Chemistry
Name:
Date:
§ 17.01L
Building Simple Electrochemical Cells
Special Safety Considerations:
Purpose
An electrochemical cell is made by combining an oxidation reaction
with a separate reduction reaction to produce a flow of electrons
(electricity). The two reactions are placed in separate cells to
prevent direct contact. A salt bridge is used to allow for movement
of ions between the cells in order to complete the circuit.
Half-cells are additive to give the potential difference expected for a
voltaic cell (E0 = E0red + E0ox). In this experiment, simple metalmetal ion half-cells, M(s) | M+(aq), will be used to establish voltaic cells. You will measure the electrical
potentials of the electrochemical cells.
Example
Cu2+ + 2e–  Cu0
Ered = –0.339 V (change sign to +0.337 V)
2+
–
Zn  Zn + 2 e
Eox = +0.762 V
The sum of the reactions is Cu2+ + Zn  Cu + Zn2+
E0 = 1.101 V
Materials
small pieces of metals:
20 drops of, 1 M each
multimeter (voltmeter)
beakers-450 mL, x 2
Pb
Pb(NO3)2
wire leads
well-plate
Cu
Cu(NO3)2
sand paper
filter paper
Fe
Fe(NO3)3
filter paper
scissors
D:\450\450.00L_Labs\430L.17 Electrochemistry\450L.17_Electrochemistry_Voltaic Cell_Actvity Series_KI Phenophthalein.docx
Zn
Zn(NO3)2
sponge
petri dish
Mg
Mg(NO3)2
KNO3
KNO3
well plate
Chemistry
Electrochemistry Lab
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Procedure – 1. Simple Electrochemical Cells & Activity Series
1. Use sandpaper or steel wool to remove any oxidation of the small pieces of metal. Hold in paper so
that your hands stay clean.
2. Place into each well, a small piece of each of the following metals and the associated nitrate solution.
The top of each piece of metal must remain dry.
3. Make salt bridges by soaking small strips of filter paper in saturated solutions of potassium nitrate.
4. Place the wire leads in contact with two different metals. Record the positive voltage. If the voltage is
negative, switch the wire connectors. The black wire is connected to the negative terminal, and the red
wire to the positive terminal.
Data: Voltage of each half-cell versus the zinc electrode
Zn
Cu
Fe
Zn
Cu
Fe
Pb
Mg
Pb
Mg
Chemistry
Electrochemistry Lab
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Question
1. How well do your data match the predicted values from the EMF reference table (use the book values on
page 441)?
Procedure – 2. Make a Voltaic Cell.
1. Using two beakers, solutions of Cu(NO2)2 and Zn(NO3)2, a multimeter and alligator clips, and a salt
bridge composed of a ‘U-shaped’ sponge soaked in a saturated KNO3 solution. Calculate the
theoretical voltage and compare it with the experiment value. What is the percent error? Discuss.
Chemistry
Electrochemistry Lab
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Procedure – 3: Electrolysis of KI solution.
Background. An electrolytic cell is constructed using an aqueous solution of KI
and a 9-V battery as the energy source.
Draw the electrochemical cell, including the oxidation & reduction reactions, the flow of
electrons and ions. Label the anode and cathode electrodes.
Materials
Potassium iodide, KI, 0.5 M
Graphite electrodes (pencil lead), x 2
Petri dish, divided into three compartments
phenolphthalein
battery
Procedure
1. Label the partitioned Petri dish “1”, “2”, and “3” on a piece of paper underneath the dish.
2. Carefully pour about approximately 8 ml of the KI solution into compartment 1 of the Petri dish until
the compartment is about 1/3rd full.
3. Add 3 drops of phenolphthalein and stir.
4. Connect one graphite electrode to one pole of the battery. Connect the other graphite electrode to the
other pole of the battery.
5. Keeping the electrodes as far apart as possible, dip the electrodes into the KI solution.
6. Let the current run for 1-2 minutes. Record any observations.
Questions
1. In this electrolytic cell, two separate half reactions occur at each electrode. What is the oxidation
reaction?
At which pole (anode or cathode) does this reaction occur?
2. What is the other reaction? At which pole does this reaction occur?
3. What is the overall reaction?
Chemistry
Electrochemistry Lab
4. At which pole did the phenolphthalein turn magenta? Explain.
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