29 Exploring Gas Laws
Purpose
In part one of this two part exploration, you will measure how the pressure of a confined gas changes with changes in the volume.
In part two, you will determine the relationship between pressure and temperature and estimate the value of absolute zero.
Background
In solids and liquids, the atoms or molecules are very close to each other leaving no room between them. For this reason, solids and liquids cannot be measurably compressed. Gases, on the other hand, have relatively large distances between the atoms or molecules as they bounce around into each other and the walls of their container. This fact allows gases to be compressed. In this experiment you will use modern equipment to recreate the experiment first done by Robert Boyle in 1661. Boyle discovered that there is a mathematical relationship between gas pressure and volume.
Gas pressure is related to how often gas molecules bounce into surfaces. When the volume of a container of gas is changed, the distance between the walls changes and the amount of time it takes for a particle to get from one wall to another changes, which results in a different number of collisions per second and, results in, a different amount of pressure.
The pressure of a constant volume of gas will be affected by changes in temperature. Since temperature is a measure of the average kinetic energy (and therefore the average speed) of gas molecules, a change in temperature will change how much time it takes for molecules to move wall to wall in a container. This implies that if the molecules stopped moving, they would no longer hit the walls and the pressure would be zero. The colder something gets, the slower the molecules move, thus the temperature at which all motion stops must be the coldest temperature possible. This temperature is called "absolute zero". In part two of this lab you will attempt to determine the relationship between pressure and temperature and also determine the numerical value of absolute zero.
Materials
• PASPORT Xplorer GLX / • Right angle Clamp
• PASPORT Chemistry Sensor / • Small Tripod Base & Rod
• Fast Response temperature probe / • 45 cm Steel Rod
• Hot plate / • 250 mL beakers, 5
• Large Test Tube / • Tongs
• Quick-release connector (with sensor) / • Three-finger Clamp
• Tubing (supplied with sensor) / • Gas law syringe
• Rubber Stopper, (1-Hole to fit test tube) / • Protective gear
Consumables
• Glycerin (C3H5(OH)3), 1 drop / • Water, 1.0 L
• Rubber band
Safety Precautions
• Remember, follow the directions for using the equipment
• Keep water away from electrical outlets, the GLX, and the PASPORT equipment
• Be very careful when using the hot plate
• Wear safety glasses and follow all standard laboratory safety procedures
Part 1 Procedure
Equipment Setup
1) Put a drop of glycerin on the barb end of a quick-release connector. Put the end of the connector into one end of a short piece (about 2.5 cm) of plastic tubing that comes with the Chemistry Sensor.
2) Put a drop of glycerin on the end of the syringe. Connect the end of the syringe to the other end of the small piece of plastic tubing.
3) Adjust the volume of air in the syringe to 20.0 mL.
1) Align the quick-release connector on the end of the plastic tubing with the pressure port of the Chemistry Sensor. Push the connector onto the port, and then turn the connector clockwise until it clicks (about one-eighth turn).
Check that the syringe and Chemistry Sensor have a secure seal by adjusting the volume from 20.0 mL down to 10.0 mL. (It should get harder to push the plunger as the volume decreases.)
Xplorer GLX Setup
Connect the Chemistry Sensor into Port #1 on the GLX.
Record Data
1) From the home screen, press the Sensor button, then the Mode button (, ).
2) Switch the mode from continuous to manual (, ).
In this mode, after you press the record button, a flag appears at the top of the GLX screen instead of a clock. The GLX will only record a data point when you press .
3) Press and enter “volume” and press .
4) Scroll down to Measurement Unit, press , enter “ml”, then press .
5) Scroll down to Number of Digits and press for one digit past the decimal place, then press , .
6) Press , to open the graph display.
7) Press and use the arrow keys to highlight the X axis label. Press then use the arrow keys to select volume and press .
8) Press record (). When you press you will be prompted to enter the volume on the syringe. Enter the volume and press . The GLX will assign the pressure reading to this value.
9) Change the volume in the syringe by compressing to about 16 ml, hold the syringe at this position and press , enter this volume and press .
10) Continue this process to obtain about 5-6 data points (don’t compress below about 6 ml or the syringe may leak).
11) When you have collected your data points, press .
Analyze
Record calculations in your lab notebook as you complete your analysis.
Data
Make a sketch of your graph of Pressure versus Volume and a sketch of your graph of Pressure versus Inverse Volume (InvVol). Be sure to label the axes.
Analysis Questions
1) What was the actual pressure - volume relationship you discovered?
2) What could have caused an error in the volume measurement in your experiment?
3) What would have happened to your results if the syringe leaked when compressed?
Part 2 Procedure
Equipment Setup
1) Connect the tubing to the Chemistry Sensor, using the directions in the Sensor Information Sheet.
1) Connect the Quick Response Temperature probe to the Chemistry Sensor. Use a rubber band to attach the temperature probe to the air chamber (test tube).
2) Set up five beakers each containing water at a different temperature (Ice, room temp., ~30°C, ~40°C, and ~50°C).
Note: Be very careful not to touch the hot plate, beaker, or hot water.
Xplorer GLX Setup
1) With the Chemistry Sensor connected to the GLX. connect the Fast Response temperature probe to the temperature port on the Chemistry Sensor.
2) Turn on the GLX and press , to open the sensor screen.
3) Use the arrow keys to scroll down the list of measurements. Toggle the Visible/Not Visible settings using the button and set the Absolute Pressure and Temperature measurements to Visible with the rest set to Not Visible.
4) Press and select Manual as the sampling mode. Press again to accept the change.
5) Press to return to the home screen and open the Digits display to begin monitoring temperature and pressure.
Record Data
1) Press to begin recording data.
2) Place the air chamber with attached temperature probe into the first beaker and observe the pressure and temperature until the readings stabilize. Press to record a data point.
3) Move the air chamber to the next beaker. Continue to observe the readings and when they have stabilized, press to record the data. Repeat this step for the rest of the beakers.
Analyze
Record calculations in your lab notebook as you complete your analysis.
1) Use the Graph Display to examine the plot of Absolute Pressure versus Temperature. Press then to select Linear Fit. Use the resulting fit to determine the relationship of pressure and temperature.
2) From the Tools menu (), select the Smart Tool () Cursor. Use the Smart Tool Cursor to find where the Linear Fit line crosses the x-axis. You will need to use the Scale/Move () function to move the axis of the graph to find the intersection point. Record the x-coordinate of the point where your line crosses the x-axis as your estimate for absolute zero in your notebook.
Analysis and Synthesis Questions
1) Based on your Pressure versus Temperature data, how is the pressure related to the temperature?
2) Do your results support your predictions? Why or why not?
3) Based on your Pressure versus Temperature data, what is your estimate for absolute zero?
4) How does your estimate for absolute zero compare to the accepted value of
–273.15ºC?