What Happens to Water When It Changes to Ice?

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Lesson 2.iv

Changing State: Freezing

Cardinal Concepts

• Freezing is the process that causes a substance to change from a liquid to a solid.
• Freezing occurs when the molecules of a liquid tiresome down enough that their attractions cause them to arrange themselves into fixed positions equally a solid.

Summary

Students volition mix ice and salt in a metal tin can to brand it very cold. They will then see liquid water and ice form on the outside of the can. Students will lookout an animation of water molecules bundled equally ice.

Objective

Students will exist able to explain on the molecular level why a low enough temperature can cause the water vapor in air to condense to liquid water and then freeze to form ice.

Evaluation

Download the student activity sail, and distribute one per student when specified in the activity. The activity sheet will serve as the "Evaluate" component of each 5-E lesson plan.

Safety

Make certain yous and your students wear properly plumbing fixtures goggles.

Materials for Each Grouping

• Empty clean metallic soup can
• Salt
• Water ice
• Metal spoon or sturdy stick
• Teaspoon
• Newspaper towel

Materials for the Teacher

• Pliers
• Duct tape

About this Lesson

If the level of humidity in your classroom is as well low, you cannot do the activities in the Explore section of this lesson. However, yous tin can still teach the lesson by showing students the video Ice on a Can. It may be helpful to show students the difference in your results.

1. Prove students that liquid water expands when information technology freezes to become solid water ice.

   Teacher Preparation

   • Place l milliliters of h2o into a plastic 100 ml graduated cylinder and place it in the freezer over nighttime.
   • The side by side twenty-four hour period, bring information technology into class and show students that the level of ice is higher than the level of water y'all started with. Explain to students that as water freezes, it expands and takes up more than space than it did as liquid water.

   Show the moving picture Ice Bomb

   This video is from the Chemistry Comes Live! series and is used with permission from the Division of Chemic Education of the American Chemical Society.

   Ask students:

   Why do you think freezing water in the metal container acquired it to burst?

   H2o molecules move further apart when water freezes. This move caused the metal container to burst.

   Why are roads likely to develop potholes during common cold winters?

   Hint: Think most what happened to the metal container.

   When water gets in small-scale cracks in the road and freezes it expands and breaks the asphalt. When this continues to happen beneath the surface, information technology somewhen forms a pothole.

   Inquire students:

   What do y'all retrieve happens to h2o molecules when liquid water changes to solid ice?

   Students learned that when water vapor is cooled, attractions between water molecules cause them to condense and get liquid water. Students may say that the water molecules slow down plenty that their attractions hold them together as ice.

   Notation: Students may say that water molecules get closer together to form ice. Water is unusual because its molecules motility further apart when it freezes. The molecules of just nigh every other substance motion closer together when they freeze. This will be covered in more particular in Chapter 3, Density.

   Requite each educatee an activity sheet.

   Students will tape their observations and reply questions well-nigh the activeness on the activity sheet. The Explain It with Atoms & Molecules and Take It Farther sections of the activity sheet will either exist completed as a grade, in groups, or individually depending on instructions. Look at the teacher guide to detect the questions and answers.

2. Have students chill a metal can so that ice forms on it.

   Question to investigate

   How can you brand the h2o vapor in air condense and and then freeze?

   Materials for each group

   • Empty clean metal soup tin can
   • Table salt
   • Ice
   • Metal spoon or sturdy stick
   • Teaspoon
   • Paper towel

   Materials for the teacher

   • Pliers
   • Duct tape

   Instructor preparation

   Use pliers to curve sharp edges on the tin can downward. Then cover the rim with 2–iii layers of duct tape to preclude possible injuries.

   Procedure

   1. Dry the outside of a can with a paper towel.
   2. Place three heaping teaspoons of salt in the bottom of the tin. Make full the can about halfway with ice.

   3. Add together some other iii heaping teaspoons of common salt.

      
   4. Add together more than water ice until the can is about filled and add another iii teaspoons of salt.

   5. Agree the can securely and mix the ice-salt mixture with a metallic spoon or sturdy stick for about 1 infinitesimal. Remove the spoon, and observe the outside of the tin can. Practise non touch it yet.

      
   6. Wait iii–5 minutes. While y'all await, watch the animations.

   Read more than near why salt lowers the temperature of an ice water mixture in the teacher groundwork section.

   Notation: After completing Stride five, you may choose to have students place a thermometer inside the can. The temperature of the common salt and water ice mixture volition be below the normal freezing bespeak of water, which is 0 °C.

