Investigation
11A
Stoichiometry
If your doctor did not tell you
how much of a medication you
need to take, you could take
too little and the medicine
would not work.
But if you take too much,
it could cause severe
consequences.
How do you know how much of a chemical is
necessary for a reaction to occur?
2
Investigation 11A: Stoichiometry
Part 1: The reaction
1. Put an empty cup on the balance
and zero it.
Measure 10.0 g of baking soda in
the cup. Record the measured
mass in Table 1.
2. Put another empty cup on the
balance and zero it.
Measure 30.0 g of vinegar in the
cup. Record the measured
mass in Table 1.
3. Add the masses of vinegar and
baking soda. Record the sum in
Table 1 (row 3).
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Investigation 11A: Stoichiometry
Part 1: The reaction
4. Slowly pour the vinegar into
the baking soda. Pouring it too
fast might cause the bubbling
to overflow!
Wait until the bubbling has
stopped and record the mass.
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Investigation 11A: Stoichiometry
Part 2: What happened?
a. What evidence did you observe that indicated
a chemical reaction was taking place?
b. Explain the difference in the total mass before and after
mixing.
c. Do you see any baking soda that has not reacted?
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Investigation 11A: Stoichiometry
Part 3: Understanding the reaction
Baking soda
(sodium bicarbonate)
Acetic acid
(acid in vinegar)
a. The balanced reaction is written on the first line of the
chart above. Calculate the formula mass of each of the
products and reactants.
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Investigation 11A: Stoichiometry
Part 3: Understanding the reaction
84.00
Baking soda
(sodium bicarbonate)
60.05
82.03
44.00
18.01
Acetic acid
(acid in vinegar)
b. One of the products is a gas. Which one?
Will this product’s mass contribute to the mass as measured on
the balance after the reaction has finished? Why or why not?
c. On the second line, write down the mass of the baking soda
and vinegar you added.
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Investigation 11A: Stoichiometry
Part 3: Understanding the reaction
84.00
60.05
82.03
44.00
18.01
d. Vinegar is 5% acetic acid
(HC2H3O2) by mass.
Multiply by 0.05 to get the
actual mass of
acetic acid.
e. Use the formula masses to calculate the number of moles
of NaHCO3 and HC2H3O2.
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Investigation 11A: Stoichiometry
Part 3: Understanding the reaction
84.00
60.05
82.03
44.00
18.01
f. How many moles of CO2 were produced?
g. Use the formula mass to calculate the mass of CO2 produced.
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Investigation 11A: Stoichiometry
Part 4: Stop and think
a. How many grams of CO2 were produced in the
reaction?
b. How does the answer to Part a explain the mass
measurement you found at the end of the experiment?
c. Did all the baking soda react? How do you know?
d. Did all the acetic acid react? How do you know?
e. What was the limiting reactant in this experiment?
How do you know?
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Investigation 11A: Stoichiometry
Part 5: An efficient reaction
To make an efficient reaction, there should not be any
reactants left over.
84.00
60.05
Steps a–d
Use this chart to
calculate how many
grams of vinegar need to
be added to react with all
the baking soda.
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Investigation 11A: Stoichiometry
Part 6: Test your hypothesis
1. Measure out 10.0 g of baking
soda in one cup.
2. Measure out the required amount
of vinegar (from your
calculations) in the other cup.
3. Write down the total mass before
you mix the reactants.
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Investigation 11A: Stoichiometry
Part 6: Test your hypothesis
• Calculate the mass of CO2 produced.
• How does this number match your experiment?
84.00
13
60.05
82.03
44.00
18.01
Investigation 11A: Stoichiometry
Part 7: Using stoichiometry
Steps a–e
Using stoichiometry, calculate how much baking
soda and vinegar you would need to make 10.0 g of CO2.
84.00
14
60.05
82.03
44.00
18.01
Investigation 11A: Stoichiometry
Part 8: Applying the principle
Perfect combustion of octane:
If the fuel is burned perfectly,
the reaction that occurs in a
gasoline engine would only
produce carbon dioxide and
water.
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Investigation 11A: Stoichiometry
Part 8: Applying the principle
Perfect combustion of octane:
a. Calculate the formula mass for octane.
b. Suppose a car uses 25 gallons of gasoline in a week.
The density of gasoline is about 2,900 g/gallon.
Calculate the mass in grams of 25 gallons of gasoline.
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Investigation 11A: Stoichiometry
Part 8: Applying the principle
Perfect combustion of octane:
c. Assume gasoline is pure octane. How many moles does
this quantity represent?
d. How many moles of CO2 are created for every 2 moles of
gasoline burned?
e. Calculate the mass of CO2 released from the perfect
combustion of 25 gallons of gasoline.
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Investigation 11A: Stoichiometry