Exploring molecular movement: does temperature matter?
In this interactive demonstration, students observe what happens to food coloring when dropped into beakers containing different temperatures of water.
Concepts: All molecules have energy and are constantly in motion. Heat is associated with the motion of molecules.
Vocabulary words: kinetic energy, beaker, molecules, motion
Context for Use
Resource Type: Activities:Classroom Activity:Short Activity:Demonstration, Activities:Lab Activity
Grade Level: Intermediate (3-5)
Description and Teaching Materials
The teacher can begin with this: You cannot see molecules, but everything in the world is made up of them. A molecule is much smaller than a grain of salt or a drop of water. Do molecules move? If so, how fast and how slowly?
2 clear beakers/glasses/graduated cylinders
The teacher should have one container with cold water, and one with hot. You can record the temperature in each container if you like. Be sure that both containers contain the same amount of water.
Discuss with the students the temperature of each container of water. Ask the students what they think will happen to a drop of food coloring placed in each container, and why they think the way they do.
Quickly place one drop of food coloring in each container and observe what happens. Use the same color in each container.
The food coloring will spread throughout the water in both beakers but at different rates. Why does this happen? The cold water will eventually become completely colored because the water molecules are moving throughout the glass. When the water is warmer, the heat energy in it causes the water molecules to move much faster. This makes the food coloring spread out more rapidly. This is an example of kinetic molecular energy.
After the initial demonstration by the teacher, the students may ask some additional questions including:
1. How much of a difference does the temperature make?
2. Does the amount of water in the container make a difference?
3. Does the color of the food coloring make a difference?
4. Does the size or shape of the container make a difference?
5. Does the height of the drop make a difference?
After the students have had the opportunity to try some more experiments, they should come together as a group to discuss their findings.
This activity was adapted from Simple Chemistry Experiments with Everyday Materials by Louis V. Loeschig, Sterling Publishing Co., New York, 1995.
Teaching Notes and Tips
We have done very little with forms of energy in the past, and this will be a start. With our current science curriculum, we have had difficulty meeting some of the standards dealing with asking questions about the natural world that can be answered scientifically and this activitiy will enable us to do so.
3.I.B.1 The student will ask questions about the natural world that can be investigated scientifically.