Activity time: 5 minutes

Materials for Activity

• Tray to hold materials
• A tall, transparent glass
• Candles, a flat (not walled) candleholder such as a plate, and matches or a lighter (three sets of candle, candleholder, and matches, if using Station Model)
• Vinegar, and a 1/4 cup measuring scoop
• Baking soda, and a tablespoon for measuring
• A tablespoon and a 1/4 cup scoop, for measuring
• Optional: Written instructions, if using Station Model

Preparation for Activity

• Gather materials.
• Review directions.
• Prepare tray with materials for experiment.
• If participants will rotate from experiment to experiment in groups (Station Model), print or write the instructions for this experiment and set at this station.

Description of Activity

This experiment requires adult supervision. It demonstrates that carbon dioxide, discovered by Priestley, snuffs the flame.

Give these instructions:

An adult lights the candle and sets it aside.

Pour about 1/4 cup of vinegar into a tall glass. Measure a tablespoon of baking soda, and add it to the vinegar. It will react with bubbles. Wait for the bubbles to calm down. The glass will have a layer of liquid at the bottom and a layer of gas on top.

Very slowly and carefully, without pouring the liquid, pour just the gas from the glass over the candle.

What did Priestley realize in this experiment? Fire requires oxygen in order to burn. When the chemical reaction of baking soda with vinegar produces carbon dioxide (which is heavier than air), the air (oxygen-rich) leaves the glass. The candle, overwhelmed by the carbon dioxide, can no longer burn.