Boyle's Law

Pressure-Volume Relationship in Gases

Background

This lab shows how the pressure of a gas changes as the volume is either increased or decreased, which is an inverse relationship, as one increases the other decreases. In our lab, our syringe was filled with the same air that we breathe, although it is also possible to test the pressure of any form of gas such as pure oxygen or pure CO2.

Procedure

To begin this lab you will need the following..

- A 20 mL gas syringe

- Vernier Gas Pressure Sensor

-Computer

-Vernier Logger Pro software


To begin this experiment, prepare the syringe with the slider set to to 10 mL mark, at this point you will put your plug on the nozzle of the syringe, which should be attached to the gas pressure sensor. At this point you will press COLLECT on the Logger Pro top menu, this will record the normal pressure at the natural, unstressed volume in the syringe. After waiting for roughly 10-15 seconds, press KEEP on the top menu of Logger pro, your data should be recorded in the table to the left hand side of your screen. Keep in mind that your volume is not the exact value of the volume in your syringe, to find the adjusted values for value, add .8 mL to your original volume of gas. This accounts for the small amount of air held in the tip on the nozzle.


Now that you have your first value, repeat the same process for step 2 where the volume of air is 7 mL. WITHOUT REMOVING THE CAP, depress the slider to the 7 mL mark. and line up the holes on the slider and the body of the syringe to place a holding pin through the aligned slots. (The best way to do so is to have one person align the slots and hold the slider down while another person places the pin) Once the pin is in place, press COLLECT on your top menu bar and wait 10-15 seconds once again. Do not forget to press collect and check that your data has been recorded on the data table to the left. Once the data has been collected, repeat the same process for the volume of 9 mL.


The same process will be repeated for the remainder of the tested volumes, the only difference being that instead of pressing the slider down, you will be pulling the slider up toward the top of the syringe. Once again, the best method is to have one person hold the slider while the other places the pin. Repeat the previous tests for the volumes of 11 mL, 13 mL, 15 mL, 17 mL, and 19 mL.


Once finished, you should see your data in the table to the left. The numbers in the left column will show the volume values, the column on the right will show the pressure values. Next, you will find a line of best fit for your graph; click the CURVE FIT button on the top menu bar, a menu should appear in the center of your screen. Choose variable power from the list in the drop down bar in the lower left corner, also edit the POWER EDIT box, typing either 1 if the relationship shown is direct, or -1 if it is inverse. You will be given a TRY FIT option, which will display a curve, adjust your curve until you see that the shown curve closely fits your data. Once you have found your best fit curve, proceed to PROCESSING THE DATA.

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What I Learned

In this experiment I found that many of my previous theories about Boyles law were proven wrong, one of them being that I first thought that pulling the slider of the syringe back was difficult for the same reason that it was difficult to press it down. After seeing the syringe and performing the experiment first hand I realized that when the slider is pressed down the air molecules are compressed more tightly than they naturally want to be, but when the slider is pulled out the molecules are stretched apart and pulled farther from each other than they want to be, which is why there is so much resistance. Overall, this lab was very helpful to identify Boyle's law, whenever I am taking a quiz or test I can remember the tests from this experiment and it helps me to put numbers on a paper into something I can put my hands on.