Melt Ice and Chill the Liquid Again What Will You Observe

Are you loving this? Not loving this? Please consider taking a moment to share your feedback with u.s.a.. Thanks!

Lesson 2.iv

Changing State: Freezing

Key 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 slow downwards enough that their attractions crusade them to arrange themselves into fixed positions equally a solid.

Summary

Students will mix ice and table salt in a metal tin to make it very common cold. They volition and so see liquid water and ice form on the outside of the can. Students will spotter an blitheness of water molecules arranged as ice.

Objective

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

Evaluation

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

Safety

Make sure you lot and your students wear properly fitting goggles.

Materials for Each Group

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

Materials for the Teacher

• Pliers
• Duct tape

About this Lesson

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

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

   Instructor Preparation

   • Identify fifty milliliters of water into a plastic 100 ml graduated cylinder and place information technology in the freezer over night.
   • The next day, bring it into course and show students that the level of ice is higher than the level of h2o you started with. Explain to students that as h2o freezes, information technology expands and takes up more space than it did as liquid water.

   Show the movie Water ice Bomb

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

   Ask students:

   Why do yous think freezing water in the metallic container acquired it to burst?

   Water molecules motility further apart when water freezes. This motion caused the metal container to burst.

   Why are roads likely to develop potholes during cold winters?

   Hint: Think about what happened to the metal container.

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

   Ask students:

   What practise you think happens to water molecules when liquid water changes to solid ice?

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

   Note: Students may say that water molecules get closer together to form ice. Water is unusual because its molecules move farther apart when it freezes. The molecules of just almost every other substance move closer together when they freeze. This will be covered in more detail in Chapter 3, Density.

   Give each student an activeness sheet.

   Students will record their observations and answer questions most the activity on the action sheet. The Explain Information technology with Atoms & Molecules and Accept It Further sections of the activity sheet will either be completed every bit a form, in groups, or individually depending on instructions. Wait at the instructor guide to find the questions and answers.

2. Have students arctic a metal tin can so that water ice forms on information technology.

   Question to investigate

   How tin can y'all make the water vapor in air condense and so freeze?

   Materials for each group

   • Empty make clean metal soup tin
   • Salt
   • Ice
   • Metal spoon or sturdy stick
   • Teaspoon
   • Paper towel

   Materials for the teacher

   • Pliers
   • Duct tape

   Teacher preparation

   Utilise pliers to curve abrupt edges on the tin can downward. Then cover the rim with 2–3 layers of duct tape to foreclose possible injuries.

   Procedure

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

   3. Add another 3 heaping teaspoons of salt.

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

   5. Hold the tin can securely and mix the water ice-salt mixture with a metal spoon or sturdy stick for well-nigh 1 minute. Remove the spoon, and observe the exterior of the tin. Do not touch information technology still.

      
   6. Wait 3–5 minutes. While you wait, watch the animations.

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

   Annotation: Subsequently completing Step 5, you may choose to have students identify a thermometer inside the can. The temperature of the salt and ice mixture will be below the normal freezing point of h2o, which is 0 °C.

   Expected results

   A thin layer of ice volition appear on the outside of the can. Students may besides see liquid h2o on the upper function of the can where information technology isn't as cold.

3. Discuss educatee observations and inquire how the attractions and motion of molecules tin explicate the changes in country.

   Enquire students:

   Await at and touch the outside of the can. What do yous discover?

   A sparse layer of ice covers the coldest part of the can. Some pocket-size drops of h2o may appear college on the can where it is not equally cold.

   Describe what happens to water molecules equally they move from being water vapor near the tin can to ice on the can.

   Water vapor molecules in the air near the can cooled when energy from the air transferred to the cold can. These water molecules slowed downward, condensed to liquid h2o, and and then froze to become ice.

   Your can might accept some h2o and some ice on the exterior of information technology. Explicate how this is possible.

   Tiny drops of water announced on the part of the can above the ice because the molecules slow down and condense to liquid h2o. Ice appears on the colder part of the tin can because the h2o vapor that came in contact with this part of the can was cooled so much that it froze.

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

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

   Project the animation Ice structure

   Signal out that when water freezes, the water molecules have slowed downwardly plenty that their attractions arrange them into fixed 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 be vibrating. The vibrations are not shown here merely are shown on the next animation.

   Project the animation Ice unlike angles.

   Explain that this animation shows different views of the ice crystal. Bespeak out that even though the water ice is common cold the molecules still accept motion. They vibrate simply cannot move past i another.

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

   Projection the paradigm H2o and Ice

   Ask students:

   • What are some of the differences between liquid water 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 by i some other. The hydrogen end of 1 water molecule is attracted to the oxygen end of another but but for a short time because they are moving.

   The molecules in ice are farther apart than in liquid water. This is why ice floats in water. The molecules in ice are in fixed positions but even so vibrate.

6. Take each grouping arrange their water molecules into a vi-sided ring of ice.

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

   

7. Discuss why different liquids have different freezing points.

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

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

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

   Ask students:

   Why practice you think different liquids have unlike freezing points?

   Assistance 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 have to slow downwards to different levels before their attractions can take hold and organize them into fixed positions every bit a solid.

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

   Tell students that the air around them is made of different kinds of gases. The attractions betwixt the molecules of gases in air (except water vapor) are so weak that they need to be 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 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. Prove some pictures of frost and introduce how substances can sometimes change direct from a gas to a solid.

   Tell students that nether some weather condition a gas tin plow direct to a solid without going through the liquid phase. Explain that this process is called deposition. Some of the ice that formed on the outside of the can may have been a issue of deposition.

   Read more than about 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 ground, windows, or grass in winter is formed by deposition.

   Give students fourth dimension to answer questions about freezing points, nitrogen, and degradation to complete their activity sheets for this lesson.

   Y'all could likewise show students images of snowflakes and videos of a snowflakes forming.

thompsondoomplast.blogspot.com

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

Share this post