Lesson

Engage

• Students will be asked how fog develops and common causes of fog. Ask the question, can fog be created in the classroom? What could possibly be used to create fog in the classroom? (Water ice cubes, breathing on a mirror or table)
• Explore how fog is really a cloud (droplets of water) and how condensation causes fog formation
• Using common ice cubes (H₂O), ask students to put together a procedure for creating fog. What are the temperatures of the ice cubes? (Completely frozen ice cubes are below 0 degrees C while melting ice cubes hover near 0 degrees C)
• What happens to ice cubes when the temperature rises? Do they become liquid or skip right to a gas? (Ice cubes become liquid first before the water evaporates) (For those that usually get snow during the cold season: What happens on a very cold, sunny day to the snow depth after a fresh snowfall? (Energy from the sun causes sublimation, which knocks out some snow depth even with temps well below freezing)

Explore

1. Students will obtain a piece of dry ice (golf ball size) and place into a 250ml beaker. Place your entire palm onto the top of the beaker describe the gradual increase in pressure on your palm.
2. Place the dry ice onto the lab table and using tongs or gloves; place a penny vertically into the ice. Observe the thermal contraction of the penny and condensation forming on the table for several minutes.
3. Place several drops of water onto the table and push the ice slowly into the small puddle. Observe the filaments of fog. After 3 minutes, move the ice away from the puddle and observe the frozen water now on the table.
4. Fill a 250ml beaker with warm water and place the piece of dry ice into the beaker so that it is completely submerged. Observe the increased fog formation and the bubbles of carbon dioxide rising to the top. Explore the idea of the dry ice boiling.
5. Place several drops of hand soap into the beaker and observe the bubble formations rising out of the beaker.

Explain

• Record several observations for each item as shown on the activity sheet.
• What causes the pressure increase on your palm? (Solid turning to gas) Is it a dramatic or subtle increase? (subtle) Would you be able to feel the pressure increase if you didn’t completely cover the top of the beaker with your palm? (probably not)
• Did the penny make a sound when you placed it into the dry ice? If it did, what was the sound and why did it make a sound? (Yes, the penny was causing increased sublimation while the penny itself was experiencing thermal contraction)
• After several minutes, why does ice form on the penny? Is that ice made of water or carbon dioxide? (Ice forms from condensation of water vapor in the room/atmosphere)
• Why did placing the dry ice into the puddle of warm water create fog? Is fog a liquid or a gas? After 3 minutes, why did the water on the table freeze? (The fog is made of tiny liquid drops. The water doesn’t change temperature that quickly because of high heat capacity and causes more sublimation. The increased sublimation means more cold carbon dioxide entering the air and therefore more condensation) (The water froze on the table because the dry ice caused the temperature of the puddle to drop below freezing).
• After placing the ice into the beaker with warm water, more fog forms. Why does more fog form when the ice is submerged in water rather than in a puddle on the table? (More fog forms because more water causes more sublimation, which causes more condensation as the cold gas leaves the beaker).
• After placing a few drops of soap into the beaker with ice, why does the soap form so many bubbles that climb out of the beaker? (The “boiling action” stirs the soap in the water and the soap bubbles become filled with carbon dioxide)

Elaborate

Smash dry ice into small pieces, place into a plastic Burrell Pipet and wrap closed with needle nosed pliers at the point. Lower the pipet with the ice into a warm water bath. Liquid carbon dioxide develops in the pipet. Explain why the ice in the pipet did not sublimate and formed liquid. How is this different from the prior activities where dry ice did sublimate? (A substance’s state (solid, liquid, and gas) is determined by temperature and also pressure. By sealing the carbon dioxide into the pipet, the increased pressure causes the dry ice to form a liquid instead of a gas at the beginning.)

