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Dry Ice Sublimation

In this demonstration, students will see up close how the process of sublimation works with dry ice as an example.

Dry ice is solid. It sublimates or changes states from a solid to a gas at temperatures of -78 degrees Celsius under normal atmospheric pressure of 1 atm. Because of its low temperature at normal atmospheric pressure, it is useful as a coolant.

When dry ice is placed into warm water, a cloud forms. This cloud is similar to the clouds we see in the sky. The cloud consists of water droplets that are trapped inside the carbon dioxide gas and eventually flow out. It forms because the dry ice is cold enough to make water from the air condense.

Safety tip: Dry ice is cold to the touch and can cause severe burns from freezing if it comes in contact with skin. Be very careful when handling dry ice and ensure to wear the proper safety gear and use the correct safety equipment.

Objectives

  • Describe the properties of a solid, a liquid, and a gas.

  • Describe the transitions between different states of matter.

Materials

  • Per Demo or Class:
    graduated cylinder, preferably tempered glass
    styrofoam container or another appropriate container for dry ice (It is very important as there are specific methods of transporting dry ice.)
    insulated gloves for handling dry ice
    tongs for handling dry ice
    goggles for eye protection
    dry ice (The dry ice should be in pellet form. This helps to control the amount that can be added at a time.)
    access to warm or hot water (The hotter the better for the cloud/fog effect.)

    Teacher tip: A 3:1 ratio of water to dry ice in volume will create a good fog effect.

Key Questions

  • Why is this called 'dry' ice?
  • What is the name of the state change that occurs with dry ice in normal atmospheric condition
  • Why do we see a cloud when dry ice is mixed with warm water?

What To Do

  1. Ensure that you have a safe area to work with and that the students are at a safe distance away.
  2. Have the graduated cylinder and empty dry ice container ready.
  3. Fill the graduated cylinder with warm or hot water.
  4. Equip yourself with the safety equipment. (goggles, tongs, gloves)
  5. Secure a piece of dry ice in the tongs and show the children. Tell the students that it is changing from a solid to gas phase, which is visible as the fog coming off the solid piece.
  6. Place the dry ice into the graduated cylinder, and watch the clouds form.
  7. Take off your gloves and wave your hand over the clouds. Ask for students’ observations and then follow-up with questions to determine their understanding. What is happening to the dry ice?
  8. To dispose of excess dry ice, place it in an empty container and leave it to sublimate in an open, secure and safe area with good ventilation. Ensure that the students do not go near it.

Teacher tip: Test out the demonstration ahead of time to determine the best ratios and methods of the procedure before the live demonstration.

Extensions

  • Why do the clouds move downwards?
  • What causes 'real clouds' and rain?