Elasticity of Gases
(Reference:  The Science Source, Elasticity of Gases #16250, 1998)

PREPARATION

400 mL  beakers - 1 for each group
1 set  weights - 1 for each group
Hotplates
Salt to cool water
Ice
Apparatus (syringe, with cap, between two pieces of wood)

BACKGROUND

You will be using a special apparatus, consisting of a syringe and wooden blocks, to experimentally verify Boyle’s and Charles’ laws of gases.  Boyle’s Law states that pressure and volume are inversely proportional or:
P µ 1/V  or  P = k/V

Where µ means “proportional to” and k is a constant of proportionality.  Charles’ Law states that volume and temperature are directly proportional or:
V µ T  or   V = kT

PROCEDURE

· Whenever you are adjusting the volume of the gas in the syringe you must remove the red cap on the syringe.
· Whenever you record the volume of the gas inside the syringe you must use an averaging procedure.

Averaging procedure*
1. Red cap is on…push piston into syringe to compress gas
2. Let system reach equilibrium
3. Note volume
4. Pull piston out to expand gas
5. Let system reach equilibrium
6. Note volume
7. Your recorded volume will be the average of these 2 volumes

You must use this averaging procedure for each volume measurement throughout the lab because the difference will be about 2 cm3.

Boyle’s Law Experiment
1. Record atmospheric pressure (from barometer)- this will remain constant
2. Record room temperature- this will remain constant
4. Record initial volume *
5. Add 500g mass (record masses in kg)
6. Record the new volume*
7. Repeat this for several data points, such that there is a change in volume of 0.5-3 cm3 with each addition

Charles’ Law Experiment
1. Again record room pressure and temperature
3. Record initial volume *
4. Heat beaker of water to boiling (volume of water must be enough to completely submerge syringe)
5. Submerge syringe using tongs
6. When the volume in the syringe has equilibrated measure and record the volume *
7. Record the temperature of the water in °C
8. Remove beaker of water from hotplate and repeat above steps at 10 °C cooled increments (90, 80, etc) for 7 or so data points.  (You may add tap water to facilitate cooling.)
9. Take your final measurement in a beaker of ice water

DATA

BOYLE’S LAW

 Volume (cm3) Mass of Weight (kg) Force on Piston (N) Area of Piston (m2) Pressure (kPa) 0 o o o o 0 o o o o 0 o o o o 0 o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o
Temperature: ______________  Barometric Pressure: _____________

CHARLES’ LAW

 Volume (cm3) Temperature (°C) Temperature (K) o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o
CALCULATIONS

The FORCE (kg×m/s2 = N) on the piston is weight, which is:

Mass  x  acceleration due to gravity (9.8 m/s2)

The PRESSURE (N/m2 = Pa) on the piston is:

Force  /  Cross sectional area of piston (in m2)

LAB REPORT

Your lab report should include the following information:

1.  Introduction
This should briefly describe the theory that you were testing experimentally and how the experiment was conducted.

2. Procedure
This should explain briefly how the experiment was performed.  Do not simply copy the procedure form the handout.  Explain any “tricks” used to insure better results.

3. Results
This section should explain and discuss the results that were obtained.  You should reference each of 3 graphs here.

Graphs
Each graph should be numbered and given a descriptive title and title block

Example:

Graph 1:  The Variation of Volume with Pressure of a Fixed Amount of Air
Note: Temperature maintained at a constant 23°C throughout measurement.
Experiment Performed by: (student names)
Date Performed: (date)

Volume vs. Pressure
Pressure is the variable that the experimenter varies, i.e. it is the INDEPENDENT variable.  Volume changes as a result of this variation in pressure so it is the DEPENDENT variable.  Pressure should be placed on the x-axis and volume on the y-axis.  The graph should be slightly curved because pressure and volume are inversely proportional to each other.

1/Volume vs. Pressure
What you should see is that this graph is nearly a straight line.  It will probably not be exactly straight because of small experimental measurement errors.  A straight line on this graph represents proportionality between pressure and 1/volume.

Volume vs. Temperature
Temperature is what you varied so it will go on the x-axis and volume on the y-axis.  What you should see is that this graph also is nearly a straight line.  Again, it will likely not be exactly straight, because of measurement error.  A straight line on the graph represents proportionality between temperature and volume.

4. Conclusions
You explain here whether the results were as expected.  If they were not, explain where error may have occurred.  Again, refer briefly to results, and if the results confirm the laws tested.

5. Sample Calculations
Show one example of each calculation.

NOTE

In technical wrting, proper pronouns are never used.  In your report, you should follow this rule.  You do not report things such as, “We varied the pressure….”.  You should say, “The pressure was varied…”.  Also, write the report as though you are recalling what was done, not as though you are giving instructions to the reader.

DISPOSAL

Student solutions can all go down the drain.

Ginger Chateauneuf, 2000.
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