Chemistry 20: Module 7: Lesson 1
1
Assignment
MODULE 7: LESSON 1 ASSIGNMENT
Lesson 1 Assignment: Limiting Reagents
Lab: Chemical Analysis Using a Graph
1.
Read “Lab Exercise 8.A: Chemical Analysis Using a Graph” on page 317 in your
textbook. You may also find the information about this reaction on page 318 useful
in completing your analysis. After you have read the lab, answer the following
questions to complete your analysis.
a.
Write the balanced chemical equation for the reaction described in this lab
exercise. (2 marks)
Pb(NO3)2(aq) + 2KI(aq) --> PbI2(s) + 2KNO3(aq)
b.
Identify the limiting reagent and the excess reagent in this lab. (1 mark)
Pb(NO3)2 is the limiting reagent.
KI is the excess reagent.
c.
What is observed when the two reacting solutions are mixed? Describe a test
that could be performed to ensure that the reactions performed were
complete. (2 marks)
- Titration
- Filtration
Chemistry 20: Module 7: Lesson 1
d.
2
Assignment
Make a graph of the data shown in “Table 1.” In this lab, the manipulated
variable is the mass of Pb(NO3)2 reacting.
Use your graph to predict the mass of PbI2(s) that will be produced from a
solution containing 2.5 g of Pb(NO3)2(s). (2 marks)
Chemistry 20: Module 7: Lesson 1
2.
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25.0 mL of 0.150-mol/L KBr(aq) is mixed with excess Pb(NO3)2(aq).
a.
Write the balanced chemical equation for this reaction. (1 mark)
2 KBr(aq) + Pb(NO3)2(aq) --> 2 KNO3(aq) + PbBr2(s)
b.
Calculate the number of moles of the limiting reagent. (1 mark)
moles KBr = 0.0250 L x 0.150 mol/L=0.00375
c.
Predict the number of moles of precipitate. (1 mark)
The ratio between KBr and PbBr2 is 2 : 1
moles PbBr2 = 0.00375/2=0.00188
d.
Calculate the mass of precipitate. (1 mark)
mass PbBr2 = 0.00188 mol x 367.01 g/mol= 0.690 g
Assignment
Chemistry 20: Module 7: Lesson 1
3.
4
Assignment
3.00 L of methane, CH4(g), is combusted with 5.50 L of oxygen gas. Assume SATP
conditions.
a.
Write the balanced chemical equation. (1 mark)
CH4 + 2O2 -------------------------> CO2 + 2H2O
b.
Determine the number of moles of each reactant. (1 mark)
3 litres methane = 3/22.4 = 0.1339mol CH4
5 litres oxygen = 5/22.4 = 0.2232mol O2
c.
Predict the limiting reagent and the excess reagent. (1 mark)
1mol CH4 reacts with 2mol O2 to produce 1mol CO2 and 2mol H2O
0.1339mol CH4 requires 2*0.1339 = 0.2678mol O2
You have only 0.2232mol O2. O2 is therefore limiting and CH4 is in excess.
Chemistry 20: Module 7: Lesson 1
d.
5
Assignment
When the reaction is complete, the atmospheric conditions change. Calculate
the volume of CO2(g) produced if the atmospheric pressure is now 102.1 kPa
and the temperature is 22.0 C. (1 mark)
PV = nRT
102.1 * V = 0.1116 * 8.314* 295
V = 2.68 litres
4.
A 12.0-g piece of copper reacts with 40.0 g of silver nitrate dissolved in solution.
What mass of silver will be formed from this reaction? (4 marks)
Cu + 2 AgNO3 → 2 Ag + Cu(NO3)2
12.0 g Cu) / (63.5463 g Cu/mol) = 0.18884 mol Cu
(40.0 g AgNO3) / (169.87323 g AgNO3/mol) = 0.23547 mol AgNO3
(0.23547 mol AgNO3) x (2 mol Ag / 2 mol AgNO3) x (107.86822 g Ag/mol) =25.4 g Ag
5.
A laboratory technician measures 1.60 g of CuCl2(s) and prepares a solution.
When the solution is complete, a 150-mg piece of Al(s) is placed into the solution
Chemistry 20: Module 7: Lesson 1
6
Assignment
and left to react. Calculate the mass of copper produced when the reaction is
complete. (4 marks)
3 CuCl2 + 2 Al → 2 AlCl3 + 3 Cu
(1.60 g CuCl2) / (134.4527 g CuCl2/mol) = 0.011900 mol CuCl2
(1.150 g Al) / (26.98154 g Al/mol) = 0.042622 mol Al
0.011900 mole of CuCl2 would react completely with 0.011900 x (2/3) = 0.0079333 mole of Al, but
there is more Al present than that, so Al is in excess and CuCl2 is the limiting reactant.
(0.011900 mol CuCl2) x (3 mol Cu / 3 mol CuCl2) x (63.5463 g Cu/mol) = 0.756 g Cu
Chemistry 20: Module 7: Lesson 1
6.
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Assignment
A 150-mL sample of a 0.600-mol/L calcium nitrate solution is mixed with 1.00 L of
0.500-mol/L NaOH(aq). Calculate the mass of precipitate produced in the reaction.