Evaluate

Multiple Choice Items

1. What happened to the penny as it was inserted into the dry ice?

a. The penny expanded

b. The penny condensed

c. The penny contracted

d. The penny gained momentum

2. When condensation developed on the penny, what was the source of the condensation?

a. Water vapor in the air

b. The dry ice

c. The penny had moisture on it to begin with

d. Your hand

3. Why did the dry ice create more fog when it was submerged in water than prior to submerging?

a. The water turned colder and helped create condensation

b. The dry ice sublimated faster and therefore more carbon dioxide gas rose out of the beaker

c. The dry ice “boiling” in the water creates more steam

d. The water in the beaker evaporated to form fog

4. Why does the fog in the beaker tend to stay in the beaker or descend out of the beaker if it overflows?

a. The air flow in the room pushes the fog down

b. The fog is colder and therefore denser than the air around it

c. The fog is warmer than the dry ice

d. The air temperature of the room is colder than the boiling water

Answers: 1-C, 2-A, 3-B, 4-B

Open-Ended Questions

1. Compare and contrast water ice and dry ice. Why is solid carbon dioxide referred to as “dry” ice? Create a Venn Diagram to show the similarities and differences. (It is referred to as “Dry” because liquid does not form on the surface the ice is sitting on as it changes form solid to gas).
2. Think of some common uses for dry ice and why it might be useful. (Camping, Fishing, And Hunting)
3. Mars has an atmosphere of mostly carbon dioxide with temperatures well below zero at the north and south poles, creating favorable conditions for dry ice formation. Scientists have also found evidence that Mars had liquid water once flowing on its surface in the past. If you were on Mars, how could you distinguish the ice that is located there as water ice from dry ice? (Mining the ice and entering it into an environment (normal sea level pressure on Earth) where temperatures are still below the freezing point of water. The dry ice would sublimate while the water ice would remain solid)

Connections to Standards

Cross-Disciplinary Extensions

Connect to Math

Convert temperatures from Celsius to Fahrenheit using the math formula. Extend to calculate what temperature value is the same in both Celsius and Fahrenheit. At what point does the Celsius scale have “higher values” than the Fahrenheit scale? (the transition point is -40 ^oF/^oC)

Connect to Reading/Writing

Learn about the conditions on Mars and write about the conditions necessary for dry ice formation at the North and South Polar regions

Next Generation Science Standards

This lesson supports the following:

• Practices of Science and Engineering
• Asking questions and defining problems
• Analyzing and interpreting data
• Constructing explanations and designing solutions
• Engaging in argument from evidence

Cross-Cutting Concepts

• Patterns
• Cause and Effect: Mechanism and Explanation

Disciplinary Core Ideas, Grades 6-8

Physical science

• Substances are made from different types of atoms, which combine with one another in various ways. Atoms form molecules that range in size from two to thousands of atoms. (MS-PS1-1)
• Solids may be formed from molecules, or they may be extended structures with repeating subunits (e.g., crystals). (MS-PS1-1)
• Each pure substance has characteristic physical and chemical properties (for any bulk quantity under given conditions) that can be used to identify it. (MS-PS1-2),(MS-PS1-3)
• Gases and liquids are made of molecules or inert atoms that are moving about relative to each other. (MS-PS1-4)
• In a liquid, the molecules are constantly in contact with others; in a gas, they are widely spaced except when they happen to collide. In a solid, atoms are closely spaced and may vibrate in position but do not change relative locations. (MS-PS1-4)
• The changes of state that occur with variations in temperature or pressure can be described and predicted using these models of matter. (MS-PS1-4)
• The temperature of a system is proportional to the average internal kinetic energy and potential energy per atom or molecule (whichever is the appropriate building block for the system’s material). The details of that relationship depend on the type of atom or molecule and the interactions among the atoms in the material. Temperature is not a direct measure of a system's total thermal energy. The total thermal energy (sometimes called the total internal energy) of a system depends jointly on the temperature, the total number of atoms in the system, and the state of the material. (secondary to MS-PS1-4)
• Temperature is a measure of the average kinetic energy of particles of matter. The relationship between the temperature and the total energy of a system depends on the types, states, and amounts of matter present. (MS-PS3-3),(MS-PS3-4)
• The amount of energy transfer needed to change the temperature of a matter sample by a given amount depends on the nature of the matter, the size of the sample, and the environment. (MS-PS3-4)
• Energy is spontaneously transferred out of hotter regions or objects and into colder ones. (MS-PS3-3)