Last updated: March 8, 2018

What Does Dissociation Mean?

Dissociation is the process by which chemical molecules (or ionic compounds such as salts, or complexes) break down into simpler constituents such as atoms, ions or radicals, usually in a reversible manner, as do CO2 and H2O at high temperatures.

Dissociation is the opposite of association and recombination. Dissociation accelerates the rate of corrosion and increased pitting in the anode area in concentration cell, for example corroding of metal pipes in water treatment. The corrosion of iron in the presence of hydrogen sulfide and water is also dependent on the dissociation of the hydrogen-sulfide molecule.


Corrosionpedia Explains Dissociation

Dissociation in chemistry is a general process in which molecules separate or split into smaller particles. For instance, when an acid dissolves in water, a covalent bond between an electronegative atom and a hydrogen atom is broken by heterolytic fission, which gives a proton (H+) and a negative ion.

The dissociation constant (Ka) is the ratio of dissociated to undissociated compound. Stronger acids have a larger acid dissociation constant (Ka) and a smaller logarithmic constant (pKa = – log Ka) than weaker acids. The increase in temperature also leads to a higher dissociation and a higher dissociation constant. At the temperature of, for example, 240°F (115°C), a tenfold number of H2O molecules are dissolved into ions.

The dissociation degree is the fraction of original solute molecules that have dissociated. In the case of very strong acids and bases, the degree of dissociation is close to 1. Less powerful acids and bases have a lesser degree of dissociation.

In aqueous solutions like acids, bases and sulfates, their molecules are partially dissolved in electrically loaded, free-moving particles, known as ions. In electrolytic dissociation, the solutions can conduct electricity and facilitate the electrochemical corrosion of "non-precious" metals due to the positive ions (cations) and negative ions (anions). However, dissociation also occurs in pure water. In this case, although to a lesser extent, water molecules disintegrate into hydrogen ions (H+) and hydroxyl ions (OH-).


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