Students expect an ice cube to float on water. They know that ice is less dense than water. In this demonstration, an ice cube will float in one container of water and sink in another container of water.

Materials

2 Beakers, 250-mL

150 mL Ethanol or isopropyl alcohol

150 mL Water

2 Ice cubes

Safety and Disposal

Have no open flames; the alcohols are flammable. Flush ethanol or isopropyl alcohol down the sink with ten volumes of water per volume of alcohol.

Procedure

1. Pour 150 mL water into one beaker and 150 mL ethanol into the other beaker prior to class. Position the two beakers where all can see and place an ice cube into each beaker. Ask the students to write an explanation as to why the cube sinks in one beaker and floats in the other beaker.

2. Allow them to ask two or three questions about this system which can be answered Yes or No and then give them time to write a new explanation if they wish. Choose students to read their explanations.

3. When a group consensus is reached that the reason for the sink/float discrepancy is because of the differences in the densities of the two liquids (water and alcohol), ask them what should happen when a piece of steel is placed on the water. Since steel is more dense than water, the steel should sink. Carefully place a straight pin on the surface of the water in the beaker. It will float. Have them explain why this more dense substance floats on water. This will provide a good lead-in to a discussion of surface tension.

Continued

	TABLE OF CONTENTS	TOPIC OVERVIEW	CONCEPT/SKILLS DEVELOPMENT	LINKS/CONNECTIONS	EXTENSIONS