# Boyle's Law

## Background Information

In this lab we wanted to determine the relationship between pressure and volume for a confined gas. As we changed the volume of the syringe we noticed a change in the pressure. We saw that the temperature remained the same. From the graph we made when we collected the data we were able to see if the experiment was direct or inverse. Since the law was made by Robert Boyle he decided to name it after himself.

## Procedure

1. Prepare the Gas Pressure Sensor and an air sample for data collection.

1. Plug the Gas Pressure Sensor into Channel 1 of the computer interface.

2. 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.

3. Attach the 20 mL syringe to the valve of the Gas Pressure Sensor.

2. Prepare the computer for data collection by opening the file “06 Boyle’s Law” from the Chemistry with Computers folder of Logger Pro.

3. To obtain the best data possible, you will need to correct the volume readings from the syringe. Look at the syringe; its 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 5.8 mL. It is this total volume that you will need for the analysis.

4. Click to begin data collection.

5. 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.

1. 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 value stabilizes.

1. When the pressure reading has stabilized, click . (The person holding the syringe can relax after 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 but before entering a value).

2. Move the piston to the 7.0 mL line. When the pressure reading has stabilized, click and type in the total volume, 7.8 mL.

3. Continue this procedure for syringe volumes of 9.0, 11.0, 13.0, 15.0, 17.0, and 19.0 mL.

4. Click when you have finished collecting data.

6. In your data table, record the pressure and volume data pairs displayed in the table.

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

1. Click the Curve Fit button, .

2. 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 .

3. 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 again. When the curve has a good fit with the data points, then click .

8. 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.

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

## Graphs, Calculations, and Data Observations

We observed in this lab that as pressure decreases, volume increases. Since the 2 are opposites they are inverses of each other on the graph- making the graph curve. While pulling and pushing the syringe, I realized that it was really tough to do either because if it's a small space like we were given, then the air trapped inside would be more compressed. Bigger spaces give it more room to roam and be free. Smaller spaces do the completer opposite. Inverse things work this way.

## End Conclusion

This lab over Boyle's Law gave me a better understanding of how volume and pressure work and what happens to one if the other is altered. It was cool to see everything and the part one thing did if we pushed or pulled the syringe.