Experiment 9 – Baking Soda
Name __________________
Lab Section __________________
Experiment 9 – Decomposition of Baking Soda
Introduction
The decomposition of any metal hydrogen carbonate will result in the formation of that metal
carbonate, water vapor, and carbon dioxide. This lab will investigate the decomposition of
sodium hydrogen carbonate, NaHCO3, commonly called baking soda. It is governed by the
following chemical equation:

2 3 () → 2 3 () + 2  () + 2 ()
In this lab, the NaHCO3 will be decomposed to form Na2CO3. The first half of the experiment
will use a pure sample of NaHCO3, and the second part will use a mixture containing only some
NaHCO3. Depending on how well the first half of the experiment is performed, the percent yield
of this reaction should be 100%. The second half of the experiment should see something less
than 100%, since it is not a pure sample.
Percent yield is defined as the actual yield divided by the theoretical yield. The actual yield is
the amount of product one produces during the experiment. The theoretical yield is the amount
of product one should have produced.
%  =
 
 100%
ℎ 
Unless there are experimental errors, the % Yield should not be over 100%. In many cases,
especially ones in which the reaction is difficult to control; the % Yield can be much lower than
100%.
In the case of impure samples, like in the second half of this lab, the % Yield can give the
percent of active material in the sample. The concept is the same. The only trick is to keep track
of which value is the actual amount, and which is the theoretical amount.
Refer to the sample calculations for more insight.
Equipment
100 or 250 mL beaker
Watchglass
Bunsen burner
Wire gauze
Iron ring
NaHCO3
Unknown sample
Experiment 9 – Baking Soda
Name __________________
Lab Section __________________
Examples
Percent Yield from a Pure Sample
A 0.685 g sample of Ca(HCO3)2 is decomposed by heating to form CaCO3. When the sample is
cooled it weighs 0.418 g. Calculate the theoretical yield of CaCO3.

(3 )2 () → 3 () + 2  () + 2 ()
To find the theoretical yield, calculate the amount of CaCO3 one expects to obtain from the
Ca(HCO3)2. Set up the mass-mole-mole-mass calculation is as follows:
0.685  (3 )2 [
1  (3 )2
162.12  (3 )2
][
1  3
1  (3 )2
][
100.19  3
1  3
]
= 0.422907  3
in proper sig figs = .    Theoretical Yield
The percent yield is actual yield divided by the theoretical yield. After decomposition, the actual
yield of CaCO3 was 0.418 g. Divide this actual yield by the theoretical yield and convert to
percentage.
% 3 =
 
ℎ 
 100%
% 3 =
0.418
0.423
 100%
%  = . %
Experiment 9 – Baking Soda
Name __________________
Lab Section __________________
Percent of Active Material in Unknown Mixture
A 1.425 g sample of powder contains KHCO3 and an unknown amount of unreactive salt. When
it is decomposed it weighed 1.225 g. Calculate the %KHCO3 in the unknown powder.

2 3 () → 2 3 () + 2 3 ()
The only mass that is truly known in this problem is the mass that was lost, namely the H2O and
CO2 (grouped as H2CO3 (g) in the equation above).
The mass of gas that was produced is merely the mass before heating minus the mass after
heating: 1.425 g – 1.225 g = 0.200 g gas released.
Using this mass, we can determine the actual amount of KHCO3 that produced this gas by the
following mass-mole-mole-mass calculation:
0.200  2 3 [
1  2 3
60.03  2 3
][
2  3
1  2 3
][
100.02  3
1  3
]
= 0.666467  3
In proper sig figs = .    Actual amount of KHCO3 in sample
The original sample was 1.425 g. If all of the sampler were KHCO3, then the amount of gas
released would be much more (0.428 g, using the same calculation as in the first example). In
this case we see that our calculated value above is the actual amount of KHCO3 that made the
gas, and our initial measured amount in the problem statement is the theoretical amount that
should have made the gas.
The percent of active material is the amount of KHCO3 that decomposed (made the gas) divided
by the total amount of material.
% 3 =
 
