Density

1
Density
2
What is Density?

• Density is the mass per unit volume of a
  substance.
• Density is measured in
• g/cm
• Kg/m
• g/mL.

3

• When we compare the masses of the same volume of
  different substances we are comparing their
  densities.
• Oil floats on water because it is less dense than
  water.

4
Density and the Particle Theory

• Every pure substance has its own characteristic
  density.
• Typically solids have greater densities than
  liquids and liquids have greater densities than
  gases.

5

• The particle theory states that different
  substances have different sized particles.
• The size of the particles determines how many
  particles can fit into a given space.
• Solids are tightly packed so they have a high
  density, gases are spaced far apart so their
  density is low.

6
Mass

• We can measure mass by using a balance or a
  digital scale.

7
Volume

• Volume is a measurement of the amount of space
  occupied by the substance.

8
How can we measure Volume?

• Liquids can be measured using a measuring cup or
  a graduated cylinder.
• Gases can be determined by measuring the volume
  of the container it is in.

9
Volume

• Irregular solids can be determined by immersing
  them into a beaker of water and measuring the
  volume of the displaced fluid.
• 4. Regular solids can be determined by measuring
  the length, width, and height
• V l w h.

10

• Displacement is the amount of space that an
  object takes up when placed in a fluid.

11
Changes in Density

• As Temperature Increases
• ?
• Particles Gain Energy
• ?
• Particles spread out
• ?
• Decrease in Density

As Temperature Decreases ? Particles Lose
Energy ? Particles closer together ? Increase in
Density
12
What Portion of an Iceberg is Submerged?

• Think about what happens when you add an ice cube
  to a glass of water?
• Not all the ice floats on the surface, some of it
  is below the surface.
• This also happens with icebergs (90 of the
  icebergs mass is found below the surface!)

13
Comparing Densities

• By comparing densities you can calculate how much
  of something will be submerged.
• Example Ice and sea water
• Density of Ice x 100
• Density of Seawater
• 0.92 x 100 89
• 1.03
• Approximately 90 of Icebergs are submerged!

14
Calculating Density

• The density of a substance can be determined by
  calculating the massto volume ratio, or
  density.
• D M
• V

Mass
Volume
15
Example

• A cube of water has a volume of 2 m and a mass of
  1000kg. What is the density?
• Check to make sure the units can go together.
• D M 1000kg 500 kg/m
• V 2 m

16
Example

• What is the mass of 1500 mL of helium, if the
  density of helium is 0.0002 g/mL?
• m D x V m 0.0002 g/mL x 1500 mL
  m 0.3 g