Key Concepts

Freezing is the process that causes a problem to readjust from a fluid to a solid.Freezing occurs as soon as the molecule of a liquid slow-moving down sufficient that their attractions cause them come arrange themselves into fixed positions as a solid.

Summary

Students will certainly mix ice and salt in a metal have the right to to make it really cold. They will certainly then view liquid water and ice form on the outside of the can. Students will certainly watch an animation of water molecule arranged together ice.

You are watching: When a substance freezes, what happens to the mass?

Objective

Students will be able to explain on the molecule level why a low sufficient temperature can cause the water vapor in waiting to condense to fluid water and then freeze to form ice.

Evaluation

Download the student activity sheet, and distribute one every student as soon as specified in the activity. The activity sheet will serve as the “Evaluate” component of every 5-E great plan.

Safety

Make sure you and your students wear correctly fitting goggles.

Materials because that Each Group

Empty clean metal soup have the right to SaltIceMetal spoon or sturdy stickTeaspoonPaper towel

Materials for the Teacher

PliersDuct tape

About this Lesson

If the level the humidity in your classroom is as well low, friend cannot execute the tasks in the discover section of this lesson. However, you can still teach the lesson by showing students the video Ice ~ above a Can. It may be valuable to present students the difference in your results.


Engage

Show students the liquid water expands when that freezes to become solid ice.

Teacher Preparation

Place 50 milliliters of water into a plastic 100 ml i graduated cylinder and place it in the freezer end night. Explore

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

Question to investigate

How have the right to you do the water vapor in wait condense and also then freeze?

Materials for each group

Empty clean metal soup deserve to SaltIceMetal spoon or sturdy stickTeaspoonPaper towel

Materials for the teacher

PliersDuct tape

Teacher preparation

Use pliers come bend spicy edges on the deserve to down. Then cover the rim with 2–3 great of duct tape come prevent feasible injuries.

Procedure

Dry the outside of a have the right to with a record towel.Place 3 heaping teaspoons that salt in the bottom that the can. Fill the can about halfway v ice.

Add one more 3 heaping teaspoons of salt.

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Add an ext ice till the have the right to is virtually filled and include another 3 teaspoons that salt.

Hold the deserve to securely and also mix the ice-salt mixture with a steel spoon or sturdy rod for around 1 minute. Eliminate the spoon, and observe the outside of the can. Perform not touch the yet.

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Discuss student observations and ask exactly how the attractions and motion of molecules can define the alters in state.

Ask students:

Look at and touch the external of the can. What perform you observe?A thin layer of ice cream covers the coldest part of the can. Some tiny drops that water may appear higher on the can where the is not as cold. Describe what wake up to water molecules as they relocate from gift water vapor near the can to ice cream on the can. Water vapor molecule in the air close to the deserve to cooled when energy from the air transferred to the cold can. These water molecule slowed down, condensed to fluid water, and also then froze to become ice. Your can could have some water and some ice cream on the outside of it. Describe how this is possible.Tiny autumn of water appear on the component of the can over the ice because the molecules slow down and condense to liquid water. Ice shows up on the colder component of the can due to the fact that the water vapor that came in contact with this component of the have the right to was cooled so much that that froze.

Give students time come answer questions around the task and the animations.

Have students compare molecular models of fluid water and also ice.

Project the image Water and also Ice

Ask students:

What are few of the differences between liquid water and solid ice?

The molecules in liquid water are closer with each other than they are in ice. Compared to various other substances, water is unexplained in this way. The molecule in the fluid are moving past one another. The hydrogen end of one water molecule is attractive to the oxygen end of an additional but just for a brief time since they are moving.

The molecules in ice cream are additional apart 보다 in fluid water. This is why ice floats in water. The molecules in ice space in addressed positions however still vibrate.

Have each group arrange their water molecules right into a six-sided ring that ice.

Students do not must orient the molecules exactly as they space in the space-filling model but they should shot to have a hydrogen atom the one molecule near an oxygen atom the another. Ask student to manage their models gently because they will require them for various other lessons.

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Discuss why various liquids have different freezing points.

Tell students that the temperature at which a substance freezes is referred to as the freeze point. The freezing suggest of water is 0 °C (32 °F). Corn oil and also isopropyl alcohol have actually lower freezing points than water. This method that they must be cooled to lower temperatures to make them freeze.

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

See more: Wh Adj-Prob Sp Cond - I Would Like To Know If When Applying

WaterCorn oilIsopropyl alcohol
0 °C
about −20 °C
−88.5 °C

Ask students:

Why carry out you think different liquids have various freezing points?Help student realize the each fluid is made up of various molecules. The molecules of a liquid are attracted to each other by different amounts. The molecules need to slow under to various levels prior to their attractions deserve to take hold and also organize them right into fixed positions together a solid.