Standard hydrogen half-cell

A half-cdl consisting of a palladium rod dipping into a 1 M Pd(NOj)2 solution is connected with a standard hydrogen half-cell. The cell voltage is 0.99 volt and the platinum dectrode in the hydrogen half-cell is the anode. Determine E° for the reaction... 

Two half-cells in the Daniell cell are each connected to the standard hydrogen half-cell (Rae D6jur)... 

Equation (6) defines the difference between two E° values. To set the individual values, we need to choose a particular redox couple as a reference. The reference used most commonly by biochemists is the standard hydrogen half-cell, in which protons at pH 0 are reduced to H2 at a... 

When a Zn (f M) Zn half-cell is connected to the standard hydrogen half-cell, zinc dissolves its half-cell is the anode because oxidation occurs in it. The measured cell voltage is 0.76 V, so... 

A galvanic cell is constructed using a standard hydrogen half-cell (with platinum electrode) and a half-cell containing silver and silver chloride ... 

Now the redox potential, Eh, is conventionally defined in terms of the potential of a cell composed of two half-cells the half-cell of particular interest (given in general terms by reaction 7.15) and the standard hydrogen half-cell (with Eh and pe assigned values of zero). The reaction in the latter case is... 

Half-cell potentials Over the years, chemists have measured and recorded the standard reduction potentials of many different half-cells. Table 20.1 lists some common half-cell reactions in order of increasing reduction potential. The values in the table were obtained by measuring the potential when each half-cell was connected to a standard hydrogen half-cell. All of the half-reactions in Table 20.1 are written as reductions. However, in any voltaic cell, which always contains two half-reactions, the half-reaction with the lower reduction potential will proceed in the opposite direction and will be an oxidation reaction. In other words, the half-reaction that is more positive will proceed as a reduction and the half-reaction that is more negative will proceed as an oxidation. 

The oxidation-reduction potentials for half reactions such as Fe" —> Fe + e are measured by putting a piece of platinum or other inert metal into a solution containing ferrous and ferric ions in standard concentrations, and combining this half cell with the standard hydrogen half cell. Again, the platinum serves to conduct electrons and to catalyze the equilibrium between ferrous and ferric ions. The electromotive force of the cell... 

The potential of the standard hydrogen half-cell can be set at zero since only differences are measured, and the hydrogen value always cancels in these differences. In the cell above, the activities of H2, Haq, and Ag° are 1, as defined for the standard hydrogen half-cell and a pure solid. Putting these into the Nernst expression above shows why we can call this the half-cell potential for the silver couple ... 

An electrode is prepared by dipping a silver strip into a solution saturated with silver thiocyanate, AgSCN, and containing 0.10 M SCN. The emf of the voltaic cell constructed by connecting this electrode as the cathode to the standard hydrogen half-cell as the anode is 0.45 V. What is the solubility product of silver thiocyanate ... 

Flg.1. 4. An example of the standard hydrogen half-cell, in the cell RIH, IHCII AgCI Ag. P. potentiometer. 

As mentioned earlier, the standard hydrogen half-cell is rather awkward to use under most circumstances. The other half-cells most frequently used in corrosion studies, along with their potentials relative to the standard hydrogen half-cell, are listed in Table 4.7. 

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