1. Section 3.3—Density
Do you want high or low density in your airbag?

2. Definitions Density- the ratio of mass to volume of a sample
How heavy is it for its size?
Lead = high density…small size is very heavy
Air = low density…large sample has very little mass

3. Density Mass Density m D = V Volume
In grams (g)
Density
In g/L or g/mL
D = m V
Volume
In liters (L) or mL
Don’t try to cancel out the units…density has “2 units” – a mass unit over a volume unit!

4. Example 1—Solving for Density
What is the density of a sample with a mass of 2.50 g and a volume of 1.7 mL?

5. Example 1—Solving for Density
m = 2.50 g
V = 1.7 mL
Example:
What is the density of a sample with a mass of 2.50 g and a volume of 1.7 mL?

6. Example 2—Solving for Mass
What is the mass of a 2.34 mL sample with a density of 2.78 g/mL?

7. Example 2—Solving for Mass
V = 2.34 mL
D = 2.78 g/mL
Example:
What is the mass of a 2.34 mL sample with a density of 2.78 g/mL?
2.34 mL ×
× 2.34 mL

8. Example 3—Solving for Volume
A sample is 45.4 g and has a density of 0.87 g/mL. What is the volume?

9. Example 3—Solving for Volume
m = 45.4 g
D = 0.87 g/mL
V = ?
Example:
A sample is 45.4 g and has a density of 0.87 g/mL. What is the volume?
V ×
× V
0.87 g/mL
0.87 g/mL

10. Graphing Density Density
Volume (mL)
Mass (g)
Density
If we make the y-axis mass and the x-axis volume then…
Then the slope equals Density!

11. Floating
Objects float when they are less dense than the substance they are in!
Fewer particles in the same space = less dense
More particles in the same space = More dense

12. If a 22.7 g sample has a volume of 47.8 mL, will it float in water?
Let’s Practice 1
Example:
If a 22.7 g sample has a volume of 47.8 mL, will it float in water?

13. If a 22.7 g sample has a volume of 47.8 mL, will it float in water?
Let’s Practice 1
m = 22.7 g
V = 47.8 mL
D = ?
Example:
If a 22.7 g sample has a volume of 47.8 mL, will it float in water?
The density of water is 1 g/mL. This sample’s density is lower. It will float.

14. What volume is a sample that is 27.5 g and has a density of 3.5 g/mL?
Let’s Practice 2
Example:
What volume is a sample that is 27.5 g and has a density of 3.5 g/mL?

15. What volume is a sample that is 27.5 g and has a density of 3.5 g/mL?
Let’s Practice 2
V = ?
m = 27.5 g
D = 3.5 g/mL
Example:
What volume is a sample that is 27.5 g and has a density of 3.5 g/mL?
V ×
× V
3.5 g/mL
3.5 g/mL