Below is a lab activity that is based on a series of virtual lab exercises and videos that have been put together by The ChemCollective, an online resource for learning chemistry. To begin, please visit the below website: http://chemcollective.org/chem/electrochem/index.php
The above link will lead you through a series of activities aimed at improving your understanding of Galvanic Cells. First you will take a series of observations to determine if process is spontaneous. Based upon those observations, you will create an activity series, listing the metals in order of their reactivity. Second, you will construct a series of virtual galvanic cells and use those to power a stopwatch. Third, you will determine the standard reduction potential of an unknown metal; comparing its reduction potential to a standard list, you will identify the unknown. Finally, you will create a situation in which the cells are not in the standard condition and measure the cell potential; using the Nernst equation, you will determine the concentration of an unknown solution.
Introduction
Please read the introduction page.
Once finished, click on the link in the bottom right of the page to progress to the next page.
Step 1: - Investigating redox reactions of some metals and solutions of metal salts
Activity: Investigating redox reactions.
After watching the video “Zinc strip in copper nitrate solution”, and reading the instructions, click on the link labeled “start” just below the drawing of the pencil tip.
Follow the direction to complete the 3x3 grid. Answer the below questions for the portion of the activity in which Sn(s) is placed in AgNO
3
(aq)
1.
Is there a reaction? (circle the correct response)
2.
How many electrons are transferred
-
3.
Write the balanced redox reaction for the combination of AgNO
3
(aq) and Sn(s)
Sn(s) +2AgNO
3
(aq) →Sn (NO
3
)
2
(aq) +2Ag(s)
Once the 3x3 square is complete, click on the link in the bottom right of the page to progress to the next page.
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Step 1: - Practice with redox reactions
1.
Of the five metal ions in the list, which is the most reactive?____Ag
+
____
2.
List the metal ions from the lowest to highest tendency to undergo reduction
Mg 2+ < Zn 2+ < Sn 2+ < Cu 2+ < Ag +
Ag
+
Cu 2+
Sn
2+
Zn
2+
Mg
2+
Once finished, click on the link in the bottom right of the page to progress to the next page.
Step 1: - Reduction tendencies of metal ions
Read the description and answer the below questions.
1.
Will Cu react with Ni
2+
? (circle the correct response)
Why?
Since the Ni 2+ falls below Cu 2+ in terms of tendency to undergo reduction, it is not able to reduce Ni 2+ .
2.
Will Sn react with Ni
2+
? (circle the correct response)
Why?
Since the Ni 2+ falls below Sn 2+ in terms of tendency to undergo reduction, it is not able to reduce Ni2+.
Once finished, click on the link in the bottom right of the page to progress to the next page.
Step 2: Explaining the electron transfer process
Read the description and watch the two videos explaining Galvanic Cells
Once finished, click on the link in the bottom right of the page to progress to the next page.
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Step 2: The Electrochemical Cell
Read the description and watch the video explaining an electrochemical cell
The following is an electrochemical cell diagram for the reaction shown in above video:
Zn (s) + Cu
2+
(aq) --> Zn
2+
(aq) + Cu (s) .
Fill in the blanks on the diagram with the correct terms or phrases.
Direction of electron flow >
>>
Direction of anion flow in salt bridge >>>
Oxidation half
Reduction half cell cell
Finish this page off by reading the description of Carrou cells.
Once finished, click on the link in the bottom right of the page to progress to the next page.
Step 2: Practice with electrochemical cells
In the Mg/Zn Carrou cell that is demonstrated and already set up write down the correct cell diagram.
Mg(s) | Mg 2+ (aq) || Zn 2+ (aq) | Zn(s)
1.
Is the reduction or oxidation half-cell written on the left side of the cell diagram?
Oxidation
2.
What is the color of the wire that leads to the oxidation half cell (this is the anode) in the above diagram?
Black
3.
What color of wire leads to the reduction half cell (this is the cathode) in the above diagram?
Red
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Now, construct your own Carrou cell for the following cell Zn|Zn2+||Ag+|Ag. Please remember that in order for the Carrou cell to function, a piece of paper must connect the cells to each other through the well containing KNO
3
4.
What is the voltage of the Zn|Zn2+||Ag+|Ag voltaic Carrou cell (remember, when correctly set up to be a galvanic cell, the voltage will be positive)?
