How Would A Thermometer In The Water Most Likely Change As The Water Freezes

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Lesson 2.4

Changing State: Freezing

Fundamental 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 downwardly plenty that their attractions cause them to accommodate themselves into fixed positions equally a solid.

Summary

Students volition mix ice and salt in a metal tin to make it very cold. They will and so run across liquid h2o and ice form on the outside of the can. Students volition picket an animation of h2o molecules arranged every bit ice.

Objective

Students volition be able to explicate on the molecular level why a depression enough temperature tin can cause the water vapor in air to condense to liquid water so freeze to course ice.

Evaluation

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

Safety

Brand sure you and your students wear properly plumbing equipment goggles.

Materials for Each Grouping

• Empty clean metallic soup can
• Salt
• Ice
• Metallic spoon or sturdy stick
• Teaspoon
• Newspaper towel

Materials for the Teacher

• Pliers
• Duct tape

Nigh this Lesson

If the level of humidity in your classroom is too depression, you cannot exercise the activities in the Explore section of this lesson. However, you can still teach the lesson by showing students the video Water ice on a Can. It may be helpful to show students the difference in your results.

1. Evidence students that liquid water expands when it freezes to become solid ice.

   Instructor Preparation

   • Place 50 milliliters of water into a plastic 100 ml graduated cylinder and place information technology in the freezer over dark.
   • The adjacent day, bring it into class and show students that the level of water ice is higher than the level of h2o you started with. Explain to students that as water freezes, information technology expands and takes up more infinite than it did as liquid water.

   Show the movie Ice Flop

   This video is from the Chemical science Comes Live! serial and is used with permission from the Sectionalization of Chemical Education of the American Chemic Club.

   Inquire students:

   Why practise you lot recollect freezing h2o in the metal container acquired information technology to burst?

   Water molecules movement farther apart when water freezes. This movement caused the metal container to outburst.

   Why are roads likely to develop potholes during cold winters?

   Hint: Recollect about what happened to the metallic container.

   When water gets in modest cracks in the road and freezes it expands and breaks the asphalt. When this continues to happen below the surface, it somewhen forms a pothole.

   Inquire students:

   What do yous think happens to water molecules when liquid water changes to solid ice?

   Students learned that when h2o vapor is cooled, attractions between water molecules cause them to condense and go liquid h2o. Students may say that the water molecules slow downward enough that their attractions hold them together as ice.

   Note: Students may say that h2o molecules become closer together to form water ice. H2o is unusual because its molecules motility further apart when it freezes. The molecules of just virtually every other substance move closer together when they freeze. This will be covered in more than detail in Chapter 3, Density.

   Give each student an activeness sail.

   Students will record their observations and answer questions nearly the activity on the activeness sheet. The Explicate It with Atoms & Molecules and Accept Information technology Further sections of the activeness canvas will either be completed as a class, in groups, or individually depending on instructions. Look at the teacher guide to find the questions and answers.

2. Have students arctic a metal can and then that water ice forms on it.

   Question to investigate

   How tin you make the water vapor in air condense and then freeze?

   Materials for each grouping

   • Empty clean metallic soup can
   • Salt
   • Ice
   • Metal spoon or sturdy stick
   • Teaspoon
   • Paper towel

   Materials for the teacher

   • Pliers
   • Duct tape

   Teacher preparation

   Apply pliers to bend sharp edges on the can down. And so embrace the rim with two–3 layers of duct tape to preclude possible injuries.

   Process

   1. Dry the outside of a can with a newspaper towel.
   2. Place 3 heaping teaspoons of salt in the bottom of the tin can. Fill the can about halfway with ice.

   3. Add some other iii heaping teaspoons of salt.

      
   4. Add more ice until the can is almost filled and add together another 3 teaspoons of salt.

   5. Hold the can securely and mix the ice-salt mixture with a metal spoon or sturdy stick for about i infinitesimal. Remove the spoon, and observe the outside of the can. Do non bear on information technology yet.

