th
Trim and Glue in Journal:
“Cornell: Practice Problems”
Hint: You can cut BOTH at the same time!
REMINDER:
Quiz is Monday
Homework due Monday

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.

What is density?
 Density is a comparison of how much matter there is in a certain amount of space.
 Each element on the periodic table has a specific density.
 The density of an element is the same no matter what the size or mass of the sample.
 Density can be used to identify elements

 Density is a physical property of a substance that is used to identify that substance.
Density of Lead
Density of Lead
Density of Lead
 The size of the object does not change the density. The density of lead is always going to be the same.

Mass
Measurement of the amount of matter
(or stuff) in an object
 Measured in grams (g)

Volume
Measurement of the amount of space an object takes up
 Measured in milliliters (ml) or cm 3

Finding Volume
 To find the volume of a liquid, use a graduated cylinder
 Make sure to read the bottom of the meniscus

• Identifying your units!
The base unit for mass (m) of an object is grams (g).
The base unit for volume of a solid is cubic centimeters (cm 3 ).
The base unit for volume of a liquid is milliliters (ml)

Which one is more dense?
 Demonstration: People in a square
 How about this: Which square is more dense?

Which one is more dense?
 Now which one is more dense?

What is density?
 Density = mass OR mass ÷ volume.
volume
 Units for density: g/cm 3 g/mL
 Why are these the units for density?
ALWAYS
REMEMBER
UNITS!

The Triangle for
Volume, Mass, and Density
Density =
Volume =
M
V
M
D
Mass =
D x V
M
D X V

To find density :
1) Find the mass of the object
2) Find the volume of the object
3) Divide : Density = Mass -
Volume
Ex. If the mass of an object is 35 grams and it takes up 7 cm 3 of space, calculate the density.

To find density :
1) Find the mass of the object
2) Find the volume of the object
3) Divide : Density = Mass -
Volume
Ex. If the mass of an object is 35 grams and it takes up 7 cm 3 of space, calculate the density.
Set up your density problems like this:
Given: Mass = 35 grams cm 3 ) Volume = 7 cm 3
Formula: D = M / V
Unknown: Density (g/
Solution: D = 35g/7 cm 3
D = 5 g/cm 3

Solving for Density
 Jack has a rock. The rock has a mass of
6g and a volume of 3cm 3 . What is the density of the rock?
 Jill has a gel pen. The gel pen has a mass of 8g and a volume of 2cm 3 . What is the density of the rock?

Solving for Mass and Volume
 Calculate the mass of a liquid with a density of 3.2g/mL and a volume of 25mL.
*Find the volume that 35.2g of carton tetrachloride (CCl
4
) will occupy if it has a density of 1.60g/mL.

 A 2.75 g sample of a substance occupies a volume of 250.0cm
3 . Find its density.
 The density of ethanol is 0.780g/mL. Find the mass of a sample of ethanol that has a volume of 150.0mL.
 A rectangular block of lead measures
2cm x 3cm x 4.5cm. If the density is
11.34g/cm 3, calculate the mass of the block.

 Jake has a book, a ruler, and a balance.
 How can Jake find the density of the book with the tools he has?
 Measure Book : Length, Width, Height
 Calculate Volume: LxWxH
 Measure mass with TBB
 Plug into Density Formula

Finding Volume
 Water Displacement Method
- Read the initial volume of water in a graduated cylinder
- Place object into cylinder
- Read the final volume of water
- Final – Initial = Volume of the object

Reading a Graduated Cylinder

Meniscus

With an Irregular Shaped Object
1 st Water Level
Initial Height of
Water
350 mL

With an Irregular Shaped Object
1 st Water Level
Initial Height of
Water
2nd Water Level
Place object into water and read level again .
350 mL
350 mL

With an Irregular Shaped Object
1 st Water Level
Initial Height of
Water
2nd Water Level
Place object into water and read level again .
425 mL
350 mL

With an Irregular Shaped Object
1 st Water Level
Initial Height of
Water
2nd Water Level
Place object into water and read level again .
425 mL
Subtraction
Problem
2 nd water level
- 1 st water level
350 mL
425 mL
- 350 mL
75 mL

m = 360 g

= m = 360 =12.0 g/cm 3
V 30
80 cm 3
50 cm 3
 Find the Mass of the solid on a balance.
 Fill the Measuring Cylinder with Water to a known
Volume.
 Add the Object.
 Work out the Volume of
Water that is displaced.
 Calculate the Density.

Water Displacement Practice
 An irregular object with a mass of 18kg displaces 2.5 L of water. Calculate the density of the object.
 An irregularly-shaped sample of Aluminum has a mass of 43.6g. The student uses water displacement to find the volume.
The initial volume reading is 25.5mL, and after the Al is added, the water has risen to 41.7mL. Find the density of the Al.

One more Example….
 A cube of gold (Au) has a side length of
1.55cm. If the sample is found to have a mass of 71.9g, find the density of Au.

Liquid Layers
 If you pour together liquids that don ’ t mix and have different densities, they will form liquid layers.
 The liquid with the highest density will be on the bottom .
 The liquid with the lowest density will be on the top .

Liquid Layers
 Which layer has the highest density?
 Which layer has the lowest density?
 Imagine that the liquids have the following densities:
 10g/cm 3 .
 6g/cm 3 .
3g/cm 3 .
5g/cm 3 .
 Which number would go with which layer?

Liquid Layers – Try with your neighbor
 Which liquid has the highest density?
 Which liquid has the lowest density?
 Which liquid has the middle density?

Liquid Layers – Try on your own!
 Imagine that the liquids on the right have the following densities:
 15g/cm 3 10g/cm 3
 3g/cm 3 9g/cm 3
 7g/cm 3 12g/cm 3
 Match the colors to the correct densities.
3g/cm 3
9g/cm 3
12g/cm 3
7g/cm 3
10g/cm 3
15g/cm 3

Review
 What is the formula for density?
 What happens if you pour together liquids that have different densities?
 Will the liquid on the top have the highest or lowest density?
 Will the liquid on the bottom have the highest or lowest density?

Supplies: Each person needs 1 cranberry, 1 Powerade, 1 diet 7 up, and 1 clear plastic cup of ice.
Prediction:
Which substance is most dense? Which substance is least dense?
Task: Poured Cranberry juice in first over a piece of ice; Gatorade in slowly over a piece of ice; and then diet 7 up slowly over a piece of ice. Observe what happens.

Reason Why: They stayed in separate layers based on sugar content.
Application
What’s Happening: think about ocean and continental crusts, apply what happened with the drink to what you know about these two crusts…
Ocean floor crust is heavier and more dense than continental crust (because of the water