In the Laboratory edited by
The Microscale Laboratory
R. David Crouch Dickinson College Carlisle, PA 17013-2896
A Low-Cost and Timesaving Microscale Heater Erik Joling,* Martin J. Goedhart, and Bregje van den Berg Microscale Chemistry Center, AMSTEL Institute, Universiteit van Amsterdam, NL-1098 SM Amsterdam, The Netherlands; *
[email protected] Trienke M. van der Spek Museum Boerhaave, NL-2312 WC Leiden, The Netherlands
A low-cost, fast-acting electric heater has been designed to replace expensive hot-plates used in microscale chemistry laboratory. It is essentially a soldering iron whose tip is replaced by an aluminum block with a drilled hole. This simple heater works surprisingly well. Between November 1996 and December 1999, we promoted the use of microscale chemistry in the classroom through a project called Microscale Experiments.1 We found that commercial electric heaters, being very expensive, were not an option for the project. The heater Williamson (1) uses, an electric 100-mL-flask heater filled with sand, is fine for use in a university- or college-level laboratory, but is too expensive for secondary schools (the 230V model lists for over U.S. $90). Moreover, it takes too long to reach a workable temperature. A hot-plate topped with a sand bath or an aluminum block (2) has the same disadvantages.
the vials and flasks used in organic, inorganic, and general chemistry as described in various microscale lab manuals (1, 4 ). It can also be used with a magnetic stirrer. The efficiency of the heater is demonstrated in Figure 3. It shows that the heater takes only 10 min to reach a temperature of 100 °C, and about 30 min to reach 250 °C. An even higher temperature of ~300 °C can be attained by wrapping the block and the flask in aluminum foil. Figure 3 also illustrates how the dimmer switch enables temperature control between 100 and 275 °C. This range is sufficient for most cases. Experience has shown that to boil a liquid in a flask or reaction tube the temperature of the sand should be 40 °C above the boiling point of the liquid. This means that one can boil liquids with boiling points up to 230 °C using this heater.
Construction of the Heater The heart of the heater is a 60-watt soldering iron. The assembled heater consists of four parts (see Fig. 1): an aluminum block, a metal shaft, a handle, and a cord with a light dimmer switch. The heater combines the advantages of the German Mikroheizgerät2 and a sand bath that fits all kinds of microglassware. It is constructed as follows. The tip of a soldering iron is replaced by an aluminum block with a drilled cavity that can hold up to 13 grams of sand. A dimmer is added in the cord for additional control of the heating. The heater can be attached to the same stand that supports the glassware apparatus, just above a magnetic stirrer. The result is a heater that works surprisingly well and can be made for less than U.S. $20. A somewhat similar heater was proposed in this Journal by Kinzer (3), but we believe that our heater is simpler and more versatile.
A
B
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Figure 1. Microscale heater. (A) Aluminum block (5.0 × 5.0 × 2.2 cm) that can contain 13 g of sand; (B) metal shaft, which should be clamped to a stand; (C) handle; (D) cord with a light dimmer switch.
Properties
sand
To speed up heating, the mass of the aluminum block and the amount of sand used are kept as low as possible. A disadvantage of a small block and a small amount of sand is that there is little room for larger flasks. Figure 2 shows the shape of the cavity, which allows enough room for flasks of various sizes. The largest flask in the Williamson kit, the 25mL filter flask, fits exactly on top of the sand bath. Our heater as constructed has universal applications: it can accommodate
port for shaft of soldering iron
aluminum block 0
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5 cm
Figure 2. Side view of the aluminum block.
JChemEd.chem.wisc.edu • Vol. 79 No. 9 September 2002 • Journal of Chemical Education
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In the Laboratory
Safety Precautions
Acknowledgments This project was carried out by the Universiteit van Amsterdam in cooperation with the Chemistry Communication Center, a foundation established by the Royal Netherlands Chemical Society (KNCV), the Dutch Association for Science Education (NVON), and the Association of the Dutch Chemical Industry (VNCI). The project was funded by the Ministry of Economic Affairs, the Ministry of Education, Culture and Science, and the Ministry of Housing, Spatial Planning and the Environment. Industry support came from the Association of the Dutch Chemical Industry and more than 60 individual companies.
9 7 6 5
250
Temperature / °C
To prevent accidental contact, the heater should be attached to a stand at a position as low as the experiment allows. The aluminum block may be further isolated by placing the heater shaft into a U-shaped rest hole cut on the side of an empty pineapple can (227 g, 8 oz) as shown in Figure 4. Another advantage of the can is that it collects spilled sand.
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Time / min Figure 3. Rate of heating at six positions (3–9) of the control.
Notes 1. More information on the project Microscale Experiments can be found on http://www.chem.uva.nl/chemeduc/microschaal. 2. The Mikroheizgerät is a part of the Mikroglasbaukasten (microscale glassware kit) produced by Aug. Hedinger in Stuttgart, Germany. The device, consisting of a fast-heating aluminum cylinder, comes with vials that fit exactly in the hole in the cylinder; the temperature is adjusted by a variable voltage control.
Figure 4. Pineapple can protection.
Literature Cited 1. Williamson, K. L. Macroscale and Microscale Organic Experiments, 3rd ed.; Houghton Mifflin: Boston, 1999; p 3. 2. Lodwig, S. N. J. Chem. Educ. 1989, 66, 77. 3. Kinzer, D. J. Chem. Educ. 1997, 74, 1333. 4. Breuer, S. W. Microscale Practical Organic Chemistry; Lancaster University: Lancaster, 1991. Landgrebe, J. A. Theory and Practice in the Organic Laboratory with Microscale and Standard Scale Experiments; Brooks/Cole: Monterrey, CA, 1993. Mayo, D. W.; Pike, R. M.; Trumper, P. K. Microscale Organic Laboratory: with Multistep and Multiscale Syntheses, 3rd ed.;
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Wiley: New York, 1994. Pavia, D. L.; Lampman, G. M.; Kriz, G. S.; Engel, R. G. Introduction to Organic Laboratory Techniques: A Microscale Approach; Saunders: Philadelphia, 1990. Singh, M. M.; Pike, R. M.; Szafran, Z. Microscale and Selected Macroscale Experiments for General and Advanced General Chemistry: An Innovative Approach; Wiley: New York, 1995. Szafran, Z.; Pike, R. M.; Singh, M. M. Microscale Inorganic Chemistry: A Comprehensive Laboratory Experience; Wiley: New York, 1991.
Journal of Chemical Education • Vol. 79 No. 9 September 2002 • JChemEd.chem.wisc.edu
