Is an "Empty" Bottle Truly Empty? Pasquale Feno Dipattimento di Chimica "G.Ciamician", Universita di Bologna, via Selmi 2 40126 Bologna, Italy When a bottle does not contain any liquid, we say that it is "empty". This statement is misleading, because it neglects the air inside the bottle. The following two simple experiments demonstrate that air occupies the volume in the bottle. The first experiment shows that the air must be removed before the bottle can be filled with water. The second experiment illustrates the one-to-one relationship between the volumes exchanged.
bottle must have contained air and must not have been "empty". Experiment II Materials An "empty" bottle A rubber stopper Two syringes
Tap water
Experiment I Materials
Procedure
An "emptv" . . bottle A glass A rubber stopper with two holes ( i.d.= 0.5 cm) A piece of tubing: length 40 cm ( i.d. = 0.5 em) A funnel Soap water Tap water
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Procedure Position the funnel in one hole of the stopper and the tubing in the other. Place the stopper firmly into the bottle as shown in Figure 1. Fill the glass with soapy water and submerge the free end of the tubing into the soapy water. Slowly add tap water to the funnel. Discussion Bubbles are produced in the soapy water. Where does the air that produces the bubbles come from and why? The soap bubbles are produced when the air, present in the "empty" bottle, is displaced by the tap water. Thus, the
Place the stopper f m l y into the bottle. Remove the piston from one syringe and push the piston completely into the other. Insert the syringes into the stopper as shown in Figure 2. They should fit tightly. Fill the empty syringe wih water and note the water level. Slowly pull out the piston from the other syringe, noting the position of the piston and the water level. Discussion Water drips into the battle only after the piston is pulled back. Why doesn't the water drip out before the piston is pulled back? Why does the wntrr drip once thc piston is pulled back? How docs thc volume of wawr that drips out of the syringe compare with the position of the piston in the other qringe? The bottle is filled with air and is sealed so that the air cannot escape. When some air is removed by pulling out the piston, an equal volume of water can flow into the bottle. Syiinges
Soap Water
Figure 1. Set-upof apparatus for Experiment I
u Figure 2. Set-upof apparatus for Experiment II Volume 69 Number 10 October 1992
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