Its Production and Uses
Gases, like carbon dioxide, often cannot be seen, felt, or smelled. Yet gases are made of molecules and atoms that chemically react with other substances
In this project, you will test for the presence of carbon dioxide. The physical and chemical properties of the gas will be examined. You will also look at means by which the gas is produced as well as some of its uses.
Purpose: To test for the presence of carbon dioxide when an acid and carbonate compound react.
- glass soda bottle
- 1⁄4 cup (63 ml) water
- 1⁄3 cup of (63ml) vinegar
- 1 teaspoon (5 ml) of baking soda
- baby-food jar with lid
- limewater (see Appendix 6)
- modeling clay
- flexible drinking straw
- Pour 1⁄4 cup (63 ml) of water and 1⁄4 cup (63 ml) vinegar into the bottle.
- Cut a 3-inch (7.6-cm) strip of tissue
- Spread the baking soda across the center of the tissue.
- Roll the paper around the baking soda. Secure the packet by twisting the ends of the paper.
- Fill the baby-food jar three-fourths full with limewater.
- Mold a walnut-size piece of clay around the end of the straw, on the end closest to the flexible section. (Do not cover the hole.)
- Drop the packet of baking soda into the bottle.
- Quickly plug the bottle's mouth with the clay around the straw. Note: The short end of the straw should be inside the bottle.
- Hold the jar of limewater near the bottle so that the other end of the straw is beneath the surface of the limewater (See Figure 33.1).
- When the bubbling ceases, observe the limewater.
- Secure the lid on the jar and allow the jar to stand undisturbed overnight.
- Observe the contents of the jar.
As bubbles from the straw enter the clear limewater, it turns milky. After standing, the solution looks clear, but there is a thin layer of white solid on the bottom of the jar.
Baking soda consists of the chemical compound sodium bicarbonate (NaHCO3). Compounds containing carbonate (CO3) react with acids such as vinegar (acetic acid) to produce carbon dioxide gas (CO2). The equation for this reaction is as follows:
Limewater, Ca (OH)2, is used to test for the presence of carbon dioxide gas because it reacts with carbon dioxide to form the compound calcium carbonate (CaCO3). The equation for this reaction is as follows:
Note: The (s) in the equation indicates that calcium carbonate is insoluble. That is, it does not dissolve. The small white particles of insoluble calcium carbonate temporarily stay suspended in the solution and give it a milky appearance. In time, gravity pulls the calcium carbonate to the bottom of the jar.
Try New Approaches
- Does the use of a different acid alter the results? Repeat the experiment replacing the vinegar and water mixture with 1⁄2 cup (125 ml) of citric acid such as lemon juice or grapefruit juice.
- Do other carbonated substances produce carbon dioxide when combined with acid? Repeat the original experiment replacing the baking soda with materials such as eggshells or marble chips, which contain calcium carbonate (limestone).
- Carbon dioxide is a product of the fermentation of sugar. The reaction of the fermentation of sugar is as follows:
- Drinking soda contains carbonated water, chemically known as carbonic acid (H2CO3). This acid readily decomposes to form water and carbon dioxide (H2CO3 → H2O + CO2). Limewater can be used to test for the presence of carbon dioxide in sodas. Repeat the original experiment replacing the empty soda bottle with a bottle filled with any brand of soda. Speed up the decomposition of the carbonated water by setting the soda bottle in a bowl of warm water. Note: heat the soda bottle only if its cap has been removed.
Zymase is an enzyme (a chemical that changes the rate of a chemical reaction). Demonstrate the production of carbon dioxide by filling the soda bottle half full with water. Add 4 tablespoons (60 ml) of sucrose (table sugar) and 1⁄4 ounce (7 g) of dry yeast. Science Fair Hint: Display photographs of the experiment along with the chemical equations of the reactions.