Summary:

This activity investigates the phase changes for water. You start with solid water, or ice, which you melt in a baggie. You then transfer this to a beaker on a hot plate to vaporize the liquid water into steam, which is gaseous water.

Learning Goals / Objectives:

Learning Objectives
1. To investigate the concept of molecular motion and how heat affects it.
2. To investigate the connection between heat, temperature, molecular motion and phase changes.

Questions to investigate
1. Does heat play a role in phase changes?
2. Does the temperature change during a phase change?

Background

The particles of a substance in the solid, liquid and gas phase differ in how strongly they are attracted to one another and how fast they are moving and how they are moving. The particles in a solid are very strongly attracted to each other and don’t move very much or very fast at all. At most they vibrate in place, but they are basically “stuck” in fixed positions. The particles of a liquid are less strongly attracted to one another, but they are moving a bit faster and can move around each other. They can rotate and translate, so they are not in fixed positions. The particles of a gas are essentially not attracted to each other at all, they are moving very rapidly and moving all over the place. They definitely do not have fixed positions. They rotate, vibrate, translate, everything! To change phase, energy must either be added or removed. To go from solid to liquid or gas, you need to add energy to increase the motion of the particles and to give the particles enough energy to disrupt the attractions between neighbors.

Setup:

Have materials set out for the students to pick up or have all materials already set up at their desks when they come in. Make sure students know how to use the hot plates, and monitor their usage carefully to avoid burns.

Anticipatory Set:

Discuss phases of matter, phase changes, and molecular motion in the different phases, prior to this activity.

Instructions / Activities:

Procedure
1. Obtain a Ziploc baggie with 5 or so ice cubes in it. Record your observations of the shape of the ice cubes. Use the balance to weigh the ice cubes and the bag. Record this measurement. Also record the temperature of the ice cubes.
2. Set the bag in a warm place and observe what happens to the shape of the ice cubes. As the ice cubes are melting, measure the temperature of the ice and water inside the bag. After the ice has melted measure the temperature again. Measure the mass of the water and the bag. Record your observations and measurements.
3. After the ice has completely melted, transfer the water carefully to a glass beaker. Note and mark the level the water reaches in the beaker. Record the temperature of the water.
4. Put the beaker on a hot plate and turn on the hot plate. Heat the water until it boils. Record the temperature of the water as it boils. Observe what happens to the water as it boils. Record your observations and measurements.
5. After a few minutes shut off the heat, remove the beaker from the hot plate and allow it to cool for awhile. Record the temperature after several minutes. Also note the level of the water. Record your observations and measurements.

Assessment:

1. Identify the different states of water at different points in this investigation.

2. Compare the mass of the ice to the mass of the water after it melted. What does this show about changes in state?

3. Do you think the mass changed during the boiling process? Why or why not? Explain based on your observations.

4. Make a graph in your lab notebook showing the temperatures you recorded during this investigation.

Wrap-up / Closure:

Close by drawing a heating curve on the board and discussing the different regions of this curve – temperature changes for single phases, and then the phase change regions where temperature doesn’t change.

Attachments: