxidising agent The theory now cause s undergoes Reducing agent undergoes Reduction Oxidation Gain of electron Loss of electron Gain of hydrogen Loss of oxygen Decrease in oxidising state But which one of these definitions is the most important and universal in all redox reactions? Gain of oxygen Increase in oxidising state can be defined as the s cause
The question is Electron transfer: Virtual or Literal Is it just a book keeping strategy Why is oxidation-reduction only taught as loss or gain of electrons in the Stage 6 syllabus? How will this affect further chemistry learning for the students?
You. Tube links: Reduction of zinc by oxygen: http: //www. youtube. com/watch? v=e 6 Xxz-VBE 6 s Patterns of oxidation numbers across the periodic table: http: //www. youtube. com/watch? v=EHe 8 -AFMs. MA Determining oxidation numbers: http: //www. youtube. com/watch? v=8_Cv. NPuuhi. M&feature=related Turn copper into gold: http: //www. youtube. com/watch? v=_g_ml 8 t. An. WE&feature=relmfu The link to our blog again! http: //oxidationreductionactivity. wordpress. com
References Anselme, J. (1997). Understanding oxidation-reduction in organic chemistry. Journal of Chemical Education, Volume 74, Number 1, pg. 69 – 72. Brown, T. L. , Lemay, H. E. , Bursten, B. E. & Burdge, J. R. (2003). Chemistry The Central Science Ninth Edition International Edition. Prentice Hall: Australia, pg. 778 – 783. Cox, A. L. & Cox J. R. (2002). Determining oxidation-reduction on a simple number line. Journal of Chemical Education, Volume 79, Number 8, pg. 965 – 967. Garnett, P. J. , Garnett, P. J. & Hackling, M. W. (1995). Student’s alternative conceptions in chemistry: A review of research and implications for teaching and learning. Studies in Science Education, Volume 25, pg. 69 – 95. Garnett, P. J. & Treagust, D. F. (1992). Conceptual difficulties experienced by senior high school studentsof electrochemistry: Electric circuits and oxidation-reduction equations. Journal of Research in Science Teaching, Volume 29, Number 2, pg. 121 – 142. Hamza, K. & Wickman, P. (2008). Describing and analyzing learning in action: an empirical study of the importance of misconceptions in learning science. Science Education, Volume 92, pg. 141 – 164. Kotz, J. C. , Treichel, P. & Weaver, G. C. (2006) Chemistry & chemical reactivity Edition 6 th. Thomson Brooks/Cole: Belmont, California. Mole, P. (2006). Skepticism in the classroom A high school science teacher in trenches. Skeptic, Volume 12, Number 3, pg. 62 – 70. Moore, J. T. (2004). Chemistry Made Simple Revised Edition. Made Simple Books: USA, pg. 125 – 129. Nakhleh, M. B. (1992). Why some students don’t learn chemistry Chemical misconceptions. Journal of Chemical Education, Volume 69, Number 3, pg. 191 – 196. Sanger, M. J. & Greenbowe T. J. (1997). Students’ misconceptions in electrochemistry: Current flow in Electrolyte solutions and the salt bridge. Journal of Chemical Education, Volume 74, Number 7, pg. 819 – 823. Sanger, M. J. & Greenbowe T. J. (1999). An analysis of college chemistry textbooks as sources of misconceptions and errors in electrochemistry. Journal of Chemical Education, Volume 76, Number 6, pg. 853 – 860. Silverstein, T. P. (2011). Oxidation and reduction: Too many definitions? Journal of Chemical Education, Volume 88, Number 3, pg. 279 – 281. Talanquer, V. (2002) Minimizing misconceptions Tools for identifying patterns of reasoning. The Science Teacher, Volume 69, Number 8, pg. 46 – 49. Tarhan, L. & Acar, B. (2007). Problem-based learning in an eleventh grade chemistry class: ‘Factors affecting cell potential’. Research in Science and Technological Education, Volume 25, Number 3, pg. 351 – 369.
References Zoller, U. (1990). Comments and criticism Students’ misunderstandings and misconceptions in college freshman chemistry (General and organic). Journal of Research in Science Teaching, Volume 27, Number 10, pg. 1053 – 1065. Weblinks: AUS-e-tute n. d. (2011). Chemistry tutorial: Oxidation and reduction. Retrieved from: http: //www. ausetute. com. au/redox. html Bodner Research Lab (2011). Oxidation and reduction. Retrieved from: http: //chemed. chem. purdue. edu/genchem/topicreview/bp/ch 9/redox. php Clark, J. (2002). Definitions of oxidation and reduction (redox). Retrieved from: http: //www. chemguide. co. uk/inorganic/redox/definitions. html Greenbowe, T. J. (2003). Chemistry experiment simulations, tutorials and conceptual animations for introduction to college chemistry (aka general chemistry). Retrieved from: http: //group. chem. iastate. edu/Greenbowe/sections/projectfolder/animationsindex. htm Isis Publication (2003). 10. 1 – Oxidation and reduction. Retrieved from: http: //ibchem. com/IB/ibnotes/full/red_htm/10. 1. htm mtchemers (2008). Oxidation numbers. Retrieved from: http: //www. youtube. com/watch? v=EHe 8 -AFMs. MA mtchemers (2008). Oxidation-reduction basics. Retrieved from: http: //www. youtube. com/watch? v=e 6 Xxz-VBE 6 s Nurd. Rage (2010). Turn pennies to silver and gold (Chemistry trick). Retrieved from: http: //www. youtube. com/watch? v=_g_ml 8 t. An. WE&feature=relmfu storm 808 b (2011). Determining the oxidation number of elements in a compound. Retrieved from: http: //www. youtube. com/watch? v=8_Cv. NPuuhi. M&feature=related
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