Volume of Gas
When baking soda and vinegar are combined, carbon dioxide is made. How much gas is generated in a chemical reaction like this? How can we measure it? This exploration gives students an opportunity to build a carbon dioxide generator, collect and measure gas.
Materials Required
• Shallow pan or bowl
• Plastic water bottle
• Water glass
• Flex straws
• Baking soda
• Vinegar
• Tissue, paper towel, or TP
• String
Procedure
1. In a shallow pan, pour about 1 inch of water.
2. Fill a water glass to the brim with water and cover with a plastic lid or something similar
3. Carefully turn the glass over by holding the plastic and then place it in the pan. This may take several tries! Some air may be in the top of the glass if you are not careful. Keep trying until there is very little air in the top of the glass.
4. Next, prepare your gas generator. Find a plastic water bottle. Poke a hole in the cap with a nail and then expand it with a pencil. Careful! Only make it big enough to snugly fit your flex straw!
5. Connect two flex straws as shown below. To connect, split one end of a straw and insert it into the other. Tape around the joint.
6. Pour 1/2 cup of vinegar into the water bottle
7. Prepare a square of paper towel or TP. Place 1/2 tablespoon of baking soda on the paper. Shape it into a ball and tie a string around it.
8. Carefully lower the baking soda bag into the bottle but do not let it touch the vinegar! Put the cap on the bottle and then make sure the straw on the other end goes under the upside-down glass. The idea here is that when we make the vinegar touch the baking soda it will make C02 and then push it out through the straw into the glass of water and bubble inside the glass. Make sure all the connections are secure. Look at the picture carefully:
9. When you are ready, tip the soda bottle and allow the vinegar to touch the baking soda. You may need to gently rock the vinegar back and forth to activate the baking soda. Bubbles should appear coming out of the other end of the straw!
10. Keep rocking the liquid and baking soda bag until no more bubbles are formed.
11. Mark the place on the glass where the CO2 pushed out the water. This is the volume of the gas.
12. Now, if you remove the glass from the experiment, empty it, and then look where the mark is, you can use measuring cups and spoons to determine the volume by pouring known volumes into the glass until it hits the mark you made.
Questions
Did you imagine that a half tablespoon of baking soda had that much carbon dioxide stored inside its molecules?
If you look at baking soda, is there anything that would make you believe that there was a gas hiding inside the powder?
Extensions
You can repeat this experiment by placing less or more baking soda in the bottle. By keeping the vinegar to the same amount, what is the ideal ratio for vinegar to baking soda? How would you find out? An alternative way to do this experiment can be found at https://www.stevespanglerscience.com/lab/experiments/puff-pop-how-to-make-a-co2-sandwich/
Discussion
If we try experiments like this:
Trial 1: 1 teaspoon Baking Soda. + 1/4 cup vinegar, and then measure the gas made
Trial 2: 1 1/2 teaspoon Baking Soda + 1/4 cup vinegar, and then measure the gas made
Trial 3: 2 teaspoons of Baking Soda + 1/4 cup vinegar, and then measure the gas made
We would find results like this:
Trial 1: 1 1/2 cups of gas
Trial 2: 3 cups of gas
Trial 3: 3 cups of gas
We notice that no matter how much more baking soda we add, the gas production is the same. Only a certain amount of baking soda can react with a fixed amount of acid in the vinegar. Chemists explain this by writing the chemical formula that shows how many molecules of each chemical are required:
1 part Baking Soda. + 1 part vinegar >>>>>> 1 part sodium acetate + 1 part water + 1 part carbon dioxide
