Chemistry 11
The Decomposition
Reaction of Baking Soda,
NaHCO3
Oscar Shi
Period 2
Laboratory Assignment
Due Date: 2011/4/14
Introduction
The objective of this experiment is to find the actual chemical equation that governs the manner in which baking
soda (sodium hydrogen carbonate NaHCO3) decomposes.
When NaHCO3 is heated, it decomposes to produce a gas and leaves behind a solid. Two possible equations for the
decomposition are:
NaHCO3 (s) + heat  NaOH (s) + CO2 (g)
NaHCO3 (s) + heat  ½ Na2OH3 (s) + ½ H2O (g) + ½ CO2 (g)
Materials and Methods
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crucible
crucible lid
clay triangles
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ring
ring stand
crucible tongs
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electronic balance
sodium hydrogen carbonate
The Procedure of the Laboratory
1. Put on safety goggles and a lab apron.
2. Obtain a clean and dry crucible and lid. Crucibles very slowly adsorb small
amounts of water vapour from the atmosphere and must be heated for a minute or
two to get rid of adsorbed water molecules before you can get an accurate “initial
mass” for a crucible. Crucibles are usually heated in clay triangles, which in turn
are set on top of rings attached to ring stands.
3. Hot crucibles can blister your bench top, so hot crucibles should be placed on
the steel base of your ring stand using your crucible tongs at all times in order to
cool down.
4. After the crucible has cooled down, accurately determine the mass of your
crucible. Record this mass on your date sheet. If a very hot crucible is put on an
electronic balance, the balance can be ruined.
5. Put about 5.00 g of sodium hydrogen carbonate in the cool crucible. Once again
using the electronic balance, record the mass of the crucible plus baking soda
accurately on your data sheet. Using the method of mass by difference, figure out
the mass of the sample and enter this into your data sheet.
6. In order to decompose, sodium hydrogen carbonate must be heated until the
crucible starts to glow an “orange-red”. Heat the crucible for at least 5 minutes
making sure the lid is on with a slight gap to let the gas escape. If there is no lid then some of the baking soda “can”
pop out thereby altering your calculations.
7. Cool down the crucible as above.
8. After the crucible has cooled down, weight the crucible and lid and sample. Record this in your data sheet.
9. Re-heat the crucible again for at least 5 minutes and let cool down. After the crucible has cooled down, take
another weighing. Record this in your data sheet. Again, using the method of mass by difference, calculate the mass
of the heated sample.
10. Dispose of the sample down the sink with water and wash the crucible and lid with water and put back all
equipment and supplies.
Pre-Laboratory Calculations
NaHCO3 (s) + heat  NaOH (s) + CO2 (g)
5.00 g NaHCO3 ×
1 mol NaHCO3
1 mol NaOH
40 g NaOH
×
×
= 2.38 g NaOH
84 g NaHCO3 1 mol NaHCO3 1 mol NaOH
NaHCO3 (s) + heat  ½ Na2OH3 (s) + ½ H2O (g) + ½ CO2 (g)
5.00 g NaHCO3 ×
1
1 mol NaHCO3 2 mol Na 2 CO3 106 g Na 2 CO3
×
×
= 3.15 g Na 2 CO3
84 g NaHCO3 1 mol NaHCO3 1 mol Na 2CO3
Result/ Data
Measurements
Mass of Empty Crucible (after initial heating)
Mass of Crucible + sample
Mass of sample
Mass (in grams)
19.208 g
24.208 g
5.00 g
Mass of Crucible + sample (after 1st heating)
nd
Mass of Crucible + sample (after 2 heating)
Mass of sample after heating
22.343 g
22.355 g
3.147 g
Questions
1. Using the mass of the sample that you started with in your lab, calculate the theoretical yield of each of the
solids in the two possible equations given in the introduction of the lab.
NaHCO3 (s) + heat  NaOH (s) + CO2 (g)
5.00 g NaHCO3 ×
1 mol NaHCO3
1 mol NaOH
40 g NaOH
×
×
= 2.38 g NaOH
84 g NaHCO3 1 mol NaHCO3 1 mol NaOH
NaHCO3 (s) + heat  ½ Na2OH3 (s) + ½ H2O (g) + ½ CO2 (g)
1
1 mol NaHCO3 2 mol Na 2 CO3 106 g Na 2 CO3
5.00 g NaHCO3 ×
×
×
= 3.15 g Na 2 CO3
84 g NaHCO3 1 mol NaHCO3 1 mol Na 2CO3
2. From your results in number 1, which of the 2 equations is the correct decomposition reaction of baking
soda? Why?
From my results in question number 1, NaHCO3 (s) + heat  ½ Na2OH3 (s) + ½ H2O (g) + ½ CO2 (g) is the correct
decomposition reaction of baking soda. Because the answer calculated from the equation is accurately close to the
weighted mass of the sample after heating.
3. What is the actual yield of your final sample in this experiment?
According to the data collected, the actual yield of the final sample in this experiment is 3.147 grams.
4. What is your percent yield for this experiment?
Percent Yield =
Actual Yield
3.147 grams
=
× 100% = 99.9% Yield
Theoritical Yield
3.15 grams
Conclusion
Every step of this experiment was taken carefully and therefore the result must hold a high accuracy. Possible source
of error cannot be excluded, however. The small particles of dirt or any other remained substance in crucible
from previous laboratory that could not be examined by naked eye might be a cause to slight errors upon
measurement readings. Temperature of the crucible was assumed to be acceptable to be placed on the electronic
scale for mass measurement. It is unknown if the air currents whether or not influenced the reading of the scale
during the experiment. The electronic scale itself or when under the influence of the environment, was another
source of error. The reading on scale increased and decreased even when the mass placed still on the balance. The
sources of errors above were assumptions and even if they did influence the accuracy, it would not have influenced
that much of it. Therefore it concludes the readings and calculations on this laboratory are highly accurate.