Relation of Temperature at Constant Pressure:
Charles’s law
Objective
Experimental estimation of absolute zero using Charles’s Law.
Introduction
The volume of a given mass of gas is directly proportional to its temperature on the
Kelvin scale when the pressure is held constant. The law is expressed mathematically
as
T1
V1
=
T2
V2
This generalization, arrived at by Jacques Charles in 1787, is known as Charles’s Law.
Charles discovered through experimentation that the volume of a gas at constant
pressure increased by 1/273 of its value at 0°C for each degree Celsius rise in
temperature, and decreased in the same manner as the temperature fell below 0°C.
Theoretically, the volume of an ideal gas would continue to decrease until it became
zero. The relationship between the Kelvin and Celsius temperature scales is
K = °C + 273.15
Kelvin temperatures, by convention, are reported without a degree sign for SI units, or
with the degree sign for non-SI metric units.
Equipment
125 mL Erlenmeyer flask
400 mL beaker
One-hole rubber stopper for flask
Water pan
Thermometer
Bunsen burner
Ring stand and iron rings
Wire gauze
Graduated cylinder
Boileezers
Ice
Clamp
Procedure
1. Dry any moisture on the inside of a 125 mL Erlenmeyer flask.
Obtain a one hole rubber stopper that fits the neck of the flask
and insert it into the flask (be sure that it has only one hole.)
Set up a hot water bath as shown (right), using the ring stand,
iron rings, wire gauze, and a 400 mL beaker [it will be necessary
to add a second ring to serve as a 'seat-belt' to prevent the
beaker from migrating off the stand]. Add a few Boileezers to
the beaker. Attach a clamp to the neck of the flask and lower it
into the beaker, being careful not to let the flask touch the
bottom of the beaker. Fasten the clamp to the iron stand. Pour
distilled water into the beaker up to the neck of the flask. Leave
enough space at the top for the water to boil without boiling
over.
2. Begin heating and bring the water to a boil. Boil gently for 5
more minutes to allow the air in the flask to come to the boiling-water temperature.
Record the temperature of the boiling water. While the water is boiling, fill a metal
pan with cool tap water.
3. Turn off the burner when you are ready to remove the flask from the boiling water
bath. Undo the clamp from the ring stand. Place your finger over the hole in the
stopper while you transfer the flask to the pan of water. Use the clamp like a handle
to carefully lift the flask out of the boiling water bath.
2
4. Keeping the stopper-end of the flask pointed downward, immerse the flask into the
pan of cool water (as illustrated below). Remove your finger from the stopper hole
after submerging the stopper-end of the flask into the water. While submerged, the
flask must remain inverted the entire time to keep the air sample trapped inside.
5. After the flask has been in the water bath for 10 minutes, record the temperature of
the water in the pan.
6. Keeping the flask inverted, adjust the water level inside the flask to match the level of
the water in the pan (see Figure 3). Keeping the flask submerged, tightly cover the
hole in the stopper with your finger, remove the flask from the water, and set it
upright. The flask will contain water that entered when the air volume decreased.
Use a graduated cylinder to measure the volume of water that entered the flask, and
record this volume.
Figure 3
7. Perform a second trial. Dry and warm the flask again. The inside of the flask must
be completely dry. Replace the one-hole stopper and heat to boiling as you did in
Step 2. While the flask is heating, prepare an ice-water bath in the water pan.
Repeat Steps 3-5, recording the temperature of the ice-water bath after the flask has
been submerged for at least 10 minutes.
8. Equalize the water levels as in Step 6, plug the stopper with your finger, remove, and
measure the volume of water that entered the flask. Record this volume.
9. Repeat these above steps [7 & 8], but use a cooling bath at an intermediate
temperature (40-60 °C).
10. Finally, determine the “full” volume of the Erlenmeyer flask by filling it with water and
inserting the rubber stopper assembly. Remove the rubber stopper and measure the
volume of water remaining in the flask. Record the “full” volume of the flask.
Cleanup
Clean your lab area and glassware before being signed out.
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Calculations
1. Determine the volume of air in the flask at boiling. This is equal to the full volume of
water that filled the flask in the last Step (10).
2. Determine the volume of air in the flask at tap-water temperature. Subtract the
volume of water that entered the flask (Step 6) from the full volume of the flask (Step
10).
volumeair = volumefull – volumewater entered
3. Determine the volume of air in the flask at ice-water temperature.
4. Convert the Celsius temperatures (for Calculations 1, 2, and 3) to Kelvin.
5. Using the Kelvin temperatures, calculate the constant which is the ratio of
volume/temperature. (Calc. 1/TK, Calc. 2/TK, etc.)
6. Graph the volume-temperature relationship of the gas using an appropriate graphing
program. The temperature scale runs from -400°C up to 100°C for volumes of 0 to
150 mL. Theoretically, gases would reach a temperature called absolute zero at a
volume of 0 mL. Use the linear fit function of the Graphical Analysis program (or
Microsoft Excel) to draw a straight line through the points on the graph, and
extrapolate the line to a zero volume. The temperature where the graph crosses the
horizontal axis is your prediction for absolute zero. Indicate this value on your graph
and record.
7. Calculate the percent error for your graphical value of absolute zero (compared to
the accepted value of -273.15 °C).
8. Compare your results to the accepted value of absolute zero, and speculate on any
differences.
Write-up
Your write-up should include the Volume versus temperature graph you generated;
including an extrapolation to a volume of 0 mL. The plot should contain sufficient
information that anyone ‘reasonably skilled in the art’ can look at it and understand what
is represented. This plot will need to be full-page & landscape in orientation.
Post Lab Questions
1. According to your graph, what is the predicted value of absolute zero in °C?
2. From your graph, what is the relationship between volume and temperature?
3. According to your graph, what volume is predicted at 100°C?
4. How does your value for absolute zero compare with the accepted value of
273.15 °C?
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Report: Charles's Law
Name
Lab Partner(s)
Section
Date performed
Data
Trial 1
Trial 2
Trial 3
Trial 4
boiling
room temp
ice water
Intermediate Temp
Temperature of
air in flask (°C)
Volume of full
flask
Volume of water
in flask
Volume of air in
flask
Temperature of
air in flask (K)
Constant
(volumeair / TK)
Slope from
graph
Results
From my graph, the temperature for absolute zero was
Percent error
%
From my graph, the temperature for absolute zero was
5
°C
K
6