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Cold concentrated nitric acid passivates Al, Cr, Be, Pb, Sn, Mn, Fe due to the

formation of protective oxide films on their surfaces.

9.2.Electrode potentials. Galvanic element

The processes of the mutual conversion of chemical and electrical forms of

energy are called electrochemical processes. They mostly occur in real systems,

in where a contact of a metal surface with an electrolyte solution exists.

st
Conductors with electron conductivity (conductors of the 1 kind) are called
nd
electrodes, and ionic conductors (conductors of the 2 kind) are called
electrolytes.

The ability of metals to form free positively charged ions is clearly manifested in

the reactions of displacing metals from their salts by other more active metals, or

during interaction with non-acidic acids. So, if a zinc plate is immersed in the
solution of copper (II) sulfate, then an redox reaction will occur.

2+
2+
Zn + Cu = Cu + Zn .

This reaction occurs, for example, in a galvanic element in which a zinc
plate (one electrode) is immersed in the zinc sulfate solution, and a copper one (the

second electrode) is in the copper (II) sulfate solution (see diagram below). Zinc is

a more active metal, so there is a potential difference between zinc and copper

electrodes. Connecting zinc and copper electrodes to the galvanometer and

connecting the solutions with a U-shaped tube filled with electrolyte solution a

galvanic element is obtained. After setting the contact in the galvanic circle, the

arrow of the galvanometer deviates in the direction towards the copper electrode.

This indicates that during the operation of the galvanic element the electrons move

from the zinc electrode to the copper one.

The galvanic element is an instrument used to convert the chemical energy of an

oxidation-reduction reaction to an electrical one. In a galvanic element the

electrons do not move directly from the reducing agent to the oxidizer, but by the

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