Cliffs AP Chemistry, 3rd Edition

Scenerio: Part II

A student constructed an electrochemical cell as shown in Figure 1:

Figure 1

The student began by constructing a half-cell using Zn as a reference electrode in 1.0 M
Zn2+(aq). The voltages between the Zn electrode and other electrodes in 1.0 M solutions of their
metallic ion at 25°C are presented in Table 4 below. A salt bridge of 1.0 M KNO 3 connected the
two half-cells. With the voltmeter set to read a positive voltage, the wire connected to the + ter-
minal on the meter, usually a red wire, was connected to the cathode, the location where
reduction was supposedly occurring (RED CAT). The other wire coming from the meter
labeled negative and usually black in color, was connected to the anode, the location where
oxidation was supposedly occurring (AN OX). However, anode and cathode definitions are for
the electrodes in solutions. The anodes produce e–and the cathodes receive them, so that the
signs outside the solutions reverse.

Table 4

Voltage Anode Cathode

Zn—Ag 1.40 Zn Ag

Zn—Cu 0.99 Zn Cu

Zn—Fe 0.55 Zn Fe

Zn—Mg 0.60 Mg Zn

Zn—-Pb 0.48 Zn Pb

To voltmeter

Metal Metal

Salt bridge

Solution Mn+ = C 1 Solution Mn+ = C 2

Laboratory Experiments