Density

Density is another property of materials with which you need to be familiar. It is different than either mass or volume but it is related to both. (That is why this topic is in its own section, rather than under "Measurement" or "Calculations.") In fact, density is the relationship between mass and volume. Density cannot be measured directly like mass and volume can. Instead it is calculated from measurements of mass and volume.

Consider two samples of iron--say a cast iron skillet and a nail. Both are made of roughly the same material. The skillet is many times larger in volume than the nail. It is also many times heavier in mass. Because there is more iron in the skillet it weighs more and it takes up more volume. Both mass and volume are called extrinsic properties because their values depend on how much material is in sample.

Definition of Density

Density is defined as the ratio of mass to volume, that is the mass of a sample divided by the volume of the sample. If you have a larger sample, it will weigh more. But it will also have a proportionately larger volume. So the ratio of the mass to the volume will remain the same. Density is called an intensive property because its value does not depend on how much of the sample you have, but rather what the sample is made of. (Properties that do change based on the amount of the sample are called extensive properties; these include mass and volume.)

Lab Work

You already know how to measure mass and you know how to measure volume. You will use those skills in the lab to determine the density of several materials. Your lab assignment for Lesson 1 will deal with density. You will start by measuring mass and volume, making sure to use appropriate precision. Then you will go on to determine the densities of several substances, and you must not forget to keep using appropriate precision.

Study Check: Density

Answer the following questions about density. (Answers follow below.)

1. The density of a material can be defined as:

a. the volume of a sample added to its mass.

b. the volume of a sample divided by its mass.

c. the mass of a sample divided by its volume.

d. the mass of a sample multiplied by its volume.

e. the gravitational attraction of the sample to the surface of the earth.

2. What is the density of a material if a 14.0-mL sample weighs 25.0 g?

a. 0.56 g/mL

b. 1.79 g/mL

c. 5.60 g/mL

d. 39.0 g/mL

e. 350 g/mL

Answers

1. The density of a material can be defined as:

c. the mass of a sample divided by its volume.

2. What is the density of a material if a 14.0-mL sample weighs 25.0 g?

b. 1.79 g/mL