Pressure vs. Temperature Gas Law Apparatus
Gas Law Apparatus
Materials Included In Kit
Mason jar, 250-mL, with special large rubber adapter*
Rubber stoppers, size #1, 3*
Syringe with stopcock (Luer-lock female spinner), 60-mL*
Syringe with tightening cloth*
Syringe extenders, 3*
*Gas law apparatus parts
Additional Materials Required
Beakers, 600-mL, 2 (for hot water and ice)
Beaker, borosilicate glass, 1-L
Thermometer, digital (for apparatus), and stopper
Thermometer for water bath
Save all equipment for future use.
- A common kitchen “turkey baster” is a convenient large pipet to remove ice water from the bath and also to add tap water or hot water as needed (steps 11, 17).
- If you are working with air, the Mason jar is already filled with air. To fill the jar with another gas such as oxygen, nitrogen, carbon dioxide, or methane, remove the pressure gauge and open both stopcocks A and B.
- Collect oxygen or carbon dioxide in the jar by the upward displacement of air. Nitrogen and methane can be collected by the downward displacement of air. A cylinder of compressed gas is best for this but you can also use a plastic bag–gas collection and distribution kit. Once the gas is flowing into the Mason jar count to 10 and shut off the gas flow.
- Special care must be taken during the assembly, use and dismantling of the Gas Law Apparatus to be certain that the apparatus is always “gas tight” and that parts of the kit are not damaged. The rubber stopper was manufactured specifically for this kit. The stopper should be dry and clean.
- The following information describes the assembly of the Gas Law Apparatus.
Clean the stopper and the mouth of the Mason jar with a dry cloth. Insert the rubber stopper into the mouth of the Mason jar. Force the stopper as far as possible into the Mason jar. The lower surface of the rim should be in complete contact with the top edge of the jar. Take note that two of the holes in the stopper are larger than the third hole. Syringe extenders will be inserted through each of the larger holes. Complete the insertion of the first syringe extender before inserting the second syringe extender. Insert the threaded end of a syringe extender into one of the larger holes in the rubber stopper. Push the syringe extender into the hole so that only the top 5 mm of the threaded part of the syringe extender is visible above the rubber stopper. You may not be able to complete this step without some mechanical assistance, as described.
- Place the rubber stopper on a solid surface. With a hammer, gently tap the Luer Lock end of the syringe extender until a depth of only 5 mm of the threaded end of the syringe extender is exposed above the rubber stopper.
- Invert the Mason jar and the rubber stopper assembly (Luer Lock of the syringe extender facing down) on the hard surface. Grasp the Mason jar with both hands and push down on the hard surface until a depth of only 5 mm of the threaded end of the syringe extender is exposed above the rubber stopper.
- A digital thermometer must be present in the small hole in the large rubber stopper. The experiment cannot be performed with an unplugged hole through the large rubber stopper. Remove the digital thermometer only if the apparatus is not going to be used in the very near future. Insert the thermometer through the hole of a size #1 one-hole rubber stopper. This is not designed to be a tight fit. A clamp will be used later to hold the whole assembly in place after it is placed in a water bath. Moisten your fingers with a drop of water. Moisten the long metal tube by rubbing your moist fingers along the length of metal tube. Hold the plastic housing of the digital thermometer and insert the metal tube through the small hole in the large rubber stopper. Push on the plastic housing until the tip of the long metal tube is approximately 1 cm above the bottom of the Mason jar.
