EARTH SCIENCE
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Density Lab INT-HON
Name______________________
Group______________________
20 Points
Date______________________
PURPOSE AND MATERIALS FOR THIS EXPERIMENT
The purpose of this activity is to familiarize you with one of the most important physical properties of matter:
density. Density can sometimes be used to identify or describe a substance. Density of a substance is defined as
the mass of the substance per unit of volume. In other words, density is the measure of how much stuff (matter)
is inside a specific amount of space. The mathematical definition for density is:
D=
m
V
In this equation, D is the density of the substance, m is the mass of the substance, and V is the amount of space,
or volume, that the substance takes up.
Many solid substances have unique or uncommon densities that make them easily identifiable. For instance, lead
(Pb) is one of the densest substances found on Earth. It is easy to identify because it is metallic and even a small
piece will weigh a lot because of its high density. In this lab, you will determine the density for six known
substances and then you will determine the density for an unknown substance. The unknown substance will be
the same as one of the six known substances. You will need to compare the densities of the known substances
to the unknown substance to determine what the unknown substance is. Make careful measurements or this
won’t work!
To determine the volume of each substance in this lab, you will use a technique called the Volume Displacement
Method. The Volume Displacement Method measures the volume of a substance by inserting the substance into
a body of water and then observing how much the water level changes. The amount of change in water level
equals the volume of the substance. For example, if you fill your aquarium up with 50,000 milliliters (mL) of water
and then draw a line where the water level is, you can determine the volume of space your pet piranha, Pinky,
takes up. This can be done by observing how much the water rises above the line when you place Pinky into the
aquarium. If the water level rises 1000 mL, then Pinky has a volume of 1000 mL.
In this lab, you will use a graduated cylinder to measure the volume of each substance. To properly read the
water level in the graduated cylinder, you will need to make sure that your eyes are level with the water level line,
as illustrated below.
Graduated Cylinder
Your Eyeball
Water Level
Line of Sight
When observing the water level line you will probably see that the water line is thick and actually appears as two
lines. You may also observe that the water level line is curved (called a meniscus) instead of being straight. If
you observe these features, you will need to follow this rule to accurately record the volume amount: Always read
the volume amount by observing the lowest point in the water level line.
You will work in groups of 3 or 4 people. You will need the following materials:
sample of copper
sample of corundum
sample of quartz
tap water
sample of magnetite
sample of galena
sample of graphite
sample of unknown substance
calculator
triple-beam balance or scale
100-mL graduated cylinder
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STATE THE PROBLEM
There are several questions that this laboratory experiment is going to attempt to answer. The main question is:
What is the unknown substance? Several other questions must be answered before this question can be
answered. These questions pertain to the densities of the other objects that we are comparing the unknown
substance to.
GATHER INFORMATION
Examine the seven known substances and the unknown one. Hold them in your hand and feel the weight (i.e.
“heft”) of each sample. Compare their weights to their sizes. The smaller, yet heavier substances should have a
higher density. Water has a density of about 1.0 g/mL, which means that every milliliter of water weighs 1 gram.
For instance, 10 mL of water weighs 10 grams.
HYPOTHESES (1 points)
Fill in the table below with your predictions for the densities of each of the listed substances. Use the density of
water as the foundation of your guesses – how many times denser than water do you think each substance is?
Also, state your hypothesis for the two questions below the table.
Substance
Density (g/mL)
Water (H2O)
Copper (Cu)
Corundum (Al2O3)
Quartz (SiO2)
Magnetite (Fe3O4)
Galena (PbS)
Graphite (C)
Unknown (?)
What substance do you think the unknown substance is? ____________________
Which do you think would affect the density of a single atom more, increasing the mass of the
atom or increasing the volume of the atom?
__________________________________________
EXPERIMENTAL PROCEDURE AND DATA COLLECTION (2 points)
1. Record the date that this activity is being conducted:
_____________________
2. Using the balance, determine the mass of each substance listed in the table on page 3. Be sure to
record the mass with two decimal places and write down the unit of measurement (grams). This means you
will have a number like 17.92 grams. You will have to estimate what the last decimal place (the Unit of
Uncertainty) is because the balance will not tell you. In other words, you will get a measurement like 17.9X
and you will have to estimate what X is.
