JOE RICH Blackhawk Christian School 7400 East State Boulevard Fort Wayne, IN 4681 5
inventory control Balloons in Lab Francisco J. ArnAiz Departamento de Quimica InorgAnica Colegio Universitario de Burgos 09002 Burgos, Spain
Balloons in chemistry laboratories are useful materials that allow us to overcome occasional obstacles in laboratory work. Connected to low pressure gas lines they work by softening pressure jumps (and a s single-use safety valves). Connected to reaction vessels, containing inert or selected atmospheres, they help to detect escaping gas and to test for slight positive pressure inside the apparatus (Fig. 1). Equipped with a stopcock, they can be used a s portable containers (Fig. 2). This allows occasional use of harmful gases in areas of the laboratory ill-prepared for this function. The most important utility I have found for balloons is connecting fittines of different sizes. This is a .. ~ ~ r.o ~ r i a t e for systems oper&ing around atmospheric pressure, especially in drying precipitates. Dry atmosphere is imperative in isolating hygroscopic to pump bstlmn aning also handling the rdrd as light shield uwsl arrangement during dnling solids and also is advisable for products that have been Figure 3. Some arrangements for drying precipitates. washed with volatile solvents, in order to avoid moisture condensation. Despite special equipment usually available
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Air Condensers
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Figure 1. Balloon as positive pressure indicator. for this purpose, I like, when possible, to use balloons cut and connected a s shown (Fig. 3). The advantages are obvious. Cut balloons are low-cost materials able to be adapted to a wide variety of funnels and filter plates. Furthermore, when using drying tubes, blockage sometimes takes place (especially if filled with P4010) being detected immediately when sucking begins, as the covering collapses inside the funnel. Finally, i t i s necessary to keep in mind that common balloons are sensitive to many organic solvents. Also, :::: the piece to be used a s
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The Limitations of Air Condensers Air was the first known refrigerant fluid. Air-refrigerated comer coils have been used for centuries in domestic equip&& for liquor preparation. However, because of its limited ~erfonnancea s a heat transfer aeent. air was soon replaced by water. This replacement wasso dramatic that in many chemistry labs air condensers are now out of use, whenever they exist a t all. Consequently, many undergraduates are familiar with several types of water condensers, but they know little about air wndensers. The Usefulness of Air Condensers In some countries, water restriction is now a fact. Even greater restrictions can be expected in the future. Recycling water as a refrigerant fluid requires at least a recirculating pump. Air is free. Usine air as a refriwrant is sufficientfor some habitual cooling opcrations, and it replaces wnrrr advantagwusly i n some part~miarc a w s such as refluxing sulventn in n d g . box 1 1 , ( b y simplifying the mstallarion, and distilling products with a melting point around room temperatureor above (the distillate is more easily recovered by heating the condenser with a heat pun). A i r condensers avoid same risk of accidents associated with water, especially when they must work for a long time without sulliuwnt surve~llanee.Thr commonest ones are those derived from water stoppage (leading to solvent escape and damage of reagents) and water overpressure (leading to flooding). Some unexplained fires in labs during the night ~
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Figure 2. Balloon as gas container.
Francisco J. ArnAizDepanamento ae Q ~ m c lnorgan a ca Co eglo Un versotar o de B~rgos 09002 Burgos (Spain)
coated types clean, a n a d aof inside because p tballoons or m with umany s ttalc abe re powder.
Journal of Chemical Education
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highly volatile and the rate of vapor condensation is low. To install several refluxing flasks fit with tubes is simple and requires minimal space.
Preparing an Air Condenser One of t h e simplest air condensers can h e prepared in -15 min. Aglass tube about 1m long a n d 8 m m i.d. i s bent by heating with a burner at 10-20 cm from one end to make a n angle of -100-llOQ. The resulting tube (A) i s connected to a flask by means of a n adapter (B) a n d a piece of silicone tubing (C) (figure). This air condenser works satisfactorily with most solvents on small-scale reactions (e.g., fitted to a 100-mL Schlenck tube charged with 40 mL of acetone. air at 20 T. without t h e h e l of ~ a fan. about 10% of the s b ~ v e nits lost after gentle reflAmfor 24h). Shorter tubes, about 5 0 cm long, a r e sufficient for less volatile solvents; a n d I have used them to pre a r e by literature methods compounds such as Cr(C0)3(~1-C,H,COOCH,) (2) a n d Mo(CO)dCzH&N)3 (3).
B
A simple air mndenser.
are suspected to have been produced by water escape followed by reaction with chemicals (e. g., an inopportune strong vibration may crack an operating water condenser in a refluxing reaction system involving sodium metal and a flammable solvent). CAUTION: I3rfore inshllling a water mndenser in an apparatus that murt operate at &lux involving sodium wire. such as for solvent punficatlon or a related *ydtem,one must make sure that t h e condenser works properly and h a s n o cracks in it. Aw condenserx are avalable from lab equipment suppliers. hut many types of tubes nlro can he used for thls funruan. Conrldenng the frequent need fur insulating disrillat ion columns, air condensers are especially useful far gently refluxing many solutions. They need not be sophisticated, nor do they require the help of a fan, provided that the solvent is not
Advantages of the Air Condenser Most of the air condenser remains out of the vertical nlane of the heater becoming morr efficienr, especially w h n rhc heating source is strong. The open end is more accessible SQ that it facilitates further eonn&tions, such as a drying tube or a bubbler. It also is more easily installed in low ceiling hoods. When distilling the solvent, having verified that the vapor condenses after passing the bend, it is suff~eientto twist the apparatus about 30Qr to hold the flaskin the original position and to take advantage of the flexibility of the silicone joint to move the tube. Acknowledgment The author i s grateful to George B. Kauffman a n d to the reviewers for their suggestions. Literature Cited
Volume 70
Number 12 December 1993
1021
