Chapter 3 • Scientific Measurement
Section 3.2. 3.3, and 3.4 To determine the densities of unknown metals.
An old riddle asks "Which is heavier, a pound of feathers or a pound of
lead?" The question is nonsensical, of course, since a pound of feathers
and a pound of lead both weigh the same, one pound. Nevertheless,
there is a clearly something different about a small lead brick and a large
bag of feathers, even though they weigh the same. The key to answering
the riddle is undersranding the relationship that exists between a
substance's mass and the voltume it occupies. This relationship is
expressed by the physical property called density. Density is defined as
the ratio of a substance's mass to the volume it occupies.
25-mL graduated cylinder
In this experiment, you will measure the mass and volume of several
unknown materials. You will then use your data to explore the
relationship between the mass and volume of the materials and to
calculate their density.
After performing this lab, if someone asks you the riddle about
feathers and lead, you can explain to them the difference between
weight and density.
In this lab, observe all precautions, especially the ones listed below. If
you see a safety icon beside a step in the Procedure, refer to the list below for its meaning.
As you perform the experiment, record your data in Data Tables 1 and 2.
1. Determine the mass of two different unknown metal samples
to the nearest 0.0 I gram, using a centigram balance. Record the
masses in Data Tables 1 and 2.
2. Find the volume of each metal sample by water displacement.
Fill a 25-mL graduated cylinder about half-full with water,
measure the volume, and record as "volume of water alone" in
Data Table I. Tilt the graduated cylinder and carefully slide one
of the metal samples down the side. Make sure the metal
sample is completely submerged in the water. Measure the
volume and record the measurement as "volume of water +
metal" in Data Table I.
Repeat Step 2, using the other metal sample. Dry both samples
and return them to your teacher.