Experiment
5-3
Limiting Reagents
Prelab = 11
Report = 116
Introduction:
In this experiment, the stoichiometry of the
chemical reaction between lead nitrate and
sodium iodide will be verified. The concepts of
limiting and excess reactants will be
demonstrated and the mole ratios expressed in
the balanced chemical equation will be
confirmed. The balanced equation for the
reaction to be examined is given below.
By the same token, if there is 1 mole of lead
nitrate and only 1 mole of sodium iodide in the
reaction mixture, the lead nitrate is said to be
present in excess. The complete reaction
would, according to the balanced equation,
consume 0.5 moles of lead nitrate and 1 mole of
sodium iodide. In this case, sodium iodide is the
limiting reagent.
Pb(NO3)2(aq) + 2NaI(aq) --->
PbI2(s) + 2NaNO3(aq)
In this experiment, you will examine all three
reaction conditions--sodium iodide and lead
nitrate present in the exact mole ratios given in
the balanced chemical equation, sodium iodide
present in excess, lead nitrate present in
excess. The reactants will be mixed in different
mole ratios, in order to attain these three
different reaction conditions. The total number
of moles of reactants will be kept the same in
each reaction mixture. The actual yield of one
product, PbI2, will be represented by the height
of the precipitate formed in the test tube, and
compared with the theoretical yield predicted
from the balanced equation. Upon completion of
each reaction, the mixture will be tested for the
presence and identity of any excess reactant.
The equation indicates that 2 moles of sodium
iodide will completely react with 1 mole of lead
nitrate to form 1 mole of lead iodide and 2 moles
of sodium nitrate. It further indicates that, if there
is 1 mole of lead nitrate and 3 moles of sodium
iodide present in the reaction mixture, there will
be 1 mole of sodium iodide left unreacted when
the reaction has reached completion. In this
case, sodium iodide is said to be present in
excess and lead nitrate is called the limiting
reagent.
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Objectives:
3. To gain familiarity with the concept of limiting
reagent.
1. To experimentally determine the mole ratio in
which lead nitrate and sodium iodide are
both completely converted to the reaction
products, lead iodide and sodium nitrate.
4. To prepare graphs comparing the actual and
theoretical yields of lead iodide. The actual
yield of lead iodide will be represented by
the height of the precipitate formed in the
test tube.
2. To observe what happens when either lead
nitrate or sodium iodide is present in
excess.
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Apparatus:
Safety goggles
250-mL beakers
Rubber stoppers
18 X 150 test tubes
Spot plate
Test tube rack
Dropper pipette
Centimeter ruler
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Reagents:
0.500M lead nitrate, Pb(NO3)2
0.500 M sodium iodide, NaI
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Safety
2. Lead nitrate is toxic. Wash your hands
thoroughly after use!
1. Wear safety goggles.
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Experiment 5-3
March
12, 2016
Page 1
Procedure:
1. Each partner obtain a clean, dry, 18 X 150
mm test tube. Record its ID number.
2. Each partner sign up for a tube on the class
data table.
3. Carefully add the volume of 0.500 M
Pb(NO3)2 and 0.500 M NaI indicated on the
chart for your mixture to your test tube.
4. Seal your tube with a rubber stopper and
invert slowly exactly three times. Do not
shake the tubes!
5. Let your precipitate settle for 10 minutes
6. Then immediately measure the height of the
yellow precipitate that is formed in your tube.
Measure from bottom to top of precipitate, not
the bottom of the tube. Measure with
precision of 1 mm.
7. Record the height of your precipitate in the
data table.
8. Now you will test the supernate (the liquid
above a settled precipitate) from your tube for
the presence of an excess reagent. Using a
CLEAN (rinse it first with DI water) dropper
pipette, remove a sample of supernate from
the tube and add one drop to a depression on
your spot plate. Add another drop to another
depression. Empty the dropper back into the
test tube and thoroughly rinse the dropper
inside and out.
9. Add a drop of 0.500 M Pb(NO3)2 to one of
the drops of supernate. Record the result (NR
or PPT) in the data table.
10. Add a drop of 0.500 M NaI to the other drop
of supernate. Record the result (NR or PPT)
in the data table.
11. Discard all waste in the bottles marked
"Waste Lead Compounds".
.
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Experiment 5-3
March
12, 2016
Page 2
Data and Observations:
(50 (0.25 each))
Student
mL
Pb(NO3)2
mL
NaI
Anthony
Isabelle
Unaiza
Kegan
Chloe
Brianna
Levi
Steven
Alison
Brandon
Nicole
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
5.00
5.50
6.00
6.50
7.00
7.50
8.00
8.50
9.00
9.50
10.00
10.50
11.00
12.00
13.00
14.00
15.00
16.00
17.00
17.00
16.50
16.00
15.50
15.00
14.50
14.00
13.50
13.00
12.50
12.00
11.50
11.00
10.50
10.00
9.50
9.00
8.50
8.00
7.50
7.00
6.00
5.00
4.00
3.00
2.00
1.00
Paul
Olivia
Michelle
Lauren
Khoa
Aaron
Tyler
Andrew
Lindsay
Bailey
ppt
height
(mm)
supernate supernate excess
mmol
rxn w/
rxn w/
reagent Pb(NO3)2
Pb(NO3)2 NaI?
?
(DA1)
?
mmol
NaI
(DA1)
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Experiment 5-3
March
12, 2016
Page 3
Max
Theo.
Yield
Ppt
(mmol)
Analysis and Conclusions:
(10) 1. Calculate the number of millimoles of lead(II) nitrate and of sodium iodide in each tube. Remember
that 0.500 M means 0.500 moles/liter or 0.500 mmol/mL. Enter the results in the data table. Show the
derivation for YOUR tube here.
Pb(NO3)2:
NaI:
(20) 2. On the same grid, using Excel plot two line graphs, one showing the height of lead iodide (on
major y-axis) actually observed versus the mmols of Pb(NO3)2, and the other showing the theoretical
yield of lead iodide (on minor y-axis) versus the mmols of Pb(NO3)2. Place mmol Pb(NO3)2 on the xaxis. Label the y-axis vertically on the left “Height of Lead Iodide (mm)” and on the right “Theoretical
Yield of Lead Iodide (mmol)”. Make sure you differentiate between the two graphs, and include a
legend. Draw your own linear trendline for each peak…you could use Microsoft word. To help putting
two y-axes on Excel, see “Adding Two Y-axes to Excel” on Angel Web under Course Handouts.
(4) 3. From your graph of actual yields, determine which tube has the greatest amount of precipitate?
Calculate the mole ratio, moles NaI / moles Pb(NO3)2, in that tube.
(4) 4. Explain any correspondence between the shapes of the two graphs. Not just are they similar, but why?
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Synthesis:
(4) 1. Consider the mixture of 6.00 mL of Pb(NO3)2 with 12.00 mL of NaI. Theoretically, should the
supernatant liquid from this mixture react with Pb(NO3)2, or with NaI. Explain in detail, but keep it in
this space.
(4) 2. Write an equation for the reaction you observed in this experiment as a double replacement
reaction.
(4) 3. Write an equation for the reaction you observed in this experiment as a complete ionic equation.
(4) 4. Draw a single line through the spectator ions in question 3.
(4) 5. Write an equation for the reaction you observed in this experiment as a net ionic equation.
Experiment 5-3
March
12, 2016
Page 4