3. Water to Ice:  Investigation 12

What changes and what stays the same as ice melts?

Plan Investigation 12

Bottle filled with water on scale

Today students complete their investigation of ice. They start by checking the bottles to answer whether weight and volume change as ice melts. At this point students should have substantial evidence for answering the question, What changes and what stays the same as ice melts? at the visible level. To learn about what is happening at a very much smaller scale, the particle level, students observe the Particle Magnifier, a computer model that introduces scientists' understanding that all matter is made of tiny particles (atoms or molecules). As the ice is warmed, students see the motion of individual particles increase to the point where the bonds holding the particles locked in position in the solid begin to break and reform. This allows the particles to slide past and collide with one another as the ice is transformed to water.

By the end of this session students will understand that, as ice melts, the weight of a sample remains the same, the volume decreases, and the kind of matter - water - remains the same. They will have been introduced to the particle model of matter and considered how the model helps to explain the transformation of a solid to a liquid.

Learning Goals

  • Understand that liquid water and ice are the same kind of matter
  • Become familiar with the particle model of matter to explain transformations of water
Sequence of experiences
1. Explore bottles Pairs 10 Mins
2. Use data All Class 5 Mins
3. Introduce Particle Magnifier (Water) All Class 15 Mins
4. Make meaning All Class 15 Mins

Materials and Preparation

Preparation:

For the class:

  • Post the investigation question in a place where all students can see it.
  • Post the class chart, "Comparing Ice and Water"; created in Investigation 10.
  • Post the class table, "Transforming Water to Ice and Ice to Water"; created in Investigation 11.
  • The Particle Magnifier (Water), using a classroom computer and projector or Smart Board.

For each group:

  • 1 digital scale
  • 2 plastic bottles of water, from the last investigation

1. Explore bottles

Pairs 10 Mins Notebook
Student weighing bottle filled with water

The class will finish their investigations of ice today. After they check the weight and volume of the melted ice, they will return to the investigation question:

What changes and what stays the same as ice melts?

Distribute materials. Give each group the same scale it has been using to weigh the water and ice in the previous classes.

Point out that there is no condensation on the containers. This should reinforce the fact that water does not seep through the plastic, and that temperature plays a role in condensation. Students:

  1. Measure and record the weight on the page [What happens to weight and volume when water freezes and ice melts?] in the Science Notebooks.
  2. Check the volume by observing the level of the water and record the observation (did the volume increase, decrease, or stay the same?) on the same page.
  3. Respond to the questions on the page [What changes and what stays the same as ice melts?] in their Science Notebooks.
  4. Enter the weight and volume data in the last two columns of the class data table.
Transforming Water to Ice and Ice to Water
Pair Weight before Freezing (grams) Weight after Freezing (grams) Volume after Freezing (Notes) Weight after Melting (grams) Volume after Melting (Notes)
1          
2          
3          
etc.          

2. Share data

All Class 5 Mins

Use the data from the class chart, Comparing Ice and Water and/or the class data table, Transforming Water to Ice and Ice to Water to address the following:

Some of the properties of ice and water are the same and some are different. Do you think ice and water are the same or different kinds of matter?

Some possible student arguments:

Transforming Water to Ice and Ice to Water
Yes, ice and water are the same kind of matter No, ice and water are not the same kind of matter
  • The container had water in it when it was first sealed, and it has water in it now, so it had to be water when it was frozen.
  • If you put a piece of ice in a glass of water and it melts, the type of material is all water.
  • The weight of a sample doesn't change when water freezes to ice and ice melts to water.
  • Ice is translucent and water is clear (transparent).
  • Ice is a solid and water is a liquid.
  • The volume of a sample of ice decreases when it melts to water.

Explain that you are going to introduce a scientific model that may help them think in a new way about the matter that makes up ice and water.

3. Introduce Particle Magnifier (Water)

All Class 15 Mins
Particle Magnifier

Explain that scientists believe all matter, including ice and water, is made of very tiny particles. Single particles of matter are much too small to see even with the most powerful microscopes available. Once enough of the particles clump together, we see them with our eyes as water, or ice, or salt, or other materials. The Particle Magnifier (Water) represents what scientists imagine they might see if they could see individual particles of ice or water at various temperatures.

Start by selecting Absolute zero on the thermometer of the Particle Magnifier (Water) and show the ice/water at increasing temperatures. At each temperature, provide a few words of context (see Notes, below) and ask:

What are the particles doing now? What has changed? What stays the same?
Temp Notes Likely student observations
Absolute zero No heat energy is present.
  • The particles are arranged in a pattern.
  • The particles are not moving.
  • All of the particles are the same size and shape.
-89°C The ice is still extremely cold, but heat energy is causing the particles to vibrate.
  • The particles are still arranged in a pattern.
  • The particles are jiggling, or vibrating.
  • The size of the particles is the same.
-15°C The ice is warmer, but is still quite frozen.
  • The particles are vibrating at a greater speed than at -89°C.
  • They are still arranged in a pattern.
2°C Enough heat energy has been added to transform ice to water.
  • The particles are no longer arranged in a pattern; they are sliding past and colliding with one another.
  • The water particles look the same as the ice particles.
20°C The water is at room temperature.
  • The particles are moving faster, still sliding past and colliding with one another.
  • The water particles look the same as the ice particles.
What do you predict will happen if I increase the temperature of the water even more?
Temp Notes Likely student observations
50°C The water is now too hot to touch, but it is not boiling.
  • The particles are moving faster, still sliding past and colliding with one another.
  • The water particles still look the same as the ice particles.

How does the Particle Magnifier explain some of the differences between solids and liquids?

  • Solid materials have a shape because the particles are locked together.
  • Liquids flow because the particles have more heat energy, have broken away from one another, and can slide past and/or bump one another.

Optional:  The Science Notebook page [Particle Magnifier ice and water particles] is there for you to assign if time permits.

4. Make meaning

All Class 15 Mins

Purpose of the discussion

The purpose of the discussion is for students to clarify their understanding of transformation of solid ice to liquid water at the particle level. Focus the discussion on the investigation question: What changes and what stays the same as ice melts?

Engage students in the focus question

Imagine a tray of ice cubes. Imagine those cubes melting. If we could zoom in and see the ice melt at the particle level - like we did with the Particle Magnifier - what do you think would change and what would stay the same as ice melts?

  • The individual particles stay the same when ice melts.
  • For both ice and water, the warmer the temperature, the more the particles move.
  • In ice, the particles are arranged in a pattern, even when they are warmed up and vibrating (jiggling but still in place).
  • In water, individual particles slide around and collide, and are not arranged in a pattern.

Revisit the Particle Magnifier (Water)

What connections do you notice between the visible evidence and changes at the microscopic level?

Visible Level Particle Level
Solid water (ice) keeps its shape and liquid water doesn't. Particles in ice are held in a shape. Particles in water aren't locked in place. They slide past and collide with one another.
At the visible level, reasoning tells us that water remains the same - ice is formed from water and returns to water when it melts. Particles in the model remain the same. Particle motion and arrangement change.

Summarize the discussion and recap the investigation

When a sample of water is transformed to ice and back to water, the weight does not change. When water freezes, the volume increases but returns to the original volume when the ice melts. The particle model of matter explains these transformations of water.

Note:  Materials typically contract when they cool and change from liquid to solid. Water is an exception: it expands when it freezes and transforms to ice.