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## Lab: Dry Ice and Water Ice

### Part I: Does Heat have to be Hot?

Your teacher will show you a demonstration in which water ice is placed on two different surfaces.

1. There is a container with a mixture of ice and water. What is the temperature?
2. There are two black squares. One is heavy and one is light. Describe the heavy one. Pay particular attention to how warm or cold it feels.
3. Describe the lighter black square. Also, is it warm or cold?
4. Your teacher will measure the temperature of the two squares. Record those temperatures here.
Heavy:                       Light:
5. Did the measured temperatures match what you thought they might be? Why or why not?
1. Make a prediction based on what you have observed so far. What will happen when an ice cube is placed on each square? Will one melt faster than the other? Explain why you think so.
2. What actually happened? Describe what happened and explain what you observed.
3. What is the temperature of the mixture of ice and water? Has some of the ice melted since you last looked at it? Does the temperature have to rise for ice to melt?
4. What melts ice, heat or temperature? Explain.

### Part II: Molecules

 Molecule: a tiny particle of matter made of two or more atoms. All molecules are a little bit sticky. All molecules are in constant random motion. Heat: the energy that makes molecules move faster if you add it to the molecules. Molecules move slower when they give up heat to something else. Heat is the power to change temperature or to cause a phase change. Temperature: a measure of the speed of molecules. Higher temperature means faster molecules. Phases of Matter: Solid: a phase matter in which the molecules are moving so slowly that their stickiness makes them stay in place. Molecules sit in one place like children sitting at their desks. Liquid: a phase of matter in which molecules move a bit faster but are all still stuck together. Molecules move around a bit like children standing in a clump waiting to get into a classroom. Gas: a phase of matter in which molecules move so fast that their stickiness is not strong enough to keep them together. Molecules move around like children on the playground, bouncing off of each other and things with lots of empty space in between.

Water (H2O) molecules are made of two atoms of hydrogen bonded to an oxygen atom. Hydrogen atoms are smaller than oxygen atoms. In the pictures above you can see how water molecules are arranged in each phase. Ice floats because of all the empty spaces between water molecules when water is solid. When a solid melts or a liquid evaporates, heat is used up. When a gas condenses or a liquid freezes, heat is given off.

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In the spaces below create some molecule drawings for the phases of carbon dioxide (CO2). A molecule of carbon dioxide has one atom of carbon in the middle bonded to two atoms of oxygen and looks like this:

 (tightly packed, nice and regular) Solid (a bit looser but random) Liquid (very few and far apart) Gas

### Part III: Dry Ice

#### Safety with Dry Ice

Dry ice is solid carbon dioxide (CO2). It has a temperature of –78°C or –108°F. As it absorbs heat it turns directly into a gas, a process called sublimation. To be safe with it, follow the rules below:

1. Do not hold dry ice in your hands or put it in your mouth. Frostbite is damage to the skin due to being frozen. This is painful.
2. Never put dry ice in an airtight container. Dry ice turns directly into a gas as it absorbs heat. The amount of gas is so very large that if it is closed up in an airtight container it will cause an explosion, harming people nearby.
3. Do not put your face into a container of dry ice. Carbon dioxide gas is the gas humans produce by combining our food with oxygen. It is bad for us to breathe and can cause people to pass out.
4. Wear safety goggles to prevent damage to your eyes. Pieces of dry ice can cause harm if they end up in your eyes because they can cause frostbite.

Your teacher will show you how to do each of the demonstrations below. You will have a chance to try each of them and record your observations.

#### Singing Spoon

Hold a piece of dry ice with a pair of tongs pressed against the table top. Press a warm spoon against the dry ice.
1. Describe what you see and hear.
2. What do you think happens to the molecules of CO2 when you press the spoon against the dry ice?
3. Why do you think it makes that noise?
4. Try putting dry ice on the ice melting blocks. How does it behave? Why?

#### Air Hockey

Use tongs to place a piece of dry ice on the table. Let it sit awhile: look at it closely while you wait about a minute. Once the bottom of the piece of dry ice has flattened out, try hitting it from the side to make it slide.
1. Describe what you see and hear.
2. What do you think happens to the molecules of CO2 where the dry ice is touching the table?
3. Why do you think it moves so smoothly?

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#### Pop-top Film Canisters

Use tongs to place a small piece of dry ice in one of the film canisters. Seal it up (this is safe because the top will pop off before the container builds up enough pressure to explode).
1. Describe what happens.
2. Try putting a quarter inch of warm water in the canister with a piece of dry ice before you seal it. Describe what happens and whether it is different from the experiment done without water.
3. What is causing the lid to pop off?
4. Why is it different when warm water is in the canister?

#### Fog

Use tongs to place one or two pieces of dry ice into a cup of cool water. Use tongs to place one or two pieces into a cup of very warm water.
1. Describe what you see.
2. What is the fog made of?
3. Why is there a difference in the amount of fog from each cup?
4. Why are the pieces of dry ice always surrounded by a little bit of fog?
Questions
1. What weird things did you notice that you want to ask your teacher about?
2. What is the term used to describe a solid turning into a gas? Use it in a sentence to describe something you observed today.
3. Did you see a liquid phase for CO2? Explain.
4. Explain how you know that a solid does not always have to melt before it turns into a gas.
5. Do you think water ice can turn directly from a solid to a gas? Why or why not?
6. Is it an exchange of heat that causes a phase change or a change in temperature that causes a phase change? Why do you think so?
Expected student responses
Last Updated: Jan 31, 2019
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