- Push the threaded metal extension of the pressure gauge as far as possible into the hole of a small (#1) rubber stopper. Push the female end of a female/spinner stopcock as far as possible into the other end of the rubber stopper. Ideally, the pressure gauge extension and the female end of the stopcock should meet in the rubber stopper. This will be referred to as the “Pressure Gauge Assembly.” Connect the spinner end of the stopcock (this stopcock will be referred to as stopcock A) to one of the syringe extenders in the large rubber stopper. Adjust (rotate) stopcocks A and B so that their handles point outward (toward the brass ring). When tightening or loosening the spinner on a stopcock, grasp the barrel of the stopcock with the finger and thumb of one hand and grasp the spinner in the finger and thumb of the other hand. When opening or closing the stopcock, grasp the blue handle of the stopcock with the finger and thumb of the other hand. Be careful that stopcock A, attached to the pressure gauge, is always closed (the handle must be perpendicular to the barrel of the syringe) whenever you are preparing to inject gases into the system. Open stopcock A (the handle must be parallel to the barrel of the syringe) only when you are ready to read the pressure gauge. Connect the female/spinner stopcock (this will be referred to as stopcock B) to the other syringe extender.
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering Practices
Developing and using models
Planning and carrying out investigations
Disciplinary Core Ideas
MS-PS1.A: Structure and Properties of Matter
MS-PS3.A: Definitions of Energy
HS-PS3.A: Definitions of Energy
Cause and effect
Scale, proportion, and quantity
Energy and matter
MS-PS1-4. Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.
MS-PS3-4. Plan an investigation to determine the relationships among the energy transferred, the type of matter, the mass, and the change in the average kinetic energy of the particles as measured by the temperature of the sample.
HS-PS3-2. Develop and use models to illustrate that energy at the macroscopic scale can be accounted for as a combination of energy associated with the motion of particles (objects) and energy associated with the relative position of particles (objects).
Answers to Questions
- Plot or obtain a graph of pressure on the y-axis versus temperature on the x-axis. Note: Extend the scale of the x-axis from –300 to 100 °C.
- Looking at the data, is the pressure of a gas proportional to its temperature over the temperature range studied? Use a computer or calculator to generate the best-fit straight line through the data points.
A plot of temperature versus pressure gives an excellent straight line through the data points. This means that the pressure of the gas is proportional to temperature over the entire temperature range studied. See the graph for the best-fit straight line.
- Extend the straight line backward to estimate the x-intercept, the point at which the line crosses the x-axis. The x-intercept corresponds to absolute zero—the minimum temperature that would be needed to reduce the pressure of a gas to zero. What is the estimated value of absolute zero? How close is your value of absolute zero to the accepted value?
The estimated value of absolute zero is –265 °C. The actual value is –273 °C. The error is due to the large distance from the experimental data points to the extrapolated value. Better accuracy would be possible if one could obtain pressure readings at below-zero temperatures.
- Guy-Lussac’s law is explained on the basis of the kinetic-molecular theory for ideal gases. Would you expect to see greater deviations from ideal gas behavior at high or low temperatures? At high or low pressures? Explain.
Deviations from ideal gas behavior become more important at low temperatures and at high pressures. At low temperatures, attractive forces between the gas molecules become more important (remember, in the KMT the presence of attractive forces is ignored). At high temperatures, gas particles have large kinetic energies, which helps them “overcome” the attractive forces between molecules. At high pressures, the gas particles are forced closer together and the attractive forces between them become stronger.
- Safety warnings on aerosol cans illustrate a real-world application of Guy-Lussac’s law. Most aerosol cans will have a warning similar to the following:
“Do not place in hot water or near radiators, stoves or other sources of heat. Do not puncture or incinerate container or store at temperatures over 120 °F.”
Use the results of this experiment to predict what will happen to the gas in an aerosol container at elevated temperatures and to explain why the warning label is needed.
An aerosol can is a constant volume container and is already “pressurized” (the internal pressure is about 2.5 atm). At high temperatures, the pressure of the gas inside the container will increase to an unacceptably high level and the container essentially becomes a bomb ready to explode. Note to teachers: There is a second reason for the safety warning. Many aerosols contain flammable gas propellants, which will ignite when released suddenly at high temperatures.
The Gas Laws Apparatus Kit is manufactured by Irwin Talesnick of S17 Science in Canada. Visit the S17 website at www.s17Science.com for information about additional gas laws equipment, supplies, experiments and instructions.