1. Density Is a physical property of matter
Every pure substance has its own density
Is important for the identification of a sample of matter
Is an intensive property of matter

2. Density Density is defined as mass per unit volume.
The relationship can be written mathematically as: OR
units: solids [ g / cm3 ]
liquids[ g / mL]
gases [ g / L]

3. Comparison of Densities
Each cube represents a volume of 1.00 cm3. The mass of each sample increases while the volume remains constant.

4. Example:
The sample of matter you have has a mass of 3.51 g and occupies a volume of 1.30 cm3.    

5. EXAMPLE:
You need to add 45.0 g of alcohol to a sample. It is difficult to weigh an exact mass of a liquid. It is much easier to measure an exact volume. Using the density of the alcohol (0.789 g/cm3), you can determine what volume you would need to add to your sample so that you would be adding only the 45.0 grams.
= 57.0 mL in the correct number of sig figs

6. Determining the Volume
In order to figure the density we need to determine the volume:
For regularly shaped objects we use direct measurement:

7. Measuring Volume by Displacement
Used for irregular shaped objects
Select a graduated cylinder large enough to put the object in
Add water and accurately record the initial volume.

8. SLOWLY add the object to be measured:
rubber stopper
rock
metal cylinder
Read the new level of the water
The water will rise an amount equal to the volume of the object

9. What not to do

10. Here’s what the cylinder should look like

11. Do the math 1 . Original reading of volume Final volume of water
This will equal the volume of the object
22.5 mL mL =  5.1 mL
    Therefore, the volume of the object by displacement is 5.1 mL

12. EXAMPLE:
An irregularly shaped piece of quartz was place in a graduated cylinder containing mL of water. The volume of the ater rose to mL. What is the volume of the water?
Final volume
24.35 mL
Initial volume mL
= volume of solid
3.90 mL

13. Classroom Exercises:
Blue Block
Mass = 79.4 grams
Volume=29.8 cubic cm.
D = 79.4 g ÷ 29.8 cm3 =
= 2.66 g/ cm3

14. Which block is more dense?
Green Block
Mass= 25.4 grams
Volume=29.8 cubic cm
D = 25.4 g ÷ 29.8 cm3 =
= .852 g/ cm3
Which block is more dense?

15. Cylinder
Radius = 3.5cm
Length = 7.25 cm
Mass = 32.3 g
What is the volume?
V = π X radius2 X height
π = 3.14
What is the density?

16. Sphere
Diameter = 7.0cm
Radius = 3.5cm
Mass = 32.3 g
What is the volume?
V = 4/3 π X radius3
π = 3.14
What is the density?

17. Density Can also be used as a means of separating components of matter
Ex: if 2 solids of a different density are mixed together, the solid with the greater density will gravitate to the bottom
When a solid object is placed in a liquid that has a great density, the solid object will float.
We will test this hypothesis in lab.

18. Density Gradient

19. The Concept of Density for Liquids and Solids
THE DENSITY CONCEPT
The picture illustrates a density gradient.
Each item (solid or liquid) is arranged in the cylinder according to its density.
The samples are arranged with the greater densities toward the bottom and the lowest density on the top.
The Concept of Density for Liquids and Solids

20. Which kind of matter is more dense?

22. Question for you- Why does ice float?
Solid H2O (ice) is less dense than liquid H2O (water).

23. Rivers never become completely frozen because as soon as water freezes, it floats up to the surface.
Fish live in the unfrozen, denser liquid water below the layer of ice.

24. Comparison of:
Liquid water  Ice
Mass = 100 g   Mass = 100 g
Volume = 100 mL  Volume = 110 mL
Density = 1.0 g/mL Density = 0.92 g/mL