Download North Georgia College and State University Chemistry 1211L

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 oK):
So... V=kT
And if we are using 2 different temperatures:
JACQUES CHARLES
(1746-1832)
and
V1=kT1 or…
V2=kT2 or…
V1/T1= k
V2/T2= 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…
V1/T1= V2/T2
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. 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).
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.
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 _________________
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 – 137.0 ml
Volume water drawn into flask – 32.0 ml
Temp. boiling water – 99.5 oC
Temp. ice water – 1. 5 oC
Barometric pressure - 747 torr
2. Why must the clamp be open while the flask is heated?