Gas Sniffers: How Can you Test for the Presence of Carbon Dioxide and Use it to Predict a Volcanic Eruption?

PROBLEM

How can you test for the presence of carbon dioxide and use it to predict a volcanic eruption?

Materials

• 1-quart (1-liter) jar with lid
• distilled water
• 1 teaspoon (5 ml) calcium oxide (lime used to make pickles)
• spoon
• baby-food jar
• measuring cup
• white vinegar
• glass soda bottle
• modeling clay
• flexible drinking straw
• scissors
• ruler
• bathroom tissue
• 1 teaspoon (5 ml) baking soda

Procedure

CAUTION: The short end of the straw should be inside the bottle. DO NOT close the opening in the straw.

1. Prepare the carbon dioxide-testing solution called limewater, using the following steps:
   • Fill the 1-quart (1-liter) jar with distilled water.
   • Add the calcium oxide and stir.
   • Secure the lid and allow the solution to stand overnight
2. Fill the baby-food jar three-fourths full with limewater. NOTE: When pouring liquid out of the jar, be careful not to pour out any of the lime that has settled on the bottom of the jar, and always secure the lid on the jar.
3. Pour ¹/₄ cup (63 ml) of water and ¹/₄ cup (63 ml) vinegar into the soda bottle.
4. Press a walnut-sized piece of clay about an inch from the end of the straw closest to the flexible section.
5. Cut a 3-inch (7.5-cm) length of bathroom tissue.
6. Spread the baking soda across the center of the tissue.
7. Roll the tissue around the baking soda. Secure the packet by twisting the ends of the paper.
8. Drop the packet of baking soda into the soda bottle.
9. Immediately plug the bottle's mouth with the clay around the straw.
10. Hold the baby-food jar of limewater near the bottle so that the long end of the straw is beneath the surface of the limewater.
11. When the bubbling ceases, observe the limewater.

Results

As bubbles from the straw enter the clear limewater, the limewater turns milky.

Why?

Baking soda consists of the chemical compound sodium bicarbonate. When this carbonate compound reacts with vinegar (acetic acid), carbon dioxide gas is produced. limewater is used to test for the presence of carbon dioxide gas because it reacts with carbon dioxide to form a white insoluble (does not dissolve) compound called calcium carbonate. This simple experiment demonstrates that the presence of a gas can be identified. Volcanologists collect gas samples from the gases escaping from fumaroles (volcanic vents from which only gas escapes) in order to identify and determine the quantity of each gas present. Studies of the gas content of volcanoes have revealed that the amount of water vapor, carbon dioxide, and sulfur dioxide often increases before an eruption. An increase in these gases is not enough evidence to predict an eruption, but gas studies along with other changes provide the scientists with indicators used to predict a possible volcanic eruption.

LET'S EXPLORE

1. Do other carbonated substances produce carbon dioxide when combined with acid? Repeat the original experiment, replacing the baking soda with materials that contain calcium carbonate (limestone), such as eggshells, marble chips, or white chalk.
2. Would using a different acid alter the results? Repeat the original experiment, replacing the vinegar and water mixture with ¹/₂ cup (125 ml) of citric acid such as lemon juice or grapefruit juice.

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