GCCD Lab Le Châtelier’s Principle Lab Report

Online Lab Experiment EQ-LCP: Le Châtelier’s PrincipleA. Instructions for Completion and Submission of Lab
1. Go to the following website:
http://dept.harpercollege.edu/chemistry/chm/100/dgodambe/thedisk/equil/equil.htm
You will see a page called “Virtual Chemistry Lab Equilibrium and LeChatelier’s Principle.
At the bottom of the opening page you will see links to sections called “Introduction”,
“Background”, “Prelab”, “Experiment” and “Postlab”. Click on “Introduction” at any time to
bring your self back to this opening page
2. Click on “Background” to read through some background information on the principles of
chemical equilibrium and Le Châtelier’s Principle.
3. When you have read the “Background” pages, do not click on the “Prelab” link. Instead go to
the Prelab section of this document, (Section B. on page 2 and 3, below), and answer the
prelab questions there (these are modified from the online version so it is important that you
answer the questions shown in this document).
4. When you have completed the prelab questions below, click on the “Experiment” link on the
website and follow the instructions there as follows:
a) Click and read the page on “General comments about the experiment” and “An example”
to see how the virtual lab works.
b) Go through the 6 simulations shown, stressing each systems in the ways available (heating,
cooling and adding various chemicals). Make observations in your notebook which will be
useful in answering the postlab questions.
5. When you have completed the virtual experiments, do not click on the “Postlab” link. Instead
go to the Postlab section of this document, (Section C. on page 4 and 5, below), and answer
the postlab questions there (these are modified from the online version).
6. Save this document with a filename based on your name e.g. lastname_initial_EQLCP and
submit it by the deadline indicated in the assignment on Canvas.
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B. Prelab Questions: Answer these questions before starting the experiment and after reading the
background information.
You can either write your answers using your MS-word editor (or equivalent), in the relevant
spaces below OR print this page, write your answers by hand, and take a picture of your answers
to submit on Canvas.
WRITE YOUR NAME AND LAB SECTION HERE: _________________________
1. Which describes a solution that contains a system at equilibrium? One in which the color of
the solution is changing slowly, or one in which the color is not changing. Explain your answer.
2. The following equilibrium is established when copper ions and bromide ions are placed in
solution.
heat + Cu(H2O)6+2 (aq) + 4 Br- (aq)
6 H2O (l) + CuBr4-2 (aq)
The tube on the left contains only copper sulfate dissolved in solution. The tube on the right is
the result of adding some potassium bromide solution. Given that the Cu(H2O)6+2 ion is blue
and that the CuBr4-2 ion is green, answer the questions below.
a) What happened to the concentration of each of the ions when the KBr was added?
b) Explain why the solution changed color.
c) Would the tube feel hot or cold, or the same, when the KBr was added?
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3. Consider the following equilibrium: Mg(OH)2 (s)
Mg+2 (aq) + 2 OH- (aq)
The tube on the left contains Mg(OH)2(s) and water. A chemical has been added to cause the
change shown in the tube on the right. Suggest a possibility for what chemical could have been
added. Explain your answer.
4. Methanol has the formula CH3OH and can be produced by the reaction of carbon monoxide
with hydrogen gas as follows: CO + 2 H2
CH3OH + heat
In an attempt to maximize the yield of methanol (amount of methanol produced), a chemist
would try to shift the equilibrium as far to the right as possible. Which of the following would
accomplish this? Explain your answer.
(a) heating the mixture
(b) adding an excess of carbon monoxide
(c) removing the methanol as it is formed
(d) adding a substance that reacts with carbon monoxide
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C. Postlab Questions: Answer these questions after completing the experiment using your
observations to help.
You can either write your answers using your MS-word editor (or equivalent), in the relevant
spaces below OR print this page, write your answers by hand, and take a picture of your answers
to submit on Canvas.
1. Explain the effect of AgNO3 on the cobalt system (experiment I ). What did you observe and
why?
2. Predict what would happen if the ammonium system (experiment II ) was heated. What would
you observe and why?
3. Predict what would happen if you cooled the iron thiocyanate system (experiment III). What
would observe and why?
4. When the chromate system (experiment IV) is heated the tube is observed to go pale yellow.
What does this tell you about the enthalpy of the forward reaction as written below?
2 CrO4-2 + 2 H+
Cr2O7-2 + H2O
5. For experiment V., when the pressure of the tube containing gaseous NO2 and N2O4 is increased
the tube goes colorless. Explain why.
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6. Consider the following equilibrium. Cu+2 (aq) + 4 NH3 (aq)
Cu(NH3)4+2 (aq)
Look at the images of a test tube below. The copper ion in solution is light blue. The
Cu(NH3)4+2 ion is a deep blue. The tube on the left contains only copper ions.
(a) Identify what chemical was added to the tube on the left to produce the results shown in
the center tube. Explain your answer in terms of how this affected the equilibrium.
(b) Identify what chemical may have been added to the center tube to produce the results
shown in the tube on the right. Explain your answer.
7. The barium ion, Ba2+, is toxic to humans. However, barium sulfate is commonly used as an
image enhancer for gastrointestinal x-rays. What does this imply about the position of the
equilibrium shown here: BaSO4 (s)
Ba+2 (aq) + SO4-2 (aq)
Explain your answer.
8. Hemoglobin (Hb) and oxygen gas form a complex (HbO2) that carries oxygen throughout the
human body. Unfortunately, carbon monoxide also binds to hemoglobin so that an equilibrium
is established as follows: HbO2 + CO
HbCO + O2
Carbon monoxide poisoning occurs when the concentration of HbO2 in the blood is reduced.
The first aid for a person suffering from carbon monoxide poisoning is to (1) remove them to
an area of fresh air, and (2) administer oxygen. Using the principles of equilibrium, explain
how each of these helps to restore the HbO2 concentration.
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