SUMMARY

In this lesson the students will explore three states of matter (solid, liquid and gas) by comparing regular ice made from water and dry ice, which is frozen carbon dioxide.

ESTIMATED TIME

30-­50 minutes

LEARNING OBJECTIVES

Learners will learn... 1. Three states of matter. 2. To transform one state of matter to another, energy must be added or subtracted/removed. 3. Gas has mass; in other words, even though gas is invisible, it still has a weight.

Learners will be able to... 1. Recognize “wet” ice versus dry ice. 2. Understand that dry ice “gasifies” to carbon dioxide gas. 3. Estimate the relative densities of solids, liquids, and gases.

 

NEXT GENERATION SCIENCE STANDARDS (Grades 2-­5)

This activity supports learning towards the following disciplinary core ideas:

PS1.A: Structure and Properties of Matter Different kinds of matter exist and many of them can be either solid or liquid, depending on temperature. Matter can be described and classified by its observable properties. (2­PS1­1)

PS1.B: Chemical Reactions Heating or cooling a substance may cause changes that can be observed. Sometimes these changes are reversible, and sometimes they are not. (2­PS1­4)

PS3.A: Definitions of Energy The faster a given object is moving, the more energy it possesses. (4­ PS3­1)

PS1.A: Structure and Properties of Matter

* Matter of any type can be subdivided into particles that are too small to see, but even then the matter still exists and can be detected by other means. A model showing that gases are made from matter particles that are too small to see and are moving freely around in space can explain many observations, including the inflation and shape of a balloon and the effects of air on larger particles or objects. (5­PS1­1)

* The amount (weight) of matter is conserved when it changes form, even in transitions in which it seems to vanish. (5­PS1­2)

PS1.B: Chemical ReactionsNo matter what reaction or change in properties occurs, the total weight of the substances does not change. (Boundary: Mass and weight are not distinguished at this grade level.) (5­PS1­2)

 

BACKGROUND INFORMATION FOR TEACHERS The world we live in, go to school in, eat in, and sleep in is a world of wonder and mystery.

Forms of matter For example, in the winter, in certain parts of the US, it snows, while in the summer, it rains. Snow is a solid form of water; rain is a liquid form of water. Those white fluffy clouds floating over your school are the same thing: solid and liquid forms of water, set against a blue sky. That blue sky—without clouds—is actually filled with water vapor, the gas form of water. Another way to think of all these forms of matter is that they are simply rearranged matter, with gas water being the most spread out, liquid water intermediate, and solid water being the least spread out or most compact. One measure of “spread­out­ness” is energy­­gases are the most energetic forms of matter, liquids have intermediate energy, and solids have the least energy. (Source for original figure: https://commons.wikimedia.org/wiki/File:Solid_liquid_gas.jpg.)

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The magic of clouds is that they represent the conversion of gaseous forms of water into either liquid water (rain; via a verb we can call “liquefy”) or solid water (snow; via a verb we can call “solidify”). Clouds start as invisible water vapor, a gas. When a gas is cooled, it can turn into liquid or a solid. But where does the gas come from that helps generate rain and snow? That gaseous water occurs via a verb we can call “gasify”—and is the result of heating of liquid or frozen solid water.

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If this figure represented all changes of matter, from gas to liquid, and from liquid to solid, we could reasonably expect to run out of gas.

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Here is a more complete figure, showing that solids can “gasify”­­turn into gas. Ice cubes in your freezer gasify; snow gasifies. More commonly, people refer to this as evaporation when liquid water is turned into gaseous water, or sublimation when frozen water is turned into gaseous water, or condensation when gaseous water cools into liquid (rain) or solid (snow, ice) forms.

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These transformations of liquids to solids, solids to liquids, and liquids to gases are familiar elements of a form of matter triangle; every change in form of matter requires adding or losing energy. Gaseous water has the most energy; liquid water has an intermediate amount of energy; and solid water has the lowest amount of energy. So to turn frozen water into liquid water, we add energy, usually from the room that our glass’s ice is melting in. The Sun also adds energy to liquid water everywhere across this planet, converting liquid water into the more energetic gaseous water.

A very important concept for this afterschool program is that though energy can be added or lost from molecules of water, those molecules of water DO NOT stop existing—though gaseous water molecules in your classroom, outside, across the sky are all invisible, they obviously exist. Just ask the next cloud, rainstorm, or snowstorm you experience! In other words, no matter what reaction or change in properties occurs, the total weight of the substances does not change, even when substances seem to disappear.

