Limiting Reagent
Introduction
The concept of the limiting reagent can be demonstrated by an analogy: Jerry works in the
Purchasing Department at a specialty car manufacturing plant in Detroit. The plant gets an order
for 100 limited edition cars for Macy’s parade. Jerry purchases 100 car bodies, 100 steering
wheels, and 100 tires. Sadly, Jerry gets fired. Do you know why?
You probably realized that Jerry did not order enough tires to make the 100 cars required. With
his order Jerry could only make 25 cars, and he would have 75 leftover car bodies and steering
wheels. In this story the tires are the “limiting reagent” and the bodies and steering wheels are “in
excess.”
Now let’s apply this concept to chemistry. Consider the balanced combustion reaction of methane
gas:
CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(g)
According to the reaction one mole of methane gas will react with two moles of oxygen gas to
produce one mole of carbon dioxide gas and two moles of steam.
Worked example: When a reaction involves a solution, the concentration of the solution is
generally reported as molarity (shown in units of molar, M, which is equal to moles of solute per
liter of solution)—e.g. a 1.50M sodium chloride solution has 1.50 moles of NaCl per liter of
1.50 mol NaCl
solution or
. Given the volume and molarity of any solution, we can calculate the
L
number of moles of solute present. For example, given 50.0 mL of a 1.50M sodium chloride
solution, we can calculate the number of moles of NaCl present as follows:
æ 1 L öæ 1.50 mol NaCl ö
50.0 mL ç
֍
÷ = 0.0750 mol NaCl
L
è 1000 mL øè
ø
What mass of precipitate could be produced if 10.0 mL of 1.500M aluminum chloride reacts with
10.0 mL of 1.500M sodium hydroxide? First, we write the balanced chemical equation:
AlCl3(aq) + 3 NaOH(aq) 
Al(OH)3(s) + 3 NaCl(aq)
The precipitate formed is aluminum hydroxide. In this example we must first calculate moles for
each reactant, then continue with the molar ratio step, then convert moles of the precipitate back to
grams.
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æ 1 L öæ 1.500 mol AlCl3 ö æç 1 mol Al(OH)3 ö÷ æ 78.0 g Al(OH)3 ö
÷ = 1.17 g Al(OH)3
10.0 mL ç
֍
֍
֍
L
è 1000 mL øè
ø è 1 mol AlCl3 ø çè 1 mol Al(OH)3 ÷ø
æ 1 L öæ 1.500 mol NaOH ö æ 1 mol Al(OH)3 ö æ 78.0 g Al(OH)3 ö
÷ = 0.390 g Al(OH)3
10.0 mL ç
֍
֍
֍
L
è 1000 mL øè
ø è 3 mol NaOH ø çè 1 mol Al(OH)3 ÷ø
Notice that the two product amounts are very different. Even though there is enough aluminum
chloride to make 1.17 grams of Al(OH)3 precipitate, there is only enough sodium hydroxide to
make 0.390 grams of Al(OH)3. Once that amount of precipitate is made, we run out of sodium
hydroxide. Thus, in this example, sodium hydroxide is the limiting reagent, aluminum chloride is
in excess, and 0.390 grams of aluminum hydroxide precipitate can be produced.
While these calculations may not be as exciting as manufacturing specialty cars, if a chemist
miscalculates limiting reagent problems he or she could get fired, cause a serious accident, and (in
the extreme case) kill someone due to an explosion or other serious accident!
In this lab you will conduct several trials of a reaction, determine the limiting reagent and the
reactant in excess for each trial, and record your observations.
Procedure:
In your Lab Notebook, before beginning the experiment, prepare a data table to record the following
data for all six trials (A1, A2, A3, B1, B2 and B3) for each solution, CaCl2 (aq) and Na2CO3 (aq) :
Data Table 1 (All Six Trials):
Data Table 2 (Trials A1, A2, A3):
For both solutions include:
mass of weighing paper
 initial volume
mass of weighing paper with precipitate
 final volume
mass of precipitate (actual yield)
 total volume
Directly below the data table, label a space to record the exact concentrations of CaCl2 (aq) and Na2CO3 (aq)
Part I. Precipitation reactions.
1. Clean and label six test tubes: A1, A2, A3, B1, B2 and B3. In each of the six test tubes, add
approximately 4 mL of 0.5 M calcium chloride solution to the six test tubes. Record initial and final
volumes for calcium chloride in the Lab Notebook. Also record the exact molarity from the reagent
bottle in the Lab Notebook. Calculate total volume delivered for each test tube and record this result in
the lab notebook.
2. Now, in test tubes A1 and B1, add approximately 1mL of 0.5 M sodium carbonate solution to each. In
each of test tubes A2 and B2, add approximately 4 mL sodium carbonate solution. In each of test tubes
A3 and B3, add approximately 6 mL of sodium carbonate solution. Record initial and final volumes for
sodium carbonate in the Lab Notebook. Also record the exact molarity from the reagent bottle in the
Lab Notebook. Calculate total volume delivered for each test tube and record this result in the lab
notebook.
3. Place each test tube in the Vortex Mixer (set to Auto/Touch; adjust the dial to a low-medium setting (a
4-5 setting on the vortex) for about 25-30 seconds. Once all six solutions have been thoroughly mixed,
place them in two separate test tube racks, separated by letter (A1, A2 and A3 in one rack and B1, B2
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and B3 in a different rack). These two sets will be treated differently. Place the “B” rack in an area on
your bench-top where it will not be disturbed. Record the time in your Lab Notebook and do not touch
these test tubes (“set B”) until you are ready for Part IV (after at least an hour has passed) so any
precipitates can settle well.
Part II. Filtration.
