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Gases Edit

1. NJ standards addressed in the unit Edit

2. Length total (days and periods) Edit

  1. Particles in random motion – Particles in balloon (pressure), Newton’s Law, Intro to KMT
  2. Lab – use metal sphere and manometer to find Absolute temperature (K) mathematically (ALG 9.3.4); learn STP
  3. Gas Laws – Boyle’s Law, Charles’ Law; related problem-solving; Shoot water bottle rockets outside
  4. Gas Laws – Guy-Lussac’s Law, Avogadro’s Law; related problem-solving
  5. Lab – 2 periods (Boyle’s Law); Students present how they built a Lung Model
  6. Ideal Gas vs. Real Gas; KMT
  7. Simple derivation of P = (1/3)(N/V)mv^2  ; connecting PV=nRT (macroscopic) and P = (1/3)(N/V)mv^2 (microscopic)
  8. Graph models; jeopardy problems; every day connections
  9. Catch-up day; A few students present ‘Hot Air Balloon’ project.
  10. Test preparation/ review session (such as jeopardy problems)
  11. Unit Test

3. Prerequisite Edit

  • What students should know and have done before the start of the unit
    • Definition of moles: when Avogadro’s Law is introduced.
    • Newton’s second (momentum) and third law [needed for deriving P = (1/3)(N/V)mv^2]
    • Pressure: learned while observing balloon; learned with particles in random motion.

4. Goals Edit

ConceptualEdit

  1. Describe the kinetic-molecular theory and explain how it accounts for observed gas behavior.
    • Understand that matter consists of particles that are in random motion.
    • Learn that an ideal gas is a simplified model in which the particles are considered point particles that obey Newton’s Laws.
    • Learn that the pressure of an ideal gas is due to the collisions of the particles with the walls and depends on the frequency of the collisions and on the forces that particles exert on the walls during each collision.
  2. State the gas laws.
  3. Compare ideal and real gases: discuss and reason why gases under low temperature and/or high pressure do not act like ideal gases.
  4. Connecting macroscopic behavior of gases with microscopic explanations.
    • Connecting the two equations for Ideal Gas Law: PV = nRT(macroscopic) and P = (1/3)(N/V)mv^2 (microscopic) and discuss their significance on the behavior of gases.
  5. Explain what gas pressure means: Microscopic representation of pressure to the visible macroscopic change due to pressure.
  6. To understand and explain the interdependence of variables that affect the behavior of gases.


QuantitativeEdit

  1. Learn how to use the conceptual understanding of the ideal gas laws: PV = nRT(macroscopic) and P = (1/3)(N/V)mv^2 (microscopic) mathematically through experimentation.
  2. To understand under what condition the gas laws (Boyle’s, Charles, Avogadro’s) apply.

Procedural Edit

  1. Learn how to devise multiple explanations of the same phenomenon.
  2. Learn how to use different explanations (hypotheses) to make predictions about the outcomes of a new experiment and then reject one of the explanations based on these outcomes.
  3. Learn to represent gas processes by using graphs and models.
  4. Learn to differentiate between absolute pressure and gauge pressure

EpistemologicalEdit

  1. To understand the interrelatedness of microscopic and macroscopic mechanisms as they apply to gases.

5. Key Concepts and Cross-Curricula Links Edit

  1. The properties of gases are dependent on four variables: pressure, volume, temperature, and amount of gas.
  2. Ideal gas particles are assumed to have perfectly elastic collisions with each other. (There are no attractive forces/Van der Waals interaction with each other; they do not exert force on one another)
  3. Ideal gas particles consist of small (essentially without volume) particles that have mass.
  4. Ideal gas particles are separated from each other by relatively large distances.
  5. Ideal gas particles are in constant, rapid, random motion.
  6. Understanding how microscopic models affect the macroscopic variables in ideal gases.
  7. Understanding of the simplistic model of ideal gases to build upon the concept of kinetic-molecular theory.

