eLearning
2009
Publication No. 91323
Decomposition of Baking Soda
Mole Relationships and the Balanced Equation
Concepts
• Decomposition reactions
• Balancing chemical equations
• Stoichiometry
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 ensure that cakes
“rise” as they bake.
As the temperature of the cake batter reaches approximately 50 °C, 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 350–450 °F
(175–230 °C) 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.
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.
Possible Decomposition Reactions
sodium bicarbonate (s) →
sodium hydroxide (s) + carbon dioxide (g)
sodium bicarbonate (s) →
sodium oxide (s) + carbon dioxide (g) + water (g)
sodium bicarbonate (s) →
sodium carbonate (s) + carbon dioxide (g) + water (g)
Materials
Baking soda, 2 g
Ring stand
Balance, 0.01-g precision
Ring support
Bunsen burner
Spatula, micro
Clay triangle
Spoon
Crucible
Weighing dish
Crucible tongs
Safety Precautions
Exercise caution when using the Bunsen burner and when handling objects that have been heated. Do not touch the crucible
or any metal that may remain hot. Use heat-resistant gloves if necessary. Wear safety goggles while performing this demonstration. Please review all Material Safety Data Sheets for additional safety, handling and disposal information.
Experiment Overview
The goal of this lab is for you to experimentally determine which of these three reactions is correct. Students will need to use
stoichiometry to determine which reaction is actually occurring inside the crucible.
Flinn Scientific—Teaching Chemistry eLearning Video Series
91323
011509
Pre-lab questions
1.
Write balanced chemical equations for all three possible decomposition reactions on the previous page.
2. For this question, assume the decomposition reaction that produces sodium hydroxide, NaOH, occurs. If you
started with 1.00 g of baking soda, NaHCO3, what mass of NaOH would you expect to produce? (This is a three
step, mass-to-mass stoichiometry problem. Show all work.)
Procedure
1. Measure the mass of the empty crucible and lid. Note: you may have an evaporating dish and watch glass intead.
2. Add about 2 grams of baking soda (sodium bicarbonate, NaHCO3) to the crucible. Your instructor will show you
what 2 g looks like. It is not critical to use exactly 2.00 g.
3. Place the lid on the crucible and measure the mass of the crucible, lid, and baking soda. Calculate the exact
mass of baking soda that you used.
4. Assemble a ring stand with ring clamp and clay triangle or wire gauze. Adjust the
clamp to an appropriate height for heating over a Bunsen burner.
5. Heat the crucible and its contents with the Bunsen burner for 10 minutes. Use a
spatula or stirring rod to carefully break up any “clumps” that form during heating.
Clumps need to be broken only once during heating.
6. When heating is done, allow the crucible to cool for at least two minutes on the
counter before massing. Make sure the crucible remains covered during this time.
After two minutes, mass the crucible and its contents.
7. Repeat with another trial if time permits. Clean the crucible between trials.
Trial 1
mass of crucible + lid
mass of crucible + lid + NaHCO3
mass of NaHCO3
mass of crucible + lid + product
mass of product
Trial 2
Post-lab questions
1. Based on your mass of baking soda that reacted, what mass of the following products would you expect?
(assuming those decomposition reactions occurred) Show all your work below.
sodium hydroxide, NaOH
sodium oxide, Na2O
sodium carbonate, Na2CO3
2. A student uses a spatula to break of clumps of baking soda, and a few grains of the solid are removed from the
crucible. How will this error affect the mass of the product that the student reports? Will it be too large, too
small, or is it impossible to determine the effect of this error? Explain.
3. A student heats the crucible for only 1 minute instead of 10 minutes. How will this error affect the mass of the
product that the student reports? Will it be too large, too small, or is it impossible to determine the effect of
this error? Explain.
4. Write a scientific explanation using the CER method for which of the three possible decomposition reactions
occurred. Use evidence from your data table and calculations to support your claim.