Phy212: General Physics II Laboratory
Instructor: Tony Zable
Page 1 of 5
Experiment: Determination of Absolute Zero
Introduction
Gases are made up of molecules that are in constant motion and exert pressure when they
collide with the walls of their container. The velocity and the number of collisions of these
molecules is affected when the temperature of the gas increases or decreases. In this
experiment, you will study the relationship between the temperature of a gas sample and
the pressure it exerts.
Using the apparatus shown in Figure 1, you will place an Erlenmeyer flask containing an air
sample in water baths of varying temperature. Pressure will be monitored with a pressure
sensor and temperature will be monitored using a temperature probe. The volume of the
gas sample and the number of molecules it contains will be kept constant. Pressure and
temperature data pairs will be collected during the experiment and then analyzed. From
the data and graph, you will determine what kind of mathematical relationship exists
between the pressure and absolute temperature of a confined gas. Lastly, you will use your
data to find a value for absolute zero on the Celsius temperature scale.
Figure 1
Materials

LabPRO interface & computer

plastic tubing with two connectors

Logger Pro

rubber-stopper assembly

Vernier Pressure Sensor

125-mL Erlenmeyer flask

Vernier Temperature Probe

four 1-liter beakers

hot plate

ice

slit stopper

glove or cloth

ring stand and utility clamp

Procedure
1. Obtain and wear goggles.
2. Prepare a boiling-water bath. Put about 800 mL of hot tap water into a 1-L beaker and
place it on a hot plate. Turn the hot plate to a high setting.
3. Prepare an ice-water bath. Put about 700 mL of cold tap water into a second 1-L beaker
then add ice and and salt (if available).
4. Put about 800 mL of room-temperature water into a third 1-L beaker.
5. Put about 800 mL of hot tap water into a fourth 1-L beaker.
6. Plug the Pressure Sensor into CH1 of the LabPRO interface and the Temperature Probe
into CH2.
PCC- Cascade Campus
Phy212: General Physics II Laboratory
Instructor: Tony Zable
Page 2 of 5
7. Open the side arm of the pressure sensor valve to allow air to enter and exit. Open its
side arm by aligning the blue handle with the arm that leads to the pressure sensor
(see Figure 2).
8. Obtain a rubber-stopper assembly with a piece of heavy-wall plastic tubing connected
to one of its two valves (shown in Figure 3).
Figure 3
Figure 2
9. Insert the rubber-stopper assembly into a 125-mL Erlenmeyer flask. Important: Twist
the stopper into the neck of the flask to ensure a tight fit. Attach the connector at the
free end of the plastic tubing to the pressure sensor valve with a clockwise turn (see
Figure 4).
both valves closed
Pressure Sensor
Figure 4
10. Place the flask into the hot water then close the side arm of the pressure sensor and
the valve above the rubber stopper, respectively. (see Figure 4). The air sample to be
studied should now be confined in the flask.
11. Prepare the computer for data collection by opening “Exp 07” from the Chemistry with
Computers experiment files of Logger Pro. The vertical axis has pressure scaled from 0
to 150 kPa. The horizontal axis has temperature scaled from about 0 to 100 °C.
12. Collect pressure vs. temperature data for your gas sample:
a. Place the flask into the ice-water bath. Make sure the entire flask is covered (see
Figure 4). Stir.
b. Place the temperature probe into the ice-water bath.
c. When the pressure and temperature readings displayed in the Meter window
stabilize, click Keep . You have now saved the first pressure-temperature data pair.
Note: Do not “Stop” the data collection run untill all data are collected.
13. Repeat Step 12 using the room-temperature bath.
14. Repeat Step 12 using the hot-water bath.
15. Repeat Step 12 using the boiling-water bath. Note: Use a ring stand, utility clamp, and
slit stopper to suspend the temperature probe in the boiling-water bath. To keep from
burning your hand, hold the tubing of the flask using a glove or a cloth. Remove the
flask and the temperature probe after you have collected this data point.
PCC- Cascade Campus
Phy212: General Physics II Laboratory
Instructor: Tony Zable
Page 3 of 5
CAUTION: Do not burn yourself or the probe wires with the hot plate.
16. End the data collection run and turn off the hot plate. Record the pressure and
