1. Chapter 2: Measurement and Problem Solving
Section 5: Density

2. Learning Objectives Calculate the density of a substance.
Use density as a conversion factor.

3. Density
The density of a substance is the ratio of its mass to its volume.

4. Density Measuring mass: use a balance Measuring volume:
Formula (l x w x h) (πr2h)
Water displacement (Vf-Vi)

5. Density Units of density: Solid substance = g/cm3
Liquid substance = g/mL

6. Example
A sample of liquid has a volume of mL and a mass of 27.2 g.

7. Density
D = m/V
m =
V =

8. Example
For a liquid substance with a density of g/cm3, what volume should be measured to deliver a mass of 68.4 g?

9. Example
A steel cylinder has a volume of 246 cm3 and a density of 7.93 g/cm3. What is its mass in kilograms?

10. Density Density is an intensive property
It does not change, no matter the size of a sample
1 kg of gold has the same density as 1 g, or 1 lb, or 1000 kg, etc.

11. Density Every substance has a unique density
you can identify an unknown substance by calculating its density and comparing it to known values

13. Temperature and Density
Density changes with temperature
For most substances, an increase in temperature results in a decrease in density

14. Temperature and Density
As temperature increases, molecules move further apart. This increases the volume of the substance while the mass remains the same – thereby decreasing the density.
So solids are more dense than liquids, which are more dense than gases

15. Density of Water The density of liquid water is 1.00 g/mL
Anything more dense than water will sink
Anything less dense than water will float

16. Density of Water
Water is one of a unique group of substances that is actually less dense as a solid than a liquid
Ice floats in water!

17. Practice
A jeweler offers to sell a ring to a woman and tells her that it is made of platinum. Noting that the ring feels a little light, the woman decides to perform a test to determine the ring’s density. She places the ring on a balance and finds that it has a mass of g. She also finds that the ring displaces cm3 of water. Is the ring made of platinum? The density of platinum is 21.4 g/cm3.

18. Practice
Mass = 5.84 g Volume = cm3

19. Practice
The woman takes the ring back to the jewelry shop, where she is met with endless apologies. The jeweler had accidentally made the ring out of silver rather than platinum. The jeweler gives her a new ring that she promises is platinum. This time when the customer checks the density, she finds the mass of the ring to be 9.67 g and its volume to be cm3. Is this ring genuine?

20. Practice
Mass = 9.67 g Volume = cm3