Purpose:
To validate Boyle’s Law using a Boyle’s law apparatus to collect and graph data comparing volume change with pressure change.
Safety/Procedure:
Person reading volume of the cylinder should wear goggles (to avoid eye injury if books fall)
*Note: do NOT copy this procedure word for word in your formal report—summarize briefly in your own words—or no points!
1. Work in groups of three—one person holding the apparatus, one stabilizing books, and one reading the piston. Please switch roles with the different trials
2. Adjust the initial volume to equalize with atmospheric pressure at 40 ml. (Just draw in air—the pressure of the air inside the syringe will equal atmospheric pressure then cap the opening of syringe)
3. Place the syringe in the cavity of the wood. The tip should just touch the counter surface. Place the other piece of wood on top of syringe.
4. record initial volume (in data table below) at initial

piston pressure (zero pressure)
5. Have one person steady the books and another reads volume.
6. Place one text book on wood, record new volume
7. Repeat step five with two books, three books, four books, and five books.
8. Remove all the books from the piston and reset the apparatus to the initial volume recorded in step two.
9. Repeat steps 4-7 two more times, remembering to reset the apparatus between sets of trials.
Data Collection:
P books
V
1
(ml) V
2
(ml) V
3
(ml) V avg
(ml) 1/V avg
(mL -1 ) P total
P total
x V avg
0
1
2
3
4
5

Data Analysis:
1.
Find the average of each set of three volumes and record these averages in the data table. (please show work)
2.
Please graph your results on one piece of graph paper. (Pressure—units are “books” on x-axis, volume (ml) on left y-axis) Does the graph indicate a linear relationship (proportional) between the pressures and their corresponding volumes? Explain
3.
According to Boyle’s law, pressure and volume have an inversely proportional relationship. If this idea is correct, you should obtain a linear relationship (straight line) when you plot pressure versus the corresponding inverse of the average volume. Calculate the inverse 1/V avg
(mL
-1
) of each volume and record these values in data table. (show your calculations!)
4.
Using the labels on the right vertical axis (1/V avg
(mL
-1
) and a pen or pencil of a different color,
Plot the pressures versus their corresponding 1/V avg
values.
5.
Do these points suggest a linear relationship? Explain
6.
The line obtained for the second plot crosses the y-axis of the graph above the origin, which tells you that there is pressure on the gas even when there are no books on the piston. Consider that
1/V = 0 only when the total pressure on the gas is zero (and the volume is infinitely large). The additional pressure is the atmospheric pressure. To find this pressure in units of books, extend the plot of P vs 1/V to the point where it intersects the x-axis. At this point, 1/v = 0. The scale distance from this point to the origin is the atmospheric pressure measured in books. Using your graph, determine this value.
7.
Add the value you found for atmospheric pressure to the pressure in books for each trial and record these values of P total
in the table.
8.
Calculate the product of P total
x V avg
for each trial and record these values in the data table.
Conclusion:
1.
What pattern does the graph of P versus V suggest?
2.
How does your graph of P versus 1/V illustrate Boyle’s law?
3.
Look at the values you calculated in the last column of the data table. How do they compare?
4.
What do these values mean in terms of Boyle’s law?
Optional Extra Credit:
Research the four-step cycle of the operation of the cylinders and pistons in an automobile engine. Find out what happens in each step of the cycle and determine and how the principle of Boyle’s law applies to the function of the engine. (credit given depends on quality of research)