In this lab, students stack books on top of a closed syringe and use the volume change to determine the mass of the books.
By the end of this lesson, students should be able to
- calculate pressure of a gas.
- explain the relationship between pressure and volume in a gas.
This lesson supports students’ understanding of
- Gas laws
- Ideal gas
Teacher Preparation: 10 minutes
Lesson: 40 minutes
For each group:
- Large, graduated, plastic plunger syringe
- Bunsen burner
- Textbooks (4)
- Computer with internet access
- Always wear safety goggles in the lab.
- Always use caution around open flames. Keep flames away from flammable substances.
- Students should wash their hands thoroughly before leaving the lab.
- When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
- Have students make sure that their syringes are completely sealed before beginning the lab. Any air leaks will cause erroneous results.
- Make sure that students are all using the same edition of the textbook and that they look up the correct edition online.
- You can have students test different gases. You could prepare syringes with different gases ahead of time and keep a class set to use from one year to another. Students should find that no matter what gas is in the syringe, the same number of books will result in the same compression.
- In order to find the actual mass of a textbook, teachers could weigh the textbook beforehand, and provide students with the value in order to solve the percent error calculation. Alternatively, if a classroom scale has the capacity, students should find the mass themselves and use it for the percent error calculation.
For the Student
- Obtain a large graduated, plastic plunger syringe. Using the low-heat setting of a Bunsen burner, gently melt/soften the tip and press it firmly on a solid nonstick surface to seal it.
- Measure the inner diameter of the syringe. Record the size in the data table.
- Reinsert the plunger. Push it in and allow it to settle in a desired spot. Record the volume of the air in the syringe in your data table.
- Now you are going to increase the pressure by adding books (carefully!!) to the top of an inverted, supported, vertical syringe. Record the volume after you add each book.
Volume of air
|Number of books||0||1||2||3||4|
- Convert the syringe diameter into inches.
- Find the cross-sectional area of the syringe in inches2 (A = Πr2).
- Look up what the ambient air pressure pushing down on the syringe. Convert that to pounds per square inch (14.7 psi = 760 mmHg = 1 atm).
- Assuming that the temperature of the gas stays constant, the gas occupies _______ mL under ________ psi of pressure.
- Using Boyle’s Law (P0V0 = PxVx where x = largest number of books), calculate how much pressure (in psi) the gas was under.
- How much of that pressure was the ambient atmospheric pressure?
- So how much of the pressure was from the books?
- The formula for pressure at psi (lb/in2) is pressure = mass/area. Find the mass of one book in pounds. Do this using two different pieces of data?
- According to Boyle’s Law, which relationship should be linear?
- P vs. V
- P vs. 1/V
- P vs. V2
- Using your data, on a piece of graph paper, plot each relationship in question one to verify your experiment demonstrated Boyle’s Law.
- If the plunger is not removed, will the mass of the gas change? Explain.
- If the plunger is not removed, will the moles of gas change? Explain.
- Using a classroom scale find the actual mass of the textbook.
- What is the percent error of your result?