Voltaic Cells
- Page ID
- 517001
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Voltaic Cells
- Create small-scale voltaic cells and measure standard reduction potential
- Investigate optimal conditions to create concentration cells
- Use the Nernst equation to calculate cell potential at nonstandard conditions (concentration cell)
Safety
Waste Disposal: All chemicals used must go in the proper waste container for disposal.
Materials and Equipment
Voltmeters with alligator clips, Well Plate, Metal electrodes (copper, aluminum, magnesium, zinc), 0.1 M metal ion solutions (CuSO4, Mg(NO3)2, Zn(NO3)2,), disposable pipets (one for each metal solution) , String (2-3 cm in length, or longer), 1 M KNO3, 10 mL graduated pipette and pipette pump, Thermometer to get room temperature.
Background
Useful Equations for Today’s Experiment
For a Concentration Cell, 
To find Standard Electrode (Half-Cell) Potentials, use Appendix L in Openstax Chemistry 2e Textbook
Procedure
Take good notes and do your calculations in your lab notebook as you complete this experiment Then fill in the summary sheet.
Part 1 (Work in Partners):
1. Using a well-plate, set up 3 voltaic cells. Each voltaic cell will be made up of two half-cells containing metal ion solution. The two half-cells for each voltaic cell must be in two adjacent wells. Fill each well about ¾ full with the following solutions:
a. Voltaic Cell A: Add 0.1 M CuSO4 in the one half-cell and 0.1 M CuSO4 in the other half-cell
b. Voltaic Cell B: Add 0.1 M CuSO4 in the one half-cell and 0.1 M Zn(NO3)2 in the other half-cell
c. Voltaic Cell C: Add 0.1 M CuSO4 in the one half-cell and 0.1 M Mg(NO3)2 in the other half-cell
3. Use the short string soaked in 1 M KNO3 as a salt bridge for each of your voltaic cells. You’ll need to make sure the string is saturated with KNO3 solution and is long enough to connect each of the half-cells but not too long that it gets in the way. Use your tweezers to help place each side of the string in each of your half-cells. You’ll want to use a new piece of string for each voltaic cell to avoid contamination.
4. Prepare your voltmeter by changing the setting to read voltage at 20V. Use the alligator clips on the wires connected to the voltmeter to secure a strip of metal to use for your electrode. Always use an electrode of the same metal that is in the solution in each half-cell. (e.g. in a half-cell containing the solution with Cu2+ ions, use a solid metal Cu electrode). For example, for the Voltaic Cell A, you will need 2 copper electrodes, one for each copper half-cell. Switch out electrodes as needed as you measure the potential of each voltaic cell. Clean off each electrode with a damp paper towel between measurements to avoid contamination.
5. Taking care to NOT TOUCH the string salt bridge with each electrode, insert the corresponding electrode into the half-cells of the first voltaic cell and quickly read and record the potential in the units of volts. If the reading is negative, this just means the anode and cathode are switched on the voltmeter. Leaving the electrodes in the alligator clips, just unplug the wires at the voltmeter and switch them to get a positive value.
6. Fill in the table on your summary sheet with your measured potential of each voltaic cell. Use the table of standard cell potential values and the equations given in the Background section to finish filling in this table before moving on to Part 2.
Part 2 (Continue to work in Partners):
Now you will investigate concentration cells. Depending on what bench you and your partner are working at, you’ll look at a different variable of voltaic cells to test the optimal conditions to get the most accurate potentials for your concentration cells. You will ONLY INVESTIGATE ONE OF THESE VARIABLES.
For all benches, you will need to prepare one or two dilutions using the metal ion solutions provided in Part 1 and the graduated glass pipette. Prepare a total of 10 mL for each dilutions. Use the dilution equation C1V1 = C2V2.
Variable #1: Concentration
If you are at the “Shower” Bench (bench closest to safety shower), you will use copper ion solutions of different concentrations to investigate how concentration difference affects the cell potential. Prepare one dilution of 0.01M CuSO4 and one dilution of 0.001 M CuSO4
Then prepare two concentration cells in the same way you prepare your voltaic cells in Part 1.
Concentration Cell A: Add 0.1 M CuSO4 in the one half-cell and 0.01 M CuSO4 in the other half-cell
Concentration Cell B: Add 0.1 M CuSO4 in the one half-cell and 0.001 M CuSO4 in the other half-cell
Add a new salt bridge string and copper electrodes to complete each concentration cell. Measure the potential of each concentration cell. Comment on how the potential is different (or the same) in your two concentration cells and explain why.
Variable #2: Metal Ion Solution in Half-Cell
If you are at the “Middle” Bench (the bench in the middle of the lab), you will use dilutions of zinc and magnesium to investigate if there is a difference in measured cell potential with different metal ion solutions and electrodes. Prepare one dilution of 0.01M Zn(NO3)2 and one dilution of 0.01 M Mg(NO3)2
Then prepare two concentration cells in the same way you prepare your voltaic cells in Part 1.
Concentration Cell A: Add 0.1 M Zn(NO3)2 in the one half-cell and 0.01 M Zn(NO3)2 in the other half-cell
Concentration Cell B: Add 0.1 M Mg(NO3)2 in the one half-cell and 0.01 M Mg(NO3)2 in the other half-cell
Add a new salt bridge string and zinc or magnesium electrodes to complete each concentration cell. Measure the potential of both concentration cells. Make observations on how the potential is different with the different metals. Compare to the standard reduction potential of each metal and explain why.
Variable #3: Size of Half-Cell container.
If you are at the “Fire Extinguisher” Bench (bench closest to fire extinguisher), you will use different size containers for your half-cells and compare their measured potential over time. You will test the effect of volume of solution used in the half-cell and how the cell potential changes over time. Prepare one dilution of 0.01 M Zn(NO3)2
Then prepare one concentration cell in a similar way you prepare your voltaic cells in Part 1. Instead of using the well plate, you will use two of the provided small beakers.
Concentration Cell: Fill one beaker about half-way with 0.1 M Zn(NO3)2 for the first half-cell and fill a second beaker about half-way with 0.01 M Zn(NO3)2 for the second half-cell.
For the salt bridge, use a longer piece of string to connect the concentration cell using the beakers. Make an initial measurement of the cell potential in your concentration cell. Then wait 10-15 minutes and take an additional measurement. Note if there are any differences and explain why.
OPTIONAL Part 3
If you still have time, use the Nernst equation to calculate the predicted cell potentials for each of your concentration cells. Note any differences from your measured values.