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Lab Partners:
Date:
Lab # 23: Decomposition of Baking Soda Stoichiometry
Chemistry 1
Background:
Due to the widespread use of sodium bicarbonate, commonly called baking soda, in many food
products, the thermal decomposition reaction has been studied extensively by food chemists. Baking soda is
used to prepare cakes in order to insure that cakes "rise" as they bake. This rise is caused by the evolution of gas
during the baking process. Two gases actually form during most baking processes.
As the temperature of the cake batter reaches approximately 50oC, the baking soda decomposes and
carbon dioxide is released. The use of baking soda is especially popular in pancakes and waffles since the high
cooking temperatures of 350-450oF (175-230oC) cause the carbon dioxide to be liberated before the dough has
set. Thus, the batter rises before it sets, and we get a light and tasty finished product.
Stoichiometry allows us to predict a theoretical yield from starting materials (reactants) in a chemical
reaction. There are three possible chemical reactions that could be occurring during the baking process. All
three of these reactions shown below are theoretically possible, yet only one reaction actually occurs.
Pre-lab questions:
1. What is the second gas generated during most baking processes?
2. Define the key terms bolded in the “Background” section of the procedure.
3. Consider the decomposition of H2O2 as in a previous lab. How many grams of oxygen would you expect
to yield if you started the reaction with 2.6 g of hydrogen peroxide? (HINT: This is a stoichiometric
calculation.)
4. If 1.0 g of oxygen gas was captured, what was the percent yield for the experiment?
Lab23-­‐BakingSodaStoich 1 Possible Decomposition Reactions:
sodium bicarbonate
→
sodium hydroxide +
(solid)
sodium bicarbonate
(solid)
→
sodium oxide
(solid)
sodium bicarbonate
carbon dioxide
(gas)
+
carbon dioxide +
(solid)
→
sodium carbonate
(solid)
water
(gas)
+
(gas)
carbon dioxide +
(solid)
water
(gas)
(gas)
Problem:
The goal of this lab is for you to experimentally determine which of these three reactions is correct. Your job is
to use stoichiometry to determine which decomposition reaction is actually occurring inside the crucible.
Material Available:
• Crucibles (lid not required)
• Baking Soda
• Balances
• Crucible tongs
•
•
•
Weighing boats
spoons
metal spatula
Safety Concerns:
Students should wear safety goggles and laboratory aprons throughout this experiment. Students should exercise
care when working with the chemicals. Clean up all spills as soon as possible. Students should wash their hands
after completing this experiment.
Directions:
1. Measure the mass of the empty crucible. _________
2. Place the empty crucible on the balance pan and then press the “zero” button. Once you see all zeros,
carefully add approximately 2.00 g of baking soda and record the exact mass of the baking soda.
_________
3. Set up the ringstand with the smaller circular ring clamp. Place the metal crucible directly onto the wire
gauze or into a clay triangle.
4. Heat the crucible and its contents with the Bunsen burner for 10 minutes. Use a spatula to carefully break up
any "clumps" that form as the heating proceeds. The clumps only have to be broken up once during the
heating process. (While you are heating, answer Analysis and Calculations questions 1 and 2.)
Remove the crucible from the clay triangle using tweezers or crucible tongs. Let the crucible cool for a
few minutes!!
Mass of crucible and final product _________
Mass of final product _____________
Lab23-­‐BakingSodaStoich 2 Analysis and Calculations:
1. Write a balanced equation for each of the three possible reactions shown on page 1.
a. Possible Reaction 1
b. Possible Reaction 2
c. Possible Reaction 3
2. Starting with the initial mass of sodium bicarbonate, perform the stoichiometry to determine the mass of
solid product produced for each of the possible reactions.
a. Amount of Solid Produced for Possible Reaction 1
b. Amount of Solid Product Produced for Possible Reaction 2
c. Amount of Solid Product Produced for Possible Reaction 3
3.
Based upon your results, which of the three reactions actually occurred? Explain how you ruled out the
two other chemical reactions?
4. Calculate your percent yield based upon your actual yield and calculated theoretical yield.
Lab23-­‐BakingSodaStoich 3