So... V=kT And if we are using 2 different temperatures:

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1 North Georgia College and State University Chemistry 1211L-Charles Law Intro and Procedure written by Katzenstein aided in part by a continuous infusion of caffeine CHARLES LAW AN INTRODUCTION OF SORTS Charles (that is Jacques not Ray) was an avid balloonist (they didn t have motorcycles back then). In any case, he made the observation that the volume of a gas at constant pressure increases when the temperature is raised. Temperature increases, volume expands; temperature decreases, volume diminishes. So V T Charles Law states that the volume of a gas is directly proportional to its temperature (in o K): So... V=kT And if we are using 2 different temperatures: JACQUES CHARLES V 1 =kt 1 or V 1 /T 1 = k ( ) and V 2 =kt 2 or V 2 /T 2 = k Since k is a constant (and constants are not supposed to change, that s why they are constants), if we are using the same gas sample (fixed sample) at a constant pressure, then V 1 /T 1 = V 2 /T 2 So far, so good. So, if we did an experiment where we were able to measure the volumes of a gas (air) sample at 2 different temperatures (also measured), we could calculate the value for k for each and if Charles was right (and he does have that smug I m right look to him), then the values for k for each experiment should be the same (or pretty darn close). EXPERIMENTAL PROCEDURE Experiment to get k at a higher temperature: 1. See the picture below to get the general gist of how you want to set up your apparatus. Likely, you will use a ring stand with a ring clamp so be sure that everything is snug, secure and balanced. It is advised that you clamp your thermometer (use a thermometer clamp as at right) to keep it at a fixed position and to avoid breakage; it not, pay some attention. You will also want to put a clamp on the end of the rubber tubing but do not close the clamp. Get the barometric pressure: #. Whenever it suits you (and not a moment before), read the barometer in the lab to obtain the atmospheric pressure or get it off the WeatherBug App. Record the barometric pressure. [Your lab instructor will assist you if needed.]

2 2. Heat the water to boiling. Note that the flask is not sealed (the rubber tubing is open to the atmosphere). Keep the water boiling; measure and record the temperature of the water after about 6 minutes. The temperature of the air within the flask should be the same as the water, ja? Experiment to get k at a lower temperature: 3. Set up an ice water bath in the trays provided by your (oh so wonderful) laboratory instructor. 4. After 6 minutes, extinguish your flame and immediately clamp the rubber tubing. 5. Rapidly, transfer the flask to the ice water bath. With the top (stoppered end) of the flask pointing down, open the clamp as shown in the illustration below. 6. Keep the flask immersed (as at left) in the ice bath for 4 minutes. Measure and record the temperature of the ice water bath. Again, the air temperature within the flask should be the same as the bath temperature, n est-ce pas? 7. After 4 minutes, raise the flask up so that the level of water in the flask is even with the water level of the bath. Seal the flask by closing the clamp and remove the flask. 7. Using a graduated cylinder, precisely measure and record the volume of water drawn into the flask Measuring the volume of the Erlenmeyer flask: 8. Take the stopper off the flask and fill it with water. Pushing out excess water, carefully reinsert the stopper. Using a graduated cylinder, precisely measure and record the volume of water in the flask (=total volume of the flask).

3 Section NAME POST LAB QUESTIONS 1. The following experimental mistakes were made. Explain what effect, if any, they would have on the V/T ratio (larger, smaller)? Why? A. The water bath was not filled to the top. B. The flask was only partially immersed in the ice bath. C. The clamp was not closed before removing the flask from the boiling water D. The assumed volume of the flask was 125 ml 2. Do your experimental results verify Charles Law? Give supporting evidence.

4 Section NAME DATA SHEET Temperature of boiling water Temperature of ice water Volume of water pulled into flask Total volume of flask Barometric pressure Calculations: #1 Volume hot dry air (total volume of flask) #2 Temp hot dry air (temperature of boiling water) V/T hot (#1/#2) #3 Volume wet cold air (volume flask volume pulled in) #4 Volume dry cold air: #3 X [(barometric pressure 5.0 torr)/barometric pressure]) #5 Temperature of cold air (temperature of ice bath) V/T cold (#4/#5) #6 Calculate % difference between V/T hot and V/T cold

5 PRE-LAB QUESTIONS Section NAME 1. Using the following data, calculate the V/T ratios and determine if Charles Law is obeyed (verified). Volume hot dry air ml Volume water drawn into flask 32.0 ml Temp. boiling water 99.5 o C Temp. ice water 1. 5 o C Barometric pressure torr 2. Why must the clamp be open while the flask is heated?