Daniel T. Haworth Marquette University Milwaukee, Wisconsin 52233
Charles' Law A general chemistry experiment
Charles' law states that a gas at constant pressure will expand 1/273 of its volume at O0C, Vo, for every degree rise in temperature. This paper describes simple apparatus which can be used t,o obtain this coefficient of expansion.
v
=
V,(l
+ at)
The apparatus (see figure) consists of a piece of bent tubing, one end of which is inserted in a one hole rubber stopper and the ot.her end of which is placed in a 1000-ml cylinder filled with water at a temperature of about 40°C. The open end of t,he tubing in the cylinder should be above the water level in the cylinder. The apparatus is assembled by first placing a gas buret over the opeu end of t,he tubing in the cylinder, and then inserting t,he rubber stoppered end of t,he tubing into a 125-ml Erlenmeyer flask. The flask is clamped in position in a 1000-ml beaker filled with water. The initial volume in t,he gas buret is determined at barometric pressure by raising the buret and recording the volume when the level of the water inside the buret, is equal to the level of the water in the cylinder. The kmperature of the water bath is also recorded. On heating t,he water bath, air is forced out of the flask into the gas buret. Volume readings on the gas buret are taken at barometric pressure approximately every five degrees rise in temperature. With the gas buret's initial reading at 2-30 cc about seveu to nine sets of data can he made. After the heating process, the total volume of the system including the glass tubing up to the initial buret reading is made by filling the apparatus with water and either measuring this volume of water inIa graduate or weighing it in a beaker on a trip scale.
The total volume at each temperature reading is found by adding the volume of the system to each iucrease in volume over the initial buret reading. A plot of temperature (OC) versus volume is made and t,he volume, VO,at 0°C is determined. The value of a is determined by using any set of volume-temperature readings. Using this value of or, the value of t when V goes to zero is found. By this technique a value of absolute zero in t,he range of -265" to -285" is found.
Apparatus for the Charles' Law experiment.
Volume 44, Number 6, June 1967
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