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Unformatted text preview: reducing agent and the acce ptor orbitals of an oxidizing agent. You will combine a series of redox couples and
measure the energy differences between them. This is typically performed in an electrochemical cell. One is
shown in Figure 2 below. www.webassig n.net/ebooks/wsug encheml1/lab_13/manual.html 3/10 4/15/13 Lab 13 - Redox Reactions Figure 2: Electrochemical Cell for the Reaction between Copper Metal and Zinc Ion
In a galvanic cell, the half- cells are vessels that contain a strip of the metal in a solution of the corresponding
metal ion. The metal strips are called e le ctrode s . The electrode at which reduction occurs is called the cathode
and the electrode at which oxidation takes place is called the anode . Connecting the electrodes through a
load forms the external circuit. As in the illustration, the load will be a voltmeter. The electrons will travel from the
high energy orbitals in the reducing agent at the anode, through the external circuit, to the lower energy orbitals in
the oxidizing agent at the cathode. To complete the circuit, a s alt bridge , which allows ions to travel from one
half- cell to the other, is used to connect the two half- cells.
When a voltmeter is used as the load, the potential
difference between the oxidizing and reducing agent can be measured. The first potential difference you will
measure will be between the Cu2+/Cu couple and the Ag+/Ag couple. You will use this to set up your voltmeter
so a positive reading is obtained. Recall from equations 4 - 6 that copper metal donates electrons to silver ions.
Copper metal is oxidized in this reaction, so the Cu2+/Cu couple is the anode. Silver ion is reduced, so the
Ag+/Ag couple is the cathode. Electrons travel toward the cathode, the more electrically positive electrode, in a
spontaneous reaction. The potential difference, Ecell, is defined as
( 13 )
Ecell = Ecath o d e − Ean o d e
In a galvanic cell, the cell potential must be positive if the cathode and anode are properly identified. You
will then measure the potential difference between the Cu2+/Cu couple and several other redox couples
consisting of metals and their ions. One of the couples will be Zn2+/Zn. From equations 1 - 3, we know that
copper(II) is reduced in this reaction, so the Cu2+/Cu c...
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