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Boyle’s Law: Pressure-Volume Relationship in Gases
The primary objective of this experiment is to determine the relationship between the pressure and volume of a
confined gas. The gas we will use is air, and it will be confined in a syringe connected to a Gas Pressure Sensor
(see Figure 1). When the volume of the syringe is changed by moving the piston, a change occurs in the
pressure exerted by the confined gas. This pressure change will be monitored using the Gas Pressure Sensor. It is assumed that temperature will be constant throughout the experiment. Pressure and volume data pairs will be
collected during this experiment and then analyzed. From the data and graphs, you should be able to determine
what kind of mathematical relationship was first established by Robert Boyle in 1662 and has since been known
as Boyle’s Law.
OBJECTIVES
In this experiment, you will
Use a Gas Pressure Sensor and a gas syringe to measure the pressure of an air sample at several different volumes. Determine the relationship between pressure and volume of a gas and describe that relationship with a mathematical equation Use LoggerPro software to collect data, analyze the data, and create useful graphs to interpret the data.
MATERIALS
Computer Vernier Gas Pressure Sensor Vernier computer interface (Lab Pro) 20 mL gas syringe Vernier Logger Pro software
PROCEDURE
- Log in to the laptop computers using your normal MEID username and password. Make sure that the computer is logging in to the “MCCCD-ORG” network.
- Open the Logger Pro software. Open the Boyle’s Law Lab file: File → Open → _Chemistry with Vernier → “06Boyle’s Law”
- Change the pressure units from kPa to atm.
- Position the piston of a plastic 20 mL syringe so that there will be a measured volume of air trapped in the barrel of the syringe (5.0 mL is a good place to start). Attach the syringe to the valve of the Gas Pressure Sensor, as shown below. A gentle half turn should connect the syringe to the sensor securely. Note: Read the volume at the front edge of the inside black ring on the piston of the syringe, as indicated by the arrow below.
- With the syringe connected to the Gas Pressure Sensor press the green button.
- Allow the air in the syringe to equilibrate with the Gas Pressure Sensor for a minute, then press the blue button. A window will pop up, type in the volume in the syringe as 5.0 mL, then click “OK”.
- Move the piston in the syringe by 2mL to a larger volume (do not move to smaller volumes). When the pressure reading is stable press the blue button. In the pop-up window, type in the volume in the syringe to the nearest 0.5mL, then click “OK”. a. The syringe may have a leak that allows air to enter while you are recording the data. If the pressure does not stabilize, but slowly goes up, the lowest pressure possible.
- Measure the pressure of the air in the syringe at various volumes. The best results are achieved by collecting at least seven data points. Move the piston of the syringe about 2mL, when the pressure stabilizes at the new volume, press the blue button again and type in the new volume. Continue in this manner, moving the piston an additional 2mL each time.
- When all of your data points have been collected, then press the red button.
PROCESSING THE DATA
- 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 inverse, k = P * V. If it is direct, k = P / V. Insert two new calculated columns into your data table: Pressure * Volume and Pressure / Volume.
- The graph that was created during data collection is a curve. A more helpful type of graph is a straight line. In order to create a graph with a straight line plot, a new calculated column for 1/Volume will need to be created.
- Insert a new graph of Pressure vs 1/Volume. Make sure that the new graph has an appropriate title, and that 1/V is being plotted along the x-axis and Pressure is being plotted along the y-axis.
- Determine the slope of the line in the new graph. The slope of the line will be equal to the value of the proportionality constant, k. a. The equation for a line is : y = (m*x) + b. For the graph you have created: y = Pressure, x = 1/Volume, m (the slope) = k, and b (the y-intercept) = the value in the box on the graph.
- Based on your data, what would be the pressure if the volume of the syringe was increased to 40.0mL. Show work to support your answer.
- Based on your data, what would be the pressure if the volume of the syringe was decreased to 2.50mL. Show work to support your answer.
- BONUS Create a new calculated column for 1/Pressure. Insert a new graph with 1/Pressure on the x- axis and Volume on the y-axis. Give this graph an appropriate title. a. Does this graph look the way you expected? Why or why not?
- Attach a printed copy of the data table and graphs to your lab.
Logger-Pro User Guide: CHM130LL Boyle’s Law Lab
Procedure - Step 2: Initial Start-Up Screen
Procedure - Step 3: Changing the Displayed Units from the Sensor
The initial screen in Logger Pro should tell you several things:
If the device is detected and which probe is connected o If the “Device not Detected” error message appears instead of an output reading, check all of the cable connections to the LabPro and the laptop. You may need to connect to a different USB port or reconnect the power cable. The default collection settings o For the Gas Pressure Sensor the default settings are Volume (mL) and Pressure (kPa) The output reading from the probe
Click on the LabPro icon
Click on the picture of the Gas Pressure Sensor
Choose the unit of “atm” from the menu
Creating a New Calculated Column in the Data Table
Processing the Data - Step 1:
Processing the Data - Step 2:
From the Data menu, choose “New Calculated Column”
In the pop-up box, Type in the “Name” and “Short Name” for the calculation
In the “Expression” box, type in your equation. o You must click on the “Variables (Columns)” button in order to choose the variables in your expression
Repeat the entire process for the second calculated column
Follow the above procedure, to create another calculated column for “Inverse Volume” Be sure to include the units
Inserting a Graph
Processing the Data - Step 3:
When a new graph is inserted, use the “Graph Options” menu to make changes to the graph
When a new graph is inserted, LoggerPro will automatically choose the last column in the data table. You will
need to change both the data set being plotted on the y-axis, and the data set being plotted on the x-axis.
From the Insert menu, choose “Graph” Right click the cursor inside the graph, a pop-up menu should appear, choose “Graph Options” Graph Options Tab – this is where you can title your graph
Select the “Axes Options” Tab
In the “Y-Axis Columns”, checkmark next to Pressure and uncheck “Inverse Volume”
In the “X-Axis” box, choose “Inverse Volume” from the drop down menu.
Click “Done”
This is a sample of what the printed data table and graphs might look like
