High School Density

by: Ron Perkins

Whether teaching general science, chemistry or physics, one of the first experiments I assigned was to determine the density of a metal using a set of different sized cylinders of aluminum in a tray.

Each Student:

• Determined both the mass and volume of a single assigned sample.
• Recorded their data point on a large classroom Mass vs. Volume Graph.
• Participated in a class discussion on: determining volume by different methods; drawing a straight line through the data points (including the origin); and calculating the slope of the line (rise over run)

Ron’s suggestions:
1. The set of aluminum cylinders (DEN-102) or PVC (DEN-120) are ideal beginning sets. The brass set (DEN-110) is interesting as one can determine the percentage of brass and zinc from the density using a CRC Handbook. The Polypropylene set (DEN-132) is interesting because the specimens float.

2. The Density Mystery Set (DEN-202) uses the element of surprise to teach students to trust their data. The set is made of two different black polymers, each with its own density. When the data is plotted, two different straight lines are produced, each with its own slope or density. Typically students will assume that the material is all the same and start questioning their own measurements. About half of the samples sink in salt water and half float

3. Our most popular set provides samples of 12 different substances (DEN-212). Also popular are the cubes of 6 metals (DEN-220). Once students have mastered mass and volume measurements, they find it interesting to be able to identify a substance by determining its density.

Advantages of using our Density Kits:

• Students learn that the density depends upon the ratio of mass to volume and not upon size of the sample.
• Students observe that some methods for determining volume are more accurate than others.
• Students discover that the slope of the “best” straight line usually gives a more accurate density value than calculating from a single piece of data.
• The teacher can immediately tell from the data points if a student needs help in measuring.
• The teacher can quickly see if all of the samples have been returned at the end of class.