Gas Temperature and Pressure

 

Gases are made up of tiny particles. The particles are in constant motion and exert pressure when they strike the walls of their container. In this simple experiment, you will use a temperature probe, a pressure sensor, and an air sample in a stoppered flask to study the relationship between gas pressure and temperature. The volume and amount of gas will be kept constant. The results will be expressed in words, in a table, with a graph, and with a mathematical equation.

 

OBJECTIVES

In this experiment, you will

use a TI Graphing Calculator, a CBL System, and a temperature probe to measure temperature

use a TI Graphing Calculator, a CBL System, and a pressure sensor to measure the pressure of an air sample at several different temperatures

make a table of the results

graph the results

predict the pressure at other temperatures

describe the relationship between gas pressure and temperature with words and with a mathematical equation

 

MATERIALS

PROCEDURE

1.Obtain and wear goggles.

2.Prepare a boiling-water bath. Put about 800 mL of hot tap water into a l-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 and add ice.

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

• Plug the temperature probe into an adapter cable in 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, as shown in Figure 1 or Figure 3.
• Connect the CBL System to the TI Graphing Calculator with the link cable using the port located on the bottom edge of each unit. Firmly press in the cable ends.
• Open the side arm of the pressure sensor valve to allow air to enter and exit. If your pressure sensor has a metal valve (see Figure 1), 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 (see Figure 2).
• Insert a 1-hole stopper fitted with a glass tube into a 125-mL flask. Twist the stopper to ensure a tight fit. Attach the plastic tubing to the glass tube in the stopper.
• 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, as shown in Figure 3. The air sample to be studied is now confined in the flask.

7.Turn on the CBL unit and the calculator. Press and select PHYSCI. Press , then press again to go to the MAIN MENU.

8.Set up the calculator and CBL for a temperature probe and calibration (in °C), and a pressure sensor and calibration (in atmospheres).

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

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

• Select COLLECT DATA from the MAIN MENU.
• Select TRIGGER from the DATA COLLECTION menu.

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

• Place the flask into the ice-water bath. Make sure the entire flask is covered (see Figure 1). Stir.
• Place the temperature probe into the ice-water bath.
• Monitor pressure and temperature on the CBL screen by pressing the [CH VIEW] button on the CBL. When "CH1" in the upper-left corner of the CBL screen blinks, the Channel 1 temperature (in °C) is displayed on the CBL. When you press [CH VIEW] again, "CH2" starts to blink—the Channel 2 pressure (in atm) is now displayed on the CBL. Continue to press [CH VIEW] to alternate between the two readings.
• When the temperature and pressure readings displayed on the CBL screen have both stabilized, press on the CBL to store the pressure-temperature data pair.

11.Select MORE DATA on the TRIGGER menu. Repeat the Step 10 procedure using the room-temperature bath.

12.Select MORE DATA on the TRIGGER menu. Repeat the Step 10 procedure using the hot-water bath.

13.Collect the boiling-water data.

• Select MORE DATA on the TRIGGER menu.
• 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. After the temperature probe has been in the boiling water for a few seconds, place the flask into the boiling-water bath and repeat Step 10.
• Remove the flask and the temperature probe after you have pressed and finished collecting data.

14.Record your data.

• Select STOP on the TRIGGER menu.
• Press to display a graph of pressure vs. temperature (°C).
• Use to examine the data points along the graph. As you move the cursor right or left, the temperature (X) and pressure (Y) values of each data point are displayed below the graph.
• Record the data pairs in your data table. Round temperature to the nearest 0.1°C and pressure to the nearest 0.01 atm.

 

DATA AND CALCULATIONS

Water bathTemperaturePressureTemperature

(°C)(atm)(K)

Ice__________________

Room temperature______ ____________

Hot __________________

Boiling__________________

 

PROCESSING THE DATA

1.Convert the Celsius temperatures (°C) to kelvins (K) and record the results in the last column of the Data and Calculations Table. Use the formula

For example, 2°C = 275 K (275 K = 2°C + 273).

2.Graph the data. Plot TEMPERATURE (in K) on the horizontal axis and PRESSURE (in atm) on the vertical axis. Begin both axes with zero (0). Draw in the best-fitting straight line passing through or near your points.

3.What is the relationship between gas pressure (P) and temperature (T) in words

 

 

4.Explain this relationship, using the idea of particle speed.

 

 

5.According to your graph, what would the pressure be at 350 K (77°C) At 200 K (–73°C) At 400 K (127°C)

 

6.Should the graph go through the origin (0,0) Explain.

 

 

 

7.Write an equation to express the relationship between pressure and temperature. Use the symbols P, T, and k.

 

 

 

EXTENSIONS

1.Use the TI-Graph Link cable and program to transfer your graph image to a Macintosh or IBM-compatible computer. Print a copy of the graph.

2.Repeat the experiment using a pure, noncorrosive gas, such as oxygen, butane, or carbon dioxide. Compare the results with your results for air.

3.Do the experiment using a dry-ice and amyl-alcohol bath or a dry-ice and acetone bath to get a temperature of about –78°C (195 K).

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Author Unknown

Questions? Comments??
Patrick Gormley, editor