Baking Soda and Vinegar

In this experiment you inflate a balloon with carbon dioxide that is produced from the reaction of baking soda and vinegar. By combining the two reactants in different ratios you can explore how there is an ideal reactant ratio to get a maximum amount of carbon dioxide. This introduces the chemical concept of limiting reagents and stoichiometry. This experiment has multiple levels to it, meaning it can be a good experiment for any level from 3rd grade to college freshmen.

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Ingesting large quantities of either (or the combination!) chemical is a bad idea, as is getting them in your eyes. This should be easy to avoid doing, so this experiment should be considered very safe.

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Required

• Plastic soda bottle(s) (smaller is better)
• Baking soda (at least 6 grams or 1 teaspoon)
• vinegar (at least 80 mL or ~ 5 tablespoons)
• balloon
• balance

• graduated cylinder or beaker

Optional

• string
• ruler
• ziploc bag
• saran wrap

• 2 L soda bottle (cut with scissors)

Note: Alka Seltzer tablets can be used instead of baking soda.

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Basic Experiment

1. Weigh out 5.7 grams of baking soda (or one teaspoon by volume). Pour the baking soda into a balloon.

2. Measure out 80 mL of vinegar (1 tablespoon is 15 mL, so this is ~ 5 tablespoons), and pour it into the soda bottle.

3. Holding the balloon so the baking soda stays inside of it (head down) fit the elastic mouth of the balloon over the top of the soda bottle (leaving the soda bottle sitting on a table). The point is to seal the system without letting the baking soda and vinegar touch.

4. Lift the head of the balloon, and gently shake it so all the baking soda falls out into the vinegar. Hold the balloon on the soda bottle so it doesn’t pop off.

5. What do you see happening in the bottle? What does it mean?

Optional Follow-Up

6. Measure the circumference of the balloon with a string, and then measure the string with a ruler. Record the amount of each ingredient added and the final size of the balloon.

7. Now we will see if there is an ideal ratio of ingredients. Repeat steps 1-6 with a clean (cleaned or new) bottle and a new balloon.

8. Try the following reaction conditions, and measure the final balloon size each time. In the second run both reactants are tripled. In the third and fourth reactions, one is tripled, while the other remains unchanged. What do you predict will happen?

. Run	. vinegar	. baking soda
1	80 mL (5 1/3 TBL)	5.7 g (1 tsp)
2	240 mL (16 TBL)	17.1 g (3 tsp)
3	240 mL (16 TBL)	5.7 g (1 tsp)
4	80 mL (5 1/3 TBL)	17.1 g (3 tsp)

9. Look at your data. What did you learn?

(This is perhaps ideal for high school or college age) For a more quantatative version of this experiment, you can do the following:

1. Fill a large basin with water
2. Put a beaker, graduated cylinder, or clear measuring cup under water so it fills up with water. One with a big mouth is preferable.
3. Hold the measuring container so it is upside down, with the top lip just under water, and most of the column sticking above water. You should notice that the water stays up in the column even though you might expect it to fall down. It won’t fall because there is no good way for air to get up into the cylinder (unless you bring it totally above the water).
4. Put baking soda (amount as any of the above runs) in a sealed plastic bag. Try to remove all the air you can before sealing it.
5. Put this plastic bag inside a second plastic bag. Also add vinegar to the second plastic bag, and seal it with as little air inside as possible.
6. Put both plastic bags under water in your basin, underneath the inverted measuring cup.

1. Use a pin or scissors to break the plastic bags, and mildly agitate. You want the baking soda and vinegar to mix and react. Bubbles will appear (carbon dioxide under water) and will rise to the top. You should catch all of the bubbles in your inverted measuring cup.

This part may take some care and consideration to do properly, but can be fun to try.

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BASIC EXPERIMENT

Q: What did you see when the baking soda was dropped into the vinegar?

A: Bubbles. The bubbles are because gas is formed, just like soda bubbles.

Q: What happened? Where did the gas come from?

A: The vinegar and baking soda reacted, and carbon dioxide was formed.

Q: Do you see any baking soda left in the end? If so, how much?

