Chemistry for Everyone
Elementary “Who Am I” Riddles R. Aldrin Denny* Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India;
[email protected] R. Lakshmi, H. Chitra, and Nandini Devi Department of Chemistry, Indian Institute of Technology, Madras 600 036, India
There is a growing concern over the decrease in student interest in the sciences. The atmosphere of entry-level science courses, particularly in the quantitative sciences, has been suggested as one cause of the loss of student interest (1). Investigations have shown that giving a formal lecture to any freshman science student by no means delivers information. Moreover, adequate learning is not guaranteed when students simply sit and listen to a lecture (2–5). To capture students’ attention to the subject and to make the lectures interesting, various methods are suggested in the literature (6–8). We suggest that some simple riddles can be used effectively to make students interact in class. This method requires the student to provide answers to riddles in order to develop the discussion about a given topic. The riddles asked need not involve a quantitative problem, but are simply a means for evoking the material being discussed, as opposed to presenting it as a lecture. Here we report simple riddles on elements and their compounds to provide novelty to the freshman lecture in chemistry. Riddles 1. Forewarned as God’s wrath I come out in Earth’s fury Chamber and Goodyear, I loved them both I change my cloak when angry 2. See you is my favorite word One, two are my positive hold Pull out the Teller, got the pride Pass many, ’coz I can’t deny 3. Pull them all and take in charge Cool so many, spoil the sky Hang in chain which DuPont like Near noble, try to tell my name 4. Alone, I cook and wrap And fly from the box I make the ash, but in blue Like a cloud, I rise 5. Stronger am I When cut I shine Form a ball, but not to play ’coz I burn away
6. As you like it Green, yellow and bright Born apart, I made’m die I’m in it, who am I? Explanation 1. Sulfur. The Bible describes sulfur as “brimstone” in Revelation 21:8, where God warned that sinners and unbelievers would be thrown into the sulfur lakes in hell. Sulfur ashes are thrown out during volcanic eruptions, and the chemically important sulfuric acid (H2SO4) was manufactured by the Lead Chamber process (9), SO2 + NO2 + H2O → H2SO4 + NO 2NO + O2 → 2NO2 An important application of sulfur was introduced by Goodyear in the vulcanization process where the soft, lowmolecular-weight rubber is converted into a highly crosslinked polymer by sulfur bridges between the polymer chains. As temperature is increased, sulfur shows a variety of colors while going from one allotrope to another. 2. Copper. The symbol of copper is Cu and its common oxidation states are +1 and +2. The copper d9 system is used by Jahn-Teller to explain the distortion of octahedral systems in coordination chemistry. Copper is a very good thermal and electrical conductor. 3. Fluorine. Fluorine is placed in the periodic table next to the noble gases. It is known as the highest electronegative element and forms a very strong covalent bond with carbon. Thus the toughest polymers, Nafion and Teflon (cf. Fig. 1), prepared by DuPont Ltd. contain all fluorine atoms hanging in the main carbon chain (Fig. 1). Fluorocarbons such as freon are used in refrigerators. However, in the 1980s it was found that freons are responsible for breaking ozone molecules in the atmosphere, leading to increased penetration of UV light and the resulting increased risk of skin cancer.
( CF2
CF2
)n
(I)
( CF2
CF2
)x ( CF2
CF
)
O
CF2
y
CF2 O
CF3 CF2
CF2
SO3– H+
(II)
Figure 1. Structure of DuPont’s Teflon (I) and Nafion (II).
JChemEd.chem.wisc.edu • Vol. 77 No. 4 April 2000 • Journal of Chemical Education
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Chemistry for Everyone
4. Aluminium. Aluminium is manufactured from bauxite and it is used in cooking vessels, wrapping foils, and aircraft. In quantitative analysis, it gives blue-tinted ash (Thenard’s blue) by the addition of cobalt nitrate (10):
firmatory test for arsenic (10).
4Al(OH)3 + 2Co2+ + 4NO3+ → 2CoAl2O4 + 4NO2 + 6H2O + O2
AsO43᎑ + 12MoO42᎑ + 3NH3 + 27H+ → (NH4)3[As(Mo3O10)4] + 12H2O
2AsO43᎑ + 5H2S + 6H+ → As2S3 + 2S + 8H2O yellow
yellow
Thenard’s blue
and forms a gelatinous white precipitate when Na2S2O3 is added (9): Al3+ + Na2S2O3 + 3H2O → Al(OH)3↓ + 2Na+ + H2S2O3 + H+ white
5. Carbon. Allotropic forms of carbon include graphite, diamond, and fullerenes (C60). Diamond shines brilliantly when cut; it is the hardest solid known, with the highest melting point (~4300 K) and thermal conductivity, as well as the lowest molar entropy (2.4 J mol ᎑1 K ᎑1). Fullerenes (large molecular carbon cages) have a structure termed “bucky balls” as shown in Figure 2 (11). The 1996 Nobel Prize was awarded to Sir Harold Kroto (University of Sussex, UK) and Robert Curl and Richard Smalley (Rice University, Houston, TX) for their contributions to the field of Figure 2. The structure of buckministerfullerenes. All fullerene. forms of carbon will burn. 6. Arsenic. In quantitative analysis, addition of copper sulfate to an evaporated solution of arsenious oxide in hot sodium hydroxide gives a bright green precipitate of copper(II) arsenate (Cu2As2O5, also known as Scheele’s green). The appearance of a yellow precipitate upon passing hydrogen sulfide gas or adding ammonium molybdate is taken as a con-
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Napoleon Bonaparte (“born apart”) died of arsenic poisoning, as was confirmed later by subjecting a sample of his hair to neutron activation analysis. The symbol for arsenic is As, and it appears in the first line of the riddle. We encourage readers to explore several such riddles in chemistry. Literature Cited 1. Office of Technology Assessment. Educating Scientists and Engineers: Grade School to Grad School; OTA Report, U.S. Congress; U.S. Government Printing Office: Washington, DC, 1988. 2. Steiner, R. P. J. Chem. Educ. 1980, 57, 433. 3. Kolz, M. S.; Snyder, W. R. J. Chem. Educ. 1982, 59, 717. 4. Genyea, J. J. Chem. Educ. 1983, 60, 478. 5. Lagowski, J. J. J. Chem. Educ. 1990, 67, 811. 6. Eckey, D. J. Chem. Educ. 1994, 71, 1051. 7. Erickson, B. L.; Strommer, D. W. Teaching College Freshmen; Jossey-Bass: San Francisco, 1991; p 97. 8. Eberhart, J. G. J. Chem. Educ. 1995, 72, 1076. 9. Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; Chapter 15. 10. Vogel’s Textbook of Macro and Semimicro Qualitative Inorganic Analysis, 5th ed.; revised by Svehla, G.; Orient Longman: New Delhi, 1982. 11. Cane, T. D.; Kroto, H. W. In Encyclopedia of Inorganic Compounds, Vol. 2; King, R. B., Ed.; Wiley: Chichester, UK, 1994; pp 531–553.
Journal of Chemical Education • Vol. 77 No. 4 April 2000 • JChemEd.chem.wisc.edu
