Charles’ Law
The Effect of Temperature on Volume
According to the kinetic theory, an increase in temperature will cause the molecules
of a gas to move faster and exert more pressure, or cause the gas to expand. Conversely,
as a gas is cooled, the molecules will move more slowly and the gas will contract, or exert
less pressure. In other words, the volume of a gas increases as the temperature increases
if the pressure remains constant. This relationship between the volume of a gas and its
temperature is known as Charles’ Law.
In this experiment, you will study the effects of temperature on gas volume and
determine the constant for the relationship, V/T.
Objectives:
In this experiment, you will:
1. determine the effect of temperature on the volume of a gas when pressure is
constant.
2. use your volume and temperature data to calculate a constant, k, showing the
relationship between these values.
Equipment:
goggles
Erlenmeyer flask (250 mL)
glass tubing or dropper
thermometer
wax marking pencil
barometer
large water bucket
one hole stopper
utility clamp
towel
graduated cylinder
1000 mL beaker
Procedure:
1. Set up the apparatus as shown in Figure-1. Use a hot plate, if available. Obtain 1
1000 mL beaker and add approximately 250 mL of tap water. Obtain 250 mL
Erlenmeyer flask. Place a one-hole stopper fitted with a dropper pipet in the flask.
Make a mark on the outside of the flask with a marking pencil noting the bottom of
the stopper. Place the flask in the beaker of water as shown in Figure-1. Make sure
that thee is space between flask and the side of the beaker to allow steam to
escape. Heat the water to boiling. Record the temperature of the boiling water as
T1 in your data table. Continue heating at this temperature for 3 to 5 minutes.
Lower the heat if necessary.
Figure 1. Heating the flask (and air) in boiling water (we will use a hot plate!)
2. Prepare a water bath in a large bucket.
3. Remove the flask from the beaker. Protect your hand with a towel while placing
your finger firmly over the end of the glass tubing. CAUTION: The flask is very
hot!! Submerge the flask in the large bucket as shown in Figure-2 (Do not allow air
to enter the flask while transferring.)
4. Remove your finger from the glass tubing and hold the flask under the water (with
open end down.) until the flask has cooled and water no longer enters. Raise the
flask (Glass tubing down), until the water level on the inside the flask is equal to
the water level on the outside, as in Figure-2. Pressure inside the flask is now equal
to the pressure outside of the flask (atmospheric pressure!). Measure the
temperature of the water in the bucket.
5. Place your finger over the glass tubing while the outside and inside water levels are
equal. Remove the flask and place it in an upright position on your lab table before
removing your finger (from the flask, not your hand. Ha! Ha!)
6. Remove the stopper from the flask and measure the volume of water that is in the
flask using a graduated cylinder.
7. Refill the flask with tap water to where you placed the mark at the bottom of the
rubber stopper. Measure this volume of water in a graduated cylinder and record it
as the total volume of the flask.
8. Repeat the procedure as Trials 2 and 3 using different temperatures.
Figure 2. Equalizing the pressure in the flask. The water level inside the flask is adjusted
to the level of the water in the bucket by raising or lowering the flask before removal.
Analysis:
1. Record data in the data table and do the calculations suggested. Convert all
temperatures and pressures to standard units of Kelvins and mmHg.
2. To do calculation 9 of the data table, solve Boyle’s law for the corrected volume:
(Pdry gas) (Vat t2) = (Patm) (Vcorrected)
3. Graph your data by plotting temperature in Kelvin’s on the horizontal axis and
volume in mL on the vertical axis for each trial. Extrapolate to locate the
temperature at which the volume would be zero for each trial. Data from all three
trials may be plotted on the same graph. Distinguish between trials with different
symbols. (The computer will do this for you by plotting different data sets on the
same graph.)
Data Table-1
Measurement
Trials
1
2
O
Initial temperature of air (hot), T1
C
K
C
O
Final Temperature of air, T2
3
O
C
K
C
O
O
C
K
C
O
K
K
K
Volume of water in flask
mL
mL
mL
Total Volume of flask
mL
mL
mL
Final Volume of flask
mL
mL
mL
mmHg
mmHg
mmHg
mmHg
mmHg
mmHg
mmHg
mmHg
mmHg
mL
mL
mL
Atmospheric Pressure (barometer
reading)
Vapor Pressure of water at T2
(consult your vapor pressure chart)
Pressure of dry gas (Patm – PH2O)
Volume of dry gas at atmospheric
pressure
Questions:
1. Look at your graph of temperature vs. volume. What relationship exists between
the variables? Explain your answer.
2. From the graph, choose two convenient temperature points (Ta and Tb). Find the
volumes that correspond to Ta and Tb from the graph (Va and Vb).
If
VαT
Then V = kT
Solving for k, we find:
K = V/T
Using the points selected, calculate the k values for each point and compare.
3. At what temperature does the extrapolated line intersect the x-axis?
4. At what temperature does Charles’ Law predict that the extrapolated line should
intersect the x-axis?
5. What is the significance of the slope of the line on your graph?
6. Explain at least 3 sources of error that took place in the experiment. Explain how
each source of error affected your lab results. What could your lab group do to
minimize these errors?
7. How would your data be affected if you did not equalize the pressure in Step-4?
8. Did the same amount of water enter the flask in all three trials? Why or why not?
9. State and explain 3 examples of Charles’ Law in our every day lives.
10. Do some research… Why (theoretically) can the Kelvin temperature never reach
absolute zero?
11. Why was it necessary to allow the two water levels to become equal in Step 4 of
the Procedure?
12. Why did the water flow into the flask in the ice bath?
13. What advantage is there in using the absolute temperature scale (Kelvins) rather
than the Celsius temperature when doing calculations involving gases?
14. Calculate the percent error for your value of absolute zero. Offer valid reasons for
your error. (In other words… give a few examples of mistakes or problems that
might occur during the lab, calculations, and graphing.)
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