Soap Bubble

Essential Question
Do different gases have different densities, or do they all mix together?

Objectives

 * Interpret gas densities based on visual properties.
 * Identify a chemical reaction's products.

Introduction & Student Background
If different liquids are heavier than one another, can different gases be heavier? In this activity, students will create a layer of carbon dioxide by using a vinegar-baking soda reaction, and see if the carbon dioxide layer is heavier than air by blowing a soap bubble.

Vocabulary

 * Gas
 * Density
 * Chemical Reaction

Materials

 * Large clear plastic box or aquarium
 * Baking soda
 * Vinegar
 * Soap bubble solution
 * Paper towels

PREP

 * 1) Spread the baking soda on the bottom of the aquarium.
 * 2) Pour vinegar in, sufficient to react with the baking soda. Do not stir the air in the aquarium. (Steps 1 and 2 can also be performed in front of the students)
 * 3) Set out the soap bubble solutions and bubble blowers..

ACTIVITY
Variation: This can also be done with a block of dry ice sublimating in the bottom of the aquarium. The aquarium should be as deep as possible to prevent air currents disturbing the carbon dioxide gas. When people see this demonstration they tend to rush up to the side and peer over the edge, and their breath will scatter the carbon dioxide, causing the bubbles to fall.
 * 1) Have students blow soap bubbles over the aquarium and let them drift down into the tank. When the bubbles encounter the carbon dioxide layer they should float.

How it Fits to Standard

 * A single kind of matter can exist as a solid, liquid, or gas. Matter is conserved.
 * Carry out investigations by using instruments, observing, recording, and drawing evidence-based conclusions.

Follow Up
Explanation: The dense carbon dioxide gas released from the baking soda and vinegar reaction is heavier than air and will remain in a layer at the bottom of the aquarium, unless it gets blown out. The soap bubbles are mainly air and a little soap, so they are denser than the air but less dense than the carbon dioxide.