# Boyle's Law

## Background Information / 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 the gas.
• Describe the relationship between gas pressure and volume in a mathematical equation
• Use the results to predict the pressure at other volumes.

## Background Information / Materials

• computer
• Vernier computer interface
• Logger Pro
• Vernier Gas Pressure Sensor
• 20mL gas sryinge

## Procedure

Prepare the Gas Pressure Sensor and an air sample for data collection.
• Plug the Gas Pressure Sensor into Channel 1 of the computer interface.
• With the 20 mL syringe disconnected from the Gas Pressure Sensor, move the piston of the syringe until the front edge of the inside black ring is positioned at the 10.0 mL mark.
• Attach the 20 mL syringe to the valve of the Gas Pressure Sensor

Prepare the computer for data collection by opening the file "06 Boyle's Law" from the Chemistry with Computers folder of Logger Pro.

To obtain the best data possible, you will need to correct the volume readings from the syringe. Look at the syringe; it's scale reports its own internal volume. However, that volume is not the total volume of trapped air in your system since there is a little bit of space inside the pressure sensor. To account for the extra volume in the system, you will need to add 0.8 mL to your syringe readings. For example, with a 5.0 mL syringe volume, the total volume would be a 5.8 mL. It is this total volume that you will need for the analysis.

Click Collect to begin data collection.

Collect the pressure vs.volume data. It is best for one person to take care of the gas syringe and for another to operate the computer.

• Move the piston to position the front edge of the inside black ring at the 5.0 mL line on the syringe. Hold the piston firmly in this position until the pressure valve stabilizes.
• When the pressure reading has stabilized, click Keep. (The person holding the syringe can relax after Keep is clicked.) Type in the total gas volume (in this case, 5.8 mL) in the edit box. Remember, you are adding 0.8 mL to the volume of the syringe for the total volume. Press the Enter key to keep this data pair. Note: You can choose to redo a point by pressing the Esc key (after clicking Keep but before entering a value.)
• Move the piston to the 7.0 mL line. When the pressure reading has stabilized, click Keep and type in the total volume, 7.8 mL
• Continue this procedure for syringe volumes of 9.0, 11.0, 13.0, 15.0, 17.0, and 19.0 mL.
• Click Stop when you have finished collecting data

In your data table, record the pressure and volume data pairs displayed in the table (or, if directed by your instructor, print a copy of the table.)

Examine the graph of pressure vs. volume. Based on this graph, decide what kind of mathematical relationship you think exists between these two cariables, direct or inverse. To see if you made the right choice:

• Click the Curve Fit button
• Choose Variable Power (y=Ax^n) from the list at the lower left. Enter the power value, n, in the Power edit box that represents the relationship shown in the graph (e.g., type "1" if direct, "-1" if inverse). Click Try Fir
• A best-fit curve will be displayed on the graph. If you made the correct choice, the curve should match up well with the points. If the curve does not match up well, try a different exponent and click Try Fir again. When the curve has a good fit with the data points, then click OK

Once you have confirmed that the graph represents either a direct or inverse relationship, print a copy of the graph, with the graph of pressure vs. volume and its best-fit curve displayed.

With the best-fit curve still displayed, proceed directly to the Processing the Data section.

## Conclusion

In the lab we conducted today, we discovered an inverse relationship between pressure and volume. This was shown in the data we collected and in the graph displayed above. As one of them (pressure or volume) increases, the other decreases.

Boyle's Law stated that for a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional. This means that when a certain gas is kept under a constant temperature, as pressure increases, volume decreases. In our experiment, we recorded pressure increased (harder to push down the syringe) as the volume decreased (less gas in the syringe).