Ontario Virtual High School Galvanic Cells Pre Experiment Questions

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Assignment: Galvanic Cells
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Assignment: Galvanic Cells
A galvanic cell transforms chemical energy released by a spontaneous redox
reaction into electrical energy. Galvanic cells are extremely useful in everyday life,
comprising the batteries that power everything from cell phones to cars.
In this assignment, you will build a variety of galvanic cells and analyze cell potential
data.
Instructions
Your task is to plan and conduct a simple experiment to test how the concentration
of a half-cell electrolyte solution affects the cell potential (voltage) of a galvanic cell.
In Step One, you will practice building various galvanic cells. In Step Two, you will
analyze the cell potential data of a galvanic cell of your choice and answer your
testable question.
Step 1: Pre-Experiment Activity
Before you begin your data analysis, build the following galvanic cells. After building
each cell, complete the following:
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Draw a diagram representing each cell. Your diagrams should include the
labels of all species, the direction of ion flow from the salt bridge, and the
direction of electron flow through the wires.
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Write each half-cell reaction.
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Write the complete redox reaction.
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Assignment: Galvanic Cells
Upload your submission to the Assignment: Galvanic Cells—PreExperiment Dropbox for your teacher to review prior to completing Step Two.
1. Zinc/Copper Cell
Create the galvanic cell by dropping all necessary materials into the
correct half-cell. Assume that there is a potassium nitrate (KNO3) salt
bridge connecting each half-cell and that the lead wires connect to a
voltmeter. Note that not all of the materials are needed to build your cell.
Black Lead Wire
Red Lead Wire
Silver Chloride
Copper (II) Sulfate
Zinc
Lead (IV) Sulfate
Zinc Sulfate
Copper
Anode Half-Cell
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Assignment: Galvanic Cells
Step 2: Planning the Experiment
1. Choose ONE of the three cells you completed in Step One to study. The results
of the experiment are in Step Three.
2. Determine your independent and dependent variables. In this experiment, you
want to test whether the concentration of electrolyte solution affects the cell
potential of the galvanic cell. In order to do this, you must change one variable
(independent) and see how it affects the other variable (dependent).
3. Once you have decided on your independent and dependent variables, write
your testable question .
4. Propose a reasonable hypothesis for the experiment. Your hypothesis should
explain how the change in your independent variable will affect your dependent
variable. Provide any relevant theory to back up your prediction.
5. Create a materials list needed to build your galvanic cell.
6. Devise a procedure that could be performed to obtain the given results (below).
This includes the steps required to build the cell and to measure the cell potential
at different electrolyte concentrations.
Step 3: Analyzing the Experiment
Choose ONE galvanic cell to analyze the results of.
Experimental Results
Zinc/Copper
Cell Potentials of a Zinc/Copper Cell at Various Concentrations
ZnSO4 (aq) (1.0 M)/ Cu(NO3)2 (aq) (1.0 M)
1.10 V
ZnSO4 (aq) (1.0 M)/ Cu(NO3)2 (aq) (0.10 M)
1.07 V
ZnSO4 (aq) (1.0 M)/ Cu(NO3)2 (aq) (0.010 M)
1.03 V
ZnSO4 (aq) (1.0 M)/ Cu(NO3)2 (aq) (0.0010 M)
1.00 V
ZnSO4 (aq) (1.0 M)/ Cu(NO3)2 (aq) (0.00010 M)
0.98 V
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Assignment: Galvanic Cells
ZnSO4 (aq) (0.10 M)/ Cu(NO3)2 (aq) (1.0 M)
1.13 V
ZnSO4 (aq) (0.010M)/ Cu(NO3)2 (aq) (1.0 M)
1.17 V
ZnSO4 (aq) (0.0010 M)/ Cu(NO3)2 (aq) (1.0 M)
1.19 V
ZnSO4 (aq) (0.00010 M)/ Cu(NO3)2 (aq) (1.0 M)
1.22 V
Analyze the data from to your chosen galvanic cell by completing the following
questions/steps:
1. From the data, what is the standard cell potential of your galvanic cell? How do
you know?
2. Calculate the ratio of product to reactant electrolyte concentrations for each
measurement. This is called the reaction quotient (Q =
[product]
[reactant]
). Put these
values into a chart similar to Table 1 below, ordering your quotient values from
least to greatest. Note: Table 1 shows the start of the table for the Zinc/Copper
cell. If you have chosen a different cell to analyze, be sure to adjust your chart
accordingly using the appropriate data set. In the second column of your chart,
take the log of each Q value. In the final column, insert the appropriate cell
potential.
Table 1
Q = [Zn2+/Cu2+]
log Q
Cell Potential (V)
= 0.0001 M/1.0 M = 0.0001
-4
1.22
0.001
-3
1.19
0.01
-2
1.17
…
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Assignment: Galvanic Cells
3. Create a graph with log Q on the x-axis and the cell potential (E°cell) on the y-axis.
What type of relationship is this?
4. Use your table to help you locate the point on your graph at which the ratio of
reactant to product concentration (Q) is equal to 1. What is the cell potential at
this point? What is the relevance of this point?
5. Where on the graph is Q1? What does this mean in relation to
electrolyte concentrations?
6. What does the graph tell you about how the cell potential of a galvanic cell
changes as the cell operates? (Hint: Remember, galvanic cells are spontaneous
reactions, which indicates the direction in which the reaction proceeds.)
Step 4: Communicating Your Results
1. Once you have analyzed the results, communicate your experimental plan and
findings in a lab report.
2. Your lab report should include the following sections: variables, testable question,
hypothesis, materials, procedure, observations, results, discussion, and
conclusion.
3. Include your cell diagram from Step One as well as your step by step instructions
in the procedure. The observations section should include your half-cell reactions
and balance redox reaction from Step One, as well as any qualitative evidence of
the cell’s redox reaction. The results section should include all tables and graphs.
The discussion section should include all of answers to the analysis questions
from Step Three.
Note
Refer to the “Formal Lab Report” page in the Scientific Skills and Formatting
module to help you write your report.
Assessment Details
Your submission should include the following:
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Your completed lab report
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Assignment: Galvanic Cells
All in-text citations and a reference list for sources used in your final report
Upload your submissions to the Assignment: Galvanic Cells—Report Dropbox.
Submit this assignment to the dropbox. This assignment will be evaluated for a grade that will
contribute to your overall final grade in this course.
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