Either a hand towel o r cloth should be used to p m t e d the hands of the demonstrator and the hands of any assistant or participant from the cold apparatus. The container should not be close to anyone's ears, b e cause if the balloon breaks, the loud noise produced could damage hearing. One could place the graduated cylinder in a pmtective sheath to contain any glass pieces that would be formed in the unlikely event that the graduated cylinder were to rupture. The author has performed this experiment many times and has not experienced any problems with breakage.
Imn Ring \
Ring Stand
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. Tapered nd
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Glass tubing Calculations The following data were obtained in a typical experiment: length of balloon filled with one mole of nitrogen gas = 110 cm, average diameter of balloon filled with one mole of nitrogen gas = 16 cm. The geometrical shape of the balloon approximates a cylinder, and a subsequent calculation yields a value of 22 L for the volume of the nitrogen gas.
Position C Pinch Clamp B
V = 3.14x 110 x 8.0' em3 The calculation is rounded to two significant figures.
To
Faucet Aspirator
Discussion This demonstration also can be used to demonstrate the first law of thermod.ynamics. The system does expansion work and the internal energy changes as the liqucd nitrogen absorbs heat from the surroundings. Also, one can condense the nitrogen gas and demonstrate liquid vapor equilibria. The main object of this experiment, however, is to give the beginning chemistry student a visualization of the molar volume of a gas.
Ammonia Fountain Improvements Submitted by Ned Steadman Brevard High School Brevard, NC 28712 Checked by Jack Lambelt Kansas State Univers ly Manhanan, KS 66506 The standard ammonia fountain demonstration found in
this Journal and demonstration manuals always has given me problems. The two main problems of this demonstration are its excessive preparation time and its questionable reliability. The following is a description of what I consider to be a far s u ~ e r i omethod r of collectine ammonia for this demonstration. This method is faster and gives better results, without priming, than any other method that I have tried. In addition, I do not have to collect the ammonia under the hood, because almost no ammonia escapes. 1. Set up the apparatus shown m the figure. 2 Dlsco~ectboth pinch clamps 3 Turn on the faucet to prov~desumon. (Reduced pressure will r e d t in the ammnnm mnvlna mtathe flark The less dense ammonia moves to the top,and the more dense air moves dawn and out of the asnirator. The flask fills with ammnnln in a short tmr. Complrtton can be checked by testma the faucet watw for t h presence ~ of ammoma wnh phenophthalein.
764
Journal of Chemical Education
1 1
Large Beaker PhenoIphthIn With HZ0 and
1
Set up for improved ammonia fountain. Any size round flask and any length of glass tubing can be used. The author used a 2-Lflask, 55 cm of glass tubing, and 7 cm of rubber tubing. 4. When the flask is full of ammonia, c o ~ e cthe t two pinch clamps at the indicated positions. 5. Turn off the faucet. 6. Remove the stopper from the bottle of ammonia and quickly replace the capon the ammonia bottle. (Littleammunla will escape, because the air rushes in as the stopper is pulled out.) 7. Place the rubber stopper (with glass tubing)down into the beaker of water and nhenolnhthalein. 8. Disconnect pinch clamp A. '(The reduced pressure in the flask will result in the water moving into the flask at e rapid rate The high dubllin, of ammonia in water will keep the flow of w&r going until the flask is almost full). 9. Dismnned the rubber hose at position C. Lift the beaker and tubing assembly out through the top of the iron ring. Remove the rubber stopper and tubing assembly from the flask and discard the contents. Replace the flask with a dry one. Assemble the apparatus as before, and it irr ready for a second demonstration. Rinsine the lower end of the stopper and tub in^ assemhly hefore insenion into the am. monia bottle is required in order to prevent contaminat m n olthe ammoma wtth phenolphthalein.
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Several scientific principles are observed in this method that are not illustrated in the conventional ammonia fountain demonstration. The cost of producing ammonia by this method is much cheaper than buying ammonia in a lecture bottle. My calculations show that with a 2.37-L bottle dedicated for this task, about 890 L of ammonia should be produced for about $13.20. A lecture bottle of ammonia can produce about 256 L of ammonia for $97.
