Text reference:
Section s 2.7-2.10
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 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 understanding the relationship that exists between a substance’s mass and the volume it occupies. This relationship is expressed
by the physical property called density. Densityis defined as the ratio of a
substance’s mass to the volume it occupies.
Density = mass of substance (g)/volume of substance (mL)
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 mat~ri,als and to calculate their
After performing this lab, if s£meone asks you the riddle about
feathers and lead, you can explain to them the difference between weight
and density.
Measure the mass and volume of several samples of matter, using the
centigram balance and the method of water displacement.
Infer whether there is a constant relationship between mass and volume for each unlmown substance.
. Compute the density of a solid object from its mass and volume.
safety goggles
1 25-mL graduated cylinder
8 centigram balances/class
1 ruler
metal samples
paper towels
Mass, Volume, and Density 37
Note the Safety Symbol used here. Review safety information on
pages 7-9.
Always wear safety goggles when working in the lab.
As you perform the experiment, record your data in Tables 4.1 and 4.2.
1. Determine the mass of two different unknown metal samples to the
nearest 0.01 gram, using a centigram balance. Record masses in Tables
4.1 and 4.2.
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 Table 4.1. 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 Table 4.1.
3. Repeat step 2, using the other metal sample. Dry both samples and
return them to your teacher.
~8
Experiment 4
Class
Name-
Date
Table 4.1 Indlv~dualDataandCalculat~ons’
Metal A
Metal B
Additional Metal Sample
mass (g/
volume of water alone (mL)
volume of water + metal (mL
volume of metal ~mL)
deusity of metal (g/mL/=
Table 4,2 Class Data: Mass and Vo]ume of Metal Samples
Metal A
Lab Pair
mass (g) volume ~mLl
Metal B
mass (g)
volume ’~mL)
Additional Metal Sample
mass (g) volume (mL)
Mass, Volume, and Density 39
Class
_ Date
..... .72f~-~
1o Comput~e the volume of each metal sample, using data from Table
4.1. Compute the density of each metal sample, showing your work (including units), in Table 4.1. Remember,
density = mass (g)/volume (mL).
2. Complete Table 4.2 by recording the mass and volume data collected
by you and youl.’ classmates.
f!~ Using the class data, plot a graph of mass versus volume. Represent
the plotted points for each metal with a different symbol. Draw a "best
fit" straight line through each group of plotted points.
"4.,.. De;termme the slope of each of the lines on your grap~h_._Rec6rid the
slope-~f.each line and your method of calculatlo_nm-Talfle 4.3. Hint: The
general equatmn4o~:_a_Ali_._ne ~s y= rex_+ b wh-~re m is the value for the slope
and b is the value for~t~h~y-mterc~Rt.. Pay special attention to the umts of
the slope ............. " ......
Table 4.3 Density Calculations from Class Data (slopes/
Metal A
Metal B
Additional Metal
Sample
y/x = --~-mL = g/mL ylx = ---~ = g/mL
1. X@at does the slope of the line for each metal represent? Hint: Look
back at Table 4.1.
2. Looking at your graph, what does this experiment demonstrate
about the density of a substance? What does it demonstrate about the
densities of different substaffces?
Mass, Volume, and Density
~c
’3. Calculate the percent error in the density calculations for the two
amples. (See Data Analysis, step 1.) Your teacher will provide the acepted value for the density of each metal.
percent error -
laccepted value - experimental valuel × 100 percent
accepted value
4. Calculate the percent error in the values of density obtained fr°m the
slopes of the lines in your graph.
42 Experiment 4
Class
Date
5. Look back at the pereent errors calculated in steps 3 and 4. Generally,
the slope of the line will give a more accurate value for density than a
single sample. Explain why this is usually true.
~ ( ~.~\ Can you identify a substance if you know its density? Explain your
~;~ \,\ansWer. Try to identify the metals used in this experiment by referring to
~ ~a~Jles of density
1. Do you think that determinmg the volumes of your n~etal samples by
measuring their dimensions and calculating would be more or less accurate than determining these volumes ,by water displacement? Explain.
Would measuring the dimensions of a solid always be possible? Exl~lain.
Mass, Volume, and Density 43