Introduction to Density

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Introduction to Density

• Density is the measurement of the mass of an
  object per unit volume of that object.
• d m / V
• Density is usually measured in g/mL or g/cm3 for
  solids or liquids.
• Volume may be measured in the lab using a
  graduated cylinder or calculated using
• Volume length x width x height if a box or
• V pr2h if a cylinder.
• Remember 1 mL 1 cm3

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How to measure the density of a solid in the
laboratory.

• Obtain a clean graduated cylinder.
• Fill the graduated cylinder with enough water to
  cover the object. Record the volume
• Carefully place the object into the water filled
  graduated cylinder.
• Record the new water level.
• The volume of the object is the Vfinal Vinitial.

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Introduction to Density

• Example An object has a mass of 50.0 g and
  occupies a volume of 52.0 mL. What is its density?

d m / V 50.0 g / 52.0 mL 0.98 g/mL

• Example A cylinderical piece of metal is 2.03
  inches high and has a diameter 17.0 mm wide and
  weighs 31.599 g. Identify the metal.

Vpr2h p (1.70 cm/2)2 (2.03 in 2.54 cm/1in)
11.7 cm3 D m/V 31.599 g / 11.7 mL 2.70
g/mL The metal is aluminum!
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Practice Problems 3 on density

• Show all of your work on the back. Use
  scientific notation when necessary and always
  given your answers with the appropriate
  significant figures.
• ___________ 1. Calculate the volume, in
  microliters, of a cylinder that is 32.42 mm long
  with a diameter of 0.0789 cm.
•  ___________ 2. Calculate the density of a
  solution if 45.0 mL of the solution weighs 7.12 x
  10-2 kg.
•  ___________ 3. The Hope diamond weighs 45.52
  carats and has a density of 3.51 g/cm3. What is
  the volume of this diamond? (1 carat 200 mg)
•  ___________ 4. A plastic material weighing 2.2
  lb is shaped into a cylinder 13.5 cm in height
  and 6.8 cm in diameter. Will this object sink or
  float in water?
•  ___________ 5. A student fills a 50.0 mL
  graduated cylinder with 25.0 mL of water, then
  places a spherical object weighing 54.367 g into
  the graduated cylinder. The new volume is 41.5
  mL. Calculate the density of the object.

15.9 mL
1.58 g/mL
2.59 cm3
2.0 g/cm3 sink
3.29 g/mL
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Group Study Problem 3 on Density

• Record your final answer on this sheet and show
  all of your work on the back. Use scientific
  notation when necessary and always given your
  answers with the appropriate significant figures.
  
• ___________ 1. Calculate the volume, in liters,
  of a box that is 189 mm long by 6.75 cm wide by
  7.88 in high.
•  ___________ 2. Calculate the density of a liquid
  if 13.476 mL of the liquid has a mass of 1156.
  cg.
•  ___________ 3. What volume of mercury will have
  a mass of 10.0 kg if it has a density of 13.6
  g/ml?
•  ___________ 4. What is the density (in g/ml) of
  a substance that weighs 2.672 lb. and occupies a
  volume of 7.98 qt.
•  ___________ 5. The mass of an irregular shaped
  object was measured to be 76.58 g. A student
  fills a 50.0 mL graduated cylinder with 20.0 mL
  of water, then places the object into the
  graduated cylinder. The new volume is 37.5 mL.
  Calculate the density of the object.