Energy basics

Energy is the ability or power to do work. This is a broad definition. It could mean the energy your body needs to get out of bed in the morning, the energy your car needs to drive you to school, or the energy your computer needs for you to be able to play a game. Energy takes many forms. To help understand energy, here are some categories or types of energy . 1 Energy is basically always either being stored or being used. When energy is stored we call it potential energy. When it is being used we call it kinetic energy (energy that comes from movement or motion). An apple is a visible example of stored chemical energy­­potential energy.

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If you eat an apple and it provides the energy to play soccer, your body is releasing the potential energy from the apple. As your body uses it, it is kinetic energy. (The energy of an apple is hidden in the bonds of sugars called fructose, which is just a 6­carbon sugar like glucose is a 6­carbon sugar. Humans mostly convert the chemical [potential] energy of food into heat energy. Unfortunately, heat energy is invisible. Just like the energy that is lost from gas when it liquefies or the energy that is gained by liquids when they gasify… invisible energy. The only evidence we have of these energy transfers is that we can see solids melting, or with dry ice, sublimating.)

For this lesson, the essential part of gaseous forms of matter and energy is that though these are invisible parts of our world, our world of wonder and mystery is a world of energy and a world of matter. When matter changes forms, we know energy has been involved.

MATERIALS AND PREPARATION

● quarters (approximately 8) ● regular ice, dry ice ● recycled empty water bottles (at least one per student) ● balloons (at least one per student) ● 2 pitchers to pour water (one warm and one cold) ● a hammer or some means of breaking the dry ice into smaller pieces ● four containers to place the ice into ● tongs or gloves to handle the ice ● infrared thermometers (optional) ● balances (optional) Before students arrive, set up a demonstration at the front of the room. Take the two containers and place a chunk of dry ice into one and a chunk of normal ice into the other. Have two other containers nearby and set these aside with a roughly equal amount of dry ice in each. Make sure you have some dry ice left over to use for the second part of the lesson. Fill a water pitcher with hot water and one with cold water (from a sink). Fill all of the water bottles ⅓ full with very warm water and have them ready for the third activity. Remember, if you use very cold water, the dry ice will not generate gas as quickly as possible.

ACTIVITY 1 & 2:

10­-15 minutes

1. When the students have all arrived for the session, have them gather around your two containers of ice and then ask if the two chunks of ice are the same. Ask them in what ways the two differ. They should notice that one of the pieces of ice has gas coming out of it and no liquid around it, whereas the other piece of ice has no gas around it but has some liquid water under or around it.

2. Ask the students if they know what the two kinds of ice are and if they know what is happening. (One piece of ice is just regular frozen water and one piece is dry ice. Dry ice is frozen carbon dioxide. Carbon dioxide freezes at ­109°F; please exercise caution with students to ensure they do not handle the dry ice with bare hands. The solid “wet” ice melts and forms liquid water, but the frozen carbon dioxide turns immediately into gaseous carbon dioxide.) 3. Ask the students if ice can turn directly into gas (yes, it depends on the conditions around the ice such as humidity in the air, wind, sunlight, etc.). What will happen if you leave the melted ice out for a long time? Will it completely disappear? (It will seem to vanish because it will become a gas. But matter can’t disappear, it can only become something else. The ice becomes water and then the water “dries up” and becomes gas.) 4. Ask the students if they think the dry ice can turn into liquid? (Yes, but it requires lots of pressure; fun Youtube distraction here). 5. If you have digital thermometers, tell they students to pass them around and take turns taking temperature measurements of the two types of ice. 6. Next ask for two volunteers to press quarters onto each type of ice. Have the kids predict whether each type of ice will act the same way and see if they can guess what will happen. Have the volunteers put on gloves and press the quarters onto the ice. 7. When you press down a quarter onto the dry ice, what happens? (The quarter should shudder and make a loud noise like a scream.) 8. Why does this happen? Why does the quarter stop making noise? (When you press a warm quarter onto the dry ice it is much warmer than the ice so it causes the dry ice to turn to gas very quickly. The gas streams out and makes the quarter shudder and “scream.” After the quarter gets too cold, the effect won’t work any more. See if the students can figure out how to “rewarm” the quarter, and replicate the effect.) 9. Ask for a volunteer to pour warm water into each of the two containers with ice. Have the students predict whether each type of ice will act the same way. Ask the students about their observations of what is happening. 10. Now pull out the other two containers of dry ice that are standing by. Ask students what they predict will happen if cold water is poured over the dry ice versus if hot water is poured over the dry ice. (The rates of sublimation [gasification] of the dry ice are very different and the dry ice reacts more strongly with the hot water because the hot water has more energy than the cold water). 11. Use the digital thermometers to track how quickly the temperatures of the hot water and cold water reach the same temperature in the presence of the dry ice.

