Experiment 4
STOICHIOMETRIC ANALYSIS OF THERMAL DECOMPOSITION
REACTION OF SODIUM BICARBONATE
Introduction
Stoichiometry is the most important and fundamental topic in chemistry and the essence of
chemical engineering. It is used in the industry to determine the amount of materials that
are required and estimate the amount of product obtained from a given reaction and aid in
deciding profitability. Stoichiometry is based on the law of conservation of mass which
states that the total mass of a reactant is equal to the total mass of the products, where the
relationships among quantities of reactant and products typically form a ratio. Stoichiometry
of a reaction is calculated from the moles and mole ratio of substances of a balanced chemical
equation which is then converted to the desired unit of substance required.
Objectives
To :
(a)
Quantify the chemical components in sodium biocarbonate upon decomposition using
heat.
(b)
Determine the decomposition reaction.
Theory
Sodium bicarbonate (baking soda) is used in many food products and the thermal
decomposition reaction has been studied extensively by food chemists. As the temperature
of the sodium bicarbonate reaches approximately 50 °C, the baking soda decomposes and
carbon dioxide is released. There are three possible chemical reactions that could be
occurring during the baking process. All three of these reactions shown below are
theoretically possible, you are required to determine the correct decomposition reaction.
Possible Decomposition Reactions:
1. sodium bicarbonate (s) → sodium hydroxide (s) + carbon dioxide (g)
2. sodium bicarbonate (s) → sodium oxide (s) + carbon dioxide (g) + water (g)
3. sodium bicarbonate (s) → sodium carbonate (s) + carbon dioxide (g) + water (g)
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 heatresistant gloves if necessary. Wear safety goggles while performing this demonstration.
Please review all Material Safety Data Sheets for additional safety, handling and
disposal information.
4.4 Procedure
1. Students required to record all necessary masses throughout the experiment.
2. Place the empty crucible on the balance pan and then press the tare/reset button. Record the
mass of the empty crucible.
3. Measure some baking soda (between 3 – 6 grams) into the crucible. Record the mass.
4. Assemble the ring stand with a circular ring support. Place the clay triangle on top of the ring
support and place the crucible containing the baking soda on top of the clay triangle
5. Heat the crucible and its contents with the Bunsen burner for ten minutes. Use a spatula to
carefully break up any “clumps” that form during heating. Clumps need to be broken only once
during heating.
6. Measure the mass the crucible and its contents. Report the mass of the product.
Result & Calculations
Before heat decomposition
Weight / (g)
crucible
Crucible + sodium bicarbonate
Sodium bicarbonate
After heat decomposition
Weight / (g)
Crucible + sodium bicarbonate
Sodium bicarbonate
1. Balanced chemical equations with proper chemical formulas for all three possible
decomposition reactions.
2. Determine stoichiometric mass predictions for each possible reaction.
3. Determine which is the correct decomposition reaction.