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Title:  Pressure, Temperature, and Volume Relationships for Gases

Purpose: To experimentally determine the relationship between pressure, temperature, and volume for a gas and the value of absolute zero.

Procedure:

Part I:  Temperature Vs. Volume Relationship:

1. In the hood, heat a capillary tube which has been sealed at one end by passing it back and forth through a Bunsen burner flame for about 5 seconds.  Remove the tube from the heat and immediately insert the open end into a small amount of dibutyl phthalate (DBT).  Allow a 1-cm length of DBT to be drawn up into the tube.  Allow the tube to cool to room temperature with its open end up.

2. Using a rubber band, attach the capillary tube, open end up, to a thermometer such that the bases of both are equal.  Make sure that the rubber band does not cover up any of the numbers on the thermometer.

3. Lower the tube and thermometer into a beaker filled with ice water, until the tube is submerged up to level of the DBT.  Be sure not to let water into the end of the tube.  When the temperature and volume are no longer changing, record their values.  Note: You will be using the scale on your thermometer to record the volume.  You may need to adjust the position of the tube against the thermometer to be able to read the value; however, once you have recorded your first value, do not adjust the tube anymore or you will affect future readings.

4. Repeat step 3 using room-temperature tap water.

5. Heat the tap water from step 4 to boiling recording volume and temperature readings at 20 degree intervals.

Part II: Pressure Vs. Temperature

1. Your instructor will demonstrate pressure Vs. temperature relationships for a gas.  Be sure to record all values.

Analysis:

1. Plot a graph of Volume (y-axis) Vs. Temperature (x-axis) as measured in  C.  Your temperature axis should start at -300 C, and your Volume axis should start at 0.  Draw the best fit line through your data points and extrapolate (i.e. extend) your line until it intersects with the x-axis.  Mark this point on your graph and label it absolute zero.

2. Using the data from Part II, make a graph of Pressure (y-axis) Vs. Temperature (x-axis) as measured in  C.  Again, your temperature axis should start at -300 C and your pressure axis should start at 0 mmHg.  Extrapolate your best fit line to the x-axis and label this intersection point absolute zero.

3. Determine the average value of absolute zero that you obtained from your graphs.

4. What is the %error in your experimental value of absolute zero?

Questions:

1. What is special about the temperature absolute zero, and what does this temperature have to do with the Kelvin temperature scale?

2. For both of your graphs, you used a best fit line to represent your data points.  Do you think that both of these graphs should truly be represented by straight lines?  Explain your answer.  Hint: Think about the values of pressure and volume at very low temperatures.