Electrochemistry

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Theory and IUPAC representation

Basic theory:

Metal in solution of its own ions will create a dynamic equilibrium; some of the metal solid will oxidise to positive ions in solution, leaving electrons behind on the surface of the metal.

This creates an attractive force, so the positive ions remain close to the negative electrode.

Some of these ions will then be reduced to solids again.

The equilibrium occurs when the rates of leaving and rejoining the electrode are equal.

What is the potential of a cell?

The equilibrium of these redox relationships can be quantified by measuring the potential difference between the "negativeness" of the metal electrode and the positive ions in the surrounding solution. The magnitude and sign of the cell potential gives an indication of the position of the equilbrium and thus allows predictions of reactions.

Standard hydrogen electrode

Standard conditions:

1M conc solution

100 kPa

298 K

Hydrogen gas is bubbled over inert porous platinum electrode.

Using the SHC:

Connect a half-cell to the SHC using a salt bridge soaked in an inert material (eg. potassium nitrate solution)

Certain metals (eg. Mg) produce positive ions more readily than hydrogen does; position of eq left on red equation)

So there is a higher buildup of electrons on the Mg electrode than on the Pt.

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