temperature values in the data table below.
Water Bath
Pressure
(Pa)
Temperature
(°C)
Temperature
(K)
Constant, k
(P/T or P.T)
Ice
Room temperature
Hot
Boiling
17. Examine the pressure vs. temperature (°C) graph. What is the general shape of the
graph?
18. Create a new “Calculated Column” to convert your temperature values from oC to K
(how are the 2 temperature scales related?). Be sure to label the column and its
units appropriately.
19.
Set the horizontal axis to the Kelvin Temperature values.
20.
Use the “Curve Fit” tool to fit your data to an appropriate function. Explore the
various fit types to obtain the best choice. Set the graph options so that the
standard deviation for the slope and y-intercept values are displayed. Write down
the equation (with calculated fit coefficients) describes your data?
21.
Cut-and-paste the graph of pressure vs. temperature (K) into Microsoft WORD. The
curve fit line should still be displayed on the graph. Print the graph.
Analysis
1. In order to perform this experiment, what two experimental factors were kept
constant?
2. Based on the data and graph that you obtained for this experiment, express in words
the relationship between gas pressure and temperature.
3. Explain this relationship using the concepts of molecular velocity and collisions of
molecules.
PCC- Cascade Campus
Phy212: General Physics II Laboratory
Instructor: Tony Zable
Page 4 of 5
4. Write an equation to express the relationship between pressure and temperature (in K).
Use the symbols P, T, and K (for the proportionality constant). Refer to step 20 in the
procedure above.
5. According to this experiment, what should happen to the pressure of a gas if the Kelvin
temperature is doubled?
6. Check this assumption by finding the pressure at -73°C (200 K) and at 127°C (400 K)
on your graph of pressure versus temperature. How do these two pressure values
compare?
Estimating Absolute Zero
Absolute zero, on the Kelvin scale, is the temperature at which the pressure of a gas
theoretically becomes equal to zero. By analyzing a graph of Celsius temperature (y-axis)
vs. pressure (x-axis) it is possible to extrapolate your data to estimate absolute zero in
Celsius units.
a. In LoggerPro, select the “Temp Celsius” for the vertical axis
and “Pressure” for the horizontal axis.
b. Rescale the temperature axis from a minimum of -300°C to a
maximum of 200°C. The pressure axis should be scaled from
0 kPa to 150 kPa.
c. Use the Linear Fit tool to obtain a best-fit curve for your data.
Be sure to set the graph options so that the standard
deviation for the slope and y-intercept values are displayed.
d. The y-intercept of the Linear Regression should represent the
extrapolated temperature at which the gas pressure is zero. Record the value of the
y-intercept and standard deviation in the table 2.
Table 2:
Y-intercept:
Standard Deviation (Y-intercept):
Slope of Graph:
Standard Deviation (Slope):
7.
How does your experimental value for Absolute Zero (in oC) compare to the accepted
value?
8.
Cut-and-paste the P vs T graph into Word and print it.
PCC- Cascade Campus
Phy212: General Physics II Laboratory
Instructor: Tony Zable
Page 5 of 5
One Last thing: Using the “Ideal Gas Law”, refer to Chapter 19 of the textbook, you will
now attempt to estimate the quantity of gas molecules in the enclosed flask.
1. Measure the volume of the enclosed flask. To do this, measure the mass of the
empty flask. Then fill the flask with water, such that the water volume is as close to
the previously enclosed gas volume as possible. Measure the combined flask and
water mass.
Mass (empty flask) : _________
Mass (w/water)
: _________
Mass (water only)
: _________
2. Using the accepted density of water (998 kg/m3), calculate the corresponding water
volume. This value should correspond to the enclosed gas cvolume.
Volume (water or encl. gas)
: _________
3. According to the Ideal Gas Law, when Pressure and Temperature are plotted in SI
units, the slope of the linear fit should be:
SlopeP vs T =
kN
V
where k is the Boltzmann constant (1.38x10-23 J/K), N is the # of gas particles, and
V is the gas volume
4. Using the equation for the slope and the measured gas volume, estimate N. Be
certain to calculate the uncertainty, N, as well.
N = _________ ± _________
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