Mr' Perez

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Mr. Perez

• Grade 6 Science
• Density

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Density

• Density is the amount of matter per unit volume
• Density is the ratio of mass (the amount of
  matter in an object) and its volume (the amount
  of space an object takes up)
• If the volume stays the same and the mass
  increases . . . the density will increase
• If the mass stays the same and the volume
  increases . . . The density will decrease

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The DMV Triangle forVolume, Mass, and Density

D x V
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Formulas for CalculatingVolume, Mass, and Density
Volume Mass Density The unit for volume is mL
or cm3 Mass Density x Volume The unit for mass
is grams (g) or kilograms (kg) Density
Mass Volume The unit for density is g/mL or
g/cm3
D x V
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Density and Temperature

• The density of gases depends on temperature
• The higher the temperature, the lower the density
  (Warm gases rise and expand to INCREASE the
  volume)
• The colder the temperature, the higher the
  density (cool gases sink and contract, and the
  volume DECREASES)

Cold Volume Decreases
Warm Volume Increases
Density A 0.00130 g/cm3 Density B 0.00065 g/cm3
Density A is greater because the volume has
decreased
Density A
Density B
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Density Sink or Float?

• The density of water at 4C is 1.0 g/mL
• An object will sink in a fluid with a lower
  density and float in a fluid with a greater
  density
• Density of Object gt Density of Water Object
  Sinks
• Density of Object lt Density of Water Object
  Floats
• Density of Object Density of Water Object
  Appears Weightless
• Why do objects appear weightless in water?
• The closer the objects density is to the waters
  density, the more it will appear suspended in
  the water

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Buoyancy Sink or Float?

• Buoyancy is the tendency of matter (solid,
  liquid, gas) to sink or to float when submerged
  in a fluid
• Why does pine wood float in water?
• The wood only displaces an amount of the water
  that has the same weight as the wood. The rest
  of the woods volume is above the water, so it
  floats.
• The density of most types of wood is lt 1.0 g/mL
• 0.35 g/mL (Density of Pine) lt 1.0 g/mL (Density
  of Water)
• Steel has a density of 7.6 g/mL.
• Why will steel sink in water?
• Because 7.6 g/mL (the density of steel) is
  greater than 1.0 g/mL (the density of water)
• How can boats made out of steel float?
• A steel ship contains a huge bubble of air (which
  has a density 0.0013) that makes its density
  less than that of the water. The air increases
  the volume, but it only has a small amount of
  mass.

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D 1.8 g/mL
D 2.5 g/mL
D 1.0 g/mL
D 0.75 g/mL
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Density Changes Heating and Cooling

• The normal pattern for most objects is that as
  the temperature increases, the density decreases.
  
• Why? Because the molecules spread out from each
  other causing the volume to increase, but the
  mass stays the same.
• D (Copper) M V
• D 890 g 100 mL
• D 8.9 g/mL (20 C / 68 F)
• D (Copper) M V
• D 890 g 104 mL
• D 8.5 g/mL (37 C / 100 F)

• As the temperature decreases, the density
  increases as the molecules become more closely
  packed together.
• This lowers the volume, but the mass stays the
  same. This pattern does not hold true for ice as
  the exact opposite occurs.
• D (of Object X) M V
• D 890 g 96 mL
• D 9.3 g/mL (0 C / 32 F)

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Comparison of Liquid Water and Ice

• Water (Liquid Phase)
• Mass 100 g
• Volume 100 mL
• Density 1.0g/mL

• Ice (Solid Phase)
• Mass 100g
• Volume 108.7 mL
• Density 0.92 g/mL

• In water, 2 atoms of hydrogen bond with 1 atom of
  oxygen to form a molecule of water
• The space between the bonds of the atoms are very
  close together

• In ice, the space between the bonds of the atoms
  are farther apart
• This causes the increase in volume and decrease
  in density

ICE
(ICE)
WATER
(WATER)
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What is the CHANGE in Volume?

• Use the formula to calculate the change in
  volume (from a liquid to ice)
• D (Water) Mass Volume D (Ice) Mass
  Volume
• D (Water) 100 g 100 mL D (Ice) 100 g
  108.7 mL
• D (Water) 1.0 g/mL D (Ice) 0.92 g/mL
• The increase in the volume of ice (from 100mL to
  108.7mL) is almost 9 percent
• The increase in volume causes most containers,
  pipes, or cans to burst
• You should not put cans in the freezer or let
  water freeze in copper pipes

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Ice and Liquid Water
The bonds between the hydrogen and oxygen atoms
in the ice structure take up more volume than
their bonds in liquid water, so the ice is less
dense than liquid water.
Notice the empty spaces within the ice structure,
as this results in a more open or expanded
structure. The ice structure takes up more volume
than the liquid water molecules, so the ice is
less dense than liquid water.
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Density Table
SINK or FLOAT In Water (D 1.0 g/mL)
Float
Float
Float
Sink
Sink
Sink
Float
(alcohol)
Float
(fuel)
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Density Column

• Density of Ice 0.92 g/mL
• Density of Liquid Water 1.0 g/mL
• Density of Corn Syrup 1.360 g/mL
• Density of Mineral Oil 0.83 g/mL