Key Concepts

Freezing is the process that reasons a substance to change from a liquid to a solid.Freezing occurs as soon as the molecules of a liquid sluggish down sufficient that their attractions reason them to arvariety themselves right into solved positions as a solid.

Summary

Students will certainly mix ice and also salt in a metal can to make it extremely cold. They will then view liquid water and also ice create on the external of the have the right to. Students will certainly watch an animation of water molecules arranged as ice.

You are watching: Why do liquids freeze at different rates

Objective

Students will certainly have the ability to explain on the molecular level why a low sufficient temperature can reason the water vapor in air to condense to liquid water and also then freeze to form ice.

Evaluation

Downfill the student task sheet, and also distribute one per student once specified in the task. The task sheet will certainly serve as the “Evaluate” component of each 5-E leskid setup.

Safety

Make sure you and also your students wear correctly fitting goggles.

Materials for Each Group

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

Materials for the Teacher

PliersDuct tape

About this Lesson

If the level of humidity in your classroom is as well low, you cannot perform the tasks in the Explore section of this lesboy. However, you deserve to still teach the leskid by reflecting students the video Ice on a Can. It may be helpful to display students the difference in your results.


Engage

Show students that liquid water expands as soon as it freezes to become solid ice.

Teacher Preparation

Place 50 milliliters of water into a plastic 100 ml graduated cylinder and also area it in the freezer over night. Explore

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

Question to investigate

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

Materials for each group

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

Materials for the teacher

PliersDuct tape

Teacher preparation

Use pliers to bend sharp edges on the can down. Then cover the rim through 2–3 layers of duct tape to proccasion feasible injuries.

Procedure

Dry the outside of a have the right to via a paper towel.Place 3 heaping teaspoons of salt in the bottom of the can. Fill the have the right to around halfmeans via ice.

Add one more 3 heaping teaspoons of salt.

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Add even more ice until the deserve to is practically filled and include one more 3 teaspoons of salt.

Hold the can secucount and mix the ice-salt mixture via a metal spoon or sturdy stick for about 1 minute. Remove the spoon, and also observe the exterior of the have the right to. Do not touch it yet.

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Discuss student observations and ask just how the attractions and movement of molecules have the right to explain the alters in state.

Ask students:

Look at and touch the outside of the deserve to. What do you observe?A thin layer of ice covers the cearliest component of the can. Some tiny drops of water may show up greater on the deserve to where it is not as cold. Describe what happens to water molecules as they move from being water vapor near the can to ice on the deserve to. Water vapor molecules in the air close to the deserve to cooled once power from the air transferred to the cold can. These water molecules slowed dvery own, condensed to liquid water, and also then froze to end up being ice. Your have the right to can have some water and some ice on the exterior of it. Exordinary exactly how this is feasible.Tiny drops of water show up on the component of the have the right to over the ice because the molecules slow-moving down and condense to liquid water. Ice appears on the cooler part of the can because the water vapor that came in call through this part of the deserve to was cooled so a lot that it froze.

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

Have students compare molecular models of liquid water and ice.

Project the photo Water and also Ice

Ask students:

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

The molecules in liquid water are closer together than they are in ice. Compared to various other substances, water is inexplicable in this way. The molecules in the liquid are relocating previous one an additional. The hydrogen end of one water molecule is attracted to the oxygen end of an additional but just for a brief time because they are moving.

The molecules in ice are further acomponent than in liquid water. This is why ice floats in water. The molecules in ice are in addressed positions yet still vibprice.

Have each team ararray their water molecules into a six-sided ring of ice.

Students carry out not must orient the molecules precisely as they are in the space-filling version however they should attempt to have actually a hydrogen atom of one molecule close to an oxygen atom of another. Ask students to manage their models gently because they will certainly need them for various other lessons.

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Discuss why different liquids have different freezing points.

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

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

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

Ask students:

Why do you think various liquids have actually various freezing points?Assistance students realize that each liquid is comprised of different molecules. The molecules of a liquid are attracted to each other by various quantities. The molecules need to sluggish dvery own to different levels prior to their attractions have the right to take host and organize them into solved positions as a solid.