Baking Soda and Vinegar Limiting Reactant Lab, Daniel R. Barnes, Chemistry, 11/22/04 10:39:55 AM
Daniel R. Barnes Name: ________________________________ Seat #: ______
Chemistry
6/1/2011 8:47:52 AM Period: ______ Date: _________________________________
Baking Soda & Vinegar Limiting Reactant Lab
PURPOSE: To demonstrate to students the concept of limiting reactants.
MATERIALS: 600 mL beaker (extra large), 250 mL beaker (large), 100 mL beaker (medium), 50 mL beaker (small), triple beam balance (the “scale”), baking soda, vinegar, rag, eyedropper, spoon or scoopula.
The 600 mL beaker will be the reaction vessel, the 250 mL beaker will be the vinegar supply beaker, the 100 mL beaker will be the baking soda supply beaker and the 50 mL beaker will be the baking soda measuring beaker.
PROCEDURE
1. Make sure the 600 mL and 50 mL beakers are clean and dry. “Zero” your scale. Place the 600 mL (extra large) and 50 mL (small) beakers on the scale, side by side, and measure their combined mass.
S tare mass = ____________________________________ g = combined mass of the empty 50mL and 600 mL beakers
2. Add 100 to the “S tare mass” value from step #1 and record the result below.
desired gross mass, vinegar only = _______________________________ g = 50 mL beaker + 600 mL beaker + desired amount of vinegar
Is the number in the above blank exactly 100 bigger than the number in the first blank? If it is, you are ready to proceed.
Add vinegar to your 250 mL (large) beaker until you have about 150 mL of vinegar.
Set the sliders of the triple beam balance to the above mass value. Place the 600 mL beaker and the 50 mL beaker on the scale. Pour vinegar from the 250 mL beaker into the 600 mL beaker until the white needles on the balance meet each other. Use the eyedropper to transfer very small amounts of vinegar back and forth between the 600 mL and 250 mL beakers until the scale balances.
How does the vinegar smell? _________________________________________________________________________________________
3. If he has not already told you, ask your instructor how much baking soda you should be using and record it in the blank below.
desired net mass of baking soda = _________________________________ g = baking soda only
4. Add this number to the “desired gross mass, vinegar only“ from step #2, and record that sum in the blank below.
desired gross mass, vinegar and baking soda = ____________________________ g = 50 mL & 600 mL beakers + vinegar + baking soda
Add baking soda to your 100 mL beaker until it is about half full.
Set the sliders on the triple beam balance to the above number (desired gross mass, vinegar and baking soda). Place the 600 mL and 50 mL beakers on the scale. Use the spoon or scoopula to transfer baking soda from your 100 mL beaker into your 50 mL beaker until the scale balances. Transfer baking soda back to the 100 mL beaker if you add too much to the 50 mL beaker.
5. Now, you should have a 600 mL beaker and a 50 mL beaker sitting on your scale, the 600 mL beaker with 100 grams of vinegar in it, and the 50 mL beaker with a certain amount of white baking soda in it. Get your teacher’s approval before going to the next step.
TEACHER’S INITIALS: _____________________________________________
6. SLOWLY pour the baking soda from the 50 mL beaker into the 600 mL beaker. SLOWLY means SLOWLY. Record your observations in the space below.
_________________________________________________________________________________________________________________
_________________________________________________________________________________________________________________
7. During this step, keep in mind that the small beaker is still on the scale and could be easily knocked off and broken. Also keep in mind that it is important not to lose any liquid from the 600 beaker. Pick up the 600 mL beaker and carefully move it far away from the 50 mL beaker. Without touching the liquid inside with any device or body part, carefully and gently swirl the 600 mL beaker clockwise and counterclockwise. This swirling should help to mix the remaining baking soda with the vinegar, speeding the reaction. The swirling should also help to loosen the carbon dioxide that may be still dissolved in the vinegar, allowing it to bubble out and escape into the air. Replace the 600 mL beaker on the scale and measure the combined mass after swirling. Continue to swirl the 600 mL beaker and re-measure the mass of the two-beaker system until there are no visible bubbles and continued swirling seems to not change the mass anymore. Record the final mass of the two beaker system in the space below.
post-reaction gross mass = __________________________________________ g = 50 mL beaker + 600 mL beaker + vinegar/BS mixture
What does the vinegar smell like now? Does it smell different than it did before you added the baking soda? __________________________
_________________________________________________________________________________________________________________
8. Ask your teacher if you should do the procedure all over again, but with a second, different amount of baking soda. Keep track of your mass data on a separate sheet of notebook paper for this second run just like you did for the first run. You don’t have to copy the front side of this worksheet word for word; just make sure that each mass measurement has a short verbal description. Whoever did most of the work during the first run-through should step aside and let other people have a chance to get their hands on the equipment during the second run.
No ballhogs! No bench-warmers! Everyone gets a turn! Everyone learns!
POST-LAB
Except where blanks are provided, answer the following questions on (a) separate sheet(s) of paper.
1. Subtract the “desired gross mass, vinegar and baking soda” from the “post-reaction gross mass”. Show your work in the spaces below.
__________________________ - ___________________________ = _____________________________ = D mass = change in mass
post-reaction gross mass gross mass, vinegar + BS change in mass
Did you get a negative number? If you did not, read the directions for the math again very carefully. If you did a second run of the procedure, show your math for the second run on the same piece of paper where you recorded your data for the second run.
What happened to the mass of the two beakers and their contents as a result of mixing the baking soda and vinegar together? Why do you think this happened? Include the chemical equation for the baking soda/vinegar reaction in your explanation.
2. Gather together the results from all the other lab groups and compile them in the data table below. Drop the negative sign from the “change in mass” values before putting them into the data table. (Extra, blank columns have been provided if you want to collect data from other periods as well, calculate averages, or whatever you want.)
3. Use stoichiometry to calculate how much CO2 should have been produced by each quantity of baking soda and put that in the “theoretical yield” column.
4. Make a graph of “Change in Mass versus Mass of Baking Soda”. On the same graph, also plot theoretical yield, but use different symbols and/or a different color for the theoretical yield data points. For instance, you could plot change in mass with red squares and theoretical yield with blue circles. Your finished graph should have two lines on it that don’t quite do the same thing.
5. Describe the shapes of the two lines (actual change in mass and theoretical yield). How are they similar? How are they different? Why are the graphs as they are? Look at the two graphs, think about what happened in the big beaker, and then estimate how much acetic acid must be present in 100g of vinegar, with at least one stoichiometric calculation to back it up. Explain your reasoning with words as well.
6. Now that you have calculated how many grams of acetic acid there are in 100 grams of vinegar, calculate the % concentration of acetic acid in the vinegar you used.
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