Pressure Bottle

Introduction

Use an ingenious pressure bottle to discover basic gas laws and properties of air.

Concepts

• Ideal Gas Law
• PV = nRT
• Air pressure
• Boyle’s Law

Background

The pressure bottle is an ordinary 1-L soda bottle with a tire valve mounted in the cap. When the cap is screwed on tightly and an airtight seal is obtained, the bottle can be pumped up just like a tire. The pressure can be varied inside the bottle by adding or releasing air using the air valve mounted in the cap. The bottle can be “inflated” using any pump that is normally used to pump up a tire. Pumps with a built-in pressure gauge are the safest, easiest and most convenient to use.

Two simple experiments are outlined below that utilize the pressure bottle. After completing these two experiments, conduct other experiments of your own design. Be sure to follow logical safety precautions when utilizing the bottle and air pumps.

Materials

Safety Precautions

The bottle is safe if used properly. The bottle should not be inflated beyond 60–80 psi. At very high pressures, the bottle might split, but it will not shatter. Eye protection should be worn during all experiments with the pressure bottle. Examine the bottle and cap prior to use for hairline or thicker cracks as these could lead to rapid decompression.

Disposal

All items are reusable and require no disposal.

Prelab Preparation

1. Place a small bead of petroleum jelly around the rim of the bottle.
2. Cap the bottle and tighten.

Procedure

Experiment A. Air Mass

1. Release all pressure from the bottle by pressing on the pressure release stem in the valve on top of the bottle. Remove the cap to release any remaining pressure in the bottle.
2. Replace the cap on the bottle. Weigh the bottle (with attached cap/valve) to the nearest 0.01 gram. Record the mass of the bottle of air. Initial mass ______________.
3. Pump air into the bottle to achieve a pressure of about 50 psi.
4. Weigh the bottle of air again. Record the mass to the nearest 0.01 gram. Final mass ______________.
5. Answer these questions:

a. How many grams of air were added to the bottle?
b. Does air have mass? Defend your answer.
c. Determine how many moles of air were added to the bottle.

1. Adjust the volume of air inside a 10-mL hypodermic syringe to read exactly 10.0 mL, then seal the syringe by firmly pressing a tip cap onto its open end. Remove the bottle cap and place the syringe inside the pressure bottle. Replace the cap and be certain that the cap is as tight as possible. Fill the bottle with air to a maximum pressure of 100 psi. What temperature change do you “feel” inside the bottle as it is being filled with air? Allow the temperature of the bottle to readjust to room temperature before proceeding with the experiment.
2. Mass the pressurized bottle. Record both its mass to the nearest 0.01 gram and estimate the volume of air inside the syringe to the nearest 0.1 mL. Note that the syringe calibrations are to the nearest 0.2 mL. Record this data on the Ideal Gas Law Data Sheet for trial 1.
3. Using a key, the tip of a pen, or other blunt object, release some of the pressure inside the bottle by pressing on the spring valve inside the tire stem until the volume of air in the syringe has changed 0.2–0.3 mL. Repeat step 2 by massing the bottle and recording the volume of air inside the syringe (trial 2). What temperature change is observed as the pressure is released? Does anything else happen inside the bottle if the pressure is released suddenly?
4. Continue the experiment by releasing more of the pressure from the bottle in small increments (a 0.2 mL–0.3 mL change in the syringe volume) until the pressure inside the bottle has been reduced to a little over one atmosphere (8–9 mL of air in the syringe). After each release, mass the bottle and record both the mass of the bottle and volume of air inside the syringe. After 5–6 trials, it may be necessary to allow the volume of air in the syringe to increase 0.5–1.0 mL for a noticeable change in mass to occur.
5. Finally, as a last trial, loosen the cap to obtain atmospheric pressure inside the bottle and mass the bottle as you did in Experiment 1. Record this mass and the volume of air in the syringe (assume it to be 10.0 mL) on your data table. Record the room temperature, barometric pressure, and its units in the space provided on the Ideal Gas Law Data Sheet.
6. Remove the cap and the hypodermic syringe from the bottle and completely fill the bottle with tap water. Using a 1-L graduated cylinder, measure the volume of water inside the bottle to the nearest 10 mL. Record the total volume of water in the space provided on the data sheet.

Student Worksheet PDF

11891_Student1.pdf

Teacher Tips

• Use a barometer to determine the atmospheric pressure or check with a local weather facility.

• If the bottle starts to leak air from the cap, remove the cap, run a bead of petroleum jelly around the liner of the cap, and retighten the cap on the bottle. Vaseline^® may also be used in place of the petroleum jelly.
• Ideal Gas Law is sometimes referred to as the Universal Gas Law.
• Use 10 mL as the approximate volume of the syringe. The volume of the actual syringe will be one possible “experimental” error. Some students may want to measure it by displacement.
• If the syringe is replaced, it may be necessary to trim the lip from the syringe in order to get it into the bottle. A wire cutters or sharp scissors can be used.
• If the bottle is replaced, be sure to avoid damaged bottles. Those with obvious flaws, scratches or marks should be avoided. Do not use water bottles since they are not designed to withstand high pressures like soda bottles.
• Your pump might dictate what bottle size you use. If an electric pump capable of 100 psi is used, a 1-L bottle is ideal. If a hand tire pump is used, a larger bottle may be required in order to get a significant mass of air. (This is because only about 50 psi is usually attained with a hand pump.)
• This is an excellent activity for teaching graphing. Some different graphs may be obtained using the sample data as follows:
  {11891_Tips_Figure_1}

Sample Data

1-L bottle
Volume: 1.04 L (1050 mL – 10 mL)
Room Temperature: 24 °C
Barometric Pressure: 30.02 inches Hg
Theoretical P/n ratio, RT/V = 23.4
Average P/n ratio: 24.2
Slope: 23.4
This is a perfect lab to use a graphing calculator. Have your students enter their data into their calculators, and then load the data into a PC using Vernier’s Graphical Analysis Program^®. The graph on the left, is a typical graph produced by Vernier’s Graphical Analysis Program for Windows.

References

Special thanks to Walter Rohr for bringing this idea to us. Walter thanks Pat Kavanah, a retired teacher from Monroe–Woodbury High School, NY, for the concept behind the bottle and further thanks Al Definer for contributing the idea of using a syringe as a pressure gauge.