Pressure -Temperature Relationship in Gases

Procedure (Water bathes can be shared between two lab groups)

1. Obtain and wear goggles.

2. Prepare a boiling-water bath. Put about 700 mL of hot tap water into a 1000 mL beaker and place it on a hot plate. Turn the hot plate to a high setting.

3. Prepare an ice-water bath. Put about 600 mL of cold tap water into a second 1000 mL beaker and add ice.

4. Put about 700 mL of room-temperature water into a third 1000 mL beaker.

5. Put about 700 mL of hot tap water into a fourth 1000 mL beaker.

6. Construct a data table in your lab notebook similar to the one below:

Sample Number	Temperature (°C)	Temperature (K)	Pressure (Atm.)
1
2
3
4

7. Prepare the temperature probe and pressure sensor for data collection.

• Insert a 1-hole stopper fitted with a glass tube into a large test tube. Twist the stopper to ensure a tight fit
• Plug the temperature probe into Channel 1 of the CBL.
• Plug the pressure sensor into an adapter cable in Channel 2 of the CBL. A 30-45 cm piece of heavy-wall plastic tubing is already connected to the end opening of the 3-way valve of the pressure sensor. Connect the plastic tubing to the glass tubing of the rubber stopper.
• Open the side arm of the pressure sensor valve to allow air to enter and exit. If your pressure sensor has a metal valve, open its side valve by turning the knob one turn counterclockwise. If your pressure sensor has a plastic valve, open its side valve by aligning the blue handle with the arm that leads to the pressure sensor.
• Close the side arm of the pressure sensor valve. If the valve is metal, firmly turn the knob clockwise to close it. If the valve is plastic, align the blue handle with the side arm. The air sample to be studied is now confined in the test tube.

8. Turn on the CBL unit and the TI-8X calculator. Press PRGM and select CHEMBIO. Press ENTER, then press ENTER again to go to the CHEM MAIN MENU.

9. Set up the calculator and CBL for a temperature probe and a pressure sensor calibrated in atmospheres.

• Select SET UP PROBES from the CHEM MAIN MENU.
• Enter "2" as the number of probes.
• Select TEMPERATURE from the SELECT PROBE menu.
• Enter "1" as the channel number.
• Select PRESSURE from the SELECT PROBE menu.
• Enter "2" as the channel number.
• USE the STORED CALIBRATION.
• Select ATM from the PRESSURE UNITS menu.

10. Set up the calculator and CBL for data collection.

• Select COLLECT DATA from the CHEM MAIN MENU.
• Select MONITOR INPUT from the DATA COLLECTION menu.
• The calculator is diplaying the the current sensor reading.

11. Collect pressure vs. temperature data for your gas sample.

• Place the test tube and the temperature probe into the ice-water bath. Make sure the entire tube is covered. Stir. When the temperature and pressure readings displayed on the calculator screen have both stabilized, record the values in your data table.

12. Repeat the Step 11 procedure using the room-temperature bath, the hot water bath and the boiling water bath.

13. Repeat the Step 10 procedure using the hot-water bath.

• Select (+) to Quit on the calculator.
• Select QUIT from the MAIN MENU.

Data Analysis

1. Enter your data into the calculator, and graph celcius temperature vs. pressure.

To Enter Data	To Graph the Data

2. Examine your graph of pressure vs. temperature (°C). In order to determine if the relationship between pressure and temperature is direct or inverse.

3. Perform a linear regresstion analysis on your data and plot the line of best fits.

Analysis	Plotting the "line of best fits"

4. Sketch your graph:

5.

Use the ROOT (or ZERO) option under the 2nd TRACE key to determine the root of the function temperature vs. pressure?

6. Is the value zero? Should the value be zero? What do you need to do in order for the temperature scale to have a valid 0,0 origin?

Questions

1. Write an equation to express the relationship between pressure and temperature (K). Use the symbols P, T, and k.

2. One way to determine if a relationship is inverse or direct is to find a proportionality constant, k, from the data. If this relationship is direct, k = P/T. If it is inverse, k = P*T. Based on your answer to Question 4, choose one of these formulas and calculate k for the four ordered pairs in your data table (divide or multiply the P and T values). Show the answer in the fourth column of the Data and Calculations table. How "constant" were your values?

3. According to this experiment, what should happen to the pressure of a gas if the Kelvin temperature is doubled? 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?