Density

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DENSITY
Here's an old joke:
What weighs more, a pound of bricks
or a pound of feathers?
The answer is they both weigh the same. Which takes up more space
though?
Obviously, the pound of feathers takes up way more space (has a greater
volume). This leads to a very useful property of matter called DENSITY.
DENSITY FACTS
Most kinds of matter expand when their temperatures rise and
contract when their temperatures drop.
Thus, density changes with temperature. Very cold water is
denser than hot water because the water molecules are closer
together.
So as temperature increases, density decreases.
The bottom line is that density is not constant.
At 4°C pure water has a density of about 1 g/cu.cm, 1 g/ml.
What is the density of ice?
Demonstrations:
Water and ice: What can you infer about the density
of these items?
Gases are always less dense than liquids and solids.
That’s why air bubbles in a glass of water move upward
and escape.
The solid states of matter generally have higher
densities than do the liquids.
One very important exception to this rule is ordinary
water. Water expands when it freezes.
The H2O molecules arrange themselves in a pattern that
takes up more space than when the molecules are in
the liquid state.
Therefore, ice floats in water.
Demonstrations:
Water and oil: What can you infer about the density of
these items?
Soda vs. Diet Soda: What can you infer about the density
of these items?
Dead Sea
Substances that have a density less than water's will float in water.
Substances with a greater density than water's will sink.
Life jackets make us less dense than water,
so we float.
Submarines can change depth in the
water when they remove or add water
to special tanks called ballast tanks.
When water is removed from the
tanks, the submarine loses mass. It
floats higher in the water. When
water is added to the tanks, the
submarine gains mass. It sinks
lower in the water because its density
is now greater.
What is the density of a rock that has a mass of 25.2 g and a volume of
11.9 mL?
Use the 3-step method to solve this problem:
1) Write the formula.
D = M/V
2) Plug in the numbers and units.
D = 25.2g / 11.9 mL
3) Complete the calculation and
show the correct unit for density.
D = 2.1 g/mL
Density is a measure of how closely the particles of a
substance are packed into a given space.
Density is found by measuring mass and volume and then
dividing the mass by the volume. The formula for density is:
D = M/V
D stands for density, M stands for mass, and V stands for
volume.
What is the density of a rock that has a mass of 32.5 g and a
volume of 12.8 mL?
Use the 3-step method to solve this problem:
1) Write the formula.
D = M/V
2) Plug in the numbers and units.
3) Complete the calculation and
show the correct unit for density.
What is the density of a rock that has a mass of 32.5 g and a
volume of 12.8 mL?
You have a rock with a volume of 15cm3 and a mass of 45 g.
What is its density?
Click for answer
You have a different rock with a volume of 30cm3 and a mass
of 60g. What is its density?
Click for answer
What is the density of a board whose dimensions are 5.54 cm x 10.6
cm x 199 cm and whose mass is 28.6 Kg?
Show your answer in grams/cubic centimeters.
Click for answer
You have a rock with a volume of 15cm3 and a mass of 45 g.
What is its density?
Back to
Problems
You have a different rock with a volume of 30cm3 and a mass
of 60g. What is its density?
Back to
Problems
What is the density of a board whose dimensions are 5.54 cm x 10.6
cm x 199 cm and whose mass is 28.6 Kg?
D = M/V
5.54 cm x 10.6 cm x 199 cm = 11686.0cm3
28.6 Kg
11686.0 cm3
D= .002447373 kg/cm3
D= .002447373 kg/cm3
.002447373
k
h
da
g
d
c
m
.02447373
.2447373
D = 2.45 g /cm3
2.447373
Back to
Problems
Substance
Density
(g/cm3)
Substance
Density
(g/cm3)
Platinum
21.4
Seawater
1.025
Gold
19.3
Water
1.00
Mercury
13.6
Ice
0.92
Lead
11.3
Oil
0.90
Silver
10.5
Paraffin
(wax)
0.87
Copper
8.9
Gasoline
0.7
Brass
8.5
Wood (oak)
0.7
Iron
7.9
Wood (pine) 0.4
Steel
7.8
Cork
0.24
Aluminum
2.7
Oxygen
0.0014
Marble
2.69
Air
0.0013
Rubber
1.1
Helium
0.0002
Work these problems in your notebook.....
1. A man is buying a copper bowl because he heard it is
the best material to whip egg whites in. If the bowl has a
mass of 142 g and a volume of 15.95 mL, is it a real
copper bowl?.
