Quick answer: An ideal gas is a collection of tiny, randomly moving particles whose average kinetic energy is proportional to the kelvin temperature. This AP Physics 2 lab on ideal gas law gives the aim, the equipment, the safety points, a step-by-step method, sample results and 7 analysis questions; the answers are on a separate page and the lab sheet is a free printable PDF.
A sealed syringe lets you vary the volume of a fixed amount of air while a sensor reads the pressure. In this lab you test whether pressure and volume are inversely proportional at constant temperature, and you use the graph’s gradient to estimate how many moles of air are trapped. It trains data analysis for AP Physics 2.
Level: AP Physics 2 (algebra-based) · Curriculum: AP P2 Unit 9
Aim
Test whether the pressure of trapped air varies as 1/V at constant temperature, and use the gradient of the graph to estimate the amount of air in the syringe.
Equipment
- 60 mL plastic syringe with luer connector
- pressure sensor and data logger
- short rigid tube (the dead volume is 3 mL)
- thermometer
Safety
Do not exceed the pressure rating of the sensor. Keep fingers clear of the plunger when you release it, and wear eye protection.
Method
- Connect the syringe, tube and sensor. Set the plunger to 20 mL and record the pressure and room temperature (294 K).
- Push the plunger slowly to 25 mL, 30 mL, 35 mL, 40 mL and 45 mL, waiting 20 s at each so the air returns to room temperature.
- At each setting add 3 mL dead volume to get the total volume V.
- Repeat the series once and average the pressures.
Results
Sample measurements (one student, pressure in kPa, volume in mL, p × V in kPa·mL):
| Syringe reading (mL) | V total (mL) | p (kPa) | 1/V (mL⁻¹) | pV (kPa·mL) |
|---|---|---|---|---|
| 20 | 23 | 101.0 | 0.0435 | 2323 |
| 25 | 28 | 83.1 | 0.0357 | 2327 |
| 30 | 33 | 70.2 | 0.0303 | 2317 |
| 35 | 38 | 61.3 | 0.0263 | 2329 |
| 40 | 43 | 53.8 | 0.0233 | 2313 |
| 45 | 48 | 48.5 | 0.0208 | 2328 |
Analysis questions
Question 1 Why the dead volume
Explain why 3 mL is added to each syringe reading.Question 2 Check the product
Calculate the mean of pV and its spread. Does the data support Boyle’s law?Question 3 The graph
Plot p against 1/V. Describe the shape and explain what it shows.Question 4 Gradient
Work out the slope of the line of best fit, in kPa·mL.Question 5 Amount of air
Convert the gradient to joules and use it with T = 294 K to find n.Question 6 Temperature control
Explain why the plunger is moved slowly and why a wait is needed between readings.Question 7 Improvement
Suggest one improvement that reduces the uncertainty in n.