6. Potential Difficulties Edit

  1. Students think they know about molecules but many of them do not understand why they believe what they believe. Often they just repeat what they have heard or read without any underlying understanding.
  2. Students often confuse air with empty space. Make sure that students understand that there is empty space between the particles of air.
  3. Students can be inconsistent with units – including absolute temperature.
  4. Students have difficulty understanding the behavior of gas particles microscopically. They usually say that the rubber walls of the balloon stop it from expanding and rarely say that the air particles outside the balloon hit the walls in the opposite direction.
  5. Students use the ideal gas law assuming that one variable is either directly or inversely proportional to another without considering that this only works if all other variables are constant.
    • Students believe that P is always inversely proportional to V when this only works when n and T are constant.
    • Students believe that P is always directly proportional to T when this only works when n and V are constant.
  6. Students are not consistent with the substance independence of the idea gas law. For example, students state that there would be a greater number of particles of the gas with the smaller molar mass.
  7. Students confuse between pressure and force.
  8. Students have difficulty connecting the microscopic behavior of gas particles with

7. Relevance Edit

  • When using every day examples, teachers cannot take it for granted that students have experienced certain things. For example, some students might have experienced the “pop” felt in his or her ears while riding an airplane or rapidly ascending in an elevator, while others have never been on an air plane or elevator.
  • Come equipped with alternative examples in case students not come across examples set up for the lessons (ex: potato gun, air plane, elevator, BB gun)

8. Curriculum Materials Edit

  • Materials: latex gloves, balloons, metal sphere, pressure gauge, cold and hot water, piston
  • Materials needed in lab: Plastic syringe apparatus (wood blocks as platform and base, piston, 25 mL syringe), ring stand, clamp, 5 chemistry textbooks, lab balance, plastic bottle, scissors, a rubber glove, balloons, and rubber bands
  • Textbook: Prenticed Hall Chemistry – Connections to Our Changing World (2nd ed.)
  • Reference book (Make formative assessment or activities of cool stuff): The Physics Active Learning Guide (2006), Five Easy lessons: Strategies for Successful Physics Teaching (2004)
  • Reference articles: Student understanding of the ideal gas law, Part I: A macroscopic perspective, Student understanding of the ideal gas law, Part II: A microscopic perspective.

9. Full Two Period Lab Edit

Lab: Gases

LEARNING GOALS OF THIS LAB:

  1. Investigate the effect of pressure on the volume of an ideal gas when other variables are held constant.
  2. Practice fitting functions to data in order to relate graphical patterns to mathematical expressions.

Boyle’s Law: Pressure and volume of a gas. You have a plastic syringe apparatus. Design an experiment to find the relationship between pressure and volume of a gas.

Available equipment: Plastic syringe apparatus1 (wood blocks as platform and base, piston, 25 mL syringe), ring stand, clamp, 5 chemistry textbooks, lab balance, air Safety: Safety goggles are not required in this lab. Be careful not to drop a book on your feet.

  • The apparatus consists of a graduated syringe with a movable piston. In order to read the volume of the trapped gas correctly, you must always read the measurement on the side of the piston that is in contact with the gas. Use the apparatus to compress a sample of air. As the pressure of the air changes, you will monitor and collect data on the resulting changes in volume.

Write the following in your report:

    1. State Boyle’s Law in your own words. Then write the mathematical equation for Boyle’s Law. Which variables are held constant?
    2. Examine the equipment that you have and decide what experiment you can design whose outcome you can predict applying the model of an ideal gas. Describe your experimental design with a labeled diagram.
    3. Use the hypothesis that the gas inside the container is ideal to predict the outcome of the experiment.
    4. What assumptions are you using in your prediction?
    5. List the sources of experimental uncertainty. How can you minimize them?
    6. Record your data in an appropriate format. Then use your data to make a graph from which a mathematical expression of Boyle’s Law can be obtained. How would you obtain pressure that is applied to the piston? Include experimental uncertainties when you record your data.
    7. Did the outcome of the experiment match the prediction within the uncertainties?
    8. What experiment did you design and perform: an observational, a testing or an application experiment? How do you know?


  • Build a Lung model

Observe the motion of your rib cage as you breathe. Available equipment: an open plastic bottle with the bottom cut off, a surgical glove, 15-inch balloons, and rubber bands.

