COMBINING VOLUMES Hydrogen Chloride and Ammonia Su6mztted by: P. A Seepharaman, The New College, Madras, India Checked hij: Jerry Janssen, Michigan State University, East Lansing PREPARATION
Obtain a one-liter florence flask, two one-hole rubber stoppers and one solid rubber stopper to fit the flask, a 25-rm length of 7-mm glass tubing, string, a 1-qt capacity polyethylene freezer bag, a pinch clamp, and a short piece of rubber tubing. A source of both hydrogen chloride gas and ammonia gas will be required. Place one of the one-hole rubber stoppers on the glass tube so that it will extend to within 1 cm of the bottom of the flask. Place the second one-hole rubber stopper on the exposed end of the glass tubing with about 2 cm of the tubing extending beyond the stopper. With siring, "Le the mouth of the plastic bag tightly around thr stopper nearest the shorter end of the tubing. Press all of the air out of the bag and fill it with ammonia. When the bag is full, close the end of the tube by placing a short piece of rubber tubing with the pinch clamp on it. Fill the flask with dry HC1 gas and close the flask with the solid rubber stopper. DEMONSTRATION
Remove the rubber tubing and pinch clamp from the
glass tube and quickly place the tube iii the flask. Press the stopper into the neck of the flask to insure a tight fit. The ammonia gas will slowly diffuse into the flask forming a white cloud of ammonium chloride. The reaction (NH, HC1 to give NH4C1)will take about five minutes for completion, The walls of the flask become coated with the white ammonium chloride and are hot to the touch. The bag will be deflated at the end of the reaction, showing a marked reduction in volume.
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REMARKS
The flask and the plastic bag must be dry. The fittings must be tight. To show the complete change in volume, one is tempted to suggest using polyethylene bags for both reactants. However, the heat of reaction is sufficient to destroy the bag in which the reaction takes place. This demonstration and another variation using glass cylinders has been described 111 the School Sczence Review, 42,528-529 (19611, John Murray, London. J m a l of Cliemcal Education . November 1961
DEMONSTRATION NOTES From time to time, items such as the following which do not require a full half-page will he listed tvQether. Some are modifications of previously published demonstrations; they may be clipped and attached to the pertinent experiment. COMMON ION EFFECT
A neat demonstration of the common ion effect blished in THE JOURNAL, 25, 489 (19481, by Sorum of the University of Wisconsin. The tration compares the volume of foam and a t which it is produced when cftlcium carbonated with buffered and unbuffered acetic acid solutions. 0. A. Taliaferro points out that the desired s are obtained only if precipitated calcium carte is used He suggests Mallmkrodt 4052 light recipitated USP, or Baker precipitated powder USP 300 or Fred Portz & Son USP light precipitated RINE WATER SUBSTITUTE
Philip Kasimer of Quinnipiac College, Hampton, onnecticut, suggests a solution of chlorine in carbon etrachloride as a substitute for chlorine water. This solution is stable for over a month and works nicely t h the identification of halide ions. See also . N. Alyea, "Demonstration Abstracts, 20-6s," THIS ~ U R ~ A 37, L , A300 (1960) RAPID FILTERING WITHOUT USING A FILTER PUMP
Dale E. Rose, Hampton High School, Hampton,
Virginia. Obtain a polyethylene bottle (like those sold in stores for dispensing mustard, etr 1, squeeze this bottle so as to force out a portion of the air, then insert the narrow tip into the funnel stem The bottle will then inflate leaving the precipitate on-the filter paper and quickly forcing the filtrate into the dispenser. WRITING ON BEAKERS, FLASKS, ETC.
Dale E. Rose, Hampton High School, Hampton, Virginia, suggests using a "magic marker" purchased from the drugstore for about $30 This writes quickly on dirty or wet glass, lasts a long time, and is removed simply by rubbing with a cloth dampened with denatured alcohol. BOILING LIQUID FREEZES WATER
Dale E. Rose, Hampton High School, Hampton, Virginia. Place acetaldehyde in a stoppered side arm flask. Connect the side arm to an aspirator. Dip the bulb of the flask in the water, remove, turn on the aspirator, and shake the flask Ice freezes on the outside of the bulb as the liquid boils on the inside Acetaldehyde is better than ether in that it is soluble in water and, therefore, leaves few vapors in the room. I t also has a lower boiling point than ether.
