Counterion

Cations B (positively charged ions) are adsorbed here on the adsorption surface A. A layer of counterions C (here anions) is deposited on top . The common ions D (cations and anions) move above it in the electrolyte solution.

A counterion is an ion that accompanies an electrically charged particle in chemistry to ensure the electrical neutrality of the system. Counterions are ions with opposite charge signs that balance the electrical charge of a cation or an anion . The term counterion is often associated with ion clouds - freely moving ions - in an electrolyte solution that accumulate in the vicinity of an ion (e.g. a micelle or another interface) with an opposite charge. If one type of ion is selectively adsorbed at the interface, a correspondingly electrically charged layer is created. The charge of this layer then leads to an accumulation of counter ions in the immediately adjacent solution layer.

Examples

• In table salt , the sodium cation (Na ⁺ ) is accompanied by the chloride (Cl ^- , an anion) and vice versa
• In the hydrofluorides of amines , fluoride (F ^- ) is the counterion
• In the hydrochlorides of amines, chloride (Cl ^- ) is the counterion
• In the hydrobromides of amines, bromide (Br ^- ) is the counterion
• In most soaps , the counterions of the fatty acid anions are either sodium or potassium cations (Na ⁺ or K ⁺ )

Individual evidence

1. ↑ Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 2: Cm-G. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1981, ISBN 3-440-04512-9 , p. 1423.