Density

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Density

• How tightly the atoms are packed together in an
  object

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DensityAt the conclusion of our time together,
you should be able to

1. Define density
2. Calculate the density of a given object if given
   the volume and mass
3. Calculate the volume or mass if the density is
   given with the volume or mass

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Density

• Density mass
• volume
• Mass the amount of matter in an object
• Volume the amount of space the object takes up
• Units g/mL (liquid) OR g/cm3 (solid)

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DENSITY - an important and useful (qualitative)
intensive physical property
13.6 g/cm3
21.5 g/cm3
2.7 g/cm3
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Familiar Saying
A rotating lithoidal fragment never accrues
lichen. A rolling stone gathers no moss!!
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Density Calculations

• 
  
  

M
D
V
Cover up whatever unit you are solving for, the
two units remaining will show you how to solve
the problem.
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Density Calculations

• Regularly Shaped Solid
• mass balance
• volume measure (l x w x h)
• Irregularly Shaped Solid
• mass balance
• volume water displacement

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Density Calculations

• Liquid
• volume read graduated cylinder
• mass tare graduated cylinder, mass
  liquid

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• Problem A piece of copper has a mass of 57.54 g.
  It is 9.36 cm long, 7.23 cm wide, and 0.95 mm
  thick. Calculate density (g/cm3).

M
D
V
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• Strategy
• 1. Get dimensions in common units.
• 2. Calculate volume in cubic centimeters.
• 3. Calculate the density.

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• SOLUTION
• 1. Get dimensions in common units.
• 2. Calculate volume in cubic centimeters.
• 3. Calculate the density.

(9.36 cm)(7.23 cm)(0.095 cm) 6.4 cm3
Note only 2 significant figures in the answer!
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Euphemisms in Science We all know that some
politicians and government spokesmen use certain
euphemistic phrases to give an aura of
respectability to descriptions of events or
actions which would be offensive when expressed
in plain English. The following is a list of
Euphemisms in Science and their translations into
plain English.
These results are correct within an order of
magnitude... Wrong!
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DENSITY

• Density is a (qualitative) intensive property of
  matter.
• does NOT depend on quantity of matter.
• like temperature
• Contrast with (quantitative) extensive property
• depends on quantity of matter.
• like mass and volume.

Styrofoam
Brick
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PROBLEM Mercury (Hg) has a density of 13.6
g/cm3. What is the mass of 95 mL of Hg in grams?
In pounds?
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Strategy
First, note that 1 cm3 1 mL

• 1. Use density to calculate mass (g) from
  volume.
• 2. Convert mass (g) to mass (lb)
• Need to know conversion factor
• 454 g / 1 lb

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Strategy

• 1. Convert volume to mass

2. Convert mass (g) to mass (lb)
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Learning Check

• Osmium is a very dense metal. What is its
• density in g/cm3 if 50.00 g of the metal
  occupies
• a volume of 2.22 cm3?
• 1) 2.25 g/cm3
• 2) 22.5 g/cm3
• 3) 111 g/cm3

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Solution

• 2) Placing the mass and volume of the osmium
  metal into the density setup, we obtain
• D mass 50.00 g
• volume 2.22 cm3
• 22.522522 g/cm3 22.5 g/cm3

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Learning Check

• Osmium is a very dense metal. What is its
• density in g/cm3 if 50.00 g of the metal
  occupies
• a volume of 2.22 cm3?
• 1) 2.25 g/cm3
• 2) 22.5 g/cm3
• 3) 111 g/cm3

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Volume Displacement

• A solid displaces a matching volume of water
  when the solid is placed in water.
• 33 mL
• 25 mL

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Learning Check

• What is the density (g/cm3) of 48 g of a metal
  if the metal raises the level of water in a
  graduated cylinder from 25 mL to 33 mL?
• 1) 0.2 g/ cm3 2) 6 g/m3 3) 252
  g/cm3
• 33 mL
• 25 mL

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A.P. TEST IN AMERICAN HISTORY

• There is a red telephone on your desk. Start
  World War III. Report in length on its
  socio-political effects on the United States, if
  any.

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DensityLets see if you can

1. Define density
2. Calculate the density of a given object if given
   the volume and mass
3. Calculate the volume or mass if the density is
   given with the volume or mass

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Learning Check

• Which diagram represents the liquid layers in
  the cylinder?
• (K) Karo syrup (1.4 g/mL), (V) vegetable oil
  (0.91 g/mL,) (W) water (1.0 g/mL)
• 1) 2) 3)

K
W
V
V
K
W
W
V
K
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Learning Check

• The density of octane, a component of gasoline,
  is 0.702 g/mL. What is the mass, in kg, of 875
  mL of octane?
• 1) 0.614 kg
• 2) 614 kg
• 3) 1.25 kg

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Learning Check

• If blood has a density of 1.05 g/mL, how many
  liters of blood are donated if 575 g of blood are
  given?
• 1) 0.548 L
• 2) 1.25 L
• 3) 1.83 L
• 4) 548 L

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Learning Check

• A group of students collected 125 empty aluminum
  cans to take to the recycling center. If 21 cans
  make 1.0 pound of aluminum, how many liters of
  aluminum (D 2.70 g/cm3) are obtained from the
  cans? (1 kilogram 2.2 pounds)
• 1) 1.00 L 2) 2.00 L 3) 4.00 L

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Water has a density of 1.0 g/ml and mercury (Hg)
has a density of 13.6 g/ml.
Which is heavier, a quart of water or a quart of
mercury?
If we have equal volumes of two different
substances, then the one with the greater density
will have the greater mass.
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15 Helpful Hints On The Lab Report from Mr. Ts
Vast Lab Experience!!!
Hint 11. Given the most inappropriate time for
something to go wrong, that's when it will occur.
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• Which is heavier, a ton of feathers or a ton of
  bricks?

Neither

• Which is larger?

Feathers

• If two objects have the same mass, the one with
  the higher density will be smaller.