Copper SHE cell

A cell for measuring the potential of the copper-SHE cell is shown in Figure 12.3.The hydrogen electrode is a device for using the reaction... 

The Zinc-Copper Cell 21-10 The Copper-Silver Cell Standard Electrode Potentials 21-11 The Standard Hydrogen Electrode 21-12 The Zinc-SHE Cell 21-13 The Copper-SHE Cell 21-14 Standard Electrode Potentials 21-15 Uses of Standard Electrode Potentials 21-16 Standard Electrode Potentials for Other Half-Reactions 21-17 Corrosion 21-18 Corrosion Protection... 

The SHE functions as the anode in this cell, and Cu ions oxidize H2 to H+ ions. The standard electrode potential of the copper half-cell is 0.337 volt as a cathode in the Cu-SHE cell. 

The measured potential of the copper-hydrogen cell is 0.337 volts (i.e., the standard copper electrode is 0.337 volts more positive than the SHE) so... 

Defining a reference value for the SHE makes it possible to determine E ° values of all other redox half-reactions. As an example. Figure 19-14 shows a cell in which a standard hydrogen electrode is connected to a copper electrode in contact with a 1.00 M solution of C U . Measurements on this cell show that the SHE is at higher electrical potential than the copper electrode, indicating that electrons flow from the SHE to the Cu... 

Fig. 6.35. The meaning of the relative potential difference across the Cu/CuS04 interface, i.e.. the relative electrode potential, (a) The electrochemical cell corresponding to the relative potential difference, (b) The relative potential difference includes a platinum-copper contact potential and the unknown potential difference across the SHE, apart from the absolute potential difference across the Cu/CuS04 interface.

Another voltaic cell consists of an SHE in one beaker and a strip of Cu metal immersed in 1 M copper(II) sulfate solution in another beaker. A wire and a salt bridge complete the circuit. For this cell, we observe the following (Figure 21-10). 

The standard electrode potentials of copper can be obtained in a similar fashion, by using a cell with a copper electrode and a SHE [Figure 19.4(b)]. In this case, the copper electrode is the cathode because its mass increases during the operation of the cell, as is consistent with the reduction reaction ... 

The half-cell reactions are reversible. Depending on the conditions, any electrode can act either as an anode or as a cathode. Earlier we saw that the SHE is the cathode (H+ is reduced to H2) when coupled with zinc in a cell and that it becomes the anode (H2 is oxidized to H+) when used in a cell with copper. 

Now considering the zinc-copper cell, which could be constructed by substituting a copper electrode in a cupric ion solution for the SHE in Figure 18.1, we could write... 

Draw a galvanic cell consisting of a SHE and the copper electrode described above. Indicate a) the anode and the cathode, b) the direction of flow of the electrons in the wire, and c) which electrode is positive and which electrode is negative. Write down the half-reactions that are occurring at each electrode, and then write down the overall chemical process occurring in the cell. 

As we mentioned, the cell voltage depends on the activities of all the ions and compounds in the cell reaction in this case it depends not only on the hydrogen gas pressure and but on acu ao,2+ as well. Standard conditions is defined as u = 1 for all products and reactants in the cell reaction, and so if the hydrogen electrode is operating under SHE conditions (uh2( ) = /njfe) = 1 bar), the copper electrode is pure Cu (acu(s) = 1) and the cupric ion concentration and activity coefficient are adjusted to give 00,2+ = 1, the ceU voltage will be the standard cell voltage, S°. 

When the standard electrode potentials are listed in decreasing value as shown in Table 14.6, an electromotive series is created which has the hydrogen half-cell reaction listed at a potential of zero. These values are reduction potentials at 25°C referred to the standard hydrogen electrode (SHE). Metals listed at the top of the series are noble or less reactive. Metals listed below the hydrogen reaction are reactive, that is, they corrode more readily. A metal listed below another metal will displace it from a solution containing the higher metal s ions. Iron, for example, wUl have copper metal plated on it when placed in a copper sulfate solution. This is an iron corrosion reaction. Metals listed below hydrogen will displace the H" " ions from acid solutions. 

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