http://www.ck12.org Chapter 23. Electrochemistry
FIGURE 23.8
The standard hydrogen electrode is an
arbitrary reference cell that is assigned a
standard reduction potential of 0.00 V.Determining Standard Reduction Potentials
When a standard hydrogen half-cell is connected to a standard copper half-cell and connected to a voltmeter (Figure
23.9 (A)), the reading is 0.34 V.
Observation of the cell shows that the copper(II) ion is reduced to copper metal, while the hydrogen gas is oxidized
to hydrogen ions. This is shown below along with the overall reaction taking place in the cell.
Oxidation: H 2 (g)→2H+(aq)+2e−
Reduction: Cu^2 ++2e−→Cu(s)
Overall: H 2 (g)+Cu^2 +(aq)→2H+(aq)+Cu(s)In this particular galvanic cell, the SHE is theanode(where oxidation takes place), and the copper half-cell is the
cathode(where reduction takes place). Electrons flow from the SHE to the copper electrode. The standard cell
potential (E◦cell) is the measured value of 0.34 V, while the potential of the SHE is defined to be zero. This allows us
to determine the reduction potential of the copper half-cell.
E◦cell=E◦red−E◦oxid
0 .34 V=E◦Cu− 0 .00 V
E◦Cu= 0 .34 V− 0 .00 V= + 0 .34 V