Click here for Example 1 which outlines the process in more detail.

Day 1: Explore

Topic: Effusion and Diffusion.

Task: To compare the effusion rates of helium gas and nitrogen gas.

Materials: Three balloons, measuring tape, helium tank, your breadth (for nitrogen gas…yes, I know, this is a HUGE REACH, but whatever, it was fun..), scotch tape, a thumbtack, and a stopwatch.

Procedure: We use a guided inquiry approach during exploration days. Whenever appropriate, I try to put the procedure development process in the hands of the students. In this lab, I gave students 15 minutes to brainstorm a procedure of their own. Students had many different procedures, but after pulling their hair for 15 minutes, the majority of groups developed a process that looked something like this:

1. Fill one balloon with nitrogen gas.
2. Fill the other balloon with helium gas to the same volume using tape to measure diameter.
3. Blow the third balloon up to ~ 2/3 the size of the other two balloons. Use this balloon as the “reference”.
4. Secure a piece of tape in nitrogen filled balloon.
5. Insert thumbtack into tape.
6. Remove tape and record time (sec) it takes for balloon to deflate to size of reference balloon.
7. Repeat for nitrogen.
8. Estimate rate by taking the reciprocal of the time.

See images of process below:



Data Analysis: Students then entered data into a class chart where effusion rates were gather across groups, a class mean was taken and percent error data was calculated. See images below:



Model: Students worked in groups to analyze the data and create a model. The group mean diffusion rate was ~ 2.6! Students ultimately, with a bit of prodding :), realized that the this was approximately the square root of 7 (how many times larger the molar mass of nitrogen is than helium). Students recorded this data and conclusion in their notebooks and were assigned a lecture on effusion and diffusion for homework (the flip).

Night 1: Flip (Instructional Video)

For homework, students were assigned an instructional screencast video that addressed their observations from the laboratory, formally defined effusion and diffusion, presented the equation for Graham’s Law, and solved a few example problems. Students reflected on the video via a google form embedded below, where they provided a 5 sentence summary of the video and entered in answer to the second worked example (video ended abruptly in the middle of the second example). Below is a quick snippet of the video:

Below is a screenshot of the google form used for reflection:



Day 2: Apply

Goal: To apply knowledge of Graham’s Law.

Task 1: Work individually and collaboratively to practice released AP Chemistry problems related to Graham’s Law of Effusion-Diffusion.

See examples of problems below:



Task 2: Use new assimilated knowledge of Graham’s Law to verify the equation with respect to diffusion, rather than simply effusion (See Day 1).

Materials: Clear plastic straw, two cue-tips, ammonia, toilet boil clear (source of hydrogen chloride), ruler.

Procedure: We again guided inquiry approach, however, because students have already explored this concept and have viewed and instructional screencast, the goal is to verify, rather than develop, Graham’s Law.

1. Simultaneously place ammonia and toilet bowl cleaner soaked cue-tips in both ends of a clear plastic straw.
2. Work together on practice problems while waiting.
3. Measure distance from top of cue-tip to cloudy ring in straw (location where ammonia and hydrogen chloride gas meet).
4. Calculate rate (distance/time) for each gas.
5. Determine value of rNH3/rHCl and share data.
6. Evaluate class mean and calculate percent error.

See images of process below:


Night 2: Prepare for Quiz

Day 3: Quiz and new cycle begins