# Density - PowerPoint by zhangyun

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```									 Density
Thur 8/30/07
Terminology: Mass vs Weight
• We may use the two terms interchangeably, but
they do refer to different things.
•   What is the difference?
•   Mass = the amount of matter in a substance
•   Weight = the amount of gravity pulling on the
object’s matter
•   Weight can change depending on location, mass
can not.
moon is less than it
would be on Earth
since you are at a
further distance
from Earth. There
is less pull from the
Earth on you.
•Because the moon
has 1/6th the gravity
of Earth, you would
weigh six times
less than what you
weigh on Earth.
Volume

• The amount of space an object takes up.
Methods for determining volume
• Measurement (length x width x height)
– Regular object
• Water Displacement
– Irregular object
Metric Volume and Length
Relationships

Insert figure 3.5
Units of mass and volume

• Mass is most often expressed in units of
grams.
• Volume is most often expressed in units of
ml or cm3.
Mass vs. Volume Graph for some substance

Mass (g)          D= m/V where slope is equal
to density of substance

Volume (mL)
Density

• What is density?
Density is the amount of mass in a given
amount of space
•   A pound of feathers vs a pound of lead. It
takes more feathers to equal a pound. Why?
•   Lead has a higher density (more matter
[mass] packed into a certain space) than
feathers.
Q: A 5 kg mass displaces water from
13mL to 156mL. What is the density?
D= M
V
To get volume: 156mL - 13mL =143mL

To get mass: 5kg x 1000g = 5000g
1kg
M

D       V
D = 5000g / 143mL = 30 g/mL
Density Sample problem 2

• 2. A 58.85mL substance is found to have
a mass of 46.2g. Using the table below,
identify the substance.
Substance           Density (g/cm3)   Solution:
Diethyl ether       0.714             D= 46.2g/ 58.85mL
Isopropyl alcohol   0.785             =0.785g/mL = 0.785 g/cm3
toluene             0.867
More Density practice
• 3. A detective uncovers a bottle of what he thinks is
chloroform at the scene of a crime. He determines the
substance has a volume of 10.3mL. If the density of
chloroform is 1.483g/cm3, what must the mass be in
order for his suspicions to be correct?
(1.483 g/cm3 x 10.3 cm3) = 15.3 g
• 4. A gas has a density of 7.44g/L. What is that in
g/dm3?

7.44 g x 1 L     x 1 mL x (10 cm)3 = 7.44 g/dm3
L     1000mL     1 cm3    (1 dm)3
Density in lab
• 5. A copper ball has a mass of 9.98g. What would
you do in a lab experiment to determine the density?
• -Water displacement: Fill a grad. cylinder ~half full of water.
Take the reading. Place the copper ball in the cylinder. Take
new reading. Subtract the two to get volume. Divide mass by
volume to get density.
• If Vinitial = 6.21mL and Vfinal= 7.70mL,what is density?
• 9.98g/(7.70mL-6.21mL)= 6.70g/mL
• 6. The theoretical value for the density of copper is
8.96g/cm3. What is the percent error of the above
experiment?

(8.96-6.70) x 100
8.96
Density
• 99.9% of gas to liquid to solid substances become more dense.
• SOLID      >        LIQUID         >       GAS

• ONE substance follows a different pattern:
• LIQUID > SOLID > GAS

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