Analysis of a Decomposition Reaction
Introduction
The Green Chemistry Program was initiated by the Environmental Protection Agency in the 1990s with
the goal of applying chemical principles to prevent pollution. The program calls for the design of chemical
products and processes that will reduce the use and generation of hazardous substances. The purpose of this lab
is to design an experiment for determining the percent composition of a solid by applying the principles of
green chemistry.
Concepts
Stoichiometry
Percent Composition
Decomposition Reaction
Background
In this lab, you will design a process to determine the weight percent of sodium bicarbonate, in a mixture of
itself and its sodium carbonate. Sodium bicarbonate undergoes decomposition when heated above 110˚C.
2NaHCO3(s)  Na2CO3(s) + H2O(g) + CO2(g)
Equation 1
At temperatures below 800˚C, sodium carbonate remains unreacted. Therefore, if a mixture of bicarbonate and
carbonate salts is heated a low temperature, all that remains after heating is the carbonate solid.
Materials
Matches or lighter
Sodium carbonate, 2g
Ring clamp
Soild mixture samples
Sodium carbonate (Na2CO3)/ sodium bicarbonate NaHCO3, 2g
Balance
Bunsen Burner
Crucible and cover
Support stand
Triangle
Crucible tongs, wire gauze
Safety Precautions
Sodium bicarbonate is slightly toxic by ingestion and is a skin irritant. Handle the crucible with only the tongs.
Do not touch the crucible with fingers or hands. There is a significant burn hazard associated with handling a
crucible – remember that a hot crucible looks like a cold one. Wear chemical splash goggles, chemical-resistant
gloves, and a chemical resistant apron. Thoroughly wash hands with soap and water before leaving the
laboratory. Follow all laboratory safety guidelines.
Procedure
Decomposition of Group I Bicarbonates
1. Use an analytical balance to find the mass of the crucible and crucible cover. Handle with tongs to avoid
getting fingerprints on the crucible and cover.
2. Record the mass.
3. Now add about 2g of your sodium bicarbonate sample to the crucible. Weigh the crucible, cover and
sample. Record the combined mass.
4. Set the crucible at an angle in the clay triangle held in the ring on the support stand. Cover the crucible
loosely with the crucible cover, and heat very gently. It is important that
the escaping vapor does not carry any of the solid along with it, so be sure
that the crystals are heated very gently for at least five minutes. (see Figure
3).
5. Turn off the gas source and remove the burner.
6. Use the tongs to remove the crucible cover and place it on wire gauze on the bench top. With the tongs,
remove the crucible from the clay triangle and place it on the wire gauze as well.
7. Allow the crucible and its cover to cool completely on the wire gauze for at least ten minutes.
8. Measure and record the mass of the crucible, cover and carbonate product.
9. Repeat the drying procedure until constant mass is obtained.
10. Record the final mass of the crucible, cover and carbonate product.
11. Dispose of the crucible contents according to your instructor’s directions. Carefully clean the crucible and
crucible cover for use in the next part of the lab.
12. Calculate the percent yield for the carbonate product.
Data
Mass of crucible, cover and bicarbonate sample
Mass of crucible and cover
Mass of bicarbonate sample
Mass of crucible, cover and sample after heating #1
Mass of crucible, cover and sample after heating #2
Mass of water vapor and carbon dioxide
Calculations
1. From the mass of bicarbonate reactant and the balanced chemical equation, calculate the theoretical mass of
carbonate solid that should be produced.
2. Calculate the mass of sodium carbonate obtained from the experiment
3. Calculate the percent yield of sodium carbonate in this experiment.
Discussion
1. Calculate the mass of water vapor and carbon dioxide that would be produced by gently heating a mixture of
1.550g of sodium bicarbonate and 0.463g of sodium carbonate.
2. What mass of sodium carbonate would remain in the crucible?
Conclusion- write one