1. Obtain three medium-flow filter papers and label them in pencil on their edges with a small “A1”,
“A2” and “A3”. Weigh each filter paper and record their masses in your Lab Notebook. Obtain
three 50 mL beakers and label them “A1”, “A2” and “A3”.
2. Set up a filtration apparatus with a plastic funnel in a ring stand. Fold and insert the filter paper “A1”
into the funnel and place the 50mL beaker “A1” beneath the funnel to catch the filtrate.
3. Pour the contents of test tube A1 into the funnel, using a D.I. wash bottle to wash any remaining
precipitate out of the test tube into the filter paper. When the liquid had passed through filter, wash it
with about 3mL of D.I. water. When this liquid had passed through the filter, repeated the wash with
another 3mL of D.I. water. SAVE the filtrate for each trial to use in Part III.
4. Remove the filter paper and carefully open it up, placing it on a watch glass. Place the watch glass on a
hot plate (set to heat setting 4, or 90°C) to dry. Record the time drying started and ended in your
notebook under observations. While the filter paper “A1” is drying, repeat steps 2-4 above with “A2”.
While the filter paper “A2” is drying, repeat steps 2-4 with “A3”. (You may filter all three
simultaneously with three ring clamps, three funnels, and three beakers if you wish. Please dry each on a
separate hot plate, though.) Note: It is a good idea to complete all of your calculations while waiting
for them to dry!
5. Weigh each filter paper when dry and record its new mass in your Lab Notebook. Calculate the actual
yield of precipitate for each trial and record this in your Lab Notebook.
6. Write and balance the chemical equation for the reaction in your Lab Notebook. Identify the
precipitate in this reaction. Calculate the theoretical yield of each of these three trials, and then
determine the percent yield for each of these trials. Determine the limiting reagent and the reagent in
excess for each trial. Be sure to clearly label each trial’s calculation and results. Results will be
graded in your lab notebook and in your formal report!
Part III. Testing the Filtrates from Set A.
1. Test the ions dissolved in the filtrate solutions by transferring a small amount of the solution from
filtrate trial A1 to two different clean test tubes with a disposable pipette. Use new disposable plastic
pipettes for each test to prevent cross-contamination.
2. Add about 1 mL more CaCl2 (aq) solution to the first new test tube and about 1 mL more Na2CO3 (aq)
to the second. Record your observations in your notebook in Data & Results Summary Table – Part III
(see page 4 as a reference).
3. Repeat steps 1-2 for the filtrates from A2 and A3. Remember: use new pipettes for each test.
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Part IV. Observing the Precipitates in Set B.
1. Now, without disturbing the precipitates, examine the test tubes in test tube rack B that were set aside
for at least an hour. Draw the three test tubes in your Lab Notebook, making sure to note the level of
the precipitates and the level of the liquid surface in each. Observe and record the physical properties of
the precipitates.
Please copy the following Data and Results Summary Tables in your lab
notebook.
Your data should be neatly entered into your lab notebook as the experiment is carried out, not on
this page.
Example Data & Results Summary Table – Parts I & II.
Trial
Volume of
CaCl2 (aq)
Volume of
Na2CO3 (aq)
Theoretical
mass
of precipitate
Limiting
reagent
Reagent in
excess
Actual mass
of precipitate
A1
A2
A3
B1
B2
B3
Percent yield
Example Data & Results Summary Table – Part III.
Trial
Predicted reagent
in excess
Observation after
adding CaCl2 (aq)
Observation after
adding Na2CO3 (aq)
A1
A2
A3
Finally, complete the Data Page and Postlab Questions, page 6.
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Name:_______________________
Section:___________________
Pre-Lab Questions
Write your answers on this page and turn it in
to your instructor before starting this experiment.
1. Betty Joe Beaker is making little stick figure donkeys for her daughter’s birthday party. Each donkey
needs one head, one body, two ears, and four legs.
Draw a stick figure donkey here 
How many donkeys can she make with 28 heads, 24 bodies, 44 ears and 68 legs?
The limiting body part is
The body parts in excess are
How many of each excess piece will be left over?
2. Complete the beaker drawings for the two reagents used in this week’s Limiting Reagent
Experiment.
Formula Reagent 1:___________
Formula Reagent 2:____________
3. Write the balanced chemical reaction for the reagents used in this week’s Limiting Reagent
Experiment.
Molecular Equation:_________________________________________________________
Total Ionic Equation:_________________________________________________________
Net Ionic Equation:__________________________________________________________
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Name:_______________________
Section:___________________
Discussion Questions
Write your answers on these pages and attach them to your report.
1. (6 pts) Consider the following reaction:
D
V2O5 (s) + 2NaOH (l) ¾¾
® 2NaVO3 (s) + H2O (g)
red
colorless
yellow
colorless
solid
liquid
solid
gas
When the red solid is mixed with the colorless liquid and heated, the mixture starts to give off a gas and
change color. When the reaction has stopped, the result is a dry, yellow solid containing small, red
particles. Which substance is the limiting reactant? Explain how you determined this.
2. (12 pts) In the beakers below, using your calculation results, draw what the filtrate solutions contained
for each trial. Show the precipitate and the excess reagents in the beakers. (Recall how we showed solution
contents in the pictures from the Chemical Reactions Lab.)
Trial A1
Trial A2
Trial A3
3. (6 pts) If sodium carbonate is the limiting reagent and calcium chloride is in excess:
a. Which ions are present in the supernatant? ________________________
b. What would happen if you added CaCl2 (aq) to the supernatant?
c. What would happen if you added Na2CO3 (aq) to the supernatant?
4. (6 pts) If calcium chloride is the limiting reagent and sodium carbonate is in excess:
a. Which ions are present in the supernatant? ________________________
b. What would happen if you added CaCl2 (aq) to the supernatant?
c. What would happen if you added Na2CO3 (aq) to the supernatant?
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