      
   6. Wait iii–5 minutes. While you await, picket the animations.

   Read more about why salt lowers the temperature of an water ice water mixture in the teacher background section.

   Note: Later completing Step 5, you lot may cull to have students identify a thermometer within the can. The temperature of the common salt and ice mixture will be below the normal freezing point of water, which is 0 °C.

   Expected results

   A thin layer of ice will appear on the exterior of the tin. Students may as well encounter liquid water on the upper part of the can where information technology isn't as common cold.

3. Discuss student observations and ask how the attractions and motion of molecules can explain the changes in state.

   Ask students:

   Look at and affect the outside of the can. What do you detect?

   A sparse layer of ice covers the coldest part of the can. Some small drops of water may appear higher on the can where it is not every bit cold.

   Describe what happens to water molecules equally they move from being h2o vapor well-nigh the tin to ice on the can.

   Water vapor molecules in the air near the tin cooled when energy from the air transferred to the cold tin. These water molecules slowed downwards, condensed to liquid water, and so froze to become ice.

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

   Tiny drops of water appear on the part of the tin can in a higher place the ice considering the molecules slow 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 tin was cooled then much that it froze.

   Requite students time to respond questions nearly the activity and the animations.

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

   Project the animation Ice structure

   Point out that when water freezes, the water molecules take slowed down enough that their attractions conform them into stock-still positions. H2o molecules freeze in a hexagonal pattern and the molecules are further apart than they were in liquid water.

   Note: The molecules in ice would exist vibrating. The vibrations are not shown here but are shown on the side by side blitheness.

   Project the animation Ice different angles.

   Explicate that this animation shows dissimilar views of the water ice crystal. Point out that even though the ice is common cold the molecules still have motion. They vibrate but cannot motility by i another.

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

   Project the epitome Water and 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, water is unusual in this way. The molecules in the liquid are moving past one another. The hydrogen cease of ane water molecule is attracted to the oxygen end of another but simply for a short time because they are moving.

   The molecules in ice are further apart than in liquid water. This is why ice floats in water. The molecules in ice are in fixed positions but still vibrate.

6. Have each group arrange their water molecules into a vi-sided ring of water ice.

   Students practice not need to orient the molecules exactly equally they are in the space-filling model but they should endeavour to have a hydrogen atom of one molecule near an oxygen cantlet of some other. Ask students to handle their models gently because they will need them for other lessons.

   

7. Hash out why unlike liquids have different freezing points.

   Tell students that the temperature at which a substance freezes is called the freezing point. The freezing bespeak of h2o is 0 °C (32 °F). Corn oil and isopropyl alcohol take lower freezing points than water. This means that they need to be cooled to lower temperatures to make them freeze.

   Table 1. Freezing points for water, corn oil, and isopropyl booze.

   Water	0 °C
   Corn oil	about −20 °C
   Isopropyl alcohol	−88.5 °C

   Ask students:

   Why do you think dissimilar liquids have dissimilar freezing points?

   Help students realize that each liquid is made up of different molecules. The molecules of a liquid are attracted to each other past different amounts. The molecules have to dull downwardly to dissimilar levels before their attractions can take hold and organize them into fixed positions as a solid.

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

   Tell students that the air effectually them is made of different 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 lodge to condense to a liquid or freeze to a solid.

   Nitrogen gas makes upward about eighty% of the air. If nitrogen is made cold enough, 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.

   Show the video Liquid Nitrogen.

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

   Tell students that nether some weather condition a gas tin can turn directly to a solid without going through the liquid phase. Explain that this procedure is called degradation. Some of the water ice that formed on the outside of the can may have been a result of degradation.

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

   Project the paradigm Frost.

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

   Requite students fourth dimension to answer questions near freezing points, nitrogen, and deposition to complete their activity sheets for this lesson.

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

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

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