Activity 1: Density, A Straight Line Function

Major Chemical Concept

Density is an intensive property; that is, it does not depend upon the amount of substance present. Unlike mass which is dependent upon the quantity of material in an object, the density of a cubic centimeter of aluminum is the same as the density of a cubic meter of aluminum. The density of any object can easily be calculated if only its mass and volume are known. Density is defined as the ratio of the mass of a body to its volume. It is also the slope of a mass versus volume plot. There are several ways to determine these quantities of mass and volume. Students will become familiar with methods for finding mass and volume, thus providing them with the necessary data to calculate density.

Level

Introductory, first-year high school chemistry..

Expected Student Background

See Related Concepts and Related Skills. Students should be proficient at reading volume and mass measuring devices to the proper precision. Their mathematics backgrounds must be sufficiently strong so that they understand the concept of slope of a line and how slope is calculated. Skills related to preparing graphs are essential in this activity (see A General Resource module).

Time

One class period (50 min).

Safety

Read the Safety Considerations in the Student Version. There are no special hazards associated with this activity.Materials (For 24 students working in pairs)

Materials (For 24 students working in pairs)

12 Graduated cylinders, 100-mL or 50-mL

12 Beakers, 250-mL

72-96 Metal cylinders (or appropriately sized bolts and screws)

12 Centigram balances with platforms, if available

12 Meters thread or nylon monofilament (fishing) line

Scissors

Advance Preparation

There are several ways to attach the thread to the metallic object in order to hang it from the balance. A particularly useful method is to use monofilament fishing line instead of thread. Cut approximately 15-cm fishing line and tie the ends together with an over-hand knot. It works best if you hold both ends together to make a ÒdoubleÓ overhand knot.s.

Figure 4. Making a double overhand knot.

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