 

ACTIVITY 3: 10­15 minutes 1. Smash up some of the dry ice into little pieces and place it into all the water bottles. As you fill each bottle place a balloon over the top. Give each student a water bottle to play with. 2. The balloons should slowly expand. Ask the students what is happening. 3. Tell them not to touch the dry ice directly, try not to spill, and to hold the bottles towards the top where there is no (supercooled) water. The bottoms of the bottle will get cold very quickly and be hard to hold. 4. The students can squeeze the bottles and try to make smoke rings and continue to observe the reaction between the water and dry ice. 5. If you have balances, try to measure the weight loss as dry ice sublimates into gas from a water bottle WITHOUT a balloon and compare this to the change in weight (there should be none) for the dry ice that sublimates into gas for the water bottle WITH a balloon. 6. Introduce the students to the following concepts. a. Matter is everything that takes up space, and has mass. b. The three most common forms of matter are: solids, liquids, and gases. 1. A solid is anything that has its own shape. 2. A liquid flows and will take the shape of the container it is in. 3. A gas, though not visible, will spread out and fill all available space. c. Names and common examples of three states of matter: solid (for example, wood, rocks), liquid (for example, water), gas (for example, air, steam). d. Matter can change from one form to another. An example would be, ice, which is a solid; melts and becomes water, which is a liquid; and when boiled (212 degrees Fahrenheit or 100 degrees Celsius) becomes steam, a gas. In fact, because of Bozeman’s elevation, water boils at 203 degrees Fahrenheit. e. Ask the students if plants, animals and/or people can change the state of matter? Explain that all three can. Plants take water and convert it into oxygen. You and your pets can eat solid and liquid food and convert them to gas­­including the stinky variety. Have you ever wondered what happens when people lose weight? Where does the mass go? It turns out you breathe most of it out as carbon dioxide and water vapor, so you convert a large part of the liquid and solids you eat to gas. We’ll learn more about that in a later lesson. f. Ask the students if temperature plays a role in matter changing states? Guide them to recognize the conditions that are associated with specific transformations, such as cooling (e.g., gas­­>liquid) or heating (e.g., liquid­­>gas) or metabolism (e.g., milkshake [“sugar” in liquid form]­­>gases or bagel [“sugar” in solid form]­­>gases). g. The principal forms of matter­­solid, liquid, gas­­reflect an upward RAMP of spacings between atoms, from closer to more distant, as in this figure. h. Have the students count the number of red dots in the diagrams below. The red dots represent (red) molecules of water, each of which can be represented chemically through the combination of two atoms of hydrogen (symbol H) and one atom of oxygen (O). Fill in the table.

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Ask the students how it is possible that the numbers they listed are NOT the same number? Remind students that matter can not disappear. j. Answer: The key is the caption, that was never shared with students: these are representations of forms of matter “in the same space”­­which means volume. That space could be a gallon of milk! From http://www.explainthatstuff.com/states­of­matter.html: Left: Solids are more dense than liquids: they have more atoms packed into the same space. The atoms are tightly packed together and stay in shape all by themselves, though they do move about on the spot. Middle: Liquids are usually less dense than solids but more dense than gases. Their atoms can move around much more, so they need a container to keep them in place (but an open container is usually okay for short periods of time). Please note that this diagram is a deliberate exaggeration: the atoms in liquids can be almost as close together as they are in solids. Right: Gases are even less dense than liquids. Their atoms go where they please, so they need a completely sealed container to keep them in place.

7. As a group, briefly discuss the following questions. This will help you better understand students’ current understanding of the topics for the activity. a. What is energy? (the ability to do work) ■ at first, keep the discussion broad­­students may bring up some of the different types of energy from the background. b. Narrow your discussion, bring up the following questions: ■ Does your body need energy (to do work)? (Yes) ■ Are you using energy right now? (Students may say no­­it is after school and they are tired/sitting still, discuss that even when sleeping our body uses energy to keep us breathing, keep our hearts beating, etc.) ■ Where do humans get the energy our bodies need? (Students will probably think of food, possibly water and sleep, explain that we will focus on the energy our bodies get from food in a future lesson)