2. What volume would a 0.451 gram sample of air
occupy if the density of air is 1.29g/L?
3. Explain the beaker in the front of the room in terms of
density.
1. A man is buying a copper bowl because he heard it is the best material to
whip egg whites in. If the bowl has a mass of 142 g and a volume of 15.95
mL, is it a real copper bowl?
D= 142g / 15.95 mL
D= 8.9 g/mL
Is it copper? YES!
2. What volume would a 0.451 gram sample of air occupy if the density of air is
1.29g/L?
D= M/V
1.29 g/L = 0.451 g/ V
make it simple
12=36/3
1.29 g/L = 0.451g/ .349 L
3. Explain the beaker in the front of the room in terms of density.
The yellow liquid at the top of the
beaker is less dense than the other
substances.
The bluish substance is more dense
than the top substance, but less
dense than the bottom substance.
The red bottom substance is the
most dense.
Essays must be between 700 to 1,000 words in length, include a list of research
sources, and fall under one of these four categories:
Together, we can feed the world.
Together, we can build a secure energy future.
Together, we can protect people and the environment.
Together, we can be innovative anywhere.
Dupont Science Essay Challenge
Write the following in each line, from most
dense to least dense....
water, oil, ice
gasoline, mercury, iron
air, oxygen, helium
sea water, ice, water
water, ice,
oil
mercury,
iron ,
gasoline
oxygen,
air, helium
seawater, water,
ice
Acrylic-clear
Aluminum- shiny silver
Brass- gold colored
Copper- copper, reddish
Oak-darker wood
Pine-lighter wood
Polypropylene-cloudy
PVC-dark gray
Steel-lighter gray, metallic, heavy
Substance
Mass
(g)
L
(cm)
W
(cm)
H
(cm)
Volume (c
m3)
Density
(g/cm3)
Sink or
Float?
D=M/V
Acrylic
Aluminum
WRITE
EQUATIONS IN
Brass
MARGIN
Copper
Oak
Pine
Polypropylene
PVC
Steel
Substanc Mass
(g)
e
L (cm) W (cm) H (cm)
Volume (
cm3)
Density (g/cm3)
Sink or
Float
?
Acrylic
18 g
2.5cm 2.5cm
2.5cm
15.6 cm3
1.1-1.2 g/cm3
S
Aluminu
m
43 g
2.5cm 2.5cm
2.5cm
15.6 cm3
2.7 g/cm3
S
Brass
134 g
2.5cm 2.5cm
2.5cm
15.6 cm3
8.4-8.8 g/cm3
S
Copper
144.3 g 2.5cm 2.5cm
2.5cm
15.6 cm3
8.94 g/cm3
S
Oak
11.0 g
2.5cm 2.5cm
2.5cm
15.6 cm3
0.6-0.9 g/cm3
F
Pine
7.5 g
2.5cm 2.5cm
2.5cm
15.6 cm3
0.35-.50 g/cm3
F
Polypropyle
ne
15 g
2.5cm 2.5cm
2.5cm
15.6 cm3
0.91-.94 g/cm3
F
PVC
22.2 g
2.5cm 2.5cm
2.5cm
15.6 cm3
1.39-1.42 g/cm3
S
Steel
126.2 g 2.5cm 2.5cm
2.5cm
15.6 cm3
7.9 g/cm3
S
Density Lab
INTRO: Understanding the concept of density is very important in the world of
science as well is in our everyday lives. Scientists use density calculations to
help analyze how “tightly packed” a material’s particles are. They also use this
calculation to be able to identify various materials due to the fact that each
substance has a unique density. In our lives, we use the concept of density to
understand the relationship between different types of materials. We use terms
such as hardness or heaviness to describe the density of various items in our
daily language.
PURPOSE: The purpose of this lab is for you to practice gathering mass and
volume measurements as well as to use your collected data to make density
calculations.
PROCEDURE: Eight items are listed in the table on the data sheet for this lab. Record the
mass, volume, method for finding volume, and density in the table.
MASS - To measure mass, use a triple-beam balance. Be sure to round your measurement
values to the nearest tenth of a gram (one decimal place) and to include a label after the
number.
VOLUME - To measure volume, choose one of the various options available (listed below)
and be sure to include a label with your final answer (either mL or cm3).
reading a graduated cylinder
multiplying length x width x height
water displacement (using a graduated cylinder and/or a spill can)
DENSITY - Calculate density using the three-step method discussed in class. Round your
answer to the tenth. Be sure to label your answer appropriately.
