TuesdaySeptember 21, 2010

(Density)

Bell Ringer Tuesday, 9-21-10A student is working with a

material that has its own volume but must take the

shape of its container. Which of the following is most likely the identity of the student’s material?

A. a block of marbleB. Coca-ColaC. nitrogen gasD. lightning

ANNOUNCEMENTS

We will have a test on Friday.

Assignment Currently Open Page Date of Notes

on Website Date Issued Date Due

WS: Tools of Science Part 2

35-36

9/7 9/14

WS: Tools of Science Part 3

37-38

9/9 9/16

WS: Analyzing Data

39-40

9/10 9/17

WS: Making a Line Graph

47-48

9/15 9/22

Density• An object made of cork feels lighter than a lead object

of the same size.• What you are actually comparing in such cases is how

much mass objects have compared with their size.

• This property is called density - the ratio of mass to volume, or mass divided by volume.

DensityThe units for density that we will use

most often are:

grams per cubic centimeter (g/cm3) for solidsgrams per milliliter (g/mL) for liquids

grams per liter (g/L) for gases

Density• Density is a physical property of a substance.

• It is an intensive property, in that it does not depend on the size of the sample because as the sample’s mass increases, its volume increases proportionately, and the ratio of mass to volume is constant.

• Density can be used as one property to help identify a substance.

DensityCork has a density of only 0.24 g/cm3, which is less than the density of liquid

water (1.00 g/mL.) Because cork is less dense than water, it floats on

water. Lead, on the other hand, has a density of 11.35 g/cm3. The density of lead is greater than that of water, so

lead sinks in water.

Density

Density• Note that Table 2-4 specifies the

temperatures at which the densities were measured, because density varies with temperature.• Most objects expand as temperature

increases, thereby increasing in volume.• Because density is mass divided by

volume, density usually decreases with increasing temperature.

Worksheet

Categories, Properties, and Phases of Matter

(Pages 53-54)