(4 marks)
Ca(NO3)2 + 2 NaOH → Ca(OH)2(s) + 2 NaNO3
(0.150 L) x (0.600 mol/L) = 0.0900 mol Ca(NO3)2
(1.00 L) x (0.500 mol/L) = 0.500 mol NaOH
0.0900 mole of Ca(NO3)2 would react completely with 0.0900 x (2/1) = 0.180 mole of NaOH, but there
is more NaOH present than that, so NaOH is in excess and Ca(NO3)2 is the limiting reactant.
moles Ca2+ = 0.150 L x 0.600 M=0.0900
moles OH- = 1.00 L x 0.500 M= 0.500 ( in excess )
Ca2+ + 2OH- = Ca(OH)2
moles Ca(OH)2 = 0.0900
mass Ca(OH)2 = 0.0900 x 74 g/mol=6.66 g or 6.67 g
Chemistry 20: Module 7: Lesson 1
7.
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Assignment
Approximately 9.10 g of lead(II) acetate is weighed out and placed in a 400-mL
solution of 0.150-mol/L sodium hydroxide. Calculate the mass of precipitate
produced in this reaction. (4 marks)
Moles Pb(CH3COO)2 = 9.10 g / 325.29 g/mol= 0.0280
Moles NaOH = 0.400 L x 0.150 M = 0.0600
Pb2+ + 2 OH- >> Pb(OH)2
Pb2+ is the limiting reactant
Pb2+ reacts with 0.0280 x 2 = 0.0560 moles of OH- to give 0.0280 moles of Pb(OH)2
Mass lead (II) hydroxide = 0.0280 mol x 241.12 g/mol= 6.75 g
Chemistry 20: Module 7: Lesson 1
8.
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Assignment
Using Stoichiometry to Save the Apollo 13 Astronauts
The solution to the problem of carbon dioxide accumulating in the Apollo 13
spacecraft required the development of a new way to use equipment already aboard
the spacecraft. In the lunar module, there was not enough LiOH(s) available to react
with all of the CO2(g) produced by three astronauts because it was designed for only
two people. The ingenious design that used scrubbers intended for one part of the
spacecraft to be used in another part allowed the NASA engineers to ensure the
safety of the astronauts.
How did NASA determine the quantity of lithium hydroxide necessary to operate
the carbon dioxide scrubber system? Was a knowledge of stoichiometry required?
The carbon dioxide scrubbers used in the Apollo missions were canisters containing
lithium hydroxide. Air in the spacecraft was circulated through the cylinders,
allowing a reaction between lithium hydroxide and carbon dioxide to take place.
2 LiOH(s) + CO2(g) → Li2CO3(s) + H2O(l)
Use the following information to answer the questions that will help you determine
the mass of lithium hydroxide necessary for the duration of the mission:

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


An average adult at rest exhales 0.50 L of air with each breath and takes
approximately 15 breaths per minute.
Approximately 4.5% of exhaled air is carbon dioxide.
Assume that conditions in the Apollo 13 lunar module were at SATP.
The Apollo 13 mission lasted for 3.7 days after the oxygen tank exploded.
Assume lithium hydroxide reacts completely with carbon dioxide gas.
(7 marks)
Chemistry 20: Module 7: Lesson 1
What volume of carbon dioxide would the three
astronauts exhale in one minute?
What volume of carbon dioxide would the three
astronauts exhale in one hour?
What volume of carbon dioxide would the three
astronauts exhale in one day?
What volume of carbon dioxide would the three
astronauts exhale in 3.7 days, the total time of the
mission after the oxygen tank exploded?
What amount, in moles, of carbon dioxide was
produced by the astronauts?
What amount of LiOH was required to react with
all of the carbon dioxide?
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Assignment
(3 persons) x (0.5 L air/person/breath) x (15
breaths/min) x (1 minute) x (0.045 CO2/air) =
1.0125 = 1 L CO2/minute.
(3 persons) x (0.5 L air/person/breath) x (15
breaths/min) x (60 minutes) x (0.045 CO2/air)
= 60.75 = 61 L CO2/hr
(3 persons) x (0.5 L air/person/breath) x (15
breaths/min) x (60 minutes) x (24 hours/day) x
(0.045 CO2/air) = 1458 L = 1.5 x 10^3 L
CO2/day
(3 persons) x (0.5 L air/person/breath) x (15
breaths/min) x (60 minutes) x (24 hours/day) x
(3.7 days) x (0.045 CO2/air) =
5395 L CO2 in 3.7 days [ignoring significant
digit considerations].
n = PV / RT = (100.0 kPa) x (5395 L) / (
(8.3144621 L kPa/K mol) x
(25 + 273.15) K) = 217.6 mol CO2
[ignoring significant digit considerations].
2 LiOH + CO2 → Li2CO3 + H2O
Chemistry 20: Module 7: Lesson 1
What mass of LiOH was required for the mission?
11
Assignment
(217.6 mol CO2) x (2 mol LiOH / 1 mol CO2)
x (23.9483 g LiOH/mol) = 10 422 g = 10.4 kg
LiOH
[ignoring significant digit considerations].
Once you have completed all of the questions, submit your work to your teacher.