Compare your answer to the correct answer posted at the front of the room. If your answer
is not close to this, you will need to re-do your measurements and calculate the density
again to get closer to the correct answer.
Substanc
e
Glycerine
Methyl
Alcohol
Wood
Rubber
Stopper
Wax
Rock
(Granite)
Mineral
Oil
Water
Mass(g Volume (
)
cm3 or
mL)
How
you
found
volum
e
Density (g/ml or
g/cm3(three-step
method)
APPLYING WHAT WE HAVE LEARNED
Would gasoline float OR sink if mixed with water? _______________
Would an ice cube float OR sink if dropped in oil? _______________
Does helium gas float OR sink in air? _______________
Mercury is a liquid at room temperature. Would an iron bolt float OR sink in mercury? _______________
Write the formula for density: ________________________________________
What equipment is used to measure an item’s volume? ______________________
What label(s) do we commonly use to represent volume? ____________________
What equipment is used to measure a substance’s mass? _____________________
What label do we commonly use to represent mass? _______________
Is it easier to measure the volume of a liquid or a solid? Explain your answer.
__________________________________________________________________
__________________________________________________________________
Do you feel that this lab has helped you develop a better understanding of the concept of density? Explain.
__________________________________________________________________
__________________________________________________________________
Density Worksheet
Density is the ratio of the mass of the substance to the volume of the substance at a given
temperature. Density has units of g/ cm3 or g/cc or g/mL for liquids and solids, and g/L for
gases. SHOW YOUR WORK!
1.
A gold-colored ring has a mass of 18.9 grams and a volume of 1.12 mL. Is
the ring pure gold? (The density of gold is 19.3 g/mL.)
2.
What volume would a 0.871 gram sample of air occupy if the density of air
1.29 g/L?
1.29g/L = 0.871g / V
(4=
D=18.9g / 1.12 mL
12/3)
.871g/1.29g/L= .675 L
D= 16.87 g/mL
3.
Pumice is volcanic rock that contains many trapped air bubbles. A 225 gram
sample occupied 236.6 mL. What is the density of pumice? Will pumice float on
water?
D = 225g/236.6mL
D= . 95
Yes, pumice will float in water!
4.
A cup of sugar has a volume of 237 mL. What is the mass of the cup of
sugar if the density is 1.59 g/mL?
1.59g/mL = m / 237 mL
1.59 x 237 = 376.83
m = 376.83 g
9 = 27/3
5.
From their density values, decide whether each of the following substances will
sink or float when placed in sea water, which has a density of 1.025 g/mL.
Float Gasoline 0.66 g/m Sink Mercury 10.6 g/mL Float Cork 0.26 g/mL
6.
A sample of lead is found to have a mass of 32.6 g. A graduated cylinder contains
2.8 mL of water. After the lead sample is added to the cylinder the water level reads 5.7 mL.
Calculate the density of the lead sample.
5.7 mL
-2.8 mL
2.9 mL
D= 32.6 g / 2.9 mL
D=11.24 g/mL
7. A little aluminum boat (mass of 14.50 g) has a volume of 450.00 cm3. The boat is place in
a small pool of water and carefully filled with pennies. If each penny has a mass of 2.50 g,
how many pennies can be added to the boat before it sinks?
Mass to Volume must be greater than 1 g/mL
450cm3 = 450 mL
needs to be greater than 450 g to sink
450 g - 14.5 g of boat = 435.5 g
435.5 g/ 2.5 g (penny)
174.2 pennies to equal density
175 pennies to sink da boat!
8.
Density varies with change in temperature. Why?
If the temperature changes, then the particles move further apart, cause thermal
expansion to occur, which would make a higher volume, which would cause a change
in density.
9.
The King of Artemesia was given a gift of a crown of gold, but he suspected that he
was being fooled. He asked his court scientist (that’s you) to prove if the crown was really
gold or not. You found the mass of the crown was 452.3 g. The volume of the crown was
53.2 ml. Is the crown made of gold? Include as much detail as you possibly can to prove
your point. Use your Density Reading for help. If the crown is not made of gold, what
material is it made of? How do you know?
D= 452.3 g / 53.2 mL
D = 8.50 g/mL
The crown can not be gold, as the density of gold is 19.3 g/mL. With a
density of 8.5 g/mL, the crown must be made out of brass. Brass looks
like gold, but is not gold at all! Brass is made up of an alloy of zinc and
copper.

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