DEMONSTRATION pubs.acs.org/jchemeduc
An Improved Copper Mirror Demonstration Maja Nikoloska and Vladimir M. Petrusevski* Institute of Chemistry, Faculty of Natural Sciences and Mathematics, Ss Cyril & Methodius University, P.O. Box 162, 1001 Skopje, Republic of Macedonia ABSTRACT: The copper mirror demonstration published recently in this Journal was improved by performing the thermal decomposition under vacuum. The extension of the demonstration prevents the deterioration of the mirror with time. Alternatively, the mirror may be protected with molten candle wax in the test tube where it was obtained. KEYWORDS: First-Year Undergraduate/General, General Public, Second-Year Undergraduate, Demonstrations, Inorganic Chemistry, Hands-On Learning/Manipulatives, Elimination Reactions, Oxidation/Reduction
n a recent issue of this Journal,1 Pike gives details for a beautiful copper mirror demonstration. The method is very simple— thermal decomposition of copper(II) formate tetrahydrate— and the obtained mirror is of excellent quality. However, the mirror does not last long unless some precautions are taken. We used the “standard size” test tubes (160 mm 16 mm) with 300 500 mg of the copper salt. The mirror formed in less than 1 min (we continued to heat for another minute or two, for a complete decomposition of the salt). The result was impressive. However, after several days, the mirror was completely corroded and deteriorated (Figure 1A)! Unlike the much more familiar silver mirror (once obtained, it could survive many decades under similar conditions), the copper mirror deteriorates quickly as a consequence of the higher reactivity of copper. In short, keeping it in an open test tube is not possible. Our first improvement was to fill the test tube with molten candle wax, immediately after the mirror was obtained. The long-term result was better, but after 1 month, a darkening of the mirror was evident (Figure 1B). We suspected that the wax contained some agent (perhaps also diluted oxygen) that induced slow corrosion of the mirror. The results were better than in open test tube, but were not good enough. We then tried to evacuate the test tube containing copper(II) formate tetrahydrate and then heat it. For this purpose, we used an ampule; an ordinary test tube was shaped into an ampule using a burner.2 After heating the ampule and forming the mirror, the ampule was sealed under vacuum. The mirror obtained in this way was of very high quality (Figure 1C) and there was no noticeable change after 3 months. We assume that it will survive for years (decades) as long as it is sealed and evacuated.
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Copyright r 2011 American Chemical Society and Division of Chemical Education, Inc.
Figure 1. Copper mirror in (A) open test tube (after three days), (B) test tube filled with wax (after one month), and (C) evacuated ampule.
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ REFERENCES (1) Pike, R. D. J. Chem. Educ. 2010, 87, 1062–1063. (2) Bukleski, M.; Petrusevski, V. M. J. Chem. Educ. 2009, 86, 30.
Published: July 05, 2011 1406
dx.doi.org/10.1021/ed101143r | J. Chem. Educ. 2011, 88, 1406–1406
