There are hundreds of lab activities out there on the concept of density, what sets this lab apart from others that I have seen is the simple method for determining the density of air using readily available supplies, pictures included. (Also, this lab includes a great preview activity of the topic of density – Do Potatoes Sink or Float? Described below. As always, this lab is adorned with the pictures that you and your students have come to expect from eyeLEARN.)
Lesson Description: I usually begin this activity by prompting curiosity in the topic with an activity that I saw on late night TV with Dave Letterman called, sink or float? I start off by holding up a potato and asking the students, do potatoes sink or float? After some lively discussions I have the students write down their hypotheses in the ‘Notes & Observation’ section of the lab, (you could also do this in a notebook or lab journal). After students write down their theories I drop the potato into a large beaker of water and observe what happens, (do you know?). Next I cut the potato in half and ask the same question. I continue to cut the potato into smaller and smaller pieces to see if there is a change in results. After these experiments and observations, we discuss the concept of density on micro and macroscopic levels to see if this can help us to understand what’s going on here.
After usually on class of demos and discussion about the concept of density student go to the lab and calculate the density of 4-6 different substances. I usually do four items, 1). A regularly shaped piece of aluminum, 2). Water, 3). Irregularly shaped piece of potato, and finally 4). Air.
I prefer to do this lab an inquiry based activity so students must decide how and what they will use to obtain the most exact value for the densities of each substance. Some stipulations that I do give are, a). must do the items in the order listed, b). they cannot get the aluminum wet, (i.e. must use a formula to find volume – dropping metal shapes into glass graduated cylinders… not good!), c). they cannot change the crazy shape of potato, (so they must use water displacement), d). for the air students are given a 60 mL syringe that has a rubber tube attached to its end, two clamps, and a stiff metal wire. Students are not told how they are to use these materials, but that finding the density of air is ‘clearly easy’ to do so with them. They are told not to get the equipment wet.
Many students struggle how to find the density of air with these items – in a good way. Usually when I do this one group stumbles upon the answer and there is a satisfying, EUREKA!, moment that other students observe creating a cascade of Ah Ha’s. [So here’s the secret. First weigh all of the items described on a scale that is at least precise +/- 0.01 grams. Next, the clamps are placed onto the tube and the plunger is pulled back. This creates a vacuum which means that if you let go of the plunger it will snap back! To prevent this from happening a hole is made in the side of the plunger so you can put the wire into this hole and prevents the plunger from being sucked back, (pictures of this apparatus are included in the lab as well as pictures of each step of the procedure.) Now the empty syringe can be weighed and the mass of air determined by subtraction. The volume of air can be determined from the scale on the side of the syringe.)
DENSITY LAB: (Potato, aluminum, water, & air)
Chemistry, Physical Sciences, and; College-Level Classes: What you get…
~ 7 pages
Activity cover sheet(s)
Background and instructions (see above also)
Prelab conceptual questions and illustrations
Results and conclusion questions
Practice and review questions all with illustrations
Optional Competency Grading
This unit activity meets or exceeds 21st Century and STEM learning expectations, and Common Core learning outcomes. Note: although eyeLEARN activities fulfill multiple CCSS, specific CCS standards are not listed because most activities are designed to be used over many graded levels so the specific CCSS may be different depending upon these factors. For a list of CCSS in your state please visit- www.corestandards.org
New – Integrated Holistic QPA, (that’s Quality Performance Assessment) created by me! This activity requires NO RUBRICS! The rubric is integrated into the activity itself. Much less work for you and far more meaningful to your students.
Working to change STEM to STEAM.