Ideal Gas Law Lab

Today marks the start of the final week for our gas laws unit.  Class began with an entry task in the form of an ungraded Google Form quiz.  With our Unit 3 Exam scheduled for Friday, the quiz provides students with yet another opportunity to self-assess, and the results will help us focus our review as the week progresses.

For our work today, in preparation for our lab tomorrow, students will review the diagram below which illustrates the connection between the three phases of matter commonly encountered on Earth, and the vocabulary associated with changing phase.  Click on the image to learn a whole lot more about the science of phase change.

To help students visualize the least familiar of the phase change reactions (the solid-to-gas and gas-to-solid phase changes), we will watch a brief video below, complete with spooky soundtrack:

Next, students created a Google Doc and began pre-writing the Lab Report for the lab tomorrow in which we will actually conduct the experiment described in the entry task.  The intent is that students will follow their written Procedure tomorrow, collect data for the Results section, and understand the purpose of the lab (Introduction) so evaluating results in the Conclusion section will occur smoothly on Wednesday.  Lab reports will consist of:

  • Student name
  • Lab report title (Dry Ice Sublimation Lab)
  • Introduction (explain the purpose of the lab, including the connection between dry ice, sublimation, volume, and the Ideal Gas Law)
  • Procedure (numbered list of steps someone could follow to recreate your experiment)
  • Results (observations from the lab, focusing on mass and volume)
  • Conclusion (what was learned, comparison of calculated volume vs measured volume, three potential sources of error, and solutions to correcting those sources of error in the future)

Class Notes:

For homework, students received the Lesson 64 Worksheet to work this evening in preparation for class tomorrow.

For the second lesson of the Gas Laws mini-unit, students worked with dry ice and watched a couple of teacher demonstrations involving dry ice.  To begin class, students worked in small groups to measure the mass of a small amount of dry ice, quickly transfer the dry ice into a balloon, and then quickly tie off the balloon to trap the sublimated carbon dioxide gas. Students then measured and recorded the mass of the dry ice added to the balloon at the beginning and at the end of the experiment, then measured the volume of the bag after the dry ice finished sublimating in order to calculate the density of carbon dioxide gas.

While waiting for the dry ice to sublimate, students hypothesized about what they might observe when water ice and dry ice were heated on a hot plate, and also what would happen when water and dry ice were added to liquid water or vegetable oil (pictured below).

Dry ice in vegetable oil (left) and water (right)

Class Notes:

Note: For students who missed class due to testing today, please watch the videos below as a substitute for participating in the lab.

For the final day of this lesson, students need to finish writing their lab report (Google Doc, shared with Mr. Swart) detailing their results from the dry ice in a balloon experiment.  The lab report must include the following clearly labeled sections:

  • Introduction (explain the purpose of the lab, including the connection between dry ice, sublimation, volume, and the Ideal Gas Law)
  • Procedure (numbered list of steps someone could follow to recreate your experiment)
  • Results – observations from the lab, including:
    • initial mass of the dry ice converted to moles of CO2
    • initial and final mass of the dry ice and balloon
    • final volume of the balloon as measured during the lab
    • calculated volume of the balloon using Ideal Gas Law (PV=nRT)
    • amount of time it took the dry ice to fully sublimate in the balloon
    • calculation of the rate of sublimation (mass of CO2 divided by sublimation time
  • Conclusion: Compare the volume measured via the Ideal Gas Law to the volume measured during the experiment.  Explain why the numbers are different.  Suggest at least two possible sources of experimental error.

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