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3. After you have determined the mass for each substance, determine the volume of space that each
substance occupies. First, fill the graduated cylinder with enough water so that the substance you are
measuring will be completely submerged. Next, record how much water is in the cylinder before submerging
the substance (Volume Before). Finally, submerge the substance and record how much water now appears
to be in the cylinder (Volume After). By subtracting your Volume Before data from your Volume After data,
you can easily calculate the volume of each substance. Record the calculated volumes into your table.
4. Determine the densities of each of your substances by dividing the mass of each substance by their
respective volumes.
5. Clean up your materials and then answer the questions in the Analysis section.
Substance
Mass (g)
Volume Before
(mL)
Volume After
(mL)
Volume of the
Sample (mL)
Density of the
Sample (g/mL)
H2O
Cu
Al2O3
SiO2
Fe3O4
PbS
C
Unknown
ANALYSIS QUESTIONS (9 points)
Answer the following questions with clear and concise answers.
1. In Column A below, relist the hypothesized densities that you predicted on Page 2. In Column B, list the
densities that you computed above for each substance. For Column D, compute the “percent error” for your
measured densities (% error = |[(Column C - Column B)/Column C]| x 100). (1 point)
Substance
A - Hypothesized
Densities (g/mL)
B - Measured
Densities (g/mL)
C – Actual Densities
of Pure Substance
(g/mL)
Water (H2O)
1.0 g/mL
Copper (Cu)
9.0 g/mL
Corundum
(Al2O3)
4.0 g/mL
Quartz
(SiO2)
2.6 g/mL
Magnetite
(Fe3O4)
5.2 g/mL
Galena
(PbS)
7.5 g/mL
Graphite (C)
2.2 g/mL
Unknown
(?)
?
D – Percent Error
(%)
Page 3 of 6
2. Compare your hypothesized densities (column A in question 1) to your measured densities of all of the
samples (column B in question 2). Which of your predictions, if any, had less than 10.1% error? (1 point)
3. Which samples are considered elements and why are they considered elements?
considered compounds and why are they considered compounds? (1 point)
Which samples are
4. If any of your predictions were wrong, why do you think that you did not get the correct density? Was it
human error? Do the samples have impurities in them? Is the actual density incorrect? If all of your
predictions were correct, how were you able to make such accurate predictions? (1 point)
5. Our sample of “copper” consisted of five pennies or another object made from copper. If we doubled our
sample of copper, what would happen to the mass of the sample? What would happen to the volume of the
sample? Would the density of the sample increase, decrease, or stay the same? Explain your answer. (1
points)
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6. The chemical formula for galena is PbS, which is one atom of lead bonded to one atom of sulfur. What is the
atomic mass for Pb? What is the atomic mass for S? What is the combined molecular mass for a molecule
of PbS? How many grams of your galena sample were caused by the mass of the lead atoms? How many
grams of the galena were caused by the mass of the sulfur atoms? Show your work. (2 points)
7. The chemical formula for quartz is SiO2, which is one atom of silicon bonded to two atoms of oxygen. What is
the atomic mass for Si? What is the atomic mass for O? What is the combined molecular mass for SiO2?
How many grams of your quartz sample were caused by the mass of the silicon atoms? How many grams of
the quartz were caused by the mass of the oxygen atoms? Show your work. (2 points)
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CONCLUSION (3 points)
8. Compare the density of your unknown substance to the densities of the other seven substances. Does it
closely match any of the densities that you calculated? If not, why do think that the densities do not match?
Which substance do you think it is? Explain how you reached your conclusion. (2 points)
9. State which change should affect density more: a change in mass or a change in volume. Explain why you
have concluded this. HINT: Atoms of elements with higher atomic numbers (i.e. more protons/electrons) are
often smaller in volume compared to atoms of elements with lower atomic numbers because of more
electrical attractions between electrons and protons. However, the mass of atoms with more protons will
always be higher than the mass of atoms with fewer protons. (1 point)
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