CHAP. 11: ELECTROCHEMISTRY [CONTENTS] 351
Example
The initial concentration of acetic acid was 1 mol dm−^3. Part of the molecules dissociated into
ions. At equilibrium, the concentration of H+ions equalled 0.1 mol dm−^3. Calculate the degree
of dissociation.Solution
The concentration of acetic acid at equilibrium isci= 1—0.1 = 0.9 mol dm−^3. By substituting
into relation (11.5) we obtain
α=1 − 0. 9
1
= 0. 1.
11.1.6 Infinitely diluted electrolyte solution
An infinitely diluted solution is formed by 1 molecule of an electrolyte Kν+Aν− in a large
amount of solvent. This system is the basic model applied when describing the behaviour of
dilute solutions.
In an infinitely diluted solution, ions do not influence one another. The degree of dissociation
equals one, regardless of the nature of the electrolyte.
11.1.7 Electrochemical system.
An electrochemical system is comprised of a vessel containing an electrolyte into which two
electrodes are dipped. The electrodes are connected by first-class conductors either with a
source of electric current—in this case we speak aboutelectrolysis, or with an electrical
device—in this case we speak about agalvanic cell. During electrolysis, chemical reactions
of ions occur at the electrodes due to the passage of electric current. In a galvanic cell, on the
other hand, electric current is generated in consequence of chemical reactions proceeding at the
electrodes.
Thecathodeis an electrode at which reduction occurs.Reductionin this context means
a reaction during which electrons are consumed. An example of a reduction is the reaction
Cu2++ 2 e−= Cu.