   Expected results

   A thin layer of ice will announced on the outside of the can. Students may also see liquid water on the upper function of the tin where it isn't as cold.

3. Hash out student observations and ask how the attractions and move of molecules tin can explain the changes in state.

   Inquire students:

   Await at and touch the outside of the tin. What do y'all detect?

   A thin layer of ice covers the coldest part of the can. Some small drops of h2o may appear college on the can where it is not as cold.

   Describe what happens to water molecules as they move from existence h2o vapor near the can to ice on the tin can.

   Water vapor molecules in the air well-nigh the can cooled when free energy from the air transferred to the cold can. These water molecules slowed down, condensed to liquid water, and and so froze to get ice.

   Your can might have some water and some ice on the outside of information technology. Explain how this is possible.

   Tiny drops of water appear on the office of the tin can to a higher place the water ice considering the molecules deadening down and condense to liquid water. Ice appears on the colder part of the can because the water vapor that came in contact with this part of the can was cooled then much that it froze.

   Give students time to answer questions about the activity and the animations.

4. Show a molecular model animation to help students visualize what happens when water freezes.

   Projection the animation Ice structure

   Betoken out that when water freezes, the water molecules take slowed downwardly enough that their attractions adapt them into fixed positions. Water molecules freeze in a hexagonal blueprint and the molecules are further apart than they were in liquid water.

   Annotation: The molecules in ice would be vibrating. The vibrations are not shown here but are shown on the next animation.

   Project the animation Ice different angles.

   Explicate that this blitheness shows different views of the water ice crystal. Indicate out that fifty-fifty though the ice is cold the molecules withal have motion. They vibrate but cannot move past one another.

5. Have students compare molecular models of liquid water and ice.

   Project the image Water and Water ice

   Ask students:

   • What are some of the differences between liquid h2o and solid ice?

   The molecules in liquid water are closer together than they are in water ice. Compared to other substances, h2o is unusual in this fashion. The molecules in the liquid are moving past one another. The hydrogen stop of 1 water molecule is attracted to the oxygen end of another only simply for a brusk fourth dimension because they are moving.

   The molecules in water ice are further autonomously than in liquid water. This is why ice floats in water. The molecules in ice are in stock-still positions simply even so vibrate.

6. Have each grouping conform their h2o molecules into a six-sided band of water ice.

   Students do non need to orient the molecules exactly as they are in the space-filling model but they should effort to have a hydrogen atom of one molecule near an oxygen atom of another. Ask students to handle their models gently because they will need them for other lessons.

   

7. Talk over why dissimilar liquids have unlike freezing points.

   Tell students that the temperature at which a substance freezes is called the freezing point. The freezing point of water is 0 °C (32 °F). Corn oil and isopropyl alcohol have lower freezing points than water. This means that they need to exist cooled to lower temperatures to make them freeze.

   Tabular array one. Freezing points for water, corn oil, and isopropyl booze.

   Water	0 °C
   Corn oil	about −xx °C
   Isopropyl alcohol	−88.5 °C

   Inquire students:

   Why exercise you recall different liquids have different freezing points?

   Help students realize that each liquid is made up of different molecules. The molecules of a liquid are attracted to each other by different amounts. The molecules accept to slow downwards to different levels before their attractions tin take hold and organize them into fixed positions as a solid.

8. Take students consider the freezing indicate of a gas.

   Tell students that the air around them is made of dissimilar kinds of gases. The attractions between the molecules of gases in air (except water vapor) are so weak that they need to exist cooled to very low temperatures in order to condense to a liquid or freeze to a solid.

   Nitrogen gas makes up about 80% of the air. If nitrogen is made cold plenty, the weak attractions between its molecules can cause it to condense to a liquid. Nitrogen condenses to a liquid at −196 °C and it freezes at −210 °C.

   Evidence the video Liquid Nitrogen.

9. Show some pictures of frost and introduce how substances can sometimes change directly from a gas to a solid.

   Tell students that under some conditions a gas tin turn directly to a solid without going through the liquid phase. Explicate that this procedure is called deposition. Some of the ice that formed on the outside of the tin can may have been a result of deposition.

   Read more than most how changes of state relate to the weather in the teacher background section.

   Projection the image Frost.

   Tell students that the frost that forms on the basis, windows, or grass in wintertime is formed by deposition.

   Give students time to reply questions well-nigh freezing points, nitrogen, and deposition to complete their activity sheets for this lesson.

   You could also show students images of snowflakes and videos of a snowflakes forming.

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Source: https://www.middleschoolchemistry.com/lessonplans/chapter2/lesson4

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