Inorganic and Applied Chemistry

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Inorganic and Applied Chemistry

The two electrons passes through the wire to the cathode solution where the following reaction takes

placer:

2 H+(aq) + 2 e- H 2 (g)

The cathode consists of platinum which is an inert conductor in contact with the 1 M H+ ions surrounded

by hydrogen gas at 1 atm. Such an electrode is called a standard hydrogen electrode which per definition

has a half cell potential (symbolised at 298 K by the symbol of^0 ) of 0.00 volt. The figure below shows

the principle in the build up of the standard hydrogen electrode.

Figure 6- 3: The standard hydrogen electrode

The standard hydrogen electrode has per definition a half cell potential of 0.0 Volt at a H+ concentration

of 1,0 M.

Even though we are capable of measure the galvanic cell potential by using the voltmeter placed between

the two electrodes, it is not possible to ensure the two half cell potentials. We thereby have to define a half

cell reaction that we may determine the other half cell potentials from. As mentioned above we have

chosen to let the half cell potential for the standard hydrogen electrode be the zero point. On the basis on

this it is possible to determine all the other half cell potentials. In the present case we may thereby say that

the half cell reaction:

Zn(s)  Zn2+(aq) + 2 e-

has the half cell potential of 0.76 volt as this is the value of the voltmeter when combined with the

standard hydrogen half cell reaction.

Electrochemistry