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2.8

Density

Density Calculations

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Density

• Compares the mass of an object to its volume

• Is the mass of a substance divided by its volume

Density expressionD liquids = mass = g or g = g/cm3

volume mL cm3

D solids = kg or kg = kg/L L m3

Note: 1 mL = 1 cm3

Density

Density calculation video

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Review the steps for problems:

1.Circle information

2. DMV it

3. Put in triangle

4. Solve

5. Add units

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Osmium is a very dense metal. What is its density in g/cm3 if 50.0 g of osmium has a volume of 2 cm3?

1) 2.5 g/cm3

2) 25 g/cm3

3) 100 g/cm3

Learning Check

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Given: mass = 50.0 g volume = 2 cm3

Plan: Place the mass and volume of the osmium metalin the density expression.

D = mass = 50.0 g volume 2 cm3

Calculator = 25 Final answer (2) = 25 g/cm3

Solution

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Volume by Displacement

• A solid completely submerged in water displaces its own volume of water.

• The volume of the solid is calculated from the volume difference.

45.0 mL - 35.5 mL

= 9.5 mL = 9.5 cm3

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Density Using Volume Displacement

The density of the zinc object isthen calculated from its massand volume.

mass = 68.60 g = 7.2 g/cm3 volume 9.5 cm3

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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What is the density (g/cm3) of 48.0 g of a metal if the level of water in a graduated cylinder rises from 25.0 mL to 33.0 mL after the metal is added?

1) 0.17 g/cm3 2) 6.0 g/cm3 3) 380 g/cm3

25.0 mL 33.0 mL

object

Learning Check

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Given: 48.0 g Volume of water = 25.0 mL Volume of water + metal = 33.0

mLNeed: Density (g/mL)

Plan: Calculate the volume difference. Change to cm3,

and place in density expression.

33.0 mL - 25.0 mL = 8.0 mL

8.0 mL x 1 cm3 = 8.0 cm3

1 mLSet Up Problem:

Density = 48.0 g = 6.0 g = 8.0 cm3 1 cm3

Solution

6.0 g/cm3

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If olive oil has a density of 0.5 g/mL, how many milliliters of olive oil are in 18 g of olive oil?

1) 3.6 mL

2) 36 mL

3) 9 mL

Learning Check

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Given: D = 0.5 g/mL mass = 18 g

Need: volume in liters

Plan: Volume is mass divided by density

Set Up Problem:

18 g x 1 mL = 0.5 g density

factor

Solution

36 mL

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Which of the following samples of metals will displace the greatest volume of water?

1 2 3

25 g of aluminum2.70 g/mL

45 g of gold19.3 g/mL

75 g of lead11.3 g/mL

Learning Check

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1Plan: Calculate the volume for each metal and select the metal sample with the greatest volume.

1) 25g x 1 mL = 9.3 mL aluminum2.70 g

2) 45 g x 1 mL = 2.3 mL gold19.3 g

3) 75 g x 1 mL = 6.6 mL lead11.3 g

Solution

25 g of aluminum2.70 g/mL

Problem 1

What is the density of an object with a mass of 60 g and a volume of 2 cm3?

Problem 1

What is the density of an object with a mass of 60 g and a volume of 2 cm3?

Density= mass = 60g =

volume 2 cm3

30 g/cm3

Problem 2

If you have a rectangular gold brick that is 2 cm by 3 cm by 4 cm and has a mass of 48 g, what is its density?

Problem 2

If you have a rectangular gold brick that is 2 cm by 3 cm by 4 cm and has a mass of 48 g, what is its density?

Volume= length x width x height

2 cm x 3 cm x 4 cm =

Density= mass = 48 g =

volume 24 cm3

24 cm3

2 g/cm3

Problem 3

If a block of wood has a density of 0.6 g/cm3 and a mass of 120 g, what is its volume?

Problem 3

If a block of wood has a density of 0.6 g/cm3 and a mass of 120 g, what is its volume?

Volume= mass = 120 g =

density 0.6 g/cm3

200 g/cm3