In the Classroom
Autocatalytic Patterning with Silver Using Tin(II) Chloride Sensitizer Jeremiah K. N. Mbindyo* and Laura J. Anna Department of Chemistry, Millersville University, Millersville, Pennsylvania 17551-0302, United States *
[email protected] B. Andrew Fell and David A. Patton Department of Industry and Technology, Millersville University, Millersville, Pennsylvania 17551-0302, United States
A silver mirror can be deposited on many types of surfaces from the reduction of the silver-diammine complex by a reducing sugar. This reaction has been the subject of several interesting chemical demonstrations published in this Journal and elsewhere (1-5). We describe three extensions of the demonstration by Kemp (1) that highlight the role of a SnCl2 sensitizer in the deposition of a silver mirror on surfaces. Silvering the Inside Walls of a Vial In the first demonstration, 0.5 mL of SnCl2 sensitizer solution1 is used to wet the inner walls of a glass vial. A second vial is wetted with the solvent used to dissolve SnCl2.2 Both vials are rinsed with ethanol, then each treated with 10 mL of silvering and 10 mL of reducing sugar solutions.1 After 2 min, the vials are emptied and rinsed with distilled water. As can be seen in Figure 1, a silver mirror forms on the sensitized vial, but not on the nonsensitized vial. Adsorbed Sn2þ initiates deposition of Ag nanoparticles on the glass surface (eqs 1-3), which then catalyze deposition of more Ag according to eq 4. In this latter reaction, the aldehyde group in dextrose is oxidized to a carboxylic acid, while Ag(I) in diammine silver is reduced to Ag(0). This is an example of an autocatalytic reaction, in which a product catalyzes its own formation. Sn2þ ðaqÞ f Sn4þ ðaqÞ þ 2e -
ð1Þ
2Ag þ ðaqÞ þ 2e - f 2Ag ðsÞ
ð2Þ
Sn2þ ðaqÞ þ 2Ag þ ðaqÞ f Sn4þ ðaqÞ þ 2Ag ðsÞ
ð3Þ
2AgðNH3 Þ2 þ ðaqÞ þ RCHOðaqÞ þ 3OH - ðaqÞ f 2Ag ðsÞ þ RCOO
-
ðaqÞ
þ 4NH3ðaqÞ þ 2H2 Oð1Þ
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Figure 2. Pattern outlined using autocatalytic deposition of silver on a transparency slide.
Silver Patterns on a Transparency Slide In the second demonstration, a paintbrush dipped in SnCl2 solution is used to trace a pattern on a projector slide. The silvering solution is then spread on top of the pattern, followed by the reducing solution. The result is selective deposition of silver on the sensitized parts of the slide (Figure 2). Patterning Glass Slides
ð4Þ
This reaction also occurs in solution, but much more slowly in the absence of a Ag catalyst. Colloidal Ag formed in solution will catalyze the deposition of more silver. Thus, eventually, a silver mirror can form on the nonsensitized vial. The sensitizer also promotes adherence of silver to the glass (6-8). 274
Figure 1. Deposition of silver on (a) glass vial sensitized with SnCl2 and (b) glass vial that was not sensitized with SnCl2.
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In the third demonstration, a glass slide is placed on top of some writing or artwork drawn on paper. A paintbrush dipped in the sensitizer solution is used to trace the writing, and then silvering and reducing solutions are added. A replica of the writing outlined with silver is formed on the glass slide as shown in the example in Figure 3. After rinsing, the pattern can be protected by placing another glass slide on top and applying scotch tape to the sides.
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Vol. 88 No. 3 March 2011 pubs.acs.org/jchemeduc r 2011 American Chemical Society and Division of Chemical Education, Inc. 10.1021/ed100552w Published on Web 01/19/2011
In the Classroom
Classroom Topics A discussion of the initial formation of Ag(0) from Ag(I) due to reduction by adsorbed Sn(II) can reinforce understanding of reduction-oxidation reactions and the formation, nucleation, and growth of nanoparticles. Reaction 4 can be used to discuss the chemistry of aldehydes and carbohydrates. Also, the thin film formed on the nonsensitized mirror can lead to a discussion of one-way mirrors and their applications in investigative work that is of interest in forensics. Notes 1. Details on how to prepare and store the solutions are given in the supporting information. 2. This solution is a mixture of 80% methanol in water acidified with a drop of nitric acid. Figure 3. Patterns outlined using selective autocatalytic deposition of silver on a glass slide.
Materials A 50 mL beaker, 100 mL amber storage bottle, hot plate, Pasteur pipet and dropper bulb, glass slides, transparency slide, painting brushes (from art store), overhead projector, 10 dram glass or plastic vials. Chemicals Ammonium hydroxide (15 M), sodium hydroxide, tin(II) chloride, methanol, 16 M nitric acid, and dextrose. Hazards The 15 M ammonium hydroxide and 16 M nitric acid are concentrated base and acid that emit strong fumes of NH3 and NO2, respectively. Both are corrosive and must be handled in a functional fume hood and proper precautions taken including wearing gloves and goggles. Sodium hydroxide is corrosive and hygroscopic. Avoid contact with skin or clothing. Methanol is highly flammable and should not be exposed to a naked flame, or heated strongly. The ammoniacal silver nitrate must be neutralized with nitric acid at the end of the experiment to avoid the formation of a potentially explosive precipitate possibly Ag3N (9, 10).
r 2011 American Chemical Society and Division of Chemical Education, Inc.
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Literature Cited 1. Kemp, M. J. Chem. Educ. 1981, 58, 655. 2. McCullough, T.; Bell, L. J. Chem. Educ. 1993, 70, 851. 3. University of Wisconsin General Chemistry Demonstrations. http://www.chem.wisc.edu/deptfiles/genchem/demonstrations/ solid_state/pages/solidstatemain.htm (accessed Dec 2010). 4. Shakashiri, B. Z. In Chemical Demonstrations; A Handbook for Teachers of Chemistry; Shakashiri, B. Z., Ed.; University of Wisconsin Press: Madison, WI, 1992; Vol. 4, pp 240-243. 5. Silversmith, E. F. J. Chem. Educ. 1988, 65, 70. 6. Mbindyo, J. K. N.; Michaylira, S. A.; DeMarco, D. M. Chem. Educator 2008, 13, 236–239. 7. Xia, Y.; Venkateswaran, N.; Qin, D.; Tien, J.; Whitesides, G. M. Langmuir 1998, 14, 363–371. 8. Peacock Laboratories. http://www.peacocklabs.com/pdf/ electrolesseilverpouringinstruc.pdf (accessed Dec 2010). 9. Jenkins, I. D. J. Chem. Educ. 1987, 64, 164. 10. Brown, S. E. J. Chem. Educ. 1927, 4, 791.
Supporting Information Available Guidelines for instructors including instructions to make and store the solutions. This material is available via the Internet at http://pubs. acs.org.
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