    1. Describe in words how the process of inhaling and exhaling air from your lungs work.
    2. Using the suggested materials and construct an apparatus that can be used as a breathing model.
    3. Describe the model. Explain how the model fits the motion of your rib cage. List any assumptions that are inherent in this model.
    4. What experiment did you design and perform: an observational, a testing or an application experiment? How do you know?
  • Reference:

[1] [2]

10. Traditional and Alternative Summative Assessments Edit

Traditional AssessmentEdit

Sample question:

  1. Come up with an example seen in everyday life where the principals of the ideal gas law are used. Write about it and explain how the ideal gas laws affect your example.
  2. Answer the following question to decide if the expression for the pressure,

P = (1/3)(N/V)mv^2 in an ideal gas makes sense.

  • Why would you expect the pressure to depend on the total number of particles N in the container? Explain
  • Why would you expect the pressure to depend on the average speed of the particles squared? Explain
  • The particle size is neglected in this equation as is any interactions between gas particles. Discuss whether pressure of a real gas for which these are taken into account should be larger or smaller than the pressure of the ideal gas calculated according to the derived expression. The gases are in identical containers (same volume) and have the same number of particles with the same average of the square of their speeds.

Alternative Summative Assessment Edit

Student Projects Edit

  • Mentos and diet coke with nozzle for pressure determination

Out of Classroom Activities Edit

  • Shoot water bottle rockets outside (Volume constant; more air builds more pressure inside and causes the water bottle rocket to shoot high).
  • Opening a carbonated beverage bottle or can (to be done outside due to messiness)
  • Student project: how does a hot air balloon work?

11. Modifications for Different Learners Edit

  • For students who have difficulty hearing: use an FM (frequency-modulated) transmission device – a wireless microphone is clipped to the teacher’s shirt and the receiver is small enough to attach to the hearing aid of which the volume can be increased or decreased without disturbing other students in the classroom.
  • For students who are not familiar with the English language: allow them to use dictionaries during exams. (However, the teacher will need to check the dictionary to see if there are other resources available written or typed).
  • For group activities: make sure that diverse learners are grouped together so they can learn from one another. (Also not to have one group dominate the whole class discussion or organization).
  • Accommodations for project due dates: students with learning disabilities may or may not be provided with extra time to complete projects.
  • Accommodations for students with ADHD: keep them away from any conditions at which they can be more easily distracted such as next to a window, or noisy vent. Should be seated in the middle front where movement of other students are minimized as well, depending on their level of ADHD.

12. Equipment List and Resources Edit

  • Materials: latex gloves, Balloons, metal sphere, pressure gauge, cold water, hot water, piston
  • Materials needed in lab: Plastic syringe apparatus (wood blocks as platform and base, piston, 25 mL syringe), ring stand, clamp, 5 chemistry textbooks, lab balance, plastic bottles, scissors, a rubber glove, balloons, and rubber bands

13. Resource References Edit

  • LeMay, H. et al. Chemistry – Connections to Our Changing World. 2nd ed. Upper Saddle River: Prentice Hall, 2000. (textbook)
  • Etkina, E., Heuvelen, A. The Physics Active Learning Guide. San Francisco, CA: Addison Wesley, 2006. (Formative assessment, activities of cool stuff)
  • Knight, Randall D. Five Easy lessons: Strategies for Successful Physics Teaching. San Francisco, CA: Addison Wesley, 2004.
  • Kautz, C. H. (2005). Student understanding of the ideal gas law, Part I: A macroscopic perspective. Am. J. Phys, 73 (11), 1055-1063.
  • Kautz, C. H. (2005). Student understanding of the ideal gas law, Part II: A microscopic perspective. Am. J. Phys, 73 (11), 1064-1070.
  • Water Bottle Rocket: http://www.ent.ohiou.edu/~et181/rocket/analysis1.html
  • Online simulation – http://ccl.northwestern.edu/netlogo/models/GasLabTwoGas

14. Reflection on Unit Implementation Edit

  • Formative assessment: get the students to discuss and present group work upon the progress through the unit and completion of this unit.
  • Summative assessment: evaluate what students have learned in this unit.
  • Students’ performance in labs: their lab reports will reflect how much concepts they have built during the lessons.
  • Students’ motivation and engagement throughout the daily activities/lessons.
  • Level of students’ understanding according the Bloom’s taxonomy.
  • Use of an evaluation rubric.

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