Expt 020 -- Misty Smoke Rings

Description

You can blow some beautiful, mystical smoke rings with dry ice and two disposable plastic cups.

Safety

Use thermal gloves and goggles when handling the dry ice. Use care in handling the hot test tube. It may cause severe burns.

Procedure

  1. Heat the mouth of a test tube in a burner flame for about 1 minute. Rotate constantly. Use the test tube to melt a hole (1.5 - 2 cm diameter) in the bottom of the wide mouth plastic cup.
    !!!Click here to See Movie.
  2. Half fill the regular cup with water, drop in 2 or 3 10-g chunks of dry ice and hold the wide-mouth cup over the top as shown in the movie. Tilt the cup slightly, then give a few small, quick squeezes to the sides of the cup.
    !!!Click here to See Movie.
  3. If at first you don't succeed, keep trying...it will be worth it! The rate at which the dry ice is subliming seems to be a critical factor, as is the stillness of the air in the room.
    !!!Click here to See Movie.
  4. If the conditions are right, the smoke rings last for several seconds, following graceful projectile arcs and then, as they approach a table top, hovering momentarily as they spread themselves out and dissipate. A dark background helps to bring out the details.
    !!!Click here to See Movie.

Questions

  1. What is dry ice?
  2. What is sublimation?
  3. What are some physical properties of CO2 gas?
  4. What is the white misty substance in the rings?
  5. Normal smoke rings follow a more or less straight path, but the smoke rings in this demo follow the path of a projectile, like a thrown baseball. Why?

Handout Makeup

Name ___________________________ Class ________

Teacher __________________________

BeckerDemos 020 Misty Smoke Rings

Watch the movie and answer the questions.

Curriculum-

Use when discussing water vapor, vapor pressure and density.

Activity-

Demonstration - Student or Teacher

Time-

Teacher Preparation: 3 minutes

Class Time: 3 minutes

Materials-

To melt the hole:

Disposal-

Allow dry ice to sublime.

Answers-

Q1. What is dry ice?
A1. Dry ice is CO2 in the solid state.
Q2. What is sublimation?
A2. Sublimation is a phase change from the solid state directly to a gaseous state, with no liquid state existing in between. Solid substances sublime if they are heated at pressures below their triple point pressure.
Q3. What are some physical properties of CO2 gas?
A3. CO2 is gas at standard temperature and pressure. It is rather dense, clear, colorless and odorless.
Q4. What is the white misty substance in the rings?
A4. Water vapor is condensed (and maybe frozen) by the cold temperature of the dry ice.
Q5. Normal smoke rings follow a more or less straight path, but the smoke rings in this demonstration follow the path of a projectile, like a thrown baseball. Why?
A5. Normal smoke rings are carried by exhaled air, which has pretty much the same chemical composition and therefore the same density as regular air. (Actually, about 4 - 5% of the air changes from O2 to CO2, but this would only lead to 1-2% increase in density -- which would probably be negated anyway because of the slightly higher temperature of exhaled air.) Because the exhaled air has pretty much the same density as the surrounding air, regular smoke rings tend to follow a straight line motion; essentially gravity's effect on the smoke ring is exactly countered by the buoyant force exerted upwards by the surrounding air. The smoke rings in this demonstration, however, are mostly CO2, which is considerably denser than the surrounding air. Thus, the gravitational force acting on such a smoke ring is greater than the buoyant force, and so its path is bent into a projectile arc.

Key Words 1-

dry ice, smoke rings