   
% 3 =
 100%
0.666
1.425
 100%
%  = . %
Experiment 9 – Baking Soda
Name __________________
Lab Section __________________
Procedure
Percent Yield of Na2CO3 from pure NaHCO3
Weigh out approximately 1 g of NaHCO3 into your beaker.
Place the watchglass on the beaker. This will act as the indicator of when the experiment is
done.
Place the beaker on the wire gauze and heat the NaHCO3. A vigorous flame will be used in
this experiment. Be sure that the tip of the cone of the flame is touching the wire gauze.
Water droplets should begin to form on the watchglass within a few minutes. Note: the
initial “fog” one sees upon heating is merely the water vapor that is naturally occurring on
the glass being driven off by the heat.
Continue to heat the NaHCO3 until the water droplets on the watchglass have disappeared.
Allow the beaker to cool to room temperature and weigh it. This is the mass of the Na2CO3
resulting from the decomposition.
Calculate the theoretical yield of the Na2CO3 from the original mass of the NaHCO3.
Percent of NaHCO3 in an Unknown Mixture
Weigh out approximately 1 to 2 g of the unknown sample into your beaker.
Repeat the steps of the previous procedure. This time, however, the resulting mass is the
expected Na2CO3 and the unreactive component of the unknown.
Use the mass lost in the experiment, the H2CO3 gas, to determine the mass of NaHCO3 in
your unknown sample.
Post Experiment Instructions
All waste can be placed in the trash or rinsed down the sink.
Return unknown vial to its place of origin.
Figure 9.1: Setup of Decomposition
Experiment 9 – Baking Soda
Name __________________
Lab Section __________________
Prelaboratory Questions
A 0.685 g sample of NaHCO3 is decomposed by heating to form Na2CO3. When the sample is
cooled it weighs 0.418 g. Calculate the theoretical yield of Na2CO3. Calculate the percent yield
of Na2CO3.

2 3 () → 2 3 () + 2 3 ()
A 4.076 g sample of powder contains LiHCO3 and an unknown amount of unreactive salt. When
it is decomposed it weighed 1.496 g. Calculate the %LiHCO3 in the unknown powder.

2 3 () → 2 3 () + 2 3 ()
Experiment 9 – Baking Soda
Name __________________
Lab Section __________________
Data Table
Percent Yield of Na2CO3 from a pure sample of NaHCO3
Trial 1
Trial 2
Mass of NaHCO3 (before heating)
__________
__________
Mass of Na2CO3 (after heating)
__________
__________
Theoretical Yield of Na2CO3 – show calculations
Theoretical Yield of Na2CO3
__________
__________
__________
__________
Percent Yield of Na2CO3 – show calculations
Percent Yield of Na2CO3
Average percent yield of Na2CO3
__________
Experiment 9 – Baking Soda
Name __________________
Lab Section __________________
Percent of NaHCO3 in an Unknown Mixture
Unknown Number ____
Trial 1
Trial 2
Mass of Unknown Mixture
Before Heating
__________
__________
Mass of Unknown Mixture
After Heating
__________
__________
Mass of gas released, H2CO3
__________
__________
Mass of NaHCO3 in Unknown Mixture – show calculations
Mass of NaHCO3 in Unknown Mixture
__________
__________
Percent of NaHCO3 in Unknown Mixture – show calculations
Percent of NaHCO3 in Unknown Mixture
__________
Average Percent of NaHCO3 in Unknown Mixture
__________
__________
Experiment 9 – Baking Soda
Name __________________
Lab Section __________________
Postlaboratory Questions
1) A 1.897 g sample of Mg(HCO3)2 was heated and decomposed. When the sample cooled, it
weighed 1.071 g. What is the % Yield of this reaction?
2) An geologist brought in a sample of ore containing Fe(HCO3)3 and some other, unreactive
material. If the sample weighed 1.394 g before it was decomposed, and 0.978 g after, what is the
%Fe(HCO3)3 of the sample?
Experiment 9 – Baking Soda
Name __________________
Lab Section __________________
3) A 1.112 g strip of magnesium is dropped into a giant container of HCl (aq). What is the
volume of the gas that is produced at 0°C and 1 atm?
4) Calcium metal is dropped into water, and 15.7 L of gas is produced at STP, what was the
mass of calcium that produced the gas?
5) If 2.112 g of Fe2O3 reacts with 0.687 g of Al, how much pure Fe will be produced?

2 3 () + 2  () → 2 3 () + 2 ()
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Experiment 9 – Decomposition of Baking Soda