A: You shouldn’t see a lot, if any. (This will depend on the concentration of your vinegar and exact measurements.) If you do the additional runs, you should see excess baking soda when you use excess baking soda. Some might dissolve (not react, but dissolve), but I believe not all of it will.

Q: How much gas would you expect to see? Is the size of the balloon reasonable? (For more advanced students)

A: Based on the stoichiometry of the reaction, we should create .068 moles of carbon dioxide. If this were at room temperature and atmospheric pressure, based on PV=nRT (below) we would see 1.5 liters of gas. Now, there was already air in the container (about one liter if you used a liter soda bottle). Additionally, the balloon provides resistance. While more reactants should produce more gas, you should not necessarily expect to see the balloon triple in size.

FIRST OPTIONAL ADD-ON

Q: When you added three times as much baking soda and vinegar, what happened? Does this make sense?

A: You get more gas (ideally three times as much, but because of the nonlinearity of the balloon size this might not be clear)

Q: When you added more of one reactant, but the base amount of the other, what happened? Did you expect this? Why?

A: You should not get any more gas than you did with the base amount of both reactants. You would expect this if you knew the chemical equation, but probably not if you don’t.

Q: Can you write a balanced chemical reaction for this process (advanced students only)? Does the stoichiometry agree with your observations?

A: See below.

SECOND OPTIONAL ADD-ON

Q: Why is this method potentially more accurate than collecting gas in a balloon?

A: It is hard to measure the initial and final volume of gas in the soda bottle/balloon set-up (although water displacment, another experiment in this databse would do that very well). It is also hard to know the pressure inside the container, as the balloon resists expansion, meaning there will be elevated air pressure inside the container. In this system, you can get an exact measure of the volume of gas created by the reaction.

Q: Why is this method potentially less accurate than collecting gas in a balloon?

A: It might be difficult to get the vinegar and baking soda to all react without having some excess stuck in a corner of a baggie, or it could diffuse out into the water basin. Also, you might miss catching some carbon dioxide. Finally, if there is any air in the bags before the reaction, you’re going to capture some air, instead of just the carbon dioxide formed byt the reaction.

Q: Which method do you think is better? Using PV=nRT, compare your errors.

A: This will depend on the exact set-up and performance of the experiments.

Q: Can you design a BETTER way to do this experiment.

A: If so, leave a comment!

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Balanced Chemical Reaction

With any chemical reaction you should be able to identify the reactants (what goes in) and the products (what comes out). In common English, this reaction was

Baking Soda + Vinegar —> Gas of Some Sort

In Chemical terms this reaction is

NaHCO ₃ + CH ₃ COOH —> NaCH ₃ COO + H ₂ CO ₃ —> NaCH ₃ COO + H ₂ O + CO ₂

Baking Soda is the first reactant, chemically known as sodium bicarbonate.
Vinegar is the second reactant, acetic acid
They combine to form aqueous sodium acetate and carbonic acid, which decomposes into water and gaseous carbon dioxide.

Stoichiometry and Measurements of Reagents

The balanced chemical equation is above. What you notice is that there is the same number of each type of atom on each side (hydrogen, sodium, carbon, oxygen are all conserved, although the combine differently to form different molecules). If you add 2 parts baking soda to one part vinegar, the above reaction tells you that one part of each will react, but the second part of baking soda has nothing left to react with. 1 teaspoon of baking soda is about 5.7 grams, or about 0.068 moles (based on a molecular weight of ~ 84g/mole). Because the balanced chemical reaction has equal parts sodium bicarbonate and vinegar (by moles) we want to add 0.068 moles of acetic acid.

Vinegar is federally required to have at least 4 g acetic acid per 100 mL. 4g is .067 moles (based on 60 g/mole), meaning that for vinegar of this acidity, about 100 mL vinegar would give you a nearly stoichiometric amount of acetic acid. Commercial vinegar is often closer to 5 g /100 mL, in which case you would only need ~ 80mL. You could make the experiment more complicated by titrating your vinegar first (for high school or college classes).

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Baking soda and vinegar are a mild base and acid. You can put them down the sink, although it is best to do so while running tap water to dilute them.

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None.

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