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Stoichiometry

Stoichiometry

Lab Tips in Stoichiometry

Volcano Lab

In this at-home lab, we'll be creating a volcano (minus all the lava, molten earth, and fire). What's the fun in that? Hey, it's better than ending up like Pompeii.

Have you ever built a paper-mache volcano? Did you take it to the next step and mix baking soda and vinegar to make it a real-life Vesuvius? Ever wonder about the chemistry behind this fake-volcano making adventure? In the words of 2 Unlimited—get ready for this.


It's volcano time.

Before we begin, we're going to need a few things:

Baking soda (NaHCO3)
Vinegar (CH3COOH)
2 plastic cups, labeled A and B
Scale
Spatula (or something to scoop out the baking soda)
Goggles & gloves

The purpose of this lab experiment is to predict the amount or carbon dioxide (CO2) that should be produced in the reaction below, and then calculate the percent yield.

CH3COOH (l) + NaHCO3 (s) → NaCH3COO (aq) + H2O (l) + CO2 (g)

Safety:

We know—we use baking soda and vinegar all the time without gloves or goggles, but wear them anyways. We're using larger quantities than normal and minimizing your exposure to any and all chemicals is a good idea.

Procedure:

1. Find and record the mass of cup A. With cup A still on the scale, add approximately 10.0 grams of baking soda to the cup. It's okay if the mass is not exact, as long as you record exactly the quantity you used. Remove cup A from the scale and tare the scale.

2. Place cup B on the scale. Weigh the cup and record its mass. Next, add approximately 50.0 g of vinegar. Again the mass does not have to be exact, as long as you record exactly the quantity you used.

3. Slowly add vinegar to cup A until the reaction has stopped. Don't add all of the vinegar, just enough to complete the reaction. You'll know the reaction is over when it stops bubbling. Why is the reaction bubbling? Check out the reaction equation again. Did you notice that the reaction forms a gas? More specifically CO2.

4. Reweigh cup A and cup B. Calculate the mass of CO2 that escaped into the atmosphere.

5. Grab the rest of your vinegar and add it to the reaction mixture. Does anything else happen? Does the reaction proceed any further?

Data

a. Mass of cup A: _______ g
b. Mass of cup A + baking soda: ________ g
c. Calculate mass of baking soda (b – a): ________ g
d. Mass of cup B with vinegar: _________ g
e. Mass of cup B after reaction: __________ g
f. Calculate mass of vinegar used (d – e): ________ g
g. Mass of cup A after reaction: ________ g
h. Calculate mass of product after reaction (g – a): ________ g
i. Calculate baking soda + vinegar (c + f): ________ g
j. Calculate mass of CO2 lost (I – h): _________ g

Discussion

1. Using the mass of the baking soda you used, calculate the mass of CO2 you would expect.
(Hint: grams → moles → moles → grams)

2. How does this compare to the amount of CO2 that you measured in the experiment?

3. Calculate the percent yield.

4. Calculate the percent error.

5. What are some possible sources of error that can contribute to your error? Please try to think of at least 3 or 4 sources.

6. What could be done to reduce the percent error?

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