1.56v
5.
What is the half reaction that is occurring at the cathode in the above cell?
Ag + (aq) + e → Ag(s)
6.
Is this
(circle the correct response)?
Reduction
Once finished, click on the link in the bottom right of the page to progress to the next page.
Step 2: Powering a stopwatch
Please watch the video showing that galvanic cells can be used to do useful work
Once finished, click on the link in the bottom right of the page to progress to the next page.
Step 3: Measuring cell potentials
Please read the description and watch the video showing how the voltage is actually measured using the Carrou cell. Construct a series of Carrou cells to determine the standard cell potential for the listed combinations. Please input the voltages, with units, in the below table.
+
+
2+
2+
2+
2+
Once finished, click on the link in the bottom right of the page to progress to the next page.
Step 3: Calculating cell potentials
Please read the description to review how one can calculate the cell potential using a set of standard reduction potentials.
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Once finished, click on the link in the bottom right of the page to progress to the next page.
Step 3: Practice with standard cell potentials
In this activity, you will measure the cell potential of a Carrou cell containing an a half cell of unknown composition. Using the known half-cell standard reduction potential, you will determine the standard reduction potential of the unknown and identify it based upon the table of standard reduction potentials that is linked below
. http://hyperphysics.phy-astr.gsu.edu/hbase/tables/electpot.html
Read the description and create one or two Carrou cells using the unknown as one of the half cells
1.
What is the balanced half-cell reaction corresponding to the reduction of metal X?
X 2+ (aq) + 2e → X(s)
2.
What cell did you use for comparison (write the balanced half reaction)? What was the voltage listed on the volt meter?
Ag(s) → Ag + + e -
Voltage of cell= -3.17
3.
What value did you obtain for the half-cell reduction potential of metal X?
E for X= -2.38
4.
Referencing the linked table of standard reduction potentials, try to identify the unknown metal.
Mg 2+ and Mg
Step 3: Applying standard cell potentials
Please read the description to review the table of standard reduction potentials is arranged the way it is. Once finished, click on the link in the bottom right of the page to progress to the next page.
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Step 4: Cells in non-standard conditions
Please read the description about non-standard cells.
In the voltaic cell, Zn|Zn2+||Cu
2+
|Cu, as the cell runs, what happens to the concentration of the various ions?
1.
The concentration of Zn 2+ will
(circle the best answer)
2.
The concentration of Cu
2+
will
(circle the best answer)
Step 4: Practice with cells in non-standard conditions
Please read the directions with respect to determining the effect of changing concentrations on cell potential.
1.
Construct a standard cell, all solutions at 1 M, for both reactions, Sn| Sn
2+
||Cu
2+
|Cu and Zn| Zn
2+
||Sn
2+
|Sn, and determine their voltage. a.
Reaction 1: Sn (s) + Cu 2+ (aq) --> Sn 2+ (aq) + Cu (s) _______.48_____
b.
Reaction 2: Zn (s) + Sn
2+
(aq) --> Zn
2+
(aq) + Sn (s) ____.62________
2.
Add water to dilute by dragging the beaker of water from the bottom right of the screen over the cell that you want to dilute. The half cell should now show the word
“Diluted” in it. What is the new voltage? a.
Reaction 1: Sn| Sn
2+
(diluted)
||Cu
2+
|Cu ______.51______
b.
Reaction 2: Zn| Zn
2+
||Sn
2+
(diluted)
|Sn ____.59________
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3.
In one reaction the voltage increases, in the other it decreases. Briefly speculate why.
In reaction 1, the concentration of Sn 2+ (on product side) has decreased, therefore the quotient decreases as well and the voltage increases in response to getting farther away from the equilibrium.
I reaction 2, the concentration of Sn2 + has decreased on the reaction side which result in lesser quotient and subsequently lesser cell voltage in response to approaching equilibrium.
4.
Using the Nernst equation, determine the diluted concentration for both cells. Show your work.
Sn| Sn
2+
(diluted)
||Cu
2+
|Cu
E cell=
E cell
° -
.0592
𝑛
logQ
= ( .34- (-.14))-
.0592
2
log (
Zn| Zn
2+
||Sn
2+
(diluted)
|Sn
You must submit your Voltaic Cells results to the dropbox by your normally scheduled lab period on Week 10.
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