Density

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Density
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Which do you think would have the greater mass?
Greater volume? Why?

• 1 kg of feathers

• 1 kg of rock

• Same mass!
• Larger volume

• Same mass!
• Smaller volume

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Volume vs. Mass

• Mass
• is the amount of matter in an object (how heavy
  something is)

• Volume
• is the amount of space something takes up

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Finding Mass

• Place the object on a scale or balance
• Units should be grams (g) or kilograms (kg)

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Finding Volume of a Regular Shape

• An object with a regular shape is measurable
  and symmetric
• Measure length (L), width (W) and height (H)
• Multiply L x W x H
• Make sure units make sense (cm3, m3)
• 4 cm x 6 cm x 5 cm 120 cm3

Conversion Factor 1 cm3 1mL
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Finding Volume of an Irregular Shape

• An object that can not easily be measured
• Use displacement
• Fill a graduated cylinder or overflow can with
  water
• Measure how much water goes up/spills out when
  object is placed in water

Remember 1 cm3 1mL
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DENSITY

• Density is defined as mass per unit volume. It
  is a measure of how tightly packed and how heavy
  the molecules are in an object.
• Density is the amount of matter within a certain
  volume (how much stuff is crammed into
  something)

Units of Density g/cm3 or g/mL Depends on
the units used for mass and volume
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Density of Phases of Matter
Which phase of matter is the densest? Which
phase of matter is the least dense? Usually the
solid phase of a substance will sink in its
liquid phase because it is more dense
SOLID
GAS

• Water is an exception!
• Because water expands when it freezes, solid
  water (ice) is actually less dense than liquid
  water

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Densities of Common Substances (g/mL)

• Solids
• Bone 2
• Brick 1.8
• Cork 0.2
• Ice 0.92
• Marble 2.7
• Paraffin 0.9
• Rubber 1.2
• Bamboo 0.3
• Oak Wood 0.7
• Pine Wood 0.6

Metals Aluminum 2.7 Copper 8.9 Gold 19.3 Iron 7
.8 Lead 11.3 Silver 10.5
Liquids Pure Water 1.0 Sea Water 1.03 Alcohol 0.8
Gylcerine 1.3 Milk 1.03 Turpentine 0.9 Mercury 13
.6 Gasoline 0.7
Note The density of a substance will always be
the same, regardless of its shape or size i.e.
the density of pure water is always 1 g/mL
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Finding Density
Density (D) is mass (m) per unit volume (v) per
divided by D m/v (m v)
Formula
D M / V M D x V
V M / D
M mass V volume D density
Divided by
Multiplied by
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Practice Problem 1
If the mass of an object is 35 grams and it takes
up 7 cm3 of space, calculate the density.
Given Mass 35 grams Volume 7 cm3 Density
? (g/ cm3)
Formula D M / V Solution D 35 g / 7
cm3 D 5 g/cm3
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Practice Problem 2
A rectangular block of copper metal has a mass of
1896 g. The dimensions of the block are 8.4 cm by
5.5 cm by 4.6 cm. From this data, what is the
density of copper?
Given M 1896 grams V 8.4 cm x 5.5 cm x 4.6
cm 212.52 cm3 D ? (g/ cm3)
Formula D M / V Solution D 1896 g /
212.52 cm3 D 8.92 g/cm3
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Practice Problem 3
Find the mass of 250.0 mL of benzene. The density
of benzene is 0.8765 g/mL.
Given V 250.0 mL D 0.8765 g/mL M ? g

Formula M D x V Solution M 0.8765 g/
mL x 250.0 mL M 219.13 g
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Practice Problem 4
What volume of silver metal will has a mass of
exactly 2500.0 g. The density of silver is 10.5
g/cm3.
Given M 2500.0 g D 10.5 g/cm3 V ?
cm3
Formula V M / D Solution V 2500.0 g /
10.5 g/cm3 V 238.10 cm3