DENSITY
Notebook Page 24
Definition
• Density is the measure of how much mass is
contained in a given volume.
• (Or: how close a substance’s molecules are)
• The density of a pure substance is always the
same, no matter how much of it you have.
• Ex: Gold is 19.3 g/cm3 at room temperature
• The density of a substance can change when its
temperature changes.
• Why?
Why is density important??
• Density is a physical property of matter.
• Density has been used for centuries to
identify substances.
Calculating Density
• Density = Mass / Volume or D = M
• The metric unit is grams per cubic centimeter or grams
per milliliter.
• The symbol for density is the Greek letter Rho (ρ)
• Use the magic triangle if you need
help isolating for a variable
• Ex: solve for V
Calculating Density
• Calculate the volume of “regularly shaped” objects by
multiplying length x width x height.
• Then divide the mass by the volume
• Remember, it must be in g/cm3
lxwxh
6m x 6m x 8m = 228 m3
228 m3 = ______ cm3
D=m/V
D = 600 g
cm3
D=
Calculating Density
• If an object is not “regularly shaped”, then it can be placed
in water.
• The amount of water displaced is the volume of the
object. Use grams per milliliter.
• Use .01 kg for the mass of the rock:
.01 kg = _______ g
D=m/V
D = ________g
mL
D=
g / mL
Sink or Float?
• All substances are compared to water
• The density of water is always 1.0 g/mL.
• If a substance floats in water, than it is less
dense than water. Ex: D = 0.6 g/mL
• If a substance sinks in water, than it is more
dense than water. Ex: D = 2.3 g/mL
Duh! That means it “ Sinks like a stone!!!”
Hey, let’s do a teacher demo!!
• Which is denser, a can of Pepsi or a
can of Diet Pepsi?
• No, you can’t drink it!!
• Yay! You are done with notes!!! 
Density Lab
pg ____
• Obj: The student will learn to identify an unknown
substance by calculating its density.
• Materials: Density blocks (or cylinders), metric ruler,
graduated cylinder with 50 mL water, digital scale,
calculator.
Procedure
1.
2.
3.
4.
5.
6.
With a partner get a digital scale, a calculator, and
either 3 density blocks or 3 density cylinders.
Determine if you need a metric ruler or a graduated
cylinder with 50mL of water. How do you know which?
Calculate the density of each block or cylinder.
Compare it to the list on the board and identify what
each block/cylinder is made of.
YOU WILL PROBABLY NOT BE ABLE TO MATCH
THE NUMBERS ON THE LAST SLIDE. THAT’S OK,
USE YOUR OBSERVATIONS TO HELP YOU PICK
THE MOST LOGICAL.
Those numbers were calculated by pros using high-tech equipment!
Data Table - Blocks
Block 1
Color
Texture
Length
Width
Height
Volume (cm3)
Mass
Density
Identity of
substance
Block 2
Block 3
Data Table - Cylinders
Cylinder 1
Color
Texture
Volume (mL)
Mass
Density
Identity of
substance
Cylinder 2
Cylinder 3
Calculate Density – Identify Substance
Cylinders
Density
Blocks
Density
Copper
8.9
Copper
8.9
Brass
8.0
Brass
8.0
Pyrex glass
2.23
Steel
7.6
Rubber
1.15
Polypropylene
0.90
Acrylic
1.4
Acrylic
1.4
Aluminum
2.7
Aluminum
2.7
Nylon
1.14
Nylon
1.14
PVC (polyvinyl chloride)
1.50
PVC (polyvinyl chloride)
1.50
Teflon
2.19
Wood (pine)
0.50
Tecaform
1.41
Wood (lignum vitae)
1.33
Wood (poplar)
0.45
Wood ( poplar
0.45
Wood (Oak)
0